Mineralocorticoids – Functions & Regulation
MINERALOCORTICOIDS – FUNCTIONS & REGULATION
Adrenal glands:
- Paired structures situated above kidney
- Layers – Outer cortex & inner medulla.
Adrenal cortex:
Essential for life
- 3 layers –
- Zona glomerulosa
- Zona fasciculata
- Zona reticularis.
- Secretions by adrenal cortex –
- Corticosteroid
- Classified into glucocorticoids, mineralocorticoids & androgens.
- All corticosteroid hormones act on intracellular cytoplasmic receptors
- Zona glomerulosa – Outermost layer & site of mineralocorticoid synthesis.
Mineralocorticoid hormone:
Aldosterone –
- Chief mineralocorticoid
- Secreted by adrenal cortex (Zona glomerulosa layer)
- Small amount of deoxycorticosterone (DOC)
- With much less mineralocorticoid activity.
Actions of aldosterone:
- Acts primarily on kidney.
1. Action on sodium:
- Increases sodium reabsorption in distal convoluted tubules & collecting ducts.
- Occurs in exchange for K+ & H+
- Increased Na2+reabsorption from sweat & digestive juices out of glandular ducts.
2. Potassium hemostasis:
- Aldosterone is a major controller of K+ homeostasis.
- K+ & H+ excretion increased.
3. Regulation of electrolyte & fluid balance:
- In regulation of fluid and electrolyte balance
- Despite effect on Na2+ & water reabsorption
- Secondary to sodium retention, water also retained
Receptors:
- Expressed at high levels in renal distal tubules & cortical collecting ducts.
- Multiple sites in brain (hippocampus), myocardium, peripheral vasculature, brown adipose tissue, colon & salivary glands.
REGULATION OF SECRETION:
- Stimulated by hyperkalemia, angiotensin-II, ACT, and hyponatremia, in reducing order of efficacy.
- Stimulation in response to hyperkalemia –
- Most important renal regulation of potassium balance.
- In response to angiotensin II –
- Through renin-angiotensin system.
- Important for hypovolemia & hypotension correction in salt depletion/renal ischemia.
- In response to ACTH –
- Results in diurnal variation of aldosterone secretion.
- Not an important physiological regulator.
- Hyponatremia – weak stimulator.
Inhibiting factors:
Atrial natriuretic peptide (ANP):
- Inhibits hormone synthesis.
Exam Question
MINERALOCORTICOIDS – FUNCTIONS & REGULATION
Adrenal cortex:
- Essential for life
- Zona glomerulosa – Outermost layer & site of mineralocorticoid synthesis.
Mineralocorticoid hormone:
Aldosterone –
- Chief mineralocorticoid.
- Acts primarily on kidney.
1. Action on sodium:
- Increases sodium reabsorption in distal convoluted tubules & collecting ducts.
- Occurs in exchange for K+ & H+
2. Potassium hemostasis:
- Aldosterone is a major controller of K+ homeostasis.
- K+ & H+ excretion is increased.
Mineralocorticoid (aldosterone) receptors:
- Expressed at high levels in renal distal tubules & cortical collecting ducts.
- Also in brain (hippocampus), myocardium, peripheral vasculature, brown adipose tissue, salivary gland & colon.
REGULATION:
- Stimulated by hyperkalemia, angiotensin-II, ACT, and hyponatremia, in reducing order of efficacy.
- Stimulation in response to hyperkalemia –
- Most important renal regulation of body potassium balance.
- In response to angiotensin II –
- Through renin-angiotensin system.
- In response to ACTH –
- Results in diurnal variation of aldosterone secretion.
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