W3 - Hormones + Feedback Loops Flashcards
Hypo-Pit-Thyroid Axis is a 3rd order FL, describe the pathway
- Stimulus causes thyrotropin RH to be released from hypo 2. this acts on the APG to release thyroid SH 3. release of T3/4 from thyroid gland
Where are the 3 -ve feedback CPs in the HPT axis?
Target organ (thyroid gland) lessens initial stimulus and the release of the TRH and the TSH
Hypo-Pit-Adrenal Axis is a 3rd order FL, describe the pathway
- Stress is sensed which causes the HT to release CRH 2. the CRH acts on the APG to produce ACTH 3. ACTH acts on adrenal gland to release cortisol
Where are the 3 -ve feedback CPs in the HPA axis?
Target organ (adrenal gland) lessens the initial stress stimulus and the release of CRH and ACTH from the HT + APG respectively
Why is the Renin-Angiotensin-Aldosterone System not an endocrine axis?
It only involves one gland
RAAS 1 - decreased blood volume/pressure means less Na+ is detected by the kidney, what happens due to this?
More prorenin (inactive enzyme) is converted to renin which can convert angiotensinogen to angiotensin 1 (a HM)
RAAS 2 - what happens to angiotensin 1?
It uses a conversion enzyme to form angiotensin 2
RAAS 3 - what does angiotensin 2 do in the zona glomerulosa?
Stimulates aldosterone synthesis which increases blood pressure
What are the 5 layers of the adrenal gland, from outermost to innermost?
Capsule, zona glomerulosa, zona fasciculata, zona reticularis, medulla
Cells in the adrenal cortex make corticosteroid HMs but what do chromaffin cells make in the adrenal medulla?
Catecholamines e.g. adrenaline/noradrenaline
What stimulates the synthesis of mineralocorticoids e.g. aldosterone in the ZG?
Change in ion conc in blood
What two things does aldosterone do to increase bp?
- increase K+ secretion into urine, 2. reabsorbs Na+ into kidney so more water retained to increase bp/volume
The zona fasciculata synthesises glucocorticoids such as cortisol, how does cortisol circulate?
Bound to albumin
Cortisol is typically associated w/ chronic stress responses, inhibiting non-essential activities/immune system (easier to be vulnerable to illness), what does it do to blood plasma glucose conc + NEFAs?
Increases both
What stimulates the release of glucocorticoids from the ZF?
ACTH from APG (HPA axis)
Zona reticularis produces adrenal androgens e.g. DHEA, this is metabolised to ??? and ??? in OTHER TISSUES
Testosterone and estrogens
What is increased DHEA and decreased DHEA associated with?
Increase - onset of puberty, decrease - later life aging
What stimulates the release of DHEA from the ZR and how does it circulate (3 ways)?
ACTH from HPA axis, bound to albumin, SHBG or if sulphated it’s soluble in water
Why is adrenaline only found in the AG?
Highest cortisol (glucocorticoid) level and this is required for PNMT to be expressed to convert NA to A
Adrenaline acts on alpha and beta GPCR receptors, what do each do?
Alpha - increases intra Ca2+ for contraction, Beta - adenyl cyclase action to produce cAMP and activate PKA
Is increasing blood flow/pressure and heart rate or increasing blood glucose conc alpha receptor or beta receptor responses?
Blood flow/pressure/HR - alpha, blood glucose - beta
Adrenaline sensitises the CNS, what two actions display this?
Pupil dilation and sweating
Hydrophilic HMs can be peptides or biogenic amines, what two types of molecules can be hydrophobic HMs?
Biogenic amines and steroid hormones
3 steps of forming peptide HMs
- signal sequence needed to traffic polyp into GA is cleaved 2. intrastrand disulfide bonds hold A and B chains together 3. C chain is cleaved to leave peptide HM (the A + B)
Which glands are central and which are peripheral?
Central - HT, PG, pineal Peripheral - gonad, adrenal, pancreas
Hydrophilic biogenic amines are melatonin and serotonin, which is the NTM/HM and what are they both made from?
Mel - HM, Ser - NTM, both made from tryptophan
Thyroid HM are hydrophobic biogenic amines, what is the difference between T3/4 and which is more common?
T3 - only 3 iodines, T4 - 4 iodines (on 5’ C), T4 is more common
What are two types of steroid HMs?
Glucocorticoids and mineralocorticoids
What typical structure features do hydrophobic HMs have?
Stereotypical hydrophobic ring structures
What 3 things are derived from cholesterol and what are derived from the progestins? What can the testosterone become?
Cholesterol - progestins, androgens, estrogens. Progestins - cortisol, aldosterone, testosterone. Testosterone - estradiol
There is a balance between alpha (glucagon) and beta cells (insulin), other than high glucose what can stimulate beta cells? (3)
Intake of food increases aa conc, stretching of stomach and incretins
What can inhibit beta cells?
Sympathetic stimulation to increase glucose to respond for fight/flight efficiently
Definition of endocrine axis?
Systems of communication between multiple endo glands and eventually the target cell
Name 3 main endocrine axes
HPA, HPG and HPT