endocrinology (adrenal glands)

Question 1

what is the anatomy of the adrenal glands

Answer 1

the adrenal glands are divided into an outer cortex (responsible for synthesis and secretion of steroid hormones) and an inner medulla responsible for catecholamine production

the medulla and cortex of the drenal glands effectively function as separate endocrine glands
- they have a different embryological origin and mostly independent blood supplies

Question 2

what is synthesize by the different part of the adrenal gland

Answer 2

glomerulosa => mineralocorticoids (aldosterone)

fasiculata => glucocorticoids (cortisol)

reticularis => sex steroids (androgens)

medulla => catecholamines (adrenaline + noradrenaline)

Question 3

what are the two catecholamines produced by the medulla

Answer 3

noradrenaline and adrenaline

in cats they are manufactured at an approximate ratio of 3:2

they are produced following acetylcholine release from sympathetic fibers innervating the adrenal medulla and thus are produced in response to a variety of stressors

following release into the circulation, they bind to adrenergic receptors on target tissues

Question 4

how are synthesized the steroid hormones

Answer 4

all the steroid hormones are synthetized, through a variety of intermediary steps (enzymatically-mediated transformations), from cholesterol

production of different types of steroid is largely located in different regions within the cortex

Question 5

explain why the cells of the zona granulosa are responsible for mineralocorticoid production

Answer 5

cells of the zona granulosa lack the 17-alpha-hydroxylase enzyme necessary for the production of cortisol and androgens

Question 6

explain aldosterone mechanism of action and regulation

Answer 6

aldosterone is the principal mineralocorticoid produced by the adrenals

the receptor on cells for aldosterone is identical to the cellular receptor for cortisol, but cells of target tissues for aldosterone contain an enzyme that destroys cortisol (but has no effect on aldosterone), rendering them aldosterone-responsive and not cortisol-responsive

the primary target for aldosterone is cells of the distal renal tubule, where it stimulates increased sodium resorption, increased potassium excretion, and increased water resorption (acting via stimulation of Na-K-ATPase)
- Aldosterone also exerts a similar effect on sweat glands, salivary glands and the colon

the two most important regulators of aldosterone secretion are the potassium concentration in the extracellular fluid and angiotensin II (produced in response to renin release from the kidneys, which in turn is stimulated by hypovolemia)
- ACTH does stimulate aldosterone production, but has only a short-term effect

Question 7

What is the mechanism of regulation of cortisol production

Answer 7

cortisol is the primary glucocorticoid produced by the adrenals and is under the control of ACTH production from the anterior pituitary

cortisol production is controlled through a classic feedback loop with cortisol suppressing CRH and ACTH production