L6- Adrenal Gland Continued Flashcards
What is the primary function of the mineralocorticoids? The secondary function?
The mineralocorticoids are hormones that promote sodium retention by the kidney.
Secondarily, they aid in water retention
What is the main mineralocorticoid?
Aldosterone
What is the precursor to aldosterone that also has mineralocorticoid action?
11-deoxycorticosterone
Which are the primary cells that have aldosterone synthase?
Cells of the zona glomerulosa- responsible for the production of aldosterone
What tissues express high levels of MR/therefore are the sites of mineralocorticoid action?
Distal tubule in the kidney, colon, salivary ducts and sweat glands.
The main target is the kidney
How does aldosterone affect potassium and sodium in the kidney?
Aldosterone stimulates sodium and water reabsorption in the kidney; increases potassium secretion (exchanges Na for K)
What physiologic effect stimulates the release of renin from JGA of the kidney?
Decreased blood pressure.
Renin is secreted into the blood and acts like a hormone, although it is not a hormone
What is the action of renin?
Cleavage of angiotensinogen (from the liver) to angiotensin I
What enzyme is responsible for the conversion of angiotensin I to the active form, angiotensin II?
ACE
What is the action of angiotensin II?
Angiotensin II is a vasoconstrictor and stimulates aldosterone release from the zone glomerulosa
Which hormone is the primary regulator of extracellular volume?
Aldosterone- stimulates sodium and water reabsorption in the kidneys, stimulates potassium secretion —> increased extracellular fluid volume and blood pressure
What is the primary role of AVP/ADH?
Regulator of free water balance -
Stimulates the distal nephron water permeability to increase water retention
This decreases plasma osmolality which secondarily affects sodium concentration in the blood (Na+ is more dilute as more water is reabsorbed from the distal nephron)
How does aldosterone affect change (what happens following binding of aldosterone to the MR)?
Aldosterone binding to the mineralocorticoid receptor causes it to dimerize and translocate to the nucleus where it alters transcription of aldosterone-regulated genes
What happens to cortisol in cells that do not have cortisol receptors (GR)?
It is converted to the inactive form- cortisone- by 11 beta-HSD2 such that it does not bind to MR
What two hormones bind to the mineralocorticoid receptor?
Both mineralocorticoids (aldosterone) and glucocorticoids (cortisol) can bind to and activate the MR.
Glucocorticoids are 10-100 times higher in concentration than mineralocorticoids, but 95% of them are bound to specific binding proteins and therefore biologically inactive
What enzyme is inhibited by carbenoxolone? What is the result?
11 beta-HSD2 is inhibited by carbenoxolone. This results in excess MR activation, as cortisol is not converted to its inactive form (cortisone)
What hormones are produced by the zona reticularis?
Weak androgens- such as DHEA/DHEAS
DHEA is a precursor for what other hormones?
More potent androgens such as testosterone, and also for estrogen
What makes a weak androgen weak?
Low binding affinity for androgen receptors
In men, 50% of total androgens in the prostate are derived from what?
Weak androgen adrenal precurors
The STAR protein is stimulated to transport cholesterol into the inner mitochondrial membrane by what hormone? What is cholesterol converted to?
ACTH- cholesterol is now converted to pregnenolone
The presence/absence of what restricts different zones of the adrenal cortex to producing only certain hormones?
The presence/absence of enzymes in the different zones of the adrenal cortex determines which hormones will be synthesized
What is the most common cause of congenital adrenal hyperplasia?
21 alpha-hydroxylase deficiency
What is the result of a 21 alpha-hydroxylase deficiency?
Excess androgen production (DHEA) and deficit of mineralocorticoids/glucocorticoids leads to virilization (masculinization), ambiguous genitalia at birth and sodium loss
