W3 - Hormones + Feedback Loops

Question 1

Hypo-Pit-Thyroid Axis is a 3rd order FL, describe the pathway

Answer 1

1. 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

Question 2

Where are the 3 -ve feedback CPs in the HPT axis?

Answer 2

Target organ (thyroid gland) lessens initial stimulus and the release of the TRH and the TSH

Question 3

Hypo-Pit-Adrenal Axis is a 3rd order FL, describe the pathway

Answer 3

1. 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

Question 4

Where are the 3 -ve feedback CPs in the HPA axis?

Answer 4

Target organ (adrenal gland) lessens the initial stress stimulus and the release of CRH and ACTH from the HT + APG respectively

Question 5

Why is the Renin-Angiotensin-Aldosterone System not an endocrine axis?

Answer 5

It only involves one gland

Question 6

RAAS 1 - decreased blood volume/pressure means less Na+ is detected by the kidney, what happens due to this?

Answer 6

More prorenin (inactive enzyme) is converted to renin which can convert angiotensinogen to angiotensin 1 (a HM)

Question 7

RAAS 2 - what happens to angiotensin 1?

Answer 7

It uses a conversion enzyme to form angiotensin 2

Question 8

RAAS 3 - what does angiotensin 2 do in the zona glomerulosa?

Answer 8

Stimulates aldosterone synthesis which increases blood pressure

Question 9

What are the 5 layers of the adrenal gland, from outermost to innermost?

Answer 9

Capsule, zona glomerulosa, zona fasciculata, zona reticularis, medulla

Question 10

Cells in the adrenal cortex make corticosteroid HMs but what do chromaffin cells make in the adrenal medulla?

Answer 10

Catecholamines e.g. adrenaline/noradrenaline

Question 11

What stimulates the synthesis of mineralocorticoids e.g. aldosterone in the ZG?

Answer 11

Change in ion conc in blood

Question 12

What two things does aldosterone do to increase bp?

Answer 12

1. increase K+ secretion into urine, 2. reabsorbs Na+ into kidney so more water retained to increase bp/volume

Question 13

The zona fasciculata synthesises glucocorticoids such as cortisol, how does cortisol circulate?

Answer 13

Bound to albumin

Question 14

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?

Answer 14

Increases both

Question 15

What stimulates the release of glucocorticoids from the ZF?

Answer 15

ACTH from APG (HPA axis)

Question 16

Zona reticularis produces adrenal androgens e.g. DHEA, this is metabolised to ??? and ??? in OTHER TISSUES

Answer 16

Testosterone and estrogens

Question 17

What is increased DHEA and decreased DHEA associated with?

Answer 17

Increase - onset of puberty, decrease - later life aging

Question 18

What stimulates the release of DHEA from the ZR and how does it circulate (3 ways)?

Answer 18

ACTH from HPA axis, bound to albumin, SHBG or if sulphated it’s soluble in water

Question 19

Why is adrenaline only found in the AG?

Answer 19

Highest cortisol (glucocorticoid) level and this is required for PNMT to be expressed to convert NA to A

Question 20

Adrenaline acts on alpha and beta GPCR receptors, what do each do?

Answer 20

Alpha - increases intra Ca2+ for contraction, Beta - adenyl cyclase action to produce cAMP and activate PKA

Question 21

Is increasing blood flow/pressure and heart rate or increasing blood glucose conc alpha receptor or beta receptor responses?

Answer 21

Blood flow/pressure/HR - alpha, blood glucose - beta

Question 22

Adrenaline sensitises the CNS, what two actions display this?

Answer 22

Pupil dilation and sweating

Question 23

Hydrophilic HMs can be peptides or biogenic amines, what two types of molecules can be hydrophobic HMs?

Answer 23

Biogenic amines and steroid hormones

Question 24

3 steps of forming peptide HMs

Answer 24

1. 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)

Question 25

Which glands are central and which are peripheral?

Answer 25

Central - HT, PG, pineal Peripheral - gonad, adrenal, pancreas

Question 26

Hydrophilic biogenic amines are melatonin and serotonin, which is the NTM/HM and what are they both made from?

Answer 26

Mel - HM, Ser - NTM, both made from tryptophan

Question 27

Thyroid HM are hydrophobic biogenic amines, what is the difference between T3/4 and which is more common?

Answer 27

T3 - only 3 iodines, T4 - 4 iodines (on 5’ C), T4 is more common

Question 28

What are two types of steroid HMs?

Answer 28

Glucocorticoids and mineralocorticoids

Question 29

What typical structure features do hydrophobic HMs have?

Answer 29

Stereotypical hydrophobic ring structures

Question 30

What 3 things are derived from cholesterol and what are derived from the progestins? What can the testosterone become?

Answer 30

Cholesterol - progestins, androgens, estrogens. Progestins - cortisol, aldosterone, testosterone. Testosterone - estradiol

Question 31

There is a balance between alpha (glucagon) and beta cells (insulin), other than high glucose what can stimulate beta cells? (3)

Answer 31

Intake of food increases aa conc, stretching of stomach and incretins

Question 32

What can inhibit beta cells?

Answer 32

Sympathetic stimulation to increase glucose to respond for fight/flight efficiently

Question 33

Definition of endocrine axis?

Answer 33

Systems of communication between multiple endo glands and eventually the target cell

Question 34

Name 3 main endocrine axes

Answer 34

HPA, HPG and HPT