Exam 2 (Lecture 9) - Mineralocorticoids

Question 1

What is the chemical nature of aldosterone?

Answer 1

Steroid hormone

Question 2

Which part of the adrenal gland secretes aldosterone?

Answer 2

Zona glomerulosa (in the cortex)

Question 3

What are the major triggers of aldosterone secretion and what are its major physiological functions?

Answer 3

1) Triggers:
- day time increases secretion
- decreased volume of circulating fluid (detected and stimulated by the renin/angiotensin system)
- increased K+ in plasma

2) Functions:
- sustains extracellular fluid volume by conserving body sodium
- preventing overload of potassium by accelerating its secretion

Question 4

Explain the operation of RAAS in the regulation of aldosterone secretion. Also, what are other functions of angiotensins and what are ACE inhibitors?

Answer 4

1) Renal hypotension and decreased Na+ concentration in distal tubular filtrate stimulate secretion of renin by juxtaglomerular cells.

2) Renin then catalyzes conversion of angiotensinogen to angiotensin I

3) Angiotensin Converting Enzymes (ACE) from the lungs then convert angiotensin I to angiotensin II; which then promotes aldosterone secretion

Angiotensin II also functions in:
- peripheral vasoconstriction and efferent arteriole vasoconstriction
- stimulates release of catecholamines from adrenal medulla
- stimulates thirst
- promotes ADH secretion

** ACE inhibitors prevent the formation of angiotensin II and thus are used for hypertension treatments

Question 5

What are the general features of cellular effects of aldosterone?

Answer 5

There are 3 hypotheses:

1) Metabolic Hypothesis
- stimulation of ATP production

2) Permeate Hypothesis
- sodium channels increase

3) Na+ Hypothesis
- synthesis of pumps

Because water is passively reabsorbed with sodium, the extracellular fluid volume expands isotonically

Question 6

Why is the bilateral adrenalectomy fatal?

Answer 6

Aldosterone is crucial for Na+ retention and K+ and H+ secretion

Without this mechanism, there is water loss which will cause peripheral circulatory failure/renal failure and result in death

Question 7

What is ANP, where is it located, how is it stimulated, and what is its function?

Answer 7

1) Atrial Natriuretic Peptide

2) Secreted by atrial myocytes and secreted in response to atrial stretch (hypervolemia, hypertension, etc)

3) Reduced both sodium and fluid levels through its actions on blood vessels, the hypothalamus, the adrenal cortices, and the kidneys.
- Also, ANP acts to antagonize the action of aldosterone, ADH, and angiotensin II

Question 8

What is Addison’s-like disease, what are some of its manifestations and how would you treat it?

Answer 8

1) Adrenocortical insufficiency (hypoadrenocorticism)

2) Most common in young to middle-aged dogs; occasionally horses

3) Symptoms include:
- hyponatremia
- hyperkalemia
- deceased Na+/K+ ratio
- increased ACTH
- decreased cortisol
- decreased aldosterone
- acidemia

4) Most common causes: autoimmune destruction of adrenal cortex
- or iatrogenic (adrenal-suppressive therapeutic agents; Mitotane/prolonged glucocorticoid administration)

5) Treatments:
- prednisone (potent; long-lasting cortisol analog)
- 9-alpha fluorocortisol (potent synthetic mineralocorticoid)