endocrine system Flashcards
(113 cards)
1
Q
endocrine system function
A
- helps body maintain homeostasis
- cell communication for body regulation via chemical messegengers / hormones
- nervous system and endocrine system
2
Q
what are endocrine glands?
A
- collections of cells that make chemical messengers
- secretory epithelial cells surrounded by vascular network
- produce hormones into interstitial fluid which will enter the blood stream
- determined by the receptor expression at the target -> hormones only have an impact on the organs with the receptor
3
Q
epithelial cells in endocrine system
A
produce the hormones
4
Q
where can endocrine target receptors be found?
A
- as part of the epithelial surface like lining of the digestive tract
- seperate organ like thyroid or pituitary glands
5
Q
exocrine glands
A
- open contact with exterior
- ducts carry secretions to the surface
6
Q
endocrine glands
A
- no open contact with exterior
- no ducts, instead produce hormones secreted into blood (then travel via vascular system)
7
Q
main components of endocrine system
A
- pineal gland
- hypothalamus
- pituitary gland
- thyroid gland
- parathyroid glands
- thymus
- adrenal glands
- pancreas
- ovary / testis
8
Q
pituitary gland
A
- 1cm diameter
- in sphenoid bone
- anterior = adenohypophysis
- posterior = neurohypophysis
- endocrine gland in the brain
9
Q
hypothalamus location
A
- lower part of the dicenphalon
- superior to pituitary
- endocrine gland in the brain
10
Q
infundibulum
A
connects the hypothalamus to the pituitary
11
Q
role of the hypothalamus
A
- oversees internal body conditions
- gets nervous stimuli from receptors throughout the body
- controls chemical and physical characteristics of blood
- secretes hormones that regulate pituitary function
12
Q
hypothalamo-hypophysial tract
A
- connects the hypothalamus and posterior pituitary
- communicates via neurons
- extends through the infundibulum
- the neurohormones from hypothalamus travel along neurons in tract and are stored in the posterior pituitary until hypothalamus detects they are needed
13
Q
hypothalamhypophysial portal
A
- connects the anterior pituitary to the hypothalamus
- via blood vessels that create direct communication
- portal blood eventully merges with general circulation
- receives hormones released from hypothalamus
- they cause the anterior pit to release its own hormones
14
Q
regulatory circuits example hypothalamis pituitary thyroid axis
A
axis=when glands signal to each other in a sequence
-> hypothalamis pituitary thyroid axis
- top level: hypothalamus (produces releasing hormones to stimulate the pituitary
- intermediate level: pituitary (produces stimulating hormones)
- target glands: thyroid (produces the hormone)
- feeds back to hypothalamus
15
Q
thyroid gland
A
- large = 20g
- 2 lobes
- lateral to trachea
- inferior to thyroid cartilage
- connects to isthmus across anterior aspect of the trachea
- very vascularised (dark red)
- regulated by the TRH (hypothalamus) & TSH (ant.pit)
- many follicles
- produce T3 and T 4 -> stored & released from follicles ot respond to TSH from pituitary
- iodine needed for thyroid hormone synthesis
- parafollicular cells: sit next to follicles & needed for calcium homeostasis
16
Q
TRH
A
thyroid releasing hormone
17
Q
TSH
A
thyroid stimulating hormone
18
Q
parathyroid glands
A
- 4 small glands on posterior of thyroid glands
- made up of:
- parathyroid (cheif) cells: small, stain darker, produce PTH
- oxyphil cells: large, stain lighter
19
Q
PTH
A
parathyroid hormone
20
Q
adrenal glands
A
- produce hormones that help regulate metabolism, immune system, blood pressure…
- inner medulla: makes epinephrine (adrenaline) & norepinephrine
- outer cortex: 3 layers - makes steriod hormones
- layers have distinct roles
- bottom layer = outermost layer
21
Q
layers of the adrenal gland and their hormones
A
- suprenal medulla = adrenaline
- zona reticularis = androgens
- zona fasciculata = glucocorticoids (cortisol)
- zona glomerulosa = mineralcorticoids (aldosterone)
- capsula
22
Q
zona fasciculata & cortisol
A
can make too much cortisol because of a pituitary tumour affecting the release of stimulating hormones
23
Q
pancreas
A
- lies behind peritoneum
- between greater curvarture of stomach & duodenum
- 15cm long
- exocrine & endocrine
24
Q
pancrease - exocrine
A
acini produce pancreatic juice carried in duct to small intestine
involved in digestive system
25
pancrease - endocrine
pancreatic islets secrete hormones into circulation
- regulates nutrient concentration in circulation (insulin & amino acids)
26
the pancreatic islets
each islet has alpha, beta, gamma cells
alpha:
- secrete glucagon if glc levels too low
beta:
- secrete insulin if glc levels too high
gamma:
- secrete somatostatin to inhibit insulin and glucagon
27
characteristics of cell signalling
1. synthesis of signal
2. release of signalling molecule by signalling cell: exocytosis, diffusion, cell-cell contact
3. transport of the signal to the target cell
4. detect change in receptor protein
5. change in cellular metabolism, function or development
6. removal of signal
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transport of signals
signals can act at short or long-range
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endocrine signalling
hormone released by endocrine cell and carried in the bloodstream to the target cell
30
paracrine signalling
signalling molecules only affect target cells in close proximity to secreting cells
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autocrine signalling
- cells respond to substances that they themselves release
- only the one cell involved
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membrane bound protein signalling
signalling between cells bound to each other by membrane bound proteins
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G proteins
- bind to GTP or GDP
- trimeric: composed of three subunits (alpha, beta, gamma)
- specialised proteins that can activate/inhibit a downstream enzyme to generate an intracellular second message
- they all have 7 membrane spanning regions with amino group extracellular and carboxyl intracellular
34
protein hormones
- insulin, GH, TSH
- synthesised by anterior pi, post.pit, pancreas and parathyroid
- hydrophilic
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steriod hormones
- cortisol, oestrogen
- synthesised from adrenal cortex, ovaries, testes, placenta
- hydrophobic
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thyroid hormones
- thyroxine
- synth. from thyroid
- hydrophobic
- amino acid derivative
- T3 and T4
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catecholamines
- adrenaline
- synth. by adrenal medulla
- hydrophilic
- amino acid derivative
38
what would be the difference in a cell producing a peptide hormone compared to a cell producing a steroid hormone?
- peptides are produced in the RER
- so cells synthesising peptide hormones will have a larger amount of RER
39
synthesis of polypeptides and proteins
- synthesized in advance (prohormones)
- require further processing to be activated
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storage and release of polypeptides and proteins
- stored in vesicles in cell
- released via exocytosis
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transport of proteins and polypeptides in blood
dissolved in plasma
- dont need to be attached to anything
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synthesis of steroids
- on demand
- in a series of reaction pathways from cholesterol
- adrenal cortex, gonads, placenta
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storage and release of steroids
- not stored b4 secretion
- cannot bind to anything for storage
- released upon synthesis by simple diffusion
44
transport of steroids in blood
primarily bound to plasma proteins
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synthesis of thyroid hormones
from tyrosine in advance
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storage and release of thyroid hormones
- stored as colloid in thyroid follicles
- released by a transport protein
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transoport of thyroid hormones in blood
bound to plasma proteins
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synthesis of catecholamines
in advance
49
storage and release of catecholamines
- stored in secretory vesicles
- released by exocytosis
50
transport of catecholamines in blood
freely dissolved
51
how is hormone secretion controlled?
by negative feedback loops
- response driven
- axis driven
sometimes positive feedback e.g. childbirth
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response driven negative feedback
- circulating levels of the product inhibits secretion of the hormone facilitating the synthesis of the product
- e.g. feedback for glands that control blood glucose
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axis driven negative feedback
- multiple feedback loops working simultaneously
- allows for fine tuning
54
what is feed-forward control?
- a direct effect of the stimulus on the control system before the action of the feedback signal occurs
- mediated by ANS
- allows the human body to prepare and adapt for changes in the environment
- example: lactation
55
lactation and feed-forward control
- hear baby crying
- oxytocin released from posterior pituitary (anticipation)
- sucking (stimulus) -> more oxytocin released + prolactin
- oxytocin stimulates own production & release in + feedback
- mother feels thirsty
56
endocrine control of fluid & salt balance
- response is to changes in plasma volume or osmotic concentrations
- water moves passively via diffusion through aquaporin channels
- body water + electrolyte content rise: dietary gains exceed environmental losses
- body water + electrolyte content falls: losses exceed gains
57
neural control of sodium and water balance
- hypothalamic thirst centre
- stimulated by:
- increase in plasma osmolarity
- decrease in plasma volume
- detected by osmoreceptors within hypothalamus -> shrink when osmolality increases
- stimulates hypothalamic thirst center
58
endocrine control of sodium and water balance
- ADH
- aldosterone
- natriuretic peptides
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ADH and water regulation
- also called vasopressin
- main stimulus: increase osmolarity
- increase membrane permeability in collecting ducts of the renal tubules
- more water can then be reabsorbed
- decreases water excretion by the kidneys by increasing water reabsorption in the collecting ducts,
60
what kind of hormone is ADH? how is it synthesized?
peptide hormone
- 9 a.a
- synthesized as pre-pro-hormone by ribosome on ER
- signal peptide cleaved as prohormone is transported into the ER
- prohormone packaged in secretory granules in ER / golgi. stored in posterior pit.
- increased plasma osmolarity results in change in membrane permeability & influx of Ca2+
- prohormones are proteolytically cleaved and ADH is secreted
61
ADH receptors
ADH V2 receptors:
- basolateral membrane of collecting tubule cells in kidney receptors
- are G- protein coupled receptors
ADH V1 receptors:
- blood vessels
- causes constriction
- leads to increased systematic vascular resistance
62
net effect of ADH
- decreases blood osmolality -> water reabsorbed by body
- increased blood volume
63
circadian rhythm and ADH
- ADH secretion increased during the night
- reduced urine production overnight
64
aldosterone
- regulates sodium excretion & reabsorption
- synthesized in zona glomerulosa of adrenal cortex
- stimulates sodium reabsorption and potassium secretion by the distal convoluted tubule and collecting duct
- stimulated by decreased blood pressure or volume
- activates the renin-angiotensin system
- promotes reabsorption of sodium and water in the distal convoluted tubule and collecting duct
- stimulates ADH production
65
layers of the adrenal cortex
- zona glomerulosa
- zona fasciculata
- zona reticularis
66
where is the adrenal cortex?
- outer part of adrenal gland
- each located on the top of each kidney
67
actions of cortisol
- affects most cells in the body
- maintains of blood glc during fasting
- increase availability of blood glc to the brain
- increases lipolysis (adipose tissue), proteolysis (muscle) + stim. gluconeogenesis (liver)
- levels differ during the day
- catabolic -> stimulates breakdown of molecules to provide energy
acts on:
- liver
- muscle
- adipose tissue
- pancreas
68
corticosteroid drugs
- mixture of glucocorticoid (cortisol) and mineralocorticoid (aldosterone) effects
- for adrenal insufficiency
- as an anti-inflammatory / immunosuppressant (asthma, eczema)
69
cortisol levels rise when respond to an acute stress like sudden illness. what would be a problem for people who take regular corticosteroids?
- would need a higher dosage
- increased bp if on long term steroids
- more prone to infection
- worse immune system
70
thyroid gland histology
- made of many spherical follicles
- follicles lind with a single layer of cuboidal epithelial cells = follicular cells
- follicles filled with colloid (made of thyroglobulin: stores thyroid hormone)
- a highly vascular gland
- also has scattered parafollicular cells that secrete calcitonin
71
iodine
needed for thyroid hormone synthesis
72
thyroid hormones
- synthesized from tyrosine (a.a derivatives)
- triiodothyronine (T3)
- tetraiodothyronine (T4)
73
thyroglobulin
- T3 and T4 synthesised & stored here
- a protein
- synthesised by ER and golgi of follicular cells
- large glycoproteins
- contain 70 tyrosines
- exocytosed into thyroid follicle lumen once formed
74
thyroid hormone regulation
- production stimulated by thyrotropin releasing hormone (TRH) from hypothalamus
- TSH from ant. pit increases T3 and T4 secretion
- T3 and T4 inhibit TSH and TRH production by negative feedback
75
cognital hypothyroidism
- inadequate thyroid hormone production
- can cause short stature
- delayed puberty
- excess + thicker skin production
- detect early in babies
- thyroid hormone levels normalised by 3 weeks old
76
what is hyperthyroidism?
- excessive activity of thyroid hormones produced & circulating in bloodstream
- autoimmune origin
77
symptoms of hyperthyroidism
- high metabolic rate
- increased skin temp + more sweating
- thickening of skin
- deeper voice
- tremor
- weight loss
78
radioiodine.
- drug used for hyperthyroidism
- given orally & taken up by the thyroid
- as single dose, lasts 2 months
- decreases the activity of the thyroid as radioiodine emits short range beta radiation -> targets the follicle cells (produce the thyroid hormones)
- treatments eventually damages follicular cells & can lead to hypothyroidism
79
what is the difference between endocrine and exocrine glands?
endocrine: releases directly into the bloodstream
exocrine: releases secretions into a duct which then empties onto an epithelial surface (e.g. skin or lumen of a hollow organ)
80
what are primary endocrine organs?
solely responsible for hormone secretion
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examples of primary endocrine organs
- hypothalamus
- parathyroid glands
- ovaries
- testes
- pancreas
- adrenal glands
- pineal glands
- pituitary glands
82
what are secondary endocrine organs?
responsible for other biological processes and hormone secretion to support and sustain their primary functions
83
examples of secondary endocrine organs
- kidney
- liver
- heart
84
what are the 4 main classifications of cell signalling by extracellular molecules
- endocrine signalling
- paracrine signalling
- autocrine signalling
- membrane bound protein interactions
85
structure of a typtical G-protein coupled receptor
- contain a single polypeptide chain
- 350-400 a.a residues
- 7 membrane spanning alpha-helices
- have an extracellular N-terminal and intracellular C-terminal
86
examples of G-protein coupled receptors
- adrenoreceptors
- dopamine receptors
- purine receptors
87
what is cell signalling amplification?
- refers to the process where a molecule binds to a receptor which then activates one or more second messenger pathways
- these activate multiple effector pathways and stimulate a response
- a multi-step signal relay pathway -> allow for specific amplification of receptor-binding events
88
long feedback loops
- very sensitive
- use negative feedback from peripheral glands -> inihibit hypothalamic and/ pit. hormones
- example: where hormones synthesized in target cells -> act on ant.pit. directly or indirectly on hypothalamic receptors -> inihibit production
89
short-loop feedback
- exists between pit gland and hypothalamus of brain
- works over shorter distance
- can restore homeostasis faster
- insensitive
- only functions if target organs destroyed, removed or non-functional
- example: pt. hormones send signals to hypothalamus
90
ultra-short loop feedback
- paracrine or autocrine effects
- cell acts upon itself or the adjacent cells
- release or hormone inhibits own production
- example: when hypothalamic releasing hormone acts on hypothalamic receptors to inhibit their releases
91
If the plasma concentration outside the cell is higher than that inside the cell, what state would the cell be in? What will happen to correct this disparity?
- water will diffuse into cell down the hypertonic osmotic gradient
- cell is hypotonic
- water will diffuse into the cell to correct this disparity
- cell will swell
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positive feedback loop
- feedback / output signal from loop increases action of affected system
- less common
- example: stretching of cervix during childbirth
93
what is a feed-forward control loop and why would this be beneficial from an evolutionary perspective?
- a loop where the control system before the action of the feedback signal occurs is directly affected by the stimulus b4 the feedback signal occurs
- beneficial for evolutionary perspective since it allows the human body to adapt to possible changes in the environment
- example: increased heart rate when anticipating exercise
94
role of calcintonin
- help regulate calcium levels in blood
- produced by c cells in thyroid gland
- it is a hormone
95
What hormones do the follicular cells produce and secrete, and what are the functions of these hormones?
- thyroid hormones T3 and T4
T3: triiodothyronine
T4: thyroxine
- help increase basal metabolic rate
96
4 common symptoms of diabetes
- increased need to urinate (essp. at night)
- increased constant thirst
- tiredness
- unplanned weight loss
97
Metformin is a commonly prescribed drug to treat Type II Diabetes. Which family of drugs does Metformin belong to and what are its' main actions?.
- is a biguanide
- used to treat type 2 diabetes -> acts on gluconeogensis in liver (increased when you have T2D)
- stimulates increase in glc uptake in skeletal muscles by reducing insulin resistance
- carb absorption decreased + fatty acid oxidation increased
- preventing the liver from converting fats and amino-acids into glucose
- works to increase AMP -> results in an increase in AMP-activated protein kinase -> activates nuclear receptors -> inhibit expression of genes that are important for gluconeogenesis -> decreases glc levels
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hypothyroidism
decreased thyroid levels
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treatment for hypothyroidism
- levothyroxine
- liothyronine
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treatment of diabetes mellitus
- insulin essential for treatment of T1D and T2D
- achieve normal blood glc levels
- normal blood glc levels in humans = 4mM (4.4-6.1mM)
- after a meal blood glc may reach up to 7.8mM
- human insulin made by recombinant DNA tech
- insulin destroyed in gut so given parenterally
- different insulin formulations have different functions
- fast & short-acting sol
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different types of human insulin to treat diabetes
- fast & short-acting soluble insulin
- intermediate-acting insulin isophane insulin
- long acting forms like insulin zinc formulations
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hypoglycaemia
low blood glc levels
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hypoglycaemic agents
- biguanides such as metformin
- used in T2D
- reduce gluconeogenesis in liver -> is increased in T2D
- increase glc uptake in skeletal muscle
- reduce carb absorption
- increased fatty acid ox
- can anorexia and encourage weight loss
- can be combined with drugs which stimulate insulin release
- results in activation of AMP-activated protein kinase (AMP Kinase) -> increases nuclear receptors that inhibits expression of genes that are important for gluconeogensis
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sulphonylureas
- reduce blood glc levels
- stimulate appetite and can lead to weight gain
- stimulate insulin secretion
- pancreatic beta cells need to work
- block ATP sensitive K+ channels in beta cells -> depolarisation -> insulin secretion
- mimic effect of glc
105
thiazolidinediones
- ploglitazone
- increase insulin sensitivity
- lowers blood glc in T2D
- reduces amount of exogenous insulin needed to sustain a certain blood glc level
- reduces hepatic glc output and increases glc uptake into muscle in response to insulin
- reduces blood glc, insulin and fatty acid concentrations
106
incretin mimetics
- exenatide
- incretins = stimulate insulin secretion, peptide hormones released from the gut (e.g. GLP-1)
- exenatide can mimic GLP-1 which is secreted after a meal and provides an early stimulus for insulin secretion
- lowers blooc glc after a meal by increasing insulin secretion and suppressing glucagon secretion
107
gliptins
- sitagliptin & vildagliptin
- incretins that block DPP-4 (enzyme that terminates actions of incretins)
- endogenous incretins are potentiated
- lowers blood glc
- used in T2D
108
adrenal gland structures + secreted hormones
- the medulla secretes catecholamines
- cortex secretes adrenal steroids
- zona glomerulosa secretes mineralcorticoids
- zona fasciculata secretes glucorticoids
109
adrenal steroids
- glucocorticoids
- mineralocorticoids
- progestins
- androgens
- estrogens
110
mineralcorticoids
- regulate water and electrolyte balance
- main one is aldosterone or fludrocortisone
- affect carb and protein metabolism
- main clinical use is replacemnet therapy in addison´s disease -> decreased aldosterone secretion
111
actions of glucocorticoids
- increase blood glc
- help regulate glc metabolism
- e.g. hydrocortisone, prednisolone, demaxamethasone
- metabolic actions
- regulatory actions
- inflammatory and immunity actions
- mediators
112
clinical uses of glucocorticoids
- replacement therapy for adrenal failure
- anti-inflammatory / immunosuppressive therapy
- asthma
- inflammatory conditions of skin and eye..
- severe allergic reactions
- cancer
113
what is antidiuretic hormone (ADH)?
A hormone that helps blood vessels constrict and helps the kidneys control the amount of water and salt in the body
