Adrenal functions Flashcards
What percentage of the adrenal gland is formed by the zona fasciculata, and what does it secrete?
- 75%
- Glucocorticoids (cortisol) and some (adrenal androgens and estrogen)
What percentage of the adrenal gland is formed by the zona glomerulosa, and what does it secrete?
- 15%
- It secretes mineralocorticoids (aldosterone)
What percentage of the adrenal gland is formed by the zona reticularis, and what does it secrete?
- 10%
1) Adrenal androgens (DHEA, Androstenedione)
2) Small amounts of estrogens and glucocorticoids)
What stimulates the release of aldosterone from the zona glomerulosa?
1) Angiotensin-II
2) Potassium
What stimulates the zona fasciculata of the adrenal cortex?
ACTH
What stimulates the zona reticularis of the adrenal cortex?
ACTH
What is aldosterone?
- Steroid mineralocorticoid hormone
- Essential for survival, released by the zona glomerulosa
- It has a short half-life
- it has 90% of the mineralocorticoid activity (as some mineralocorticoids share some of the glucocorticoid functions)
- 40% of it is free
How is aldosterone regulated?
1) Renin-angiotensin-aldosterone mechanism
2) Decreased Na+ will stimulate the release of aldosterone
3) ACTH will to some extent
4) Increased potassium level will stimulate its release to
Through which type of receptor does Ang-II promote the secretion of aldosterone?
- G-protein signaling, which induces the hydrolysis of PIP2 to IP3 and Diacylglycerol, which will lead to an intracellular increase in calcium and thus exocytosis
What are the different functions of aldosterone?
- It acts on the principal cells of the late distal tubule and collecting ducts
1) It stimulates the absorption of sodium
2) It increases the secretion of potassium
3) It increases the secretion of hydrogen ion
What is the mechanism of action of aldosterone?
It synthesizes N+ transporters (like Na+/K+ pumps) and channel proteins
- Excess aldosterone will cause hypokalemia, alkalosis (due to hydrogen loss), and muscle weakness, while hyperkalemia will cause cardiac toxicity
What is meant by the aldosterone escape (natriuresis/diuresis) phenomenon?
The amount of sodium not excreted due to the effects of aldosterone won’t affect the osmolarity very much as water is reabsorbed via osmotic absorption, thirst is also triggered due to high sodium levels, + the release of ADH which will reduce the water loss and osmolarity further
- This will all balance the Na and prevent hypernatremia
What are the effects of androgens?
- Dehydroepiandrosterone (DHEA)
1) They are converted to testosterone and estrogen in the peripheral tissues (mainly in the peripheral tissues)
2) The amount synthesized in the adrenal gland is small compared to the gonads
3) ACTH regulates the secretion of adrenal androgens
What are glucocorticoids?
- Steroid hormone (cortisol/hydrocortisone) which has 95% of G.C function
- 4% of the glucocorticoid is corticosterone but it has significant activity
To what protein is the cortisol hormone bound?
1) Cortisol-binding hormone (transcortin)
2) Albumin
- 90/95% of cortisol is bound to transcortin
What are the functions of glucocorticoids?
1) Suppresses the immune system
2) Promotes gluconeogenesis in the liver (Insulin-antagonist)
3) Extra-hepatic protein catabolism
4) Lipolysis by the adipose tissue
5) Inhibits uptake of glucose in tissue leaving it for the brain and heart mainly
Describe the cycle that controls the levels of glucocorticoids
1) CRH (Controlled by stress and circadian rhythm “it is more in the morning)
2) CRH will release ACTH
3) ACTH will release Cortisol
- Cortisol will negatively inhibit ACTH & CRH
What are the effects of short-term stress?
1) Increases the HR
2) Increases the BP
3) The liver will convert glycogen to glucose and release it to the blood
4) Dilation of the bronchioles
5) Changes in blood flow, leading to a decreased systemic activity and reduced urine output
6) Increases the metabolic rate
What are the long term effects of stress?
1) Sodium and water retention by the kidneys
2) Increased blood volume and pressure
3) Protein and fats are converted to glucose/broken down for energy
4) Increased blood glucose
5) Suppression of the immune system
What is the effect of cortisol on inflammation?
1) It has an anti-inflammatory & immuno-suppressive effect
2) It blocks the early stages of the inflammatory process
- Reduces inflammation and increases the speed of healing rapidly
What is the mechanism by which cortisol exhibits its anti-inflammatory effects
1) Stabilizes the lysosomes (proteolytic enzymes won’t escape)
2) Decreases the permeability of the capillaries
3) Decreases the migration of WBCs and phagocytosis of inflamed cells
4) Decreases the production of T-lymphocytes and antibodies
5) Reduces fever by decreasing the release of IL-1
What are the anti-allergic effects of cortisol?
1) Blocks the inflammatory response
2) While the basic allergic reaction wont be affected it can be life-saving
3) Decreases the number of Eosinophils, basophils, and lymphocytes
4) It increases the number of RBC
5) Large doses of cortisol will lead to the atrophy of the lymphoid tissues and decrease the production of T-cells and antibodies, decreasing the immunity
How is the release of cortisol controlled?
1) Long-loop inhibition: Where cortisol will inhibit its own release through the hypothalamus (Inhibiting the release of CRF)
2) CRF controls ACTH (the main regulator) and CRF is controlled by negative feedback
At what time during the day is CRF highest?
1) It is the highest in the very early morning
2) Lowest near midnight
