ENDO Flashcards
(112 cards)
1
Q
What are the different types of cell to cell communications?
A
Electrical (nervous) and chemical (endocrine) communication
2
Q
What are the different types of chemical communications?
A
- Autocrine: chemical messengers that act on secreting cell
- Paracrine: chemical messengers that act on cells close to secreting cell
- Endocrine: chemical messengers that travel in blood to target cells far way
- Neurocrine: chemical messengers that are released by neurons
3
Q
What are the differences between nervous and endocrine communication?
A
- Nervous has more rapid signaling than endocrine
- Endocrine signals have a longer duration of action than nervous
- Endocrine signals use hormones; nervous signals use predominantly neurotransmitters
- Hormones travel to target sites far from site of secretion; neurotransmitters bind to target sites across the synaptic cleft
4
Q
What is the general mechanism of action for a given hormone?
A
Hormone is released -> travels to target cells -> binds to specific receptor -> instigates cell response
5
Q
What are the different receptor types and what type of ligands bind to them?
A
Membrane (extracellular) receptor– lipophobic ligands bind to these
Cytosolic (intracellular) receptor– lipophilic ligands bind to these
6
Q
Describe the second messenger system
A
Lipophobic messengers can not enter the cell to create a cell response– they bind extracellularly. Hence, second messengers are used intracellularly to activate a cell response
7
Q
Name some common second messengers
A
cAMP; cGMP; DAG; IP3; Ca2+
8
Q
What are the different types of extracellular receptors?
A
- G-protein coupled receptor: activates G-protein which in turn activates amplifier enzymes -> second messengers -> cell response
- Ion channel-receptor: ligand binding causes channel to open or close
- Enzyme-receptor (tyrosine kinase): ligand binding activates the enzyme. Further enzymes are activated via docking proteins
- Integrin receptor: the cytoskeleton is manipulated causing cell movement
9
Q
What is a neurotransmitter?
A
Neurotransmitters are chemical messengers that released from the axon terminal of a neuron, diffuse across a synapse and bind to receptors on the postsynaptic membrane. Neurotransmitters can be excitatory (cause depolarisation and increase action potentials) or inhibitory (cause hyperpolarisation and decrease action potentials)
10
Q
What is a neurohormone?
A
Neurohormones are chemical messengers that are released by a neuron into blood circulation.
11
Q
What is signal transduction?
A
The conversion of signal energies (e.g. conversion of electrical signals into chemical signals at axon terminals)
12
Q
Differentiate between ionotrophic and metabotrophic receptors
A
Ionotrophic receptors affect the activity of ion channels; metabotrophic receptors affect cell activity/metabolism
13
Q
Outline how a G-protein coupled receptor can initiate a cell response via cAMP second messengers
A
- Ligand-receptor complex formed
- GDP converted into GTP -> G-protein is activated
- G-protein activates adenylyl cyclase
- Adenylyl cyclase converts ATP into cAMP
- cAMP opens calcium channels (increasing Ca2+)
- cAMP activates Protein Kinase A
- Protein Kinase A and Ca2+ phosphorylate proteins, thus bring about a cell response
14
Q
How can one ligand produce a cell response of a very high magnitude?
A
There is signal amplification at every step of signal transduction
15
Q
What are the factors that can influence the magnitude of a cell response?
A
- Affinity of receptors for ligands
- Number of receptors available
- Concentration of ligand
16
Q
Name and describe the locations of the major endocrine glands
A
- Hypothalamus (brain), pituitary (brain), thyroid (larynx), parathyroid (posterior thyroid), thymus, pancreas (abdomen), adrenal (on top of kidney), gonads (scrotum or internal)
17
Q
Distinguish between an exocrine and endocrine gland
A
Exocrine glands secrete via a duct system onto an epithelial surface; endocrine glands secrete into blood circulation
18
Q
What is up regulation?
A
Up regulation occurs when the number of receptors (and their affinity) for a specific ligand increases
19
Q
What is down regulation?
A
Down regulation occurs when the number of receptors (and their affinity) for a specific ligand decreases
20
Q
What is saturation of receptors?
A
The degree as to which receptors are occupied by specific ligands
21
Q
What is an agonist?
A
An agonist is a chemically-similar ligand that binds to a receptor and activates the cell response of a normal ligand
22
Q
What is an antagonist?
A
An antagonist is a chemically-similar ligand that binds to a receptor but does not activate the cell response of a normal ligand
23
Q
What is permissiveness?
A
Permissiveness is where the action of one hormone is only permitted by the presence of another hormone
24
Q
What is synergism?
A
Synergism is when two hormones produce a greater effect than their combine additive effect
25
What are the different types of hormones?
- Proteins and peptides
- Steroids
- Eicosanoids
- Tyrosine derived: catecholamines and thyroid hormones
26
What types of hormones are lipophilic/lipophobic?
Lipophilic: eicosanoids, steroids and thyroid hormones
Lipophobic: proteins and peptides, catecholamines
27
Outline how protein hormones are synthesised
- Preprohormones are synthesised by ribosomes and cleaved into prohormones
- Prohormones is cleaved/modified in the golgi apparatus into hormones
- Hormones are packaged in vesicles (by golgi) and stored until secretion
28
Outline how steroid hormones are synthesised
- Blood cholesterol enters mitochondria
| - Mitochondria synthesises steroids from cholesterol
29
How do protein, steroid, catecholamines, thyroid and eicosanoid hormones circulate?
- Protein: free form
- Steroid: bound to plasma proteins
- Catecholamines: free form
- Thyroid: bound to plasma proteins
- Eicosanoids: bound to plasma proteins
30
Outline how a G-protein coupled receptor can initiate a cell response via IP3 and DAG second messengers
- Ligand-receptor complex formed
- G-protein activated -> activates phospholipase C
- Phospholipase converts phosphatidyl inositol biphosphate (PIP2), from membrane phospholipids, into inositol triphosphate (IP3) and diacyl glycerol (DAG)
- IP3 releases Ca2+ stores from ER -> Ca2+ brings about a cell response
- DAG activates Protein Kinase C -> PKC brings about cell response
31
Outline how calcium functions as a second messenger
- Ligand-receptor complex opens ion channels to increase intracellular calcium concentration
- Ca2+ binds to calmodulin -> activating it
- Calmodulin activates calmodulin-dependent protein kinase
- Cell response
32
What types of hormones have intracellular receptors?
Steroids, thyroid and eicosanoids?
33
How do intracellular receptors initiate a cell response?
- Ligand-receptor complex formed
- Complex binds to nucleus
- Gene expression altered -> cell response
34
What are the three hormone regulation mechanisms?
- Humoral: hormone secretion regulated by concentration of substrate in blood (e.g. electrolytes, blood glucose)
- Hormonal: hormone secretion regulated by other hormones
- Neural: neural pathway controls secretion of hormone
35
What is a circadian rhythm?
A circadian rhythm is a rhythm of hormone release that spans for 24 hours (a day)
36
What is an infradian rhythm?
A rhythm of hormone release that spans for longer than a 24 hour cycle
37
Describe a negative feedback loop
A negative feedback loop is when increased hormone secretion results in the inhibition of further release
38
Describe a positive feedback loop
A positive feedback loop is when increased hormone concentration results in further release
39
Define a long feedback loop
A long feedback loop is a feedback loop between a peripheral endocrine gland to the pituitary/hypothalamus
40
Define a short feedback loop
A feedback loop between the pituitary gland and the hypothalamus
41
Define an ultrashort feedback loop
An autocrine feedback loop between the hypothalamus itself
42
What is euglycemia?
Normal levels of glucose
43
What is hyperthyroidism?
High levels of thyroid secretion
44
What is hypopituitarism?
Low levels of pituitary secretion
45
Outline primary, secondary and tertiary endocrine disorders
- Primary: deficiency in the peripheral endocrine gland
- Secondary: deficiency in the pituitary gland
- Tertiary: deficiency in the hypothalamus
46
What is a tropic hormone?
A tropic hormone is a hormone that stimulates the secretion of another hormone
47
What is an ultradian rhythm?
A rhythm of hormone release that spans for less than a 24 hour cycle
48
Name the two general types of plasma protein
Albumin and globulin
49
What hormone is most active: free hormones or bound hormones?
Free hormones are biologically active, whereas bound hormones are not
50
What controls the plasma concentration of a hormone?
Its secretion rate as well as its metabolism and excretion rates
51
Do free hormones or bound hormones have the longer half-lives? Why?
Bound hormones have the longer half-lives as they cannot be readily metabolised and excreted from the body (due to the hormone-binding plasma proteins)
52
What is the function of the hypothalamus?
The hypothalamus coordinates visceral functions to maintain homeostasis
53
Where is the hypothalamus located? What brain structure is it a part of?
The hypothalamus is located below the thalamus at the floor of the 3rd ventricle. It is a part of the diencephalon structure
54
What is a nucleus? (in the hypothalamus)
A nucleus is a grouping of neuronal cell bodies that coordinate together
55
What are the two types of neurons in the hypothalamus?
- Magnocellular: large cell body
| - Parvocellular: small cell body
56
What is the scientific name for the pituitary gland? What are the names for its two lobes?
Pituitary gland: hypophysis
Anterior lobe: adenohypophysis ("adeno"=gland)
Posterior lobe: neurohypophysis ("neuro"= neuronal endings)
57
Where did the anterior and posterior lobes originate from (embryonic origin)?
The anterior lobe originated from the pharyngeal ectoderm; the posterior lobe originated from the neural ectoderm
58
Name the five cell types in the anterior pituitary and a hormone they secrete
1. Somatotropes: growth hormone (GH; somatotropin)
2. Corticotropes: adenocorticotropic hormone (ACTH; corticoptropin)
3. Thyrotropes: thyroid-stimulating hormone (TSH; thyrotropin)
4. Gonadotropes: follicle stimulating/luteinizing hormone (FSH/LH; gonadotropins)
5. Lactotropes: prolactin (PRL; lactrotropin)
59
What are the two types of hypothalamic regulatory hormones? What do they do?
- Releasing Hormone (RH): stimulates synthesis and release of hormone from anterior pituitary
- Inhibiting Hormone (IH): prevents synthesis and release of hormone from anterior pituitary
60
Outline how the hypothalamus controls anterior pituitary secretion
The hypothalamus is connected to the anterior pituitary gland via portal blood vessels-- hypothalamic-hypophyseal portal vessels.
1. Blood from the superior hypophyseal artery reaches the primary capillary plexus at the median eminence of the hypothalamus
2. Parvocellular neurons secrete regulatory hormones into primary capillary plexus
3. Blood transports from primary capillary plexus to the secondary capillary plexus via the long hypophyseal veins
4. Regulatory hormones reach the anterior pituitary at the secondary capillary plexus-- anterior pituitary glands secrete hormones into inferior hypophyseal artery
61
Outline how the hypothalamus controls posterior pituitary secretion
The hypothalamus is connected to the posterior pituitary gland via a neuronal tract-- hypothalamic-hypophyseal tract.
1. Magnocellular neurons from hypothalmaus make up the hypothalamic-hypophyseal tract and traverse down to the posterior pituitary gland
2. Magnocellular neurons secrete neuropeptides into inferior hypophyseal artery
62
What are the hormones released by the anterior pituitary gland?
```
Growth Hormone (GH)
Prolactin (PRL)
Thyroid stimulating hormone (TSH)
Luteinizing hormone (LH)
Follice-stimulating hormone (FSH)
Adenocorticotropin hormone (ACTH)
```
63
Which anterior pituitary hormones are proteins and polypeptides; glycoproteins and peptides?
Proteins and Polypeptides: GH, PRL
Glycoproteins: TSH, FSH, LH
Peptide: ACTH
64
What are the 4 hypothalamic releasing hormones (RHs)?
Thyrotropin Releasing Hormone (TRH)
Gonadotropin Releasing Hormone (GnRH)
Corticotropin Releasing Hormone (CRH)
Growth Hormone Releasing Hormone (GHRH)
65
What are the 2 hypothalamic inhibitory hormones?
Somatostatin (GH inhibiting hormone)
| Dopamine (prolactin inhibiting hormone)
66
What are the neuropeptides released from the posterior pituitary?
Anti-direutic Hormone (ADH)/ Arginine vasopressin and oxytocin
67
Where are the neuropeptides released from the posterior pituitary gland synthesised?
They are synthesised by magnocellular neurons in the supraoptic and paraventricular nuclei of the hypothalamus
68
How is neuropeptide transported from the hypothalamus into the posterior pituitary gland via magnocellular neurons?
Neuropeptide is transported via magnocellular neurons by a mechanism known as axoplasmic flow, where vesicles containing hormone travel along the axons of neurons. The vesicles are then stored at the axon terminal before release.
69
Are ADH and Oxytocin structurally similar?
They are very similar as they are both nanopeptides (nine amino acid peptide chain) and only differ at two places on that peptide chain
70
What is a neuroendocrine reflex? Give an example.
A neuroendocrine reflex is where neural stimulation leads to an endocrine effect.
An example is the suckle reflex, where tactile receptors on the lactating breast are stimulated and send neural signals to the hypothalamus. The hypothalamus then secretes oxytocin, which stimulates the milk ejection reflex.
71
Where is oxytocin secreted from?
Oxytocin is secreted by magnocellular neurons in the posterior pituitary gland.
72
What type of hormone is oxytocin?
Oxytocin is a peptide hormone
73
How is oxytocin synthesised?
Oxytocin is synthesised by magnocellular neurons in the supraoptic and paraventricular nuclei of the hypothalamus. It is then transported to posterior pituitary gland via axoplasmic flow
74
In what form does oxytocin circulate?
Oxytocin circulates in free-form (peptide hormone)
75
What is the major target tissue(s) for oxytocin?
Oxytocin's major target tissues are the lactating breast and the uterus during pregnancy
76
When is oxytocin released? What are its major actions?
Oxytocin is released during lactation and parturition (child birth).
During lactation, it stimulates the contraction of myoepithelial cells in the alveoli of the lactating breast which brings about the milk ejection reflex.
During child birth, oxytocin promotes rhythmic contractions of the uterus and dilation of the cervix. This is the parturition reflex.
77
How is oxytocin secretion regulated?
Oxytocin secretion is regulated by neuroendocrine reflexes (positive feedback from neural stimulation)
78
What is the effect of oxytocin hyposecretion and hypersecretion?
Oxytocin does not have hyposecretive or hypersecretive disorders
79
Where is ADH secreted from?
ADH is secreted from the posterior pituitary gland by magnocellular neurons
80
What type of hormone is ADH?
ADH is a peptide hormone
81
How is ADH synthesised?
ADH is synthesised by magnocellular neurons in the supraoptic and paraventricular nuclei of the hypothalamus
82
In what form does ADH circulate?
ADH circulates in free form (peptide hormone)
83
What is the major target tissue(s) for ADH?
The major target tissues for ADH are nephrons in the kidney and blood vessels
84
What are the major actions of ADH at its target tissues?
ADH promotes aquaporin activity in the nephron to increase water reabsorption. In turn, this concentrates urine (decreases overall urine volume) and increases the volume of extracellular fluid as well as diluting blood
ADH also promotes the constriction of blood vessels which increases blood pressure
85
How is ADH secretion regulated?
ADH secretion is regulated by neural feedback. ADH is secreted in response to high blood osmolarity to dilute the blood. It is also released during dehydration to stimulate water reabsorption by the kidneys
86
What is the effect of ADH hyposecretion and hypersecretion?
ADH hyposecretion or inactivity leads to diabetes insipidus where an individual experiences frequent urination and excretes watery urine (very high water content)
87
Where is prolactin secreted from?
Prolactin is secreted by lactotropes in the anterior pituitary gland
88
What type of hormone is prolactin?
Prolactin is a polypeptide hormone
89
How is prolactin synthesised?
Prolactin is synthesised via polypeptide hormone synthesis pathways by lactotropes in the anterior pituitary gland
90
In what form does prolactin circulate?
Prolactin circulates in free form (polypeptide hormone)
91
What is the major target tissue(s) for prolactin?
The major target tissue for prolactin are the breasts
92
What is the major action of prolactin at its target tissue?
Prolactin stimulates breast development and milk production during pregnancy and lactation. It binds to a tyrosine-kinase type receptor via Janus Kinase (JAK)
93
How is prolactin secretion regulated?
Prolactin secretion is promoted by thyrotropin-releasing hormone (TRH) and inhibited by dopamine
94
What is the effect of prolactin hyposecretion and hypersecretion?
Hypersecretion of prolactin inhibits GnRH release -> inhibits LH and FSH release -> inhibition of ovulation and sperm production -> infertility
Typically no hyposecretion
95
What is a trophic hormone?
A trophic hormone is hormone that regulates growth and development of glands/tissues
96
Where is the thyroid gland located?
It is anteriorly located below the larynx, wrapped around the trachea. It extends up to the 6th tracheal ring
97
What is the thyroid isthmus?
The thyroid isthmus joins the two lobes of the thyroid gland
98
What is a pyramidal lobe in the thyroid? How common is it?
The pyramidal lobe is a third, pointed lobe that occurs in the centre of the thyroid. It occurs in about 50% of people
99
What is a thyroid ima artery? How common is it?
The thyroid ima artery is a blood vessel that extends anteriorly from the aortic arch to the pyramidal lobe of the thyroid. It occurs in 3-10% of people.
100
Describe the functional structure of the thyroid gland
The thyroid is composed of follicles which contain follicular epithelial cells surrounding a fluid called colloid. Colloid contains glycoproteins and thyroglobulin
101
What are the key differences between an inactive and active thyroid gland? Refer to the thyroid follices.
Inactive: colloid abundant; follicles are large; follicular cells are flat
Active: follicles are small; follicular epithelia are cuboidal or columnar as they absorb colloid via endocytosis
102
What are the two major thyroid hormones?
Triiodothyronine (T3) and Tetraiodothyronine (T4/Thyroxine)
103
How do T3 and T4 differ structurally?
T3 has 3 iodine molecules; T4 has 4 iodine molecules
104
What is reverse T3 (RT3)?
RT3 is an inactive form of T3 that is released into circulation along with T3 and T4
105
Where are T3 and T4 secreted from?
T3 and T4 are secreted from the follicular cells of the thyroid gland
106
What type of hormones are T3 and T4?
T3 and T4 are tyrosine amino-acid derived (iodinated tyrosine)-- lipophilic
107
How are T3 and T4 biosynthesised?
- Thyroglobulin (glycoprotein) is synthesised by follicular cells and released into colloid
- Thyroglobulin has multiple tyrosine molecules attached to it
- A Sodium/Iodide co-transporter actively pumps I- ions into follicle cell
- Pendrin exchanges intracellular iodide for Cl- from colloid
- Thyroid peroxidase oxides I- into I2 (iodine-- reactive form)
- Iodine binds to tyrosine on thyroglobulin (organification) creating monoiodotyrosine (MIT)
- MIT+ MIT -> DIT
- MIT + DIT -> T3
- DIT + DIT -> T4
- Thyroid Hormones re-enter follicle cell where they are stored (still attached to thyroglobulin) awaiting release
- Protease (deiodinase) cleaves T3 and T4 from thyroglobulin and the hormones enter circulation
108
In what form do T3 and T4 circulate?
Majority of TH released is T4. Around 99% of TH circulate in bound form. They mostly bind to thyroxine-binding globulin (TBG). Can also bind to transthyretin (thyroxine-binding prealbumin) and albumin.
T4 has a higher affinity for binding proteins than T3
109
What is the major target tissue(s) of T3 and T4?
Nearly all tissues in the body have receptors for T3 and T4, except for the gonads and brain
110
What are the major actions of T3 and T4 at its target tissue?
T3 and T4 promote carbohydrate, protein and lipid metabolism by activating genes that encode for specific enzymes
111
How is T3 and T4 secretion regulated?
T3 and T4 secretion is promoted by TSH release by the thyrotropes of the anterior pituitary.
T3 and T4 release inhibits TSH release
112
What are the effects of hypothyroidism and hyperthyroidism?
Hypothyroidism can cause mental and physical slowing; poor resistance to the cold; brachycardia (low heart rate); mental retardation and dwarfism in children
[Fill out hyperthyroidism]
