which are the 2 most common endocrine disease
diabetes melltius
thryoid disease
what’s the difference between primary and secondary endocrine disorder
a primary endocrine disorder: the defect is in the cells that secrete the hormones.
secondary disorder is lack of hormone or its receptor - there is too much or too little tropic hormone.
where is the pituitary gland found
in the sella turcica just below the optic chiasm
- The pituitary gland is located behind the eyes on a stalk, known as the infundibulum, at the base of the brain (below the third ventricle, hypothalamus and the optic chiasm). The pituitary gland is enclosed within the sphenoid bone.
- The pituitary is physically connected to the hypothalamus through the pituitary stalk; it is also connected functionally by the hypophyseal portal circulation and supraoptic-hypothalamic tract.
what’s the relationship between hemianopias and pituitary tumours
Pituitary tumours put pressure on the optic chiasm and lead to hemianopia.
because the pituatary gland sits in a pit in the midline just above the optic chiasm, tumours press on this and cause deficits in the periphery of visual fields
describe the development of, and the anatomy of the pituitary gland
Divided into the anterior lobe (adenohypophysis) and the posterior lobe (neurohypophysis)
The anterior pituitary develops from an upgrowth of the lining of the mouth (Rathke’s pouch) and the posterior lobe develops from downward growth of the diencephalon (neural).
The anterior pituitary is much larger, and forms a cup around the posterior pituitary
describe the formation of the posterior lobe of the pituitary gland
as the 3rd ventricle forms it pushes the tissue down to form the neural portion of the adult pituitary gland
this becomes the NEUROHYPOPHYSIS (posterior lobe)
describe the function of the posterior pituitary
The posterior lobe of the pituitary gland is controlled by magnocellular neurons that project from the paraventricular nucleus (PVN) and the supraoptic nucleus (SON) of the hypothalamus.
Axons project into the posterior pituitary gland along the hypothalamic-hypophyseal tract.
secretes hormones including oxytocin and vasopressin (ADH).
what are neurophysins
Neurophysins are carrier proteins that transport the hormones along the axons of magnocellular neurons to the posterior pituitary, these are also synthesised in the PVS and SON as they are parts of the precursor molecules.
describe how oxytocin and vasopressin are released from the pituitary
These hormones are synthesised in the PVN and SON of the hypothalamus, and then transported along the magnocellular neurons to the posterior pituitary.
The posterior pituitary stores oxytocin and vasopressin within axon terminals, until hypothalamic neurons fire and cause the hormones to be released into the blood via the inferior hypophyseal artery.
describe the function of the anterior pituitary
Secretions of the anterior lobe are also controlled by neuronal factors secreted from the hypothalamus.
Releasing hormones are synthesised in the PVN, they then travel down magnocellular neurons (aided by neurophysins), which terminate in the external layer of the median eminence.
From here the hormones pass into the primary capillary plexus, through the hypophyseal portal veins and into the secondary capillary plexus in the anterior pituitary.
These releasing hormones reach their target cells in the anterior pituitary and stimulate protein synthesis and secretion either through AC-cAMP-PKA-CREB or PLC/IP3/Ca pathways. Hormones are then released into general circulation.
what does the hypophyseal portal system consist of
primary capillary plexus
hypophyseal portal veins
secondary capillary plexus
list the hormones (not releasing hormones) secreted by the anterior pituitary
growth hormone (GH)
thyroid stimulating hormone (TSH)
adenocorticotropic hormone (ACTH)
follicle-stimulating hormone (FSH)
luteinising hormone (LH)
prolactin (PRL).
list the releasing hormones secreted by the hypothalamus
growth hormone releasing hormone (GHRH) - 44aa
growth hormone inhibiting hormone (GHIH)
thyrotropin releasing hormone (TRH) - 3aa
corticotropin releasing hormone (CRH) - 41aa
gonadotrophin releasing hormone (GnRH) - 10aa
prolactin inhibiting hormone (PIH)
how is prolactin release controlled
There is currently no known releasing factor for prolactin, however it appears to be under dominant negative control, where dopamine is the main inhibitory factor
After the pituitary stalk is damaged, the first effect will be increased prolactin levels.
describe the histology of the adenohypophysis, and what is seen with a H&E stain
The bulk of adenohypophysis is the pars distalis, composed of winding cords of epithelial cells flanked by vascular sinusoids.
H&E stain reveals three cell types amongst the epithelial cells, this reflects differences in hormonal content; acidophils, basophils, chromophobes
which colour do acidophils stain with H&E, and what kind of cells are they (and what hormones do they produce)
stain red/orange
they’re cells that contains polypeptide hormones
- somatotrophs - produce GH
- Lactotrophs - produce prolactin
which colour do basophils stain with H&E, and what kind of cells are they (and what hormones do they produce)
stain blue
they’re cells that contain glycoprotein hormones:
- thyrotropes - thyroid stimulating hormone
- gonadotropes - LH or FSH
- corticotropes - adrenocorticotrophic hormone
which colour do chromophobes stain with H&E, and what kind of cells are they (and what hormones do they produce)
stain very poorly
they’re cells that have minimal or no hormonal content
Many of the chromophobes may be acidophils or basophils that have degranulated and thereby are depleted of hormone
Some chromophobes may also represent stem cells that have not yet differentiated into hormone-producing cells.
what is the function of thyrotrophs
secrete TSH
TSH stimulates thyrotrophs to produce TSH, it also stimulates prolactin release from lactotrophs
what is the function of gonadotrophs
to release LH, and FSH
these stimulate steroid biosynthesis and germ cell maturation in the gonads
what is the function of corticotrophs
to release ACTH (Adrenocorticotrophic hormone)
stimulates steroid biosynthesis in adrenal cortex
what is the function of somatotrophs
release somatotrophin aka GH
to stimulate growth bia IGF-1 (insluin-like growth factor)
what is the function of lacotrophs
produce lactin
this stimulates lactation
describe the structure of TSH, LH and FSH
heterodimeric glycoproteins
they have identical alpha sub-units and differing beta sub-units that confer speciality
describe the structure of ACTH
ACTH is a 39aa peptide produced by the post-translational processing of POMC gene (pro-opiomelanocortin)
Other products include alpha-melanocyte stimulating hormone (MSH) and beta-endorphin.
describe the structure of GH and prolactin (PRL)
GH and prolactin are peptides with similar structures and both have internal disulphide bonds at equivalent positions
They are able to stimulate each other’s receptors (homologus receptors)
describe the intermediate pituitary lobe
(remnant of the hollow of the anterior pituitary forming around the posterior pituitary)
Pars intermedia is closely associated with pars nervosa (posterior) and separated from pars distalis (anterior) by the hypophyseal cleft.
MSH is the main hormone secreted from pars intermedia.
In adulthood, pars intermedia is either very small or entirely absent.
describe the control of the synthesis and secretion of anterior pituitary hormones
under dual control of;
- hypothalamic releasing hormones
- hypothalamic inhibitory factors
these hypothalamif factors are synthesised in the parvicellular neurones and are screted at the median eminence of the 3rd ventricle
describe the role of Thyrotrophin Releasing Hormone (TRH)
stimulates thyrotrophs to produce TSH
it also stimulates prolactin release from lactotrophs
describe the role of Gonadotropin-Releasing Hormone (GnRH)
stimulates gonadotrophs to produce LH and FSH (gonadotrophins)
describe the role of Corticotropin Releasing Hormone (CRH)
stimulates corticotrophs to produce ACTH
describe the role of Growth Hormone Releasing Hormone (GHRH)
stimulates somatotrophs to produce GH
what are the 2 pathways by which hypothalamic releasing hormones work
describe the dual control pathway of GH secretion
what is the rule regarding the control of the anterior pituitary, and what is the exception to that rule
anterior pituitary stimulated by hypothalamic releasing hormones (& may be suppressed by hypothalamic inhibitory factors)
Prolactin appears to be under dominant negative control by dopamine (from arcuate nucleus) ∴ stimulus = less inhibition
describe and give examples of the short-loop negative feedback in the anterior pituitary
stimulus to anterior pituitary is controlled by negative feedback loops within the pituitary itself.
LH and FSH decrease frequency and amplitude of GnRH impulses.
GH suppresses subsequent synthesis and secretion of GHRH
describe and give examples of the long-loop negative feedback in the anterior pituitary
these are hormone signals arising from outside of the hypothalamo-pituitary complex. Examples include the thyroid, gonadal and adrenal axes;
- effects of gonadal steroids on GnRH - LH and fSH act on gonads which stimulate production of steroids which feedback on GnRH signal
- effects of corticosteroids on CRH - ACTH acts on adrenal glands to produce corticosteroids which feedback to hypothalmus to turn off CRH
sumarise the Hypothalamo-pituitary-thyroid (HPT) Axis
summarise the Hypothalamo-pituitary-gonadal (HPG) Axis:
summarise the Hypothalamo-pituitary-adrenal (HPA) Axis:
describe how chronic stress override endocrine negative feedback mechanisms
Higher centres of brain can over-ride hypothalamopituitary drive to endocrine axes
Over-rides negative feedback on CRH and ACTH - causing hyperactivity in adrenal axis (increased cortisol)
the hyperacitivty in the adrenal axis causes ;
- Loss of GnRH (so stress is a contraceptive)
- Loss of GHRH (so stress effects growth potential)
list some causes of funcational disconnections of the pituitary gland
- cranial trauma - interrupt flow between hypothalamus and pituitary - stops releasing hormones and injure neuronal axis. also pituitary stalk commonly injured therefore loss of protection
- Pressure on the pituitary stalk, usually secondary to pituitary tumour, which causes occlusion of the hypophyseal portal circulation.
- cytokines from inflammation or infection.
- midline defects e.g. septo-optic dysplasias
- defects in migration of hypothalamic neurones e.g. Kellman’s syndrome
describe Kallman’s syndrome
There is no migration of hypothalamic neurons and they end up in the nose causing anosmia (inability to perceive odor).
There is also hypogonadism, infertility and inability to start puberty.
which part of the pituitary does irradiation effect the most
Anterior pituitary cells are sensitive to irradiation, causing progressie loss of cell function.
Somatotrophs (GH) are most sensitive.
name 2 examples of funcation pituitary tumours
very rare
- prolactinomas
- ACTH-hypersecretion
describe the effects of prolactinomas
Functional pituitary tumours
They’re very rare. They secrete prolactin.
They cause infertility by supressing the HPG axis
Prolactinomas can be shrunk to an operable size by administering a dopamine agonist (bromocriptine)
describe the causes of ACTH hypersecretion
either from pituitary corticotrophs as in Cushing’s disease
or ectopically from small cell lung tumours
describe the effects of ACTH secretion in Cushing’s disease
caused by hypersecretion of ACTH from adrenocorticotrophic anterior pituitary tumours, which are insensitive to cortisol negative feedback
Patients will also be hyperpigmented with acanthosis nigricans (thickened dark patches of skin around groin and neck)
why is ectopic ACTH not supressed by cortisol
e.g. from small cell lung tumours
in HPA (Adrenal) axis cortisol suppresses CRH and this in turn supresses stimulus to ACTh synthesi and secretion
ectopic ACTh secretion isn’t dependent on CRH and so will not be supressed by cortisol (which only supresses endogenous ACTH)
describe the effects of GH hypersecretion
Hypersecretion of GH from pituitary somatotrophs causes bones and cartilage to grow in infants causing gigantism
In adulthood the epiphyseal plates have fused, thus only cartilage grows causing acromegaly
describe the effects of TSH hypersecretion
very rare
most measurements of raised TSH reflect under-active thyroid gland or assay errors
describe the structure of oxytocin
Oxytocin is a nine amino acid peptide that is synthesized in hypothalamic neurons
Oxytocin is also secreted from a few other tissues, including the ovaries and testes
Oxytocin differs from ADH in two of the nine amino acids
Both hormones are packaged into granules and secreted along with carrier proteins called neurophysins
describe the role of oxytocin in the stimulation of milk ejection
how does the suckling reflex causes milk ejection
baby suckles → stimulates mechanoreceptors in mammilary gland tissue → signal to hypothalamus and stimulate release of oxytocin and prolactin
oxytocin caused increases milk ejection (via ducts)
prolacin causes ncreased milk production
describe the role of oxytocin in uterine smooth muscle contractions at birth
describe the role of oxytocin on the establishment of maternal behaviour
describe 2 neural reflexes that mediate oxytocin secretion
1. suckling reflex - The act of nursing or suckling is relayed within a few milliseconds to the brain via a spinal reflex arc. These signals impinge on oxytocin-secreting neurons, leading to release of oxytocin
2. the Fergusson reflex - released during labour to stimulate contraction of uterine smooth muscle, this is a positive feedback loop
how can crying stimulate lactation in mothers
strong neural reflexes, which release prolactin as a result of baby’s cry and mechanical stimulation
describe the structure of hydrophilic hormones
they’re peptide/protein hormones
Rendered water-soluble by virtue of the polar peptide bonds and/or the polar amino-acid side-chains (catecholamines are hydrophilic hormones because they possess numerous polar hydroxyl groups)
The water-solubility of glycoprotein hormones is increased further by the additional presence of N-linked and/or O-linked carbohydrate chains
Prostaglandins, while lipid derivatives, are rendered hydrophilic by the presence of a carboxylic acid group
unable to pass through the hydrophobic core of the plasma membrane
THEREFORE, to influence the activity of intracellular enzymes, the binding of hydrophilic hormones to their cell surface receptors must initiate a transmembrane signalling pathway that typically involves second messengers and protein kinase/phophatase enzymes
describe the structure of hydrophobic hormones
- In general, these are non-polar molecules, often comprising cyclic carbon structures which may be derivatives of:
- cholesterol (as for the steroid hormones)
- tyrosine (as in the case of the thyroid hormones).
- or derivatives of the fat-soluble vitamins, A & D.
- Hydrophobic hormones can diffuse across the plasma membrane to interact directly with intracellular receptors
- In the unbound state, these receptors can be located either in the cytoplasm or in the nucleus (dependent on the precise identity of the receptor)
- In either event, ligand-activated receptors must translocate into the nucleus and dimerise in order to bind to DNA and exert their actions as ligand-dependent transcription factors, either increasing or decreasing the rate of transcription of target genes
give examples of hydrophobic hormones
- Steroid hormones* – progesterone, cortisol, aldosterone, testosterone, oestradiol
- Thyroid hormones* – thyroxine, MIT, T4, T3
fat-soluble vitamins
how are the the plasma concentration of a peptide/protein hormone or catecholamine controlled
at both the level of hormone synthesis and at the level of secretion.
describe the relationship between rate of secretion and rate of synthesis of hydrophilic hormones
their rate of secretion is directly proportional to the rate of their synthesis
which kind of hormone is heaptic metabolism more relevant to
more important for the clearance of hydrophobic than hydrophilic hormones
Where (in a target cell) might you find the receptor for a hydrophobic hormone?
nucleus
cytosol
In general, how do hydrophilic hormones affect metabolism?
Activation of transmembrane signal transduction pathways – generation of second messengers – activation of protein kinases and or phosphatases – phosphorylation/ dephosphorylation of enzymes
In general, how do hydrophobic hormones affect metabolism?
Activation of intracellular receptors – “ligand-dependent transcription factors” – bind to DNA and affect the level of expression of target genes (including enzymes)
Suggest 3 possible reasons why the homeostatic relationship between X and Y might fail:
- defect in synthesis and/or secretion of hormone X
- defect in action of hormone X
- defect in the ability of the gland that synthesises hormone X to respond to the solute Y
Suggest 4 possible reasons why the negative feedback between hormones “C” and “B” might fail
- Defect in the synthesis of hormone “C”
- Defect in the secretion of hormone “C”
- Defect in the cellular response(s) to hormone “C”
- Ectopic production of hormones “A” and/or “B” outside the normal endocrine axis.
Assume that hormone “C” acts to increase the concentration of “S”.
Explain what would happen to the concentration of the stimulatory hormone “A” and of the solute/ion “S” if a mutation in the receptor for hormone “C” were to render the patient resistant to the actions of this hormone?
Loss of negative feedback by hormone “C” would lead to increased concentration of hormone “A” Loss of stimulatory action of hormone “C” would allow concentration of the solute “S” to fall
Which of the factors listed above (if any) is NOT relevant in determining the concentration of the steroid hormone, progesterone?
Rate of secretion – since steroids are hydrophobic such that rate of secretion (by diffusion) is determined by the rate of synthesis
Indicate how each of these have to change in order to decrease the concentration of a hydrophilic hormone
gove exmaples of hormones sensed by nuclear receptors
steroid and thyroid hormones
why are nuclear recetpors classified as transcription factors
because they have the ability to directly bind to DNA and regulate the expression of adjacent genes
how does ligand binding to nuclear receptor affect gene expression
ligand binding to a nuclear receptor results in a conformational change in the receptor, which, in turn, activates the receptor, resulting in up-regulation or downregulation of gene expression.
describe what happens when ligands bind to type 1 nuclear receptors
Ligand binding to type I nuclear receptors in the cytosol results in the dissociation of heat shock proteins, homo-dimerization, translocation (i.e., active transport) from the cytoplasm into the cell nucleus, and binding to specific sequences of DNA known as hormone response elements (HREs)
Type I nuclear receptors bind to HREs consisting of two half-sites separated by a variable length of DNA, and the second half-site has a sequence inverted from the first (inverted repeat)
give examples of type 1 nuclear receptors
androgen receptor
oestrogen receptors
glucocorticoid receptor
progesterone receptor
descibe the domans of nuclear receptors
N-terminal regulatory domain: Contains the activation function 1 (AF-1) whose action is independent of the presence of ligand. The transcriptional activation of AF-1 is normally very weak, but it does synergize with AF-2 in the E-domain to produce a more robust upregulation of gene expression.
DNA-binding domain (DBD): Highly conserved domain containing two zinc fingers that binds to specific sequences of DNA called hormone response elements (HRE)
Hinge region: Thought to be a flexible domain that connects the DBD with the LBD. Influences intracellular trafficking and subcellular distribution
Ligand binding domain (LBD): The structure of the LBD is referred to as an alpha helical sandwich fold in which three anti parallel alpha helices (the “sandwich filling”) are flanked by two alpha helices on one side and three on the other (the “bread”)The ligand binding cavity is within the interior of the LBD and just below three anti parallel alpha helical sandwich “filling”.Along with the DBD, the LBD contributes to the dimerization interface of the receptor and in addition, binds coactivator and corepressor proteins. The LBD also contains the activation function 2 (AF-2) whose action is dependent on the presence of bound ligand
C-terminal domain: Highly variable in sequence between various nuclear receptors.
how do type 2 nuclear receptors work
Type II receptors, in contrast to type I, are retained in the nucleus regardless of the ligand binding status and in addition bind as hetero-dimers (usually with RXR) to DNA
In the absence of ligand, type II nuclear receptors are often complexed with corepressor proteins
Ligand binding to the nuclear receptor causes dissociation of corepressor and recruitment of coactivator proteins
Additional proteins including RNA polymerase are then recruited to the NR/DNA complex that transcribes DNA into messenger RNA
what’s the function of type 3 nuclear receptors
referred to as orphan receptors - have no known endogenous ligands
Some of these receptors such as FXR, LXR, and PPAR bind a number of metabolic intermediates such as fatty acids, bile acids and/or sterols with relatively low affinity
These receptors hence may function as metabolic sensors
what’s the function of type 4 nuclear receptors
Bind as monomer or dimers but only a single DNA binding domain of the receptor binds to single half site.
how are hydrophilic hormones found in the plasma
Hydrophilic hormones can dissolve in the plasma without needing transport by binding proteins, although there are exceptions (about half of the catecholamines are loosely bound to plasma albumin).
describe the difference between endocrine, paracrine, autocrine, and juxtacrine hormones
Endocrine - Act on cells far from the site of release. Are secreted into the blood. Only target cells express the receptor, e.g. insulin and adrenaline
Paracrine - Act on nearby cells only. They diffuse in the interstitial fluid and are rapidly inactivated by local enzymes, e.g. histamine
Juxtacrine - The hormone is either bound to the membrane (this requires physical contact between cells) or the hormone is secreted into the extracellular matrix
Autocrine - Act on the cell that released the hormone, e.g. T-cells and interleukin-2
describe the basic structure of hormone receptors
name and give examples of the 4 types of hormone receptors
explain the generalised signal transuction process
- Hormone is released. The hormone may enter into the bloodstream in order to reach targets all over the body, or may only be released into the tissue fluid, to reach nearby cells
- Hormone binds to receptor on plasma membrane of cell. Hormone binding induces a conformational change in the receptor’s cytosolic region that alters its function
- This causes an increase in the concentration of second messenger inside the cell, which amplifies the hormone effect
- Effectors in the cytosol, which may be pumps, enzymes or gene transcription factors are stimulated or inhibited by the 2nd messenger
- The signalling pathway is shut down. Effectors return to original state, and messengers are removed or become ineffective.
describe what generally happens when a hormone binds a g-protein coupled receptor
Hormone-bound receptor causes the exchange of GDP for GTP, activating the Gα subunit. The (dissociated) Gα subunit then interacts with an enzyme, until it hydrolyses the GTP to GDP, becoming inactive again (takes seconds to minutes)
which kind of responses are g-protein coupled receptors involved in
They are involved in responses to hormones, neurotransmitters, odours, tastes, and light
describe the 4 groups of G alpha sybunits ate their actions
Gs - activates adenylyl cyclase, increasing [cAMP]
Gi - inhibits adenylyl cyclase, reducing [cAMP]
Gq - activates phospholipase C, increasing [DAG], [IP3] and [Ca++]
Gt - activates retinal cyclic GMP phosphodiesterase
whcih specific part of the g-protein coupled receptor interacts with the g-protein alpha subunit
The 3/4 and 5/6 cytosolic loops
what’s the role of the Gβγ in g-protein coupled hormone receptors
may alter specificity of receptor-G-protein binding (help determine which receptors interact with which g-protein)
co-operate in transduction
shut the pathway down
describe what happens when adrenaline binds at the β-Adrenergic Receptor
the β-Adrenergic Receptor activates Gs alpha
PKA has 2 catalytic and 2 regulatory subunits
- Adrenaline comes, binds to receptor, changes conformation of the 3,4 5,6 loops à now they’re able to interact with g-protein
- Cause g-protein to drop GDP and pick up GTP from inside cell à changes shape of Gs alpha subunit which can therefore no longer bind to beta and gamma subunits which go away
- The alpha subunit interacts with the adenylate cyclase and activates it (AC only active as long as it binds to the Gs alpha subunit)
- The AC now active can convert ATP into cAMP
- cAMP binds to PKA, and releases the catalytic subunits which then phosphorylate lots of different proteins
describe the activation of the heterotrimeric G-protein at the molecular level
Switch II is hidden by the βγ subunits. switch 2 forms a alpha helix
the extra phsophate from GTP stabilises the helical switch 2
The stabilised switch II interacts and activates adenylyl cyclase
When the GTP is hydrolysed, switch II becomes disordered.
what’s the effect of vibrio cholerae toxin on the heterotrimeric g-protein
it inhibits the ability of Gs α to breakdown GTP into GDP
THEREFORE: Overactive adenylyl cyclase in enterocytes of intestine - responsible for watery diarrhoea
describe how PKA is able to alter metabolic pathways both long-term and short term
The binding of 4 x cAMP to the two R subunits causes them to dissociate from the catalytic subunits, activating them.
SHORT TERM: Protein kinase A phosphorylates several enzymes, such as hormone-sensitive lipase (+), acetyl CoA carboxylase (-), glycogen synthase (-)
LONG TERM: it also phosphorylates the transcription factor CREB (+).
Protein kinase A is thus able to immediately alter metabolic pathways, and have longer term effects via gene transcription
describe the structure of PKA
Protein kinase A, an R2C2 heterotetramer, is a serine/threonine kinase.
It recognises the consensus sequence:Arg,Arg,X,Ser/Thr,Z
The regulatory subunits have the sequence: Arg,Arg,Gly,Ala,Ile
what are the effects of the cAMP/PKA pathway on the liver (and which are the relevant hormones)
adrenaline, NA, glucagon
to increase glycogenolysis and gluconeogenesis
what are the effects of the cAMP/PKA pathway on the adipose tissue (and which are the relevant hormones)
adrenaline and ACTH
increases lipolysis
what are the effects of the cAMP/PKA pathway on the ovarian follicles (and which are the relevant hormones)
FSH, LH
Increased synthesis of oestrogen and progesterone
what allows our cells to be so sensitive to small concentrations of hormones
- The adrenaline:receptor complex is able to catalyse GDP:GTP exchange on multiple G-proteins.
Each activated Ga subunit can only bind to one adenylyl cyclase. - Each active adenylyl cyclase can catalyse the formation of many molecules of cAMP.
It take 4 molecules of cAMP to activate 2 x PKA subunits. - Each active PKA subunit can phosphorylate many proteins.
describe receptor enzymes
These receptors have an extracellular ligand-binding domain, and an enzyme active site on the intracellular section, connected by a single transmembrane segment.
- Many of these enzymes are tyrosine kinases (RTKs), e.g. the insulin receptor.
- There are also some with serine/threonine kinase activity.
- Another group have guanylyl cyclase activity (convert GTP to cGMP)
In these receptors, ligand binding either activates the enzyme activity, or brings it in proximity to its target.
describe receptor tyrosine kinases
These functions as dimers, with an extracellular hormone-binding domain, and an intracellular protein tyrosine kinase domain.
Upon binding of hormone (many are growth factors), RTK monomers cross-phosphorylate each other.
Phosphorylation of the RTK makes it a site of attachment for proteins with SH2 domains, or PTB domains - localising proteins at the membrane.
For the insulin receptor, cross-phosphorylation causes the kinase to become fully active.
describe how the epidermal growth factor works
- Binding of EGF to each EGFR monomer induces a structural change that allows the monomers to dimerize. Proximity of the cytosolic domains allows cross-phosphorylation
- Tyrosine-phosphates act as docking sites for Grb-2, which is attached to Sos
- Sos catalyses the exchange of GDP for GTP on membrane-bound Ras, activating it
- GTP:Ras binds and activates Raf, a membrane-bound protein kinase
- A series of protein kinases are phosphorylated and activated, resulting in the phosphorylation of several transcription factors, altering their activity.
what is Sos and how does it work
Sos is a guanine nucleotide exchange factor (GEF)
it catalyses the exchange of GDP for GTP on the Ras protein
But only when it has been recruited to the membrane via Grb-2.
what is Ras, and how does it differ to heterotrimeric G-proteins
Ras is a small G-protein. Unlike the heterotrimeric G-proteins, Ras is monomeric
Ras also has a slower GTPase activity than heterotrimeric G-proteins
The GTPase activity can be greatly increased by GAPs (GTPase activating proteins)
Ras:GTP binds to, and activates, Raf
describe why some EGFR signalling can cause cancer
EGFR is overexpressed in some epithelial cancers.
In this case, a small amount of receptor can dimerize in the absence of ligand.
Since the tyrosine kinase activity is already present, this is enough to initiate signal transduction, thereby sending an inappropriate ‘grow and divide’ signal to the cell.
A therapeutic antibody can be used totargets the extracellular domain of the receptor, sterically blocking the ability of the receptor to dimerise.
This has been successfully used in colorectal cancers.
describe how insulin receptor signalling works
- Binding of insulin to the dimeric receptor forces the PTK domains together, followed by cross-phosphorylation.
- The first round of cross-phosphorylation fully activates the kinase activity, and is followed by more cross-phosphorylation.
- These phosphorylated tyrosine residues act as docking sites for IRS-1 (insulin receptor substrate 1), which gets phosphorylated.
- Phosphorylated IRS-1 can bind PI-3K (phosphoinositide-3 kinase), which, now located at the membrane, phosphorylates PIP2 at position 3, forming PIP3 (phosphatidylinositol-3,4,5 trisphosphate).
- PIP3 allows both PDK1 (phosphoinositide-dependent kinase-1) and PKB (protein kinase B) to associate with the membrane via their PH (pleckstrin homology) domains.
- Phosphorylated PKB dissociates from the membrane and phosphorylates its target proteins
which pathway pathway is responsible for GLUT4 translocation?
the insulin receptor signalling pathway
why is IRS-1 described as a docking protein
as it can bind many proteins, including Grb-2 (thereby activating the MAPK pathway)
where is IRS-1 normally found
IRS-1 is already associated with the membrane due to its PH domain, which can bind PIP2. Once phosphorylated, it can dissociate from the insulin receptor
There are other proteins that can assemble at the phosphorylated insulin receptor, including IRS-2, a homologous protein.
Insulin is therefore capable of simultaneously stimulating numerous pathways, involving short-term and long-term effects
what is TGF-β, and what is its role
The TGF-β family is a large family of proteins involved in regulating development
These signalling proteins normally prevent proliferation of most mammalian cells by inducing synthesis of proteins that inhibit the cell cycle
Most mammalian cells secrete at least one TGF-β isoform, and have receptors on their surface
Bone morphogenetic protein (BMP7 - a TGF B) induces bone formation in cultured cells and is now used clinically to strengthen bone fractures
TGF-β proteins also play a role in tissue organisation, promoting expression of extracellular matrix proteins and adhesion molecules
explain how TGF-β causes activation of its receptor
TGF-β binds to TBR-II, whose serine/threonine kinase activity is constitutively active.
This allows it to bind to TBR-I, and phosphorylate its glycine-serine rich (GS) domain, activating the S/T kinase activity.
TBR-I can then phosphorylate a class of transcription factors called R-Smads.
Upon phosphorylation, two R-Smads and a Co-Smad form a heterotrimer, and the nuclear localisation signals are also exposed.
In the nucleus, the heterotrimer interacts with transcription factors to cause expression of particular target genes.
describe why the link between TGF-β and cancers
The TGF-β receptor pathway often inhibits growth in cells.
Loss of either TBRI or TBRII function due to inactivating mutations is found in many human tumours.
These tumours are resistant to growth inhibition by TGF-β.
Mutations in the Smad proteins also prevent TGF-β signalling, most human pancreatic cancers contain a deletion in Smad4 (a Co-Smad).
describe the structure of cytokine receptors
Cytokines are a family of small (~160 aas) signalling molecules, with a characteristic arrangement of four alpha helices, controlling the growth and differentiation of a number of cells.
Cytokine receptors do not have an intrinsic enzyme activity, rather they recruit an enzyme.
The receptors all have a tyrosine kinase called JAK bound to their cytosolic domains, which phosphorylate transcription members of the Signal Transduction and Activation of Transcription (STAT) family.
Although cytokine receptors can activate other pathways, e.g. the MAPK pathway, the JAK/STAT pathway is normally only activated by cytokines.
what is erythropoietin
Erythropoietin is a cytokine released by the kidney in response to low oxygen
It stimulates the transcription of genes in erythroid progenitors that prevent them from undergoing apoptosis, and stimulate them to differentiate into erythrocytes (RBCs)
The use of supplemental erythropoietin to increase the level of erythrocytes in the blood is banned in international athletic competitions
The use of supplemental erythropoietin is also dangerous, as the surplus erythrocytes can clot small blood vessels. Several athletes have died of stroke during exercise due to erythropoietin doping
describe how the erythropoietin receptor works
- A JAK2 kinase with low activity is bound to the cytosolic domain of EpoR
- Epo simultaneously binds two EpoRs, bringing the JAK kinases close enough for each to phosphorylate the ‘activation lip’ of the other. This lowers the Km of the kinase for its substrate, activating it
- The JAK kinases phosphorylate the receptors allow STAT5 to bind (via SH2 domains), and also get phosphorylated
- The phosphorylated STAT5s dissociate from the receptor, dimerise, exposing a nuclear localisation sequence
- The STAT5 dimer enters the nucleus and its DNA-binding domain binds to specific DNA regulatory sequences to control the expression of target genes
describe how the JAK/STAT Pathway is switched off, and the importance of this
SHP1 is a phosphotyrosine phosphatase,that binds the phosphorylated receptor and dephosphorylates JAK kinase, inhibiting the pathway when cytokines are no longer binding to the receptor
A mutant version of the erythropoietin receptor was discovered in an athlete that caused them to have higher levels of RBCs than normal, despite unusually low levels of erythropoietin
This mutant receptor was missing some of the tyrosines normally phosphorylated during signal transduction
The receptor was able to bind and activate STAT5, but was unable to bind the SHP1 phosphatase, resulting in increased intracellular signalling in the erythroid progenitor cells, and more RBCs than usual
what are the 2 main functions of the pancreas
exocrine - acinar cells. and these screte into ducts and channels which carry products outside of body/into body cavities (salivary glands, sweat glands, pancreas mammillary glands etc)
endocrine - islets of langerhans
describe the anatomical position of the pancreas
Lies deep in the stomach
Tail is close to spleen
Head is encircled by duodenum
which 3 parts does the pancreas consist of
LOBULES: acinar cells that secrete enzymes & fluid
DUCTS: intercalated ducts joint to form pancreatic duct - this fuses with common bile duct before emptying into the duodenum
ISLETS OF LANGERHANS: dedicated to endocrine function
describe the nerve supply of the islets of langerhans
Sympathetic adrenergic input: Splanchnic nerve – from coeliac plexus
Parasympathetic cholinergic input: Vagus nerve
list the types of cells found in the islets of langerhans
α cells - Glucagon
β cells - Insulin
δ cells - Somatostatin
PP cells - Pancreatic polypeptide
describe the structure and formation of insulin
what is the function of prohormone convertases 1 and 2
to cleave pro-insulin to produce insulin, and proglucagon into glucagon
what does preproglucagon give rise to
Processed by prohormone convertases 1 and 2
Differential processing in alpha cells vs L-cells
glucagon in the alpha cells of the pancreas
GLP1, GLP2 in L-cells
what’s the paracrine role of somatostatin
suppresses insulin and glucagon
what is the role of pancreatic polypeptide
Secreted after eating and suppresses appetite
what is the role of Islet Amyloid PolyPeptide (IAPP or amylin)
appears to supress insulin secretion
summarise the actions of inulin and glucagon with respect to hypo and hyperglycaemia
list the factors that stimulate insulin secretion
- EATING A MIXED MEAL: ↑Glucose , Amino acids, Gut hormones released postprandially - (GLP-1, GIP = INCRETINS)
- Glucagon
- AUTONOMIC INNERVATION: Acetylcholine . Alpha1 adrenergic receptors, Beta2 adrenergic receptors
list the factors that inhibit insulin secretion
↓ Glucose
- Somatostatin - intraislet pancreatic somatostatin, Gastric somatostatin
- Alpha2 adrenergic receptors (species dependent)
describe the process fo insulin secretion (from glucose uptake)
- Glucose sitting outside the cell is brought to the pancreas, it enters cell via GLUT2
- It undergoes glycolysis and releases atp → Rise in ATP:ADP ratio and this leads to closure of ATP-sensitive potassium channel
- Leads to accumulation of potassium and depolarisation there à leads to opening of voltage-gated calcium channel which lets calcium in
- Calcium binds to the storage granules which contain insulin → degranulation → fusion of vesicles with cell membrane → release
list the factors that stimulate and those that inhibit insulin secretion
list the factors that stimulate somatostain secretion
describe the roles of Endocrine vs Paracrine Somatostatin
describe the role of insulin in carbohydrate metabolism
↑ blood [glucose] stimulates release of Insulin:
- Facilitates entry of glucose to tissues, especially in: Liver, Muscle, Adipose
- Stimulates the liver to store glucose in the form of Glycogen
which is the organ that can either take up or release glucose
liver
what is glucose disposal, and what are the 2 kinds
it’s the rate of uptake into peripheral tissue
it can be either inslin mediated, or non-inlsulin mediated mediated
Insulin mediated: Skeletal muscle + adipose tissue
Non-insulin mediated: CNS + other tissues
how does insulin facilitate glucose uptake
facilitated diffusion via hexose transporters such as GLUT4 (major transporter in muscle, adipose)
in the absence of insulin GLUT4 stored in cytoplasmic vesicles
when insulin comes along you get fusion of vesicles and Insertion of glucose transporters in plasma membrane
describe the structure of hexose transporters
where is SGLUT1 expressed, and what are its characteristics
Intestinal mucosa, kidney tubules
Cotransports one molecule of glucose or galactose along with two sodium ions
Does not transport fructose.
where is GLUT-1 expressed, and what are its characteristics
Brain, erythrocyte, endothelial cells, fetal tissues
Transports glucose (high affinity) and galactose, not fructose
where is GLUT-2 expressed, and what are its characteristics
Liver, pancreatic beta cell, small intestine, kidney
Transports glucose, galactose and fructose.
A low affinity, high capacity glucose transporter
serves as a “glucose sensor” in pancreatic beta cells
where is GLUT-3 expressed, and what are its characteristics
Brain, placenta and testes
Transports glucose (high affinity) and galactose, not fructose.
The primary glucose transporter for neurons.
where is GLUT-4 expressed, and what are its characteristics
Skeletal and cardiac muscle, adipocytes
The insulin-responsive glucose transporter
High affinity for glucose
where is GLUT-5 expressed, and what are its characteristics
Small intestine, sperm
Transports fructose, but not glucose or galactose
describe the effects of insulin on the liver
what are 2 factors that stimulate glycogen reserve breakdown
absence of insulin
and
presence of glucagon
what happens to cells as blood [glucose] drops
Many cells become unable to take up glucose and switch to alternative fuels for energy eg. FA
Neurones need constant supply of glucose
how is fed glucose utilised
how is fasting glucose made and utilised
what’s the role of Glycogen Synthase & Glycogen Phosphorylase in breakdown of glycogen
Both enzymes can be converted between active and less active forms using a system of protein kinases:
PKA phosphorylates and activates PKB, which activates GP
PKA phoshorylates and inactivates GS, which prevents cycling of glucose-1-P ⇒ Glycogen breakdown
explain the glycogen synthase/glycogen phosphorylase coordination
summarise the effects of phosphorylation on anabolism vs catabolism
ANABLOSIM = PHOSPHATASES (insulin)
CATABOLISM = KINASES (glucagon)
Insulin DEPHOSPHORYLATES By activating PHOSPHATASES This leads to net glycogen synthesis
Glucagon PHOSPHORYLATES By activating KINASES This leads to net glycogen breakdown
explain the process by which Glucagon Switches ON Glycogen Phosphorylase
describe the 2 ways in which Glucagon Switches OFF Glycogen Synthetase (GS)
describe the 2 ways by which Insulin Switches ON Glycogen Synthetase (GS)
describe the effects of insulin and glucagon on the liver
what are the important effects of insulin on lipid metabolism
- Promotes synthesis of fatty acids in the liver
- Inhibits breakdown of fat in adipose tissue
Therefore from a whole body perspective, insulin has a fat-building effect
describe insulin’s effect on TAG
ANABOLIC - Increases net TAG synthesis:
- Activates acetyl-CoA carboxylase to generate malonyl CoA and therefore fatty acids
- Inactivates hormone-sensitive lipase (HSL)
describe glucagon’s effects on TAG
CATABOLIC - Stimulates net breakdown of TAG stores (spares glucose)
- Inactivates acetyl-CoA carboxylase
- Activates hormone-sensitive lipase (HSL)
describe how Glucose metabolism linked to Lipogenesis
- Pyruvate enters citric acid cycle – citrate can exit for FA biosynthesis (role for acetyl-CoA)
- Glycolysis generates α-phospho-glycerate – backbone of TAG
- Pentose phosphate pathway generates reduced cofactors for FA biosynthesis
explain glucagon’s effect on Acetyl-CoA Carboxylase
describe insulin’s effect on Acetyl-CoA Carboxylase
explain Hormone Sensitive Lipase’s role in FA synthesis
why do glucagon and glucocorticoids upregulate HSL
To increase fat metabolism, to spare plasma glucose
what is diabetes
A metabolic disorder of multiple aetiologies
Chronic hyperglycaemia
Disturbances of carbohydrate, fat and protein metabolism
Resulting from defects in:
insulin secretion
insulin action
or both
outline the 2 main types of diabetes
Type 1 Diabetes
ß-cell destruction
Absolute lack of insulin
Type 2 Diabetes
Defective insulin secretion (ß-cell dysfunction)
Insulin resistance
Relative lack of insulin
other than T2DM and T1DM, list some other types of diabetes
Maturity onset diabetes of the young (MODY)
Gestational diabetes
Other types of diabetes: Pancreatic / Endocrine / Drugs / Other genetic syndromes
describe continuum of diabates
list the signs and symptoms of diabates
Weight loss
Polydipsia (drinking too much)
Polyuria (too much urine)
Lethargy & general malaise
Recurrent infections (often skin or urine)
In type 2 often NO symptoms
outline the WHO criteria for the diagnosis of diabetes
what is Hb1AC
RBCs containing HB are exposed to glucose in the blood, and glucose enters RBCs via GLUT1
if it’s not used for glyoclysis this glucose sticks to HB in non-enzymatic reaction (glycosylation) and this happens at the N-terminus of the Beta chain
The higher the glucose the faster the glycosylation - Normally 4-6%
Reflects average blood glucose over ~90 days
describe impaired glucose tolerance
Patient has trouble metabolising glucose
- stage of impaired glucose regulation
- fasting plasma glucose < 7.0 mmol/L
- 75g OGTT 2-hour value > 7.8 but < 11.1
describe impaired fasting glycaemia (IFG)
Patient has trouble controlling glucose even when they haven’t eaten
- fasting plasma glucose > 6.1 mmol/L but < 7.0
- OGTT needed to exclude diabetes
how are and IGT and IFG managed, and why
Risk ↑ for CV disease ± diabetes IGT
2-5% per year progress to diabetes
Early treatment may reduce progression to diabetes:
- Healthy eating advice / weight management / exercise effective in slowing progression
- Metformin useful but less effective
Annual OGTT or HbA1c to diagnose diabetes
list the goals of diabates management
Manage symptoms
Prevent acute and late complications
Improve quality of life
Avoid premature diabetes-associated death
Provide an individualised approach
list 5 chronic complications of diabates
nephropathy - vessles in kidnyes start shutting off and cause renal failure
erectile dysfunction is an indication of: blood flow, nerve function and cardiovascular disease
briefly outline T2DM and its causes
Strongly linked to increase in obesity
what are the core defects of T2DM
- ß-cell malfunction
- Insulin resistance
outline treatments of T2DM
- Diet and exercise Weight loss
- Bariatric surgery?
- Oral hypoglycaemic agents;
- Sulphonylureas, metformin
- Gliptins, thiazolidinediones, gliflozins
- GLP-1 analogues
- Insulin therapy
how can surgery be useful in treating diabetes/obesity
- decrease in levels of glycated Hb (Hb1AC)
- drop in fasting plasma glucose
- patients can be on less diabetic medications
- drop in BMI
fill in this table for T2DM care strategy
in T2DM treatment, why do we give a lower limit of 6.5 for glycaemia levels
because hypoglycaemia kills faster than hyperglycaemia
list 3 ways to monitor glycaemic control
briefly outline the ‘patahology’ of T1DM
Generally < 30 yrs
Beta cell destruction
↓insulin
Need insulin to survive
Absence of insulin causes ketogenesis
Ketoacidosis kills
list the factors that lead to T1DM
what is the treatment for T1DM
INSULIN
1-3 insulin injections/day of the same insulin
Multiple daily injections (4-5) with different insulins
Continuous subcutaneous insulin infusion (‘ pump ’)
what’s the purpose of insulin anaolgues
Created to alter pharmacokinetics meaning alter how quickly the insluin appears in the blood
list the 3 kinds of insulin analogues
- inhibit hexamerisation → more rapid acting
- bind albumin → slow acting, longer lasting
- form insoluble depots under skin → ultra slow acting
describe this insulin Time-action curve
purple - works immediately
pink - inconvenient as when you eat blood sugar too high and then when the insulin arrives (late) the blood sugar goes down even more and so you get hypoglycaemia
dark blue - prolonged action
describe regimen tailor-made insulin
describe gestational diabetes mellitus
During pregnancy - Macrosomia, resp distress, early delivery
macrosmia = larger baby normally caesarean needed
Resolves after delivery but may recur w/subsequent pregnancies
Risk factors: Obesity, family history T2DM, prev GDM
↑future risk of T2DM, hypertension
TREATMENT: Insulin, metformin Rx
describe MODY
Different genetic background to T2DM as it’s monogenic T2DM is polygenic)
Strong family history of diabetes - autosomal dominant
Diabetes develops at an early age (<25 years)
6 genes identified so far: GCK, HNF1α, HNF1β, HNF4α, IPF1, NeuroD (not autoimmune - defect in insulin sceretion)
TREATMENT: Diet or tablets (don’t treat with insulin)
list 4 causes of pancreatic diabates
surgery
pancreatitis
cystic fibrosis (defects in endo and exocrine secretions)
tumours
list 2 causes of endocrinopathy-caused diabetes
Cushing’s
acromegaly
list 3 drugs that carry risk of drug-induced diabetes
Glucocorticoids
thiazide diuretics
ß blockers
list some genetic causes of diabetes
MODY
Myotonic dystrophy, DIDMOAD
Insulin resistance syndromes
describe the pathophysiology of T1DM
describe the histological changes in a diabetic pancreas in T1DM vs T2DM
what are the effects of Lack of insulin in Type I Diabetes patient
Glucose transport and utilization reduced → ↑glucose
Lack of insulin → unopposed ↑glucagon
↑protein breakdown, ↑glycogenolysis, ↑gluconeogenesis, ↑hepatic glucose output, ↑lipolysis ↑ketogenesis (increased ketogenesis because TAGs broken down into FAs+ glycerol and FAs used to make ketone bodies)
Patient becomes catabolic
Becomes dehydrated because of polyuria
Progressive deterioration → decompensation, diabetic ketoacidosis, coma
how would a graph of plasma glucose concentrations of diabetics vs non-diabetics look
summarise the metabolic disturbances in T1DM
what are the 2 main characteristics of T2DM
Insulin resistance
ß-cell malfunction
why is T2DM described as a Complex Metabolic Disorder
involves a bunch of conditions
describe the mechanisms of insulin resistance
describe the pathogenesis of T2DM
Often revealed by Long-term complications
explain the Interaction of genes, obesity and environment in T2DM
describe how dysfunctional adipose tissue can cause T2DM
adipose tissue can send distress signals (via cytokines which attract inflammatory cells - t-cells, macrophages etc) when it’s no longer able to cope ⇒ presence of inflammatory cells leads to state of chronic inflammation throughout the body
adipose tissue expams to accumulate the fat in subcutaneous tissue AND in visceral organs (lesser extent)
where the body can’t store fat anymore in its normal deposits it starts putting it elsewhere (Ectopic fat) ⇒ this can be in the liver causing fatty liver disease or in the heart linked to cardiovascular disease or in the muscles or pancreas (in pancreas it leads to defects in insulin secretion
list some complications of diabetes
- Increased incidence of cardiovascular disease
- Peripheral vascular disease
- Renal disease (microangiopathy)
- Retinal disease (microangiopathy)
- Lens opacity (cataracts)
- Neuropathy (impaired nerve conductance): Autonomic (bladder, stomach, blood vessels, erections), Sensory, Motor
- Skin infections (gangrene, thrush and other yeasts)
- Osteoarthritis
describe the process of glycation of proteins in hyperglycaemia
Excess glucose increases glycation of Hb
We use HbA1c as a easily accessible measure of glycaemia
HbA1c reflects average glycaemia over past 90 days or so (dependent on red blood cell life)
describe how increased glucose/lipids can cause nephropathy, neuropathy, retinopathy, atherosclerosis
describe the role of SOD (Superoxide dismutase) and how this is altered in diabetes
SOD’s role is to detoxify free radicals and generate H2O2, which is disposed of in one of 2 ways:
- catalse: H20 +O2
- glutathione: H2O
BUT in diabetes we glycate SOD which inhibits the enzyme and so we get accumulation of free radicals which damage the cell
what causes increased oxidative stress in diabates, and why can that contribte to insulin resistance and β-cell dysfunction?
the increase in oxidative stress causes an internal inflammatory response linked to both insulin resistance and β-cell dysfunction
explain the effects of hyperglycaemia on the sorbitol pathway
When glucose levels are high, sorbitol and fructose accumulate in the cells since they diffuse relatively slowly and they aren’t absorbed
This causes osmotic effects (water drawn into cells) which may damage cells such as lens cells and nerve cells
what causes retinopathy in diabetes
glycation of basement membrane, exudation, bleeding
what causes cataracts in diabetes
accumulation of polyols in lens
what causes neuropathy in diabetes
glycation of BM, blood supply to nerves blocked
what causes skin infections in diabetes
poor blood supply leads to poor healing, high glucose levels encourage pathogenic growth
what can you see here
what can you see here
what differences can you see in the retina of someone with Diabetic retinopathy vs normal
what causes foot infections in T2DM
High levels of glucose make a rich medium for organisms infecting the skin
Contributed to by damage to small blood vessels
Sensory neuropathy leads to foot numbness and damage e.g. from ill-fitting shoes
what’s the relation between T2DM and risk of cardiovascular disease
what’s the relation between T2DM complications and HbA1c
how can T2DM cause heart attack
infiltration of the intima muscles with macrophages which produce cytokines which lead to proliferation of the smooth muscle layer underneath and they accumulate cholsterol and become called FOAM CELLS
these foam cells produce athersclerotic lesions which grown into the lumen of the blood vessel
when it grows large enough it blocks the flow of blood through the cessel
in a coronary vessel this leads to angina
when the clot ruptures and causes a thrombus you get a heart attack
3 ways in which diabetes can cause athersclerosis
Impaired Endothelial function:
↓NO production, therefore greater arterial contraction and reduced blood flow
Also increased platelet activation due to lack of NO
Modification of lipoproteins:
LDL particles oxidised/glycated
Macrophages have receptors for AGE
Take up modified LDL to form ‘foam cells’
Proliferation of smooth muscle cells:
Macrophage activation
Chemokine release
Lowering HbA1c by 1% significantly reduces risk of
Diabetes-related death
Myocardial infarction
Microvascular complications
Peripheral vascular disease
What is the optimum HbA1C?
- It is not true that the lower you go the better things are
- ‘Normal’ HbA1c of <6.5% (<48 mmol/mol):
- is difficult to achieve without causing hypos
- may be associated with ↑mortality
- We aim for 6.5-7.5% (48-59 mmol/mol)
- Quality of life is paramount
Compare the effects of insulin and glucagon on the following processes. Put arrows on either side of the list to represent an increase, a decrease or no effect.
Diabetes is a disease that affects an increasing proportion of the population, now of the order of ____ %. The majority of diabetics have the ____________ onset form also known as Type ___ diabetes or by the abbreviation ____________ . Diabetes may be due to a decrease in the secretion of the hormone _______________ , a hormone secreted by the______________ , or due to a ______________sensitivity to it. The latter condition may be treated by drugs such as __________________________________. The acute effects of diabetes result from increased concentrations of _________________ in the blood, leading to the symptoms of______________________ , _______________ and ultimately to ______ , after which death will ensue if not treated. In uncontrolled diabetes, there are also profound changes in lipid metabolism with large increases in the concentrations of _______________________ and _________________________________ . Oxidation of the former may give rise to the formation of ________________________________ with consequent decreases in the pH of the blood. In diabetes, protein metabolism is also affected and the most obvious symptom is ___________________ . Treatment of uncontrolled diabetes may be achieved by use of the hormone isolated from another species, usually the ________ . Recombinant human hormone is available, but gives rise to ______________ _______________ in a minority of patients
Diabetes is a disease that affects an increasing proportion of the population, now of the order of 5-7 %. The majority of diabetics have the late onset form also known as Type 2 diabetes or by the abbreviation NIDDM. Diabetes may be due to a decrease in the secretion of the hormone insulin, a hormone secreted by the pancreas, or due to a reduced sensitivity to it.
The latter condition may be treated by drugs such as biguanides. The acute effects of diabetes result from increased concentrations of glucose in the blood, leading to the symptoms of glycosuria, polyuria and ultimately to coma, after which death will ensue if not treated.
In uncontrolled diabetes, there are also profound changes in lipid metabolism with large increases in the concentrations of non esterified fatty acids and triacylglycerols. Oxidation of the former may give rise to the formation of ketone bodies with consequent decreases in the pH of the blood. In diabetes, protein metabolism is also affected and the most obvious symptom is muscle wasting.
Treatment of uncontrolled diabetes may be achieved by use of the hormone isolated from another species, usually the pig. Recombinant human hormone is available, but gives rise to reactive hypoglycaemia in a minority of patients
someone presents with T2DM
He is emaciated due to loss of muscle and body fat. Possibly drowsy. Most likely an insulin - dependent diabetic Tests should be made to test for blood or urinary glucose and ketone bodies Immediately the breath should be smelt to see if is sweet Plasma insulin levels should be measured K + and bicarbonate should be determined to assess the need for correction of blood pH with bicarbonate. Has been treated successfully with insulin
What is the relevance of these chemical reactions to diabetes?
This can lead to the glycation of enzymes and structural proteins, irreversibly if AGEPs are formed
Underlies many long term effects of diabetes
What does this reaction have to do with the differences in the retinas on the displayed photographs?
Lead to modifications (glycation) in the basement membranes of capillaries in the eye and other tissues
Formation of exudates due to overproduction of these glycoproteins and increased permeability and weakness
Bleeding into vitreous humour occurs - blindness
what part of the eye, other than the retina, could be affected by this reaction
Crystallin in lens glycated causing cataract
Why is the following reaction relevant to diabetes?
This is the sorbitol pathway found in liver and other tissues. Increased glucose concentrations increase this minor pathway by a mass action effect
Since the transport systems in most cells are slow for sorbitol and fructose, they tend to accumulate and cause osmotic disturbances.
How could this reaction influence cellular function in tissues outside the liver?
In sensitive cells such as the nerves, the osmotic effects cause cell damage and contribute to neuropathy, although other factors including protein glycation play a role
They can cause distortion of the lens cells and also contribute towards problems with vision.
These days, few diabetics die after their condition has been diagnosed. However, they are at risk from other diseases that affect the non-diabetic population. This includes increased risk of _________ disease , the leading cause of death also among non-diabetics.
The elevated glucose concentrations leads to the _________ of proteins in which the amino acid residue _________ is modified by glucose reversibly to form a _________ base.
Further chemical reactions give rise to the formation of Amadori products and ultimately to the irreversible cross-linking of proteins and the formation of AGEP which is an abbreviation for ___________________________.
Examples of circulating proteins that may be modified by glucose to the first stage, are the complexes that carry cholesterol around in the blood and are known as __________________.
These may become cross-linked to proteins in the extracellular matrix of the arterial wall and are then recognised by receptors known by the abbreviation_________ on _________, a cell type that internalises the total protein complex, leading to pathological changes in the artery wall know as _________.
These days, few diabetics die after their condition has been diagnosed. However, they are at risk from other diseases that affect the non-diabetic population. This includes increased risk of cardiovascular disease , the leading cause of death also among non-diabetics.
The elevated glucose concentrations leads to the glycation of proteins in which the amino acid residue lysine is modified by glucose reversibly to form a Schiff’s base.
Further chemical reactions give rise to the formation of Amadori products and ultimately to the irreversible cross-linking of proteins and the formation of AGEP which is an abbreviation for advanced glycation end products.
Examples of circulating proteins that may be modified by glucose to the first stage, are the complexes that carry cholesterol around in the blood and are known as low-density lipoproteins.
These may become cross-linked to proteins in the extracellular matrix of the arterial wall and are then recognised by receptors known by the abbreviation RAGE on macrophages, a cell type that internalises the total protein complex, leading to pathological changes in the artery wall know as atherosclerosis
Pancreas arises from dorsal and ventral outgrowths of ______. These outgrowths arise from the ______.
endoderm
foregut
In neonate, islets are highly vascularised and receive both sympathetic and parasympathetic neural inputs from the following nerves respectively:
sympathetic nerve =
parasympathetic nerve =
sympathetic nerve = splanchnic nerve
parasympathetic nerve = vagus nerve
What proportion of the normal pancreas (% by mass) is endocrine tissue?
2%
How many amino-acid residues are there in total in:
human insulin?
human C-peptide?
glucagon ?
somatostatin ?
human insulin: 51 amino acids
human C-peptide: 35
glucagon: 29 amino acids
somatostatin: 14
How is insulin packaged prior to secretion?
Hexamers co-ordinated by Zn – surrounded by C-peptide
list some factors that increase insulin release
Increased [glucose]
Increased [free amino-acids]
Increased [GI hormones]
Increased [glucagon]
Noradrenaline (at low conc.)
Acetylcholine
list some factors that decrease insulin release
Decreased [glucose]
Pancreatic somatostatin
Gastric somatostatin
Noradrenaline (at high conc.)
Adrenaline
Which of the following statements accounts for the phenomenon of insulin -mediated glucose disposal (IMGD) into skeletal muscle and adipose tissue?
A. insulin increases the synthesis of GLUT1
B. insulin increases the synthesis of GLUT4
C. insulin increases the insertion of GLUT1 into the plasma membrane
D. insulin increases the insertion of GLUT4 into the plasma membrane
D. insulin increases the insertion of GLUT4 into the plasma membrane
Insulin stimulates the synthesis of glycogen by glycogen synthetase whereas glucagon inhibits the activity of this enzyme. State two mechanisms via which glucagon inactivates glycogen synthetase:
- Stimulates phosphorylation via cAMP-dependent kinase / PKA
- Inhibits dephosphorylation by phosphoprotein phosphatase (secondary to stimulation of glycogen phosphorylase a)
Insulin stimulates the synthesis of fatty acids via polymer acetyl CoA carboxylase whereas glucagon inhibits the activity of this enzyme.
State three similarities between the control of acetyl CoA carboxylase and glycogen synthetase:
- Inactivated by phosphorylation – activated by dephosphorylation
- Both activated by insulin – insulin inhibits phosphorylation by cAMP-dependent kinase / PKA
- Both inactivated by glucagon – glucagon increases phosphorylation by cAMP-dependent kinase / PKA
In addition, insulin stimulates activation of both enzymes by increasing activity of phosphoprotein phosphatase
Which protein kinase is inhibited by insulin but stimulated by glucagon to mediate antagonistic effects on the activity of glycogen synthetase?
cAMP-dependent kinase / PKA
which cells form the pancreatic islets of Langerhans
Some cells, which bud off from the pancreatic ducts, proliferate to form the pancreatic islets of Langerhans
how is recombinant insulin made
The two cDNA sequences encoding the α- and β-chains of insulin are translated in E.coli, isolated, purified and chemically combined with the 3 disulphide bonds at the appropriate molecular positions
the magnitude of the insulin response to oral intake of protein reflects the combined effects of the rise in plasma amino-acids and the increased levels of gastrin, secretin and CCK
list and explain 3 characteristic features of T1DM
hyperglycaemia - Lack of insulin action means glucose is not taken up and stored in muscle, liver and fat which causes increased circulating blood glucose levels
ketoacidosis - Muscle, liver and fat turn to other energy sources such as fatty acid. Increases production of acetyl CoA - condensed into ketone bodies which acidify the blood
osmotic diuresis - High circulating levels of glucose eventually overcome the ability of the kidneys’ glucose reabsorption systems so that glucose spills into urine
list and explain 2 characteristic features of T2DM
osmotic diuresis - High glucose levels in the urine combined with a high excretion of H+ as a result of the acidity, water flows into the bladder
Advanced Glycation End Products (AGEP) - When present at high levels in the circulation the glucose can covalently link to proteins in the blood or on walls of blood vessels, a process known as glycation
list some autoantibodies found to be associated with T1DM
islet cell autoantibodies (ICA)
insulin (IAA)
glutamic acid decarboxylase (GAA or GAD)
protein tyrosine phosphatase (IA2 or ICA512)
The number of antibodies, rather than the individual antibody, is thought to be most predictive of progression to overt diabetes
approximately 50% of the genetic risk for T1DM can be attributed to the HLA region
The highest risk HLA-DR3/4 DQ8 genotype has been shown to be highly associated with beta-cell autoimmunity
list some possible treatments for T1DM
Islet transplantation – some success but limited by availability of islets
Artificial islets approved in 2012
Immunosuppressive therapy of those at risk – in trial
Prophylactic injections of insulin or other preventative agents in those at risk of diabetes may delay onset of diabetes
what’s the role of autoantibodies in the pathogenesis of T1DM
Although the role of autoantibodies in the pathogenesis of the disease is debated, their presence indicates a dysregulation of the humoral immune response
Circulating autoantibodies to beta cell antigens are present in the majority of patients with Type 1 DM. These autoantibodies can be detected before and at time of clinical diagnosis of disease
how do Anti-idiotypic antibodies regulate both autoantibody binding and their levels?
neutralizing autoantibodies
inhibiting the secretion of autoantibodies
here is an equilibrium between autoantibodies and their anti-idiotypic antibodies, preventing autoimmunity
B lymphocytes that produce autoantibodies function as autoantigen presenting cells. Inhibiting their binding to autoantigen by anti-idiotypic antibodies may prevent development of autoimmune disease
what’s the main factor distinguishing T2DM from T1DM
Circulating levels of insulin distinguish T2 from T1DM.
Patients invariably have normal or excessive circulating levels insulin - pancreas is not completely destroyed. β-cells lose the ability to secrete insulin with progression
Severe insulin resistance is associated with accumulation of amyloid plaques in the β cells. May contribute to the death of pancreatic cells
Importantly most T2’s do not have islet cell antibodies. Suggests destruction of pancreas by non-immune mechanisms in T2DM
what are the different ways in which we can prevent IGT progression to DM
Lifestyle interventions aimed at weight loss of 5-10% of with moderate aerobic exercise such as brisk walking for 150 minutes a week are the most effective
Effective pharmacologic interventions include metformin, acarbose and orlistat
Although thiazolidinediones, such as rosiglitazone, can decrease the rate of progression to diabetes, they pose a significant risk of fluid overload and heart failure
Where does insulin resistance first arise
Insulin resistance arises first in muscle and fat and then at later stages in the liver
describe the (molecular) development of insulin resistance
describe the effects of insulin resistance of FAs, BP, androgen levels
n insulin resistance there is increased release of fatty acids into the circulation and then reconversion of these acids by the liver into triacylglycerols which are recirculated as VLDL in high concentrations (dyslipidaemia)
The high levels of insulin have other consequences – e.g. stimulation of some cells of the sympathetic nervous system leading to hypertension
n some cases it may increase androgen production by ovaries which contributes to the hormonal disturbances seen in PCOS – which may include masculinisation
describe the Glucose-stimulated Insulin Secretion mechanism
Glucose homeostasis relies critically on detection of variations in blood glucose concentrations by pancreatic beta cells, and their subsequent timely release of the appropriate amount of insulin
Glucose sensing by pancreatic beta cells requires glucose uptake and metabolism through the glycolytic pathway
Activation of the Krebs cycle and oxidative phosphorylation generates ATP, and the increase in the ATP to ADP ratio induces plasma membrane depolarization by closing an ATP-dependent K+ channel
This leads to the opening of voltage-dependent Ca2+ channels, and the entry of calcium then triggers insulin granule exocytosis
Glucose uptake by beta cells is catalyzed by the low affinity, high-capacity glucose transporter GLUT2
GLUT2 expression is markedly down-regulated in conditions in which glucose-stimulated insulin secretion is lost
Feeding mice a high-fat diet, which is known to dysregulate insulin secretion, and is associated with a reduction of GLUT2 expression at the plasma membrane
In Fanconi–Bickel syndrome, caused by mutation of GLUT-2 often present with postprandial hyperglycemia and reduced insulin levels
Humans have in addition GLUT-1 and GLUT-3, which may compensate for the absence of GLUT-2
list some genes associated with MODY
MODY patients often present early in life
what is mitochondiral diabetes, causes, prevelance, and symptoms
Families with heritable form of diabetes inherited from mother with a variable penetrance
Caused by mutations in mitochondria (hence maternal transmission)
Accounts for 1-2% of all diabetes
Often misdiagnosed as either T1 or T2DM
When mutant mitochondria predominate - oxidative capacity is reduced. In β-cells this results in reduced capacity to secrete insulin in response to glucose as insulin secretion is linked to glycolysis
Symptoms: e.g. muscle weakness, deafness, neurological problems and lactic acidosis, Maternally inherited diabetes and deafness (MIDD)
what is gestational diabetes
Severe insulin resistance caused by hormonal changes and metabolic stress of pregnancy
In women with low insulin secretory capacity this can result in a form of diabetes
Affects 2% of pregnancies of non diabetic women
Symptoms normally disappear after birth but 60% of these women go on to develop diabetes in later life
list some similarities and differences between T2DM and MODY
Similarities: no Islet cell antibodies, 0 cell destruction
Differences: patients age, autosomal dominant inheritance, no association with obesity
name some genes responsible for the different types of MODY
MODY1: Caused by mutations in Hepatic Nuclear Factor 4a (HNF-4a). Estimated to cause 1% of MODY. Insulin secretion normal at birth but decreases dramatically with age
MODY2: Caused by mutations in glucokinase thus affecting glucose sensing in pancreas. Estimated to cause 15% of MODY. Insulin secretion impaired at birth but remains relatively stable
MODY3: Caused by mutations in Hepatic Nuclear Factor 1a (HNF-1a). Estimated to cause 70% of MODY. Insulin secretion normal at birth but decreases dramatically with age
MODY4: PDX-1 transcription factor in 0 cells involved in regulating insulin gene expression. Estimated to cause 1% of MODY
MODY5: HNF 10 transcription factor. Estimated to cause 1% of MODY
MODY X: Estimated to cause 11% of MODY
Rare Conditions Which Have Similar Symptoms to Type-2 Diabetes
Antibodies to insulin receptor or to insulin
Mutations in insulin receptor (these can cause Leprechaunism)
Glucagonomas
what is the effect of hyperthyroidism on diabetes
There is an increased occurrence of insulin resistance and diabetes in hyperthyroid patients – the reason is unclear
what is the effect of acromegaly and GH on diabetes
Around 60% of acromegalics are insulin resistant and around 20% are diabetic
GH acts as a counter regulatory hormone as shown by the fact that administration of growth hormone in normal subjects causes insulin resistance in insulin target tissues (very similar pattern to that seen for glucocorticoids)
growth hormone deficient children are hypoglycaemic
GH has no effect on insulin secretion
what is the effect of glucocorticoids on diabetes
Excess glucocorticoids from either endogenous sources (usually a tumour) or from exogenous administration clearly can induce severe insulin resistance and even frank Type-2 diabetes
The effects are mainly by causing insulin resistance in insulin target tissues
cell function is normal and there is a rise in compensatory insulin release
The diabetes is usually reversible if steroid levels are reduced
The mechanism may be an effect on IRS1 by decreasing the level of tyrosine phosphorylation of the protein
what is the effect of adrenaline on diabetes
Adrenaline counteracts the effects of insulin and also blocks insulin secretion
Excess adrenaline induced by conditions such as phaeochromocytoma or by exogenous adrenaline administration will stimulate breakdown of glucose stores in cells and decrease the ability of the body to clear glucose from the blood
Like glucorticoids, adrenaline is reported to decrease the tyrosine phosphorylation of IRS1
why can T1DM occur with other autoimmune conditions (and which)
Because it’s an autoimmune disease, type 1 diabetes can occur along with other autoimmune diseases such as hyperthyroidism from Grave’s disease or the patchy decrease in skin pigmentation that occurs with vitiligo
Signs of an emergency with type 1 diabetes include:
Shaking and confusion
Rapid breathing
Fruity smell to the breath
Abdominal pain
Loss of consciousness (rare)
There are four main kinds of injectable insulin
The type of insulin you use will depend on your individual needs and lifestyle:
Short-acting insulin: e.g. Actrapid: soluble insulin starts working within 30 to 60 minutes and lasts six to eight hours. Insulin analogues start working within 15 minutes and last for up to five hours. Examples are insulin aspart, insulin lispro and insulin glulisine
Intermediate-acting insulin: isophane insulin starts working after one to two hours and lasts 10 to 14 hours. Examples are Humulin I and Insulatard
Long-acting insulin: these start working after one to two hours and last for up to 24 hours. Examples are insulin zinc suspension, protamine zinc insulin, and the insulin analogues insulin glargine and insulin detemir. The latter two insulins are now the most widely used long-acting insulins
Biphasic insulins : mixtures of short-acting and intermediate-acting insulins in different proportions, such as 30/70, 50/50. Examples are NovoMix 30, Humulin M3, Insuman comb and Humalog Mix25.
There are three common insulin regimes
Twice daily doses of short- and intermediate-acting insulin
These are given before breakfast and before the evening meal
The short-acting doses cover the insulin needs of the morning and evening
The intermediate-acting doses cover the afternoon and overnight
The pre-mixed insulin injections are convenient for this type of dosing
Three times a day dosing
Short-acting and intermediate-acting insulin before breakfast
Short-acting insulin before the evening meal
Intermediate-acting insulin before bed
Moving the second intermediate-acting dose to before bedtime gives better coverage of the overnight period
Multiple daily doses
Short-acting insulin is used before each main meal
An intermediate or long -acting insulin is used before bedtime to give coverage overnight
T_here are other types of regimes - for example diabetes in some older people can be adequately controlled with a single daily injection of long-acting insulin_
when are we likely to use pump treatment of diabetes
Pump treatment is sometimes used in young people with diabetes
It involves a constant drip-feed of insulin throu gh a needle in the skin and extra insulin doses with meals
he feed is controlled by a small portable pump called an infusion pump
This treatment is now becoming more common where good blood glucose control cannot be obtained by multiple daily injections of insulin, or where hypoglycaemia is a major problem with injections of insulin
Multiple injections are increasingly being favoured, because they give the most flexibility and are most capable of mimicking natural insulin release
how do we measure patient compliance in diabetes
There is a correlation between A1c levels and average blood sugar levels as follows
While there are no guidelines to use A1c as a screening tool, it gives a physician a good idea that someone is diabetic if the value is elevated
Right now, it is used as a standard tool to determine blood sugar control in patients known to have diabetes
what test do we give patients when the diabetes diagnosis is uncertain
A Glucose Tolerance Test
- The patient fasts overnight
- The patient rests during the test
- Smoking is not permitted
- A fasting glucose sample is taken
- A glucose solution is given by mouth (75g in 300ml water)
- Blood and urine samples are taken after 2hours
what is GH’s role in hypoglycaemia
when we’re lacking energy GH has a role to preserve cognitive functions so it stops fat cells and muscles taking up the glucose via inuslin mediation and so it blocks some of insulin’s actions to keep glucose in circulation to keep our brain functioning
what are possible OGTT results
Which of the following options is the single best way to determine whether there was an insulin secretory defect?
A. Absence of insulin
B. Absence of C-peptide
C. Presence of antibodies to β-cells
D. A and B
E. B and C
E. B and C
C-peptide is made in the same molar concentrations as insulin and because it’s the shortest sequence it has an betterimmunogenic detection system than insulin
we wouldn’t measure insulin!!
Which form of Diabetes Mellitus is the most likely diagnosis from the following finding?
- Normal to high insulin
- Normal C-peptide
- No β-cells antibodies
- Aged 45
- Female
Type II DM
not gestational because of age, and not MODY because of age too
mitochondrial is very rare so not likely
not T1DM because normal c-peptide and is usually diagnosed earlier in life
Which form of Diabetes Mellitus is the most likely diagnosis from the following finding?
- Normal to high insulin
- Normal C-peptide
- No β-cells antibodies
- Aged 18
- Male
- Normal weight
- Mother normal
- Affected father
- No deafness
MODY
because young and normal weight
what does IFG mean
glucose values are at the top end of the normal range
when would you diagnose someone with IGT
raised levels of glucose seen after a glucose tolerance test showing abnormal glucose metabolism
We can gain an insight into how glucose metabolism has been regulated over a period of several weeks by measuring circulating levels of which factor?
Haemoglobin HA1c
We can gain an insight into how much insulin was secreted over a period of several days by measuring levels of which circulating factor?
C-peptide
The mechanism by which insulin resistance is manifested (not via dysfunction of glucose transport) on the proteins downstream of insulin binding, are called?
Insulin receptor substrates (IRS)
Tissues become less sensitive to insulin because of an increase in?
Lipolysis
the more you breakdown lipids the more FAs there’ll be in circulation and high FA levels reduce insulin sensitivity
Diabetes might also be induced by interactions with other endocrine systems. In Cushing syndrome an excess of which circulating factor will cause insulin resistance?
Cortisol
Diabetes might also be induced by interactions with other endocrine systems. In Polycystic Ovarian Syndrome (PCOS) an excess of which circulating factor will cause insulin resistance?
Androgen
Diabetes might also be induced by interactions with other endocrine systems. In phaeochromocytomas an excess of which circulating factor will cause insulin resistance?
Epinephrine (Adrenaline)
Diabetes might also be induced by interactions with other endocrine systems. In acromegaly an excess of which circulating factor will cause insulin resistance?
Growth Hormone
You might recognise Maturity Onset Diabetes of the Young (MODY) by which of the following findings?
A. Young age and absence of obesity
B. Clear genetic inheritance
C. Normal to raised C-peptide levels
D. Absences of beta cell antibodies
`
E. All of the above
You might recognise Mitochondrially-Induced Diabetes Mellitus by which of the following findings?
A. Impaired glucose tolerance inherited from the maternal line
B. Reduced mitochondrial activity and deafness
C. Increased exercise tolerance
D. Both A and B
E. A, B and C
D. Both A and B
Which of the following options is used to treat Type 1 Diabetes Mellitus?
A. Dietary restriction
B. Sulphonylureas
C. Biguanides
D. Thiazolidinediones
E. None of the above
E. None of the above
In type 1 diabetic treatment insulin injections are used to bring about required metabolic changes. Select the best option for their mechanism of action?
A. Decreases glucose metabolism and suppresses gluconeogenesis
B. Decreases glucose metabolism and stimulates glycolysis
C. Decreases glucose metabolism and suppresses glycolysis
D. Increases glucose metabolism and suppresses gluconeogenesis
E. Increases glucose metabolism and stimulates gluconeogenesis
D. Increases glucose metabolism and suppresses gluconeogenesis
Summary Diabetic Treatment T1 T2
Type 1 • Insulin replacement
Type 2 (& other insulin resistance): • Insulin sensitizers • Diet and lifestyle • Co-morbidities • Other hormones • CHD
Where is GH secreted from, stored and released
GH is secreted from the somatotroph cells in the anterior pituitary
GH is stored and released from preformed granules
10% of pituitary dry weight
talk about the chemistry of GH
A single chain protein
2 disulphide bonds
2 forms: 22 kD (major) OR 20 kD (minor)
Half-life = 15 mins
Similar to prolactin
what’s similar about Somatostatin and GH (structure and mechanism)
Both GHRH (10aa) and somatostatin (14aa) are small hypothalamic peptides
Both act on G-protein coupled receptors on somatotrophs:
- GHRH activates adenylyl cyclase
- Somatostatin acts via an inhibitory G protein to inhibit adenylyl cyclase
which hormones sensitise somatotrophs to GHRH, and what does this cause
Androgens & oestrogens
This accounts for the pubertal rise in GH and the growth spurt
give exmaples of Metabolic products which influence GH release
Amino acids such as arginine stimulate GH release
Glucose and free fatty acids suppress GH release
give 3 examples of factors that inhibit GH and 3 that stimulate
Inhibit GH: Cortisol • Glucose • Free fatty acids
Stimulate GH: Arginine • Thyroid hormones • Gonadal hormones
how does GH promote growth and anabolism
via the GHR
both directly by tyrosine kinase activation and indirectly via IGF-1
which receptor superfamily is the GH receptor a part of
The GHR is a member of the cytokine receptor superfamily
explain the mechanism by which GH binds GHR
Binding of the hormone realigns the subunits by rotation and closer apposition, resulting in juxtaposition of the catalytic domains of the associated tyrosine-protein kinase JAK2 below the cell membrane
Activated JAK2 phosphorylates the GHR on tyrosine residues, which in turn recruits members of the signal transducer and activator of transcription (STAT)
STAT dimerization and translocation to the nucleus to modulate target gene transcription such as IGF-1 and SOCS (suppressor of cytokine signaling)
SOCS terminate the GH signal cascade
- GH receptors must dimerise to get the functionality*
- Site 1 binding causes twist in other receptor so they come together, and brings the signaling molecules closer in the transmembrane area*
- Once the receptor is activated it activates a cascade of kinases called JAK*
- When GH binds it activates an intracellular mechanism to activate JAK2, which activates a downstream signaling pathway called the STAT signal à activated STAT can dimerise and translocate into the nucleus where they can activate a cascade of events*
- Once the receptor has been activated for amount of time it activated SOCS to turn off the GH signaling through that receptor*
- Lots of GH can desensitise its receptor*
which syndromes are associated with insensitivity to GH vs excessive GH
Insensitivity to GH (Laron syndrome) can result from mutations in the GHR, whereas excessive activation results in gigantism and acromegaly
In humans there are 2 groups of receptors respond to GH:
Lactogenic receptors: both GH + PRL activate
Somatogenic receptors: only GH activates
how do we treat GH deficient children
Must treat GH deficient children with human GH
what are the physiological actions of GH
METABOLIC:
- Decreases glucose metabolism – opposing insulin
- Increases lipolysis
- Increases protein synthesis (anabolic)
- (increases milk yield in cows)
OTHER:
- Increases IGF production from liver etc
- Increases chondrocyte and cartilage formation
- INDIRECT ACTIONS via IGF-I
- GROWTH PROMOTION
- Clonal expansion of chondrocytes
- Growth of bones, soft tissue & viscera
describe the structure of IGF-1 vs insulin
describe the Major Role Of GH In Transforming Fibroblasts
describe how GH and IGF-1 act on the growth plate
when does GH become the most important factor for growth
GH is the dominant endocrine regulator of growth. However, for the first year, growth is largely dependent on nutrition as significant GH receptors appear at 7 months of age
when and why does growth stop
When puberty ends: Sex steroids have increased: androgens in boys,oestrogens in girls
These close the growth plates and growth stops
what is aromatase, and when would you want to inhibit it
describe 2 methods we use to measure GH
- immunoassay: ELISA (Enzyme Linked Immunosorbent Assay) since GH is a 22kDa protein
- Large-scale routine use
- Very precise and sensitive
- Does not measure biological potency directly - doesn’t measure if GH active or not
- bioassays:
- Used to measure potency of new batches of recombinant GH
- Rarely used to check bioactivity of patient GH
insensitive + imprecise
- in vitro/ immortalised target cells/ hGH receptor
- colorimetric/ luminescent responses via reporter genes
what are the 6 ways (not methods!!) in which we can measure growth
- height vs age
- rate of growth vs age
- bone age/maturation
- pubertal stages
- height vs chronological age (population)
- SD score
how do we measure growth in height vs age for less than 2yrs and more than
less than: supine length (lying down)
more than: standing height, using a stadiometer, careful positioning, reproductible, repeat regularly
plot height vs years graph
how do we measure growth in rate of growth vs age
how do we measure growth through bone age/maturation
how do we measure growth through pubertal stages
- Delayed or precocious puberty?
- Assessed by staging : Pubic and auxillary hair, Development of boy’s external genitalia, Girl’s breast development
TANNER’S STAGE: pubertal maturation described in terms of sequences
describe boy’s tanner stage: development of external genitalia
Stage 1: Prepubertal
Stage 2: Enlargement of scrotum and testes; scrotum skin reddens and changes in texture
Stage 3: Enlargement of penis (length at first); further growth of testes
Stage 4: Increased size of penis with growth in breadth and development of glans; testes and scrotum larger, scrotum skin darker
Stage 5: Adult genitalia
describe girl’s tanner stages: breast development
Stage 1: Prepubertal
Stage 2: Breast bud stage with elevation of breast and papilla; enlargement of areola
Stage 3: Further enlargement of breast and areola; no separation of their contour
Stage 4: Areola and papilla form a secondary mound above level of breast
Stage 5: Mature stage: projection of papilla only, related to recession of areola
Tanner stages: Boys and girls - pubic hair stages:
- Prepubertal (can see velus hair similar to abdominal wall)
- Sparse growth of long, slightly pigmented hair, straight or curled, at base of penis or along labia
- Darker, coarser and more curled hair, spreading sparsely over junction of pubes
- Hair adult in type, but covering smaller area than in adult; no spread to medial surface of thighs
- Adult in type and quantity
how do we measure growth with height vs chronological age (population)?
Appropriate reference population must be used
Generations change, linked to improved nutrition and economic conditions
how do we measure growth with SD score?
a normalised system derived from the position of an individual on the population chart showing height v age i.e. Assessment 5
SD score = (observed – mean height )
SD for that age and sex
Normal SDS scores lie between –2 and +2
So we’d quote the SD and expect the normal population to lie within 2SDs of the mean (50th percentile)
describe the GH axis
GHRH is released from the hypothalamus à travels down the pituitary stalk to bind to the GHRH receptor which is on the surface of the somatotroph cells and stimulates them to produce and secrete growth hormone
We also have somatostatin neurons (anterior to GHRH neurons) and they also secrete their products into the median eminence à down pituitary stalk and binds to the somatostatin receptors on the somatotroph cell, and that inhibits GH secretion
Ghrelin (from stomach) is known to regulate GH secretion. Releases GH from anterior pituitary through its own receptor
The main growth actions in the body are mediated by IFF-1, causes a range of pastnatal body growth
So GH produces growth via its receptor but also through indirect actions such as IGF-1
IGF-1 and GH feedback through the normal negative feedback systems to control own secretion at both the pituitary and the hypothalamic level
what does GH need in order for it to be turned on
transcription facotr PIT1
Why does a one-off GH sample not tell you anything
because of the pulsatile release
where is the The human GH/ chorionic somatomammotropin (CS) locus
chromosome 17
GH-N is expressed preferentially in the somatotropes of the anterior pituitary, while GH-V and the CS genes are expressed in the syncytiotrophoblasts of the placenta
HS I and II are pituitary specific
HS IV is placenta specific, and HS III and V are found in both pituitary and placenta but nowhere else
HS (hypersensitivity sites) are areas where gene transcription initiate
what is involved in the clinical observation in management of patients with growth disorders
Patient history: rule out multiple non-endocrine causes eg respiratory/ cardiac/ renal problems
Appearance: proportionate growth?
Anthropometric measurements: growth velocity/ bone ge/ pubertal stages etc
how do we usually Measure serum GH:
by immunoassay
Need 0.5 ml blood ⇒ Send to Chemical Pathology for immunoassay
describe the secretion pattern of serum GH, and how do we then test for serum GH
Pulsatile secretion
24 hr profile, taking blood samples every 20 mins
major peaks during sleep stages 3 or 4
delayed sleep/ delayed rise in GH
cannot interpret a single random sample
24 hr profile inconvenient for patient and lab
what abnormalities do these 2 graphs indicate
1st one shows classic idiopathic GH deficiency - absent or only feeble peaks
2nd one shows GH excess - continuous secretions of high GH, with absent pulsatility
what is the use of Dynamic Function Tests for GH secretion, and explain the types
Widely used: Deals with the problem of irregular secretion, two kinds
(a) Provocative tests
(b) Suppression tests
what happens to GH secretion with age
declines with age, during and after the 3rd decade of life
how do we measure IGF-1 levels
by immunoassay
not as widely used as GH measurements
confined to specialist centres
when do we measure IFG binding proteins
measured in specialist centres FOR DIFFICULT CASES
reasearch (not routine)
what GH did we use before as treatment, and what do we use now
nitially GH replacement was in the form of cadaveric pituitary GH as GH from other species does not stimulate growth in humans
The development of Creutzfeldt-Jakob disease (a degenerative brain disorder) in those who were treated with hGH produced in this way, led to the discontinuation of all products derived from the human pituitary gland
This has led to development of artificial (recombinant) hGH (rhGH) to treat children with growth disorders since 1985
- An alternative approach to height augmentation employs agents that impede puberty and, in particular, oestrogen production (in both sexes), which is responsible for ultimate epiphysial fusion such as gonadotropin-releasing hormone agonists and, more recently, aromatase inhibitors*
- These approaches have been used as sole treatments or in various combinations, with varying efficacy and safety*
list some Key points for diagnosis of classic idiopathic GH deficiency
• Proportionate growth/ normal appearance
Truncal obesity/ immature face
Low rate of growth: low SD score
No or poor GH response to an ITT provocation test
Nil or feeble peaks in a 24hr profile
Low IGF1
how would we treat classic idiopathic GH deficiency
what condition does a GH-resistant patient have, and list some key points for diagnosis
laron syndrome
- Rare, autosomal recessive condition
- Very low SD score/ growth velocity
- Proportionate growth but with a very immature face
- NORMAL GH LEVELS
- Low IGF-1
describe the mechanism for Laron Syndrome
treatment for Laron Syndrome
ALL WE CAN DO IS MANAGE SYMPTOMS REALLY
Defective GH receptors:
- Recombinant hGH not effective
- Trials with recombinant IGF-1
Note: one patient described with partial deletion in gene for IGF-1:
- Severe intrauterine growth retardation
- Post-natal growth failure
- Sensorineural deafness/mental retardation/GH resistance
what dpes achondroplasia involve, and what is it due to
- Disproportional growth failure
- Short limbs
- Normal GH
- No response to GH treatment
- Defective chondrocyte growth in growth plates ⇒ Leads to short long bones and limbs
- Due to defective receptors for fibroblast growth factor (FGF)
- Therefore not responsive to GH as GH is not the problem
what does coeliac disease involve
what is the effect of Hypothyroidism on growth
effect of Juvenile Cushing’s Syndrome on growth
effect of Pseudohypoparathyroidism on growth
Turner’s syndrome patient appearance
XO. the designation of a cell in an individual in whom only one sex chromosome is present. Either the other X or the Y chromosome is missing so that each cell is monosomic and contains a total of 45 chromosomes. All XO individuals are females with Turner’s syndrome
what is Precocious Puberty
- Early sexual maturity
- Initially rapid growth
- But growth stops early
- Premature epiphyseal fusion
DUE TO: have enough calroies so GnRH signal get sturned on
effect of delayed puberty on growth
- Puberty after 15 years
- 1:50 prevalence
- M:F ratio is 6:1
- Growth slows around year 10
- Height falls below 3rd centile
- Bone age delayed by 2 years
• LH/FSH low
• GH normal
- Catch-up growth occurs
- Reaches full growth potential
what do we treat with OXANDROLONE, and what are its actions
delayed puberty
- Anabolic steroid
- Weak androgen
- Cannot be aromatised to oestrogen
- Therefore does not advance bone age or lead to growth plate closure. So does not shorten pre-pubertal window of time
- Stimulates growth of boys with pubertal delay: increases natural GH
- Lower doses used for girls
what does Anorexia Nervosa involve
- Prevalence 1:100 for females
- Hypothalamic turn-off
• Low GnRH release
• Fasting GH and cortisol raised
effects of Intrauterine Growth Retardation
- Low birth weight
- Placental insufficiency?
- Poor catch-up growth
effects of Cranial Irradiation on growth
- E.g. for leukaemia or brain tumours
- Pituitary particularly radiation sensitive
- Low GH
which chronic illnesses impact growth the most?
Congenital heart disease
- Chronic obstructive or infective pulmonary disease
- Chronic renal failure
effects of Psychosocial Deprivation on growth?
- Emotional and social upheaval
- Hypothalamic turn-off
- Lack of GHRH
what is excessive GH secretion before puberty called, and describe the growth velocity compared to normal
gigantism
Prolonged pre-pubertal linear growth period prior to an exaggerated growth spurt
Results in excessive height attainment
what is the delayed puberty in gigantism due to
compromised pituitary function due to somatotroph compression of other pituitary cells in the restricted space of the sella turcica giving reductions in other pituitary functions
what causes the excessive GH secretion in gigantism
Due to a benign tumour of the somatotrophs
Autonomous, unregulated, non-pulsatile GH secretion
Note incidence of pituitary tumours: PRL > ACTH > GH
LH / FSH / TSH very rare
how is gigantism diagnosed, and how is it treated (+complications of treatment)
Poor prognosis if untreated
Easily recognised syndrome.
The high SD score should be picked up in childhood and the tumour, which can be imaged with an MRI scan, removed surgically
After surgery:
- In some cases impaired endocrine function can recover, if the normal but compressed pituitary tissue has been preserved
- For others, difficulties in growth, development and sexual maturation may persist. Careful replacement therapy needed for a normal life
why is there no icreased height in acromegaly
post-puberty
No increased height possible because of oestrogen closure of growth plates
describe acromegaly onset
nsidious in onset
pituitary tumours in 25% at post mortem – usually stain for prolactin
which hormones altered in acromegaly, and what effects does this have
Raised GH causes raised IGF1
Gives rise to:
- Proliferation of bone, cartilage and soft tissues + increase in size of other organs
- Enlarged hands and feet, jaw protrusion and dental malocclusion
why does acromegaly increase risk of DM
Raised GH opposes insulin
Increased risk of diabetes mellitus with associated symptoms:
• Polydipsia / polyuria / recurrent urinary tract infections / retinopathy / neuropathy
Acromegaly treatments
- Somatostatin analog (octeotride)
- Dopamine agonist (bromocriptine)
- Mutated GH which prevents receptor dimerisation/ activation
Surgical: • Transphenoidal route guided by MRI scan usually
• Transfrontal route if tumour is large
Radiotherapy: • Conventional supervoltage: slow effect in tumour reduction: often results in eventual hypothyroidism
what tends to be the cause of pituitary tumours
Mutations in classic oncogenes and tumor-suppressor genes are rarely associated with pituitary tumours
In fact, most mechanisms of endocrine tumourigenesis differ significantly from those associated with haematological malignancies and non-endocrine tumours
Instead, tumourigenesis is promoted by hormones and growth factors that are implicated in pituitary development
when do we use GH for children
- Growth hormone deficiency in children
- Growth hormone use following cranial irradiation
- Small for gestational age (SGA)
- Growth delay in children with chronic renal failure
- Turner Syndrome
- Prader-Willi Syndrome
when do we use GH for adults
Growth hormone deficiency continued into adulthood
what controls growth in the foetus, and what controls it in an infant
foetus: IGF-2
infant: nutrition rather than GH/ IGF-1 most important during year 1
describe the life-time growth velocity (+causes)
Postnatal growth rapid (15cm/y)
Declines by 3 to a plateau (6cm/y)
At puberty GH/IGF-1 rise - get growth spurt
Oestrogens close the growth plates at the end of puberty in boys and girls
After puberty GH steadily declines throughout adult life resulting in :
- The “somatopause”?
- Central adiposity
- Decreased muscle mass
Growth hormone receptor-deficient people (Laron Syndrome) do not get two of the major diseases of aging, cancer and diabetes
Therefore GH activity in adults who are beyond their growing years may be harmful!
what’s the formula for working out SD score
standard deviation score = (observed height - mean height for age and sex)/ SD for that age and sex
normal values then lie between -2 and +2
signs and symptoms of acromegaly
The Head • Large tongue • Interdental separation - separation of teeth due to alveolar bone growth • Prominent supraorbital ridge • Prognathism - growth of the mandible leading to a jutting jaw • Visual field defects • Goitre - due to generalised visceral enlargement • Headaches
The Body • Galactorrhoea • Hirsuties
• Heart failure • Generalised organomegaly - increase in size of heart, kidney, spleen, liver etc. • Hypertension • Impotence • Amenorrhoea
The Limbs • Increase in size of hands and feet • Tight-fitting rings • Carpal tunnel syndrome • Proximal myopathy • Arthropathy • Oedema
The most common presenting complaint is that of a change in appearance. This is can be seen by studying old photographs
Acromegaly usually presents as a subtle disease with the clinical features developing over many years
Some patients may present with galactorrhoea as in some tumours, both somatotrophin and prolactin are secreted
Approximately a quarter of acromegaly patients have an impaired glucose tolerance due to the increased gluconeogenesis produced by the growth hormone.
4 tests for diagnosis of acromegaly
An important test in the diagnosis of acromegaly is the glucose tolerance test. The patient is given a 75g glucose meal, and blood tests are taken at half-hourly intervals. In a normal patient the growth hormone levels will be suppressed, but in the acromegaly patient the growth hormone levels are unsuppressable
Another unique test that can be used in the diagnosis of acromegaly is by the administration of TRH. This is a unique test as only in acromegaly will there be a doubling of the blood levels of growth hormone
Another test that is routinely done is the blood level of the somatomedins (IGF-1), which will almost always be raised in acromegaly
Imaging is obviously a very important part of the diagnosis. A routine plain radiograph of the skull will show an enlarged pituitary fossa in approximately 70% of patients with acromegaly. The best way to identify the tumour is by using a CT scan or an MRI scan
list some risks of obesity
T2DM
Hyperinsulinaemia
glucose intolerance
hypertension and stroke
coronoary heart disease
some cancers - breast, endometrial, ovarian, gall bladder, colon
obese people often suffer from metabolic syndrome - a group of risk factors that typically occur together, and increase the risk for coronary artery disease, and T2DM
these risk factors include central obesity, high BP, dyslipidaemia, hyperglycaemia, mild chronic inflammation
describe the lethal tellow mutant mouse obesity model
mouse has ectopic expression of the agouti protein due to a deletion in the promotor
expression of this protein antagonises some neurons, and disrupts their function
these neurons normally act to inhibit feeding behaviour, but in the mutant mice this is inhibited
describe the obese mouse obesity model
this mouse doesn’t express the product of the ob gene: leptin
leptin is primarily secreted by the adipocytes, circulating levels reflect body fat
leptin acts on hypothalamus to depress apetite AND affects insulin signalling (absence causes insulin resistance)
if you give them leptin you see a dramatic reduction in weight, also seen in humans whose obesity is caused by chromosomal mutations causing leptin deficiency
BUT IN MOST OBESE HUMANS leptin levels are high, and they appear to show leptin resistance which may be due to decreased uptake across BBB
describe the diabetic obese mouse obesity model
doesn’t express prodcut of db gene: so no leptin receptor (form that’s invovled in signalling)
same phenotype as obese mouse
adminstering leptin however does NOT treat the obesity here
describe the traditional view of adipose tissue during fed vs fasting state
fed: insulin stimulates glucose uptake which is used to synthesise TAGs. these are stored in large droplet for later use
fasting: low insulin or adrenaline stimulates lipolysis of stored TAG,a dn the released NEFA enter plasma as fuelf or other tissues
SO ADIPOSE TISSUE WAS SEEN SIMPLY AS A WAY OF STORING ENERGY FOR LATER USE
Describe the insulin signalling pathway in adipocytes (for immediate responses)
describe the insulin signalling pathway in adipocytes (proliferative effects)
how does brown adipose tissue stimulate heat
non-shivering thermogenesis
upon stimulation by NA (beta 3 receptor) lipolyiss and FA oxidation are activated
the proton gradient generated by the ETC is then waster via UCP1
describe some differences between white and brown adipose tissue
in brown, the TAG droplets are multilocular, the mitochondria are larger, and higher in density
it’s highly innervated by the SNS, and the capillary network is denser (to distribute the heat around the body)
describe the development of adipose tissue from stem cell to mature adipocyte
which is the transcription factor necessary for adipogenesis
PPARy
an increase in adipogenesis is associated with smaller adipocytes, less ectopic deposition (in muscle, liver), and improved insulin sensitivity
PPARy is also needed for maintenance of the adipocyte’s differentiation
what are thiozolidinediones, and what’s their effects
synthetic ligands to PPARy (trasncription factor required for adipogenesis)
they increase adipogenesis
they have been shown to increase insulin sensitivity, lower plasma glucose, and alter the secretory profile of adipose tissue away from the pro-inflammatory direction
what are lipodystrophies, effects, symptoms and treatment
clinical disorders, often involving lipoatrophy or selective loss of adipose tissue from some regions
genetic or acquired
patients often have aspects of metabolic syndromes; dyslipidaemia, hypertension, insulin resistance
some symtpoms can be alleviated by adminstering adipocytokines such as leptin or adiponectin
lipodystrophies highlight the benefit of adipose tissue
what happens in familial partial lipodystrophy 3, symptoms and cause?
progressive, gradual loss of subcutaneous adipose tissue from extremities, normally begining at puberty
increased deposition of TAG in muscles & liver
hypertriglyceridaemia, low HDL, severe insulin-resistance leading to diabtetes and othe rmetabolic irregularities
caused by mutations of the gene coding for PPARy (2 mechanisms, on another card)
describe the 2 mechanisms by which familial partial lipodystrophy 3 causes mutation of gene coding for PPARy
1. DOMINANT NEGATIVE: the faulty copy is expressed, and translocates to the nucleus but interacts with PPARy-binding proteins, inhibiting the activity of the wild-type OR binds to the DNA-binding sites but doesn’t increase expression and outcompetes the wild-type PPARy ⇒ more difficult to stimulate cells to become adipocytes
2. HAPLOINSUFFICIENCY: due to the non-functional allele, there’s only 50% expression of a functional gene product so that the normal effects of PPARy on gene expression are greatly reduced ⇒ idek
how can PPARy mutations cause obesity
mutated PPARy2 (mutation disrupts phosphorylation site for MAPK) is overactive and so stimulates MORE differentiation of pre-adipocytes to adipocytes and so subjects would have greater obesity, but lower fasting insulin levels
describe the distriubution of adipose tissue
what are possible effects of high visceral adipose tissue
visceral adipose tissue drains directly into the portal vein to the liver
VAT is hyperlipolytic, resistance to insulin signalling –> causing liver insulin resistance
insulin resistance in the liver causes it to increase production of VLDL and glucose
difference between hyperplasia and hypertrophy
hyperplasia is an increase in cell number, and is a relatively healthy way to increase TAG storing capacity
hypertrophy is an increase in cell size, and is associated with several problems
adipokines secreted by smaller adipocytes are anti-inflammatory and also insulin-sensitising, but those secreted by larger adipocytes are pro-inflammatory, also insulin-desnsitising, more cell death which = recruiting macrophages
how do leptin levels change?
leptin secretion increases with overfeeding, fluctuates in response to feeding in response to insulin; increasing with overfeeding and decreases with fasting
FUNCTION: decrease food intake and increase energy expenditure
obese people have high leptin
give one reason why diets high in fat or fructose are associated with obesity
they don’t increase leptin secretion as they don;t stimulate insulin production
describe the levels of leptin in an obese person centrally and peripherally
high plasma levels
low in CSF (+decrease hypothalamic response to leptin)
leptin can cross BBB via saturable transport mechanism
what is metreleptin, describe 3 uses
recombinant methionyl human leptin
- lipodystrophy - normalises fat and carb metabolism, increases insulin secretion & sensitivity
- obesity: not as effective, but may cause weight loss with amylin
- weight loss maintenance: could be used in future to counteract decrease in resting metabolic rate, and help maintain weight lost
list some effects of leptin (outside of metabolism)
has a role in immunity and immune system development
it’s a chemoattractant, and the high levels secreted by adipocytes in obesity MAY be responsbile for macrophages’ infiltration of adipose tissue
also has effect on reproductive system
what is adiponectin
hormone, normally found in high levels in plasma
only secreted by mature adipocytes
plasma levels LOWER in obesity, and also in large adipocytes
expression depends on PPARy, and inhibtied by TNF-α
what are low levels of adiponectin associated with
hyperinsulinaemia
insulin resitance
future T2DM risk
how can we increase levels of adiponectin
dieting
excercise
synthetic ligands to PPARy, such as thiozolidinediones
how does adiponectin act on muscle, and how does it act on the liver
muscle has a receptor AdipoR1 and adiponectin causes an increase in glucose uptake, an dincreases beta oxidation which is a cause of the decrease in muscle lipid stores, and this increases inuslin insensitivity
liver has AdipoR2 and also has improved insulin sensitivity in response to adiponectin, decreasing liver gluconeogenesis and plasma glucose
describe the anti-inflammatory actions of adiponectin
inhibits TNF-α secretion by monocytes and macrophages
what kind of inflmmation in obesity, and what causes it?
mild but chronic inflammation
may be due to hypoxia in expanding adipose tissue, or high levels of FFA stimulating Toll-like receptors
many inflammatory markers are high in plasma, including CRP, IL6, serum amyloid
adipose tissue produces IL6, IL8, IL1, TNF-α, IL1β, chemokines, etc
THESE PROTEINS STIMULATE IMMUNE RESPONSES, recruiting immune cells and stimuilating maturation (of immune cells)
these proteins also inhibit preadipocyte maturation
severity of chronic inflammation correlates well with the size of visceral adipocytes
give examples of anti and pro-inflammatory proteins (in obesity)
ANTI-INFLAMM: IL-10 and aidponectin, both produced less as obesity increases
adiponectin inhibts activation of macrophages, and stimulates them to produce anti-inflammatory cytokines e.g. IL-10
PRO-INFLAMM: Leptin, IL-6, angiotensin, TNF-α, all increased in plasma of obese people
1/3rd of circulating adipose IL-6 is produced by adipose tissues, levels predict onset of T2DM. also inhibits adiponectin expression
IL-6 makes the liver make inflammatory proteins such as CRP
RAAS is also overactive in obese people
what are crown-like structures
macrophages are typically clustered around individual adipocytes forming CLSs
CLSs always found around dead adipocytes that have undergone necrosis (inflamm) rather than apoptosis (non-inflamm)
adipocyte death was increased with the size of the adipocytes, even in lean individuals
infilitrating macrophages may then secrete large amounts of pro-inflammatory cytokines - infiltration has been show to occur BEFORE hyperinsulinaemia
how does inflammation lead to insulin resistance in obesity
saturated FAs e.g. can inhibit this pathway
Inflammatory signalling pathways interacting with, and inhibiting components of the insulin signalling pathway, e.g. by serine phosphorylation of IRS (making it more difficult to start up this pathway shown)
why do we get exctopic lipid deposition in obesity?
inability of subcutaenous tissues to handle the load of fat storage so TAG storage spills over into visceral adipose tissue, skeletal muscle and liver
this extopic deposition can lead to an increase in other compounds such as ceramide that alter signalling pathways
how does adiponectin decrease ectopic lipid storage in muscle
it activates AMPK which favours FA oxidation in skeletal muscle via AdipoR1
thsi decreases ectopic lipid sotrage in muscle and increases its sensitivity to insulin
how does adiponectin decrease hyperglycaemia
it decreases expression of PEPCL and G6Pase (involved in glucoconeogenesis)
how is adiponectin anti-inflammatory
it opposes the action of TNF-α
Give an example of an anti-inflammatory drug that’s able to reduce insulin resistance
aspirin
give examples of vasoconstrictors and vasodilators produced by the endothelial cells lining blood vessels
vasodilators: NO, prostacyclin
vasoconstrictors: ROS, endothelin-1, RAAS components
how does leptin contribute to hypertension
how does inflammation contribute to hypertension
describe how the RAAS is involved in hypertension
describe adinopectin’s role in CVD and hypertension
describe adiponectin levels in cancer patients
v.low
and hypoadiponectinaemia is marker for aggressive phenotype
also adiponectin can supress cell proliferation, stop cell growth and favour apoptosis
how can adipose tissue facilitate cancer development
produces growth factors that stimulate angiogenesis (blood vessels develop that supply the tumour)
also leptin is an agiogenesis promotor and it acts with VEGF (produced by macrophages that infiltrate chronically inflamed adipose tissue)
TNF-α can be angiogeneic at low levels, and IL-6 increases expression of VEGF
Leptin is a chemoattractant for monocytes and macrophages and
describe the mechanism by which tumour cells metastisize via circulation
what’s the blood supply to the thyroid gland
external carotid
subclavian artery
BLOOD SUPPLY IS IMPORTANT AS IT IS AN ENDOCRINE GLAND
describe the anatomy of the thyroid gland
what are the parathyroid glands, and where are they in relation to the thyroid
4 parathyroid glands attached to posterior surface of thyroid
Sense Ca AND Secrete PTH
describe the morphology of the thyroid gland
follicles (made up of follicular epithelial cells) surround a centre filled with a substance called colloid
C-cells are found betweent he follicles, and these make calcitonin
how do underactive follicles look like
how do overactive follicles look like
describe the embryological development of the thyroid gland
arises from an outpouch between the anterior 2/3s and posterior 1/3rd of the tongue
the ball of cells migrats downwards and forwards, and gets to its final position at 12 weeks
this is dependent on transcription factors such as PAX8
during this time the thyroid can leave bits of itself behind and we occasionaly see these as embryological remnants
list some embryological abnormalities of the thyroid gland
what does this show
it’s a section of normal thyroid
follicles lined by cuboidal epithelium, containing colloid
what does this show
normal thyroid: colloid (thyroglobulin) stained red
colloid in lumen
what kind if stain is used here, and describe what it shows
Normal thyroid: immunofluorescent stain using anti-thyroid autoantibodies from a hypothyroid patient
furry edge to thyroid peithlium as they have villi
which 2 hormones does the thyroid make, and by which cells
THYROID FOLLICLES → T4 and T3
C-CELLS → Calcitonin
what is calcitonin
Peptide hormone
Antagonises PTH: ↓Ca (when plasma concn too high)
Probably not significant in human Ca metabolism
why is high blood flow important for the thyroid
4-6 ml / min / g thyroid tissue i.e. twice that of the kidney!
High blood flow important for:
- delivery of Iand TSH
- to export T3 and T4
what is responsible for the audible “bruit” of an overactive thyroid gland
the high blood flow
describe the vascularisation of the thryoid gland
summarise the process by which TH is made in the epithelial cells
what stimulates thyroid epithelial activity
TSH
what effects does TSH stimulation have
what are the raw materials required for the synthesis of TH
tyrosines and iodide
describe tyrosines’ role in TH
- Glycoprotein scaffold called thyroglobulin
- Synthesized by thyroid epithelial cells
- Secreted into the lumen of the follicle
- Colloid is a pool of thyroglobulin
- 1 thyroglobulin = 134 tyrosines
- Only a handful of these are actually used to synthesize T4 and T3
describe iodide’s role in TH
- Avidly taken up from blood by thyroid epithelial cells
- Via sodium-iodide symporter or “iodine pump”.
- Once inside the cell, iodide is transported into the lumen of the follicle along with thyroglobulin via pendrin
describe the role of thryoid peroxidase in TH synthesis
- thyroglobulin contains a bunch of tyrosine molecules
- organification: TP attached iodide to tyrosine rings (reaction catalysed by TP using H2O2 - made seperately in the cell using O2 + NADPH)
- So you get either DIT or MIT (2 or 3 iodides)
- coupling: take the ring from one structure and stick it onto the other to make a 2-ringed structure; 2 DITs makes T4, and DIT+MIT makes T3
describe how the accumlating THs are released from colloid into blood
how do tyrosines and iodides get into the colloid
TSH from blood binds it receptor on the thryoid epithelial cell, which stimulates the cell to:
- import Na+ and I- into the cell via NIS
- iodide exported via pendrin to follicle lumen
at the same, the cell is stimulated to produce thyroglobulin which is secreted into the colloid pool
what impacts TSH secretion/levels
negative feedback via T4/T3
what are the normal levels of circulating TH
0.3 – 4.5 mU/L
Total T4 = 60 – 150 nmol/L
Total T3 = 1.2 – 2.9 nmol/L
what percentage of the total [TH] is physiologically active
0.1% because this isn’t bound to protein and so is free to get across cell membranes
give the amounts of free T3 and T4
Free T4 is 9-22 pmol/L
Free T3 is 3-6 pmol/L
describe how TH is transported in the blood
- 9% bound to proteins;
- thyroxine binding protein
- transthyreitin
- albumin
- 1% free
which of the TH is more bioactive
T3
describe 5 physiological actions of thryoid hormone
- Increase basal metabolism - goes to mostyl generating heat
- Promote growth and development (with GH)
- Cardiovascular
Positively chronotropic
inotropic
- CNS:
Regulates alertness
Development of fetal brain
- Modulate actions of other hormones
Insulin – antagonistic
Adrenaline – synergistic: ↑lipolysis, glycogenolysis, ↑HR
GH releasing hormone – ↓secretion (via negative feedback)
TRH – ↓secretion and release (TRH to release TSH - so negative feedback)
describe how T3/T4 effect gene transcription
T4 is the circulating prohormone for T3, and T4 is deiodinated to from T3 which acts on nulcear receptors
explain the effects of D1/2/3 on T3/T4
Name the 3 cellular actions of T4/T3
differentiation
growth
energy
what kind of receptors are thryoid hormone receptors
nuclear receptors
members of the steroid-thyroid hormone receptor family
bound to DNA in their resting state
explain how TH is actively repressed in transcription in resting state
at resting state the THR is bound to TRE (thryoid respons element) alongside RXR
RXR+THR are bound to a complex of repressors (SMRT,NCoR)
this complex is bound to HDAC which chnages the formation of chromatin on the DNA and causes the DNA to bind owund up in histones which actively represses it
explain the role of TH in active transcription
when T3 binds, the complex of THR+RXR swaps the repressor complex for co-activators (SRC-1, PACF etc)
these co-activators mediate interactions with the basic transcription complex: RNA pol II and it’s accessory factors TATA andTBA etc
because HDAC has been kicked off histones can be acetylated which opens up the chromatin so DNA opens up
it’s ready to be transcribed
describe TH role in permissive transcription
this is the state in between active repression and active transcription
involves the absence of RXR and THR
But you can still have a co-activator complex and you get a half-way state where the genes are transcribed at a lower level than they would be if they were actively transcribed
what are the 2 types of alpha hormone receptor
ASK SOMEONE TO EXPLAIN THE SLIDE
how exactly does TH influence basal metabolism
mitochondria can transcribe some genes, and t3 binfd THR on some mitochondria and influences the basal metbaolism rate
list the different functions of TH
how does an increase in fat activate TH
increase fat leves = increased [leptin]
this stimulates the body to increase basal metabolism to burn more fat by:
- acting directly on adipose tissue
- activating sympathetic system
describe T3’s effects on the mitochondria
T3 also targets the mitochondria directly:
Regulates energy metabolism directly
Increases nuclear expression of key regulatory factors such as PGC-1 , nuclear respiratory factor (NRF-1), mitochrondrial RNA polymerase (Polrmt), mitochondrial basal transcription factor (Tfam)
Binds truncated TR 1 in mitochondria triggering copying of mtDNA
Binds AdNT (adenine nucleotide transporter) to promote ‘proton leak’ and heat generation
what kind of results would you expect to see with hyperthyroidism (T3, T4, TSH levels)
high T3
high T4
very low TSH
this is because the high T3 and T4 feedback on the pituitary and supress TSH
list the signs and symptoms of hyperthyroidism
list some clinical feature of hyperthyroidism, general to thyrotoxicosis
list some clinical feature of hyperthyroidism, specific to graves disease
list some causes of hyperthyroidism
Graves’ disease (most common)
Multinodular goitre or Toxic adenoma (2nd most common)
Thyroiditis: subacute, Hashimoto, De Quervain
Ectopic TSH: hCG in early pregnancy, recombinant TSH
Drugs: Amiodarone, Exogenous iodine (JodBasedow), Thyroxine!
Ectopic thyroid tissue: metastases from thyroid carcinoma, struma ovarii
Pituitary disease: TSHoma
briefly describe Grave’s disease
describe how you get thyrotoxicosis in graves disease
you have TSH-R antibodies which bind the TSH-R and stimulate it, producing T3/T4
TH feedback on pituitary which reduces TSH release, but antibody stimulation persists as it’s not subject to negative feedback
describe the relapsing/remitting in Grave’s disease
TSH-R Abs do not always stimulate
TSI = Thyroid stimulating antibodies
TBII = TSH-R binding inhibitory immunoglobulins
later on in disease progression, some patients start producing TBII which just blocks (without stimulating) the receptor therefore leading HYPOthyroidism
describe the immunology of Grave’s disease
what does Polyglandular autoimmune syndrome type II involve
- Type 1 DM - autoimmune attack on Beta cells
- Addison’s disease - autoimmune attack on adrenal cortex
- Pernicious anaemia - autoimmune attack on gastric parietal cells
- Vitiligo - autoimmune attack on melanocytes in skin
- Hypoparathyroidism - autoimmune attack on parathyroid glands
describe how thyroid eye disease develops
TSI bind to orbital muscle Ag ⇒ Inflammatory cell infiltrate, secretion of cytokines ⇒ cytokins cause fibroblast proliferation ⇒ Fibroblasts secrete Glycosaminoglycans (BABY NAPPY) ⇒ Oedema due to water retention (pushes eyes forwards), fibrosis
name the 2 diagnostic tests for hyperthyroidism
Thyroid autoantibodies
Thyroid scintigram (not used much now)
describe the thyroid autoantibody test
a diagnostic test for hyperthyroidism
Anti Thyroid peroxidase (TPO) and Anti Thyroglobulin (TG) are non-specific and insensitive
Anti TSH-R Abs: specific for Graves’ disease (95%)
describe the thyroid scintigram test
a diagnostic test for hyperthyroidism
inject Tc-99m pertechnetate (radioactive label) then scan under gamma camera
what test was used here, and describe what you see
Thyroid scintigram
Thyroid uptake in Graves vc MNG (Multinodular Goiter);
GRAVES: outline normally shaped, and uptake even
MNG: tracer unevenly distriubuted with lumps in some places
what does this scan show
tracer concentrated in one lump, and the rest of the gland is supressed because TSH is supressed therefore the rest of thyroid is inactive
what does this scan indicate and why
thyroiditis (release of all TH in gland –> causing the thyrotoxicosis)
as poor upatke, and also can see iodine overload
list the 2 classes of medical treatment (drugs) for hyperthyroidism, and where do they act
Antithyroid drugs (PTU, carbimazole)
Lugol’s iodine
ACT ON THYROID PEROXIDASE ENZYME
what are Antithyroid drugs useful for, name 2 examples
PTU, carbimazole
Useful for Graves’ disease (50% remit at 18 months)
Toxic MNG/adenoma will not remit
Rash/urticaria/arthralgia (up to 10%)
Agranulocytosis (0.2%)
what is Lugol’s iodine useful for
blocks production of T4/T3 by Wolff-Chaikoff effect (give someone overload of iodine therefore switching off the gland)
Effective for 10 days
Then becomes hyperthyroid (Jod-Basedow effect)
which 3 conditions seen here?
outline radioiodine treatment
when would we use surgery in the treatmeant of hyperthyroidism
In patients who are unable to take drugs or RAI
Large goitre
list some complications of surgery in treatment of hyperthyroidism
what kind of results would you expect to see in someone with primary hypothyroidism
low T4
low T3
high TSH
in which kind of thryoid disease can goitres occur
either hypo or hyperthyroidism
list some signs and symptoms of hypothyroidism