HORMONES INFLUENCING RENAL ACTIVITY
- Hormones acting on kidney (produced by other organs):
– ADH, Aldosterone, Natriuretic peptides (ANP, BNP) & Parathormone.
- Formed in supraoptic nucleus of hypothalamus.
- Secreted by posterior pituitary.
- Increases water reabsorption
– By increasing water permeability in late DCT & on cortical and medullary collecting ducts.
– More pronounced in medullary collecting duct.
– Because of maximum urinary concentration occurrence.
- Acts via V2 receptors & aquaporin-2 water channels.
2. ALDOSTERONE:
- Secreted from adrenal cortex.
Renal actions:
- Actions localized to distal tubular & collecting ducts.
– Stimulates basolateral Na2+ – K+ ATPase.
– Generates Na2+ movement gradient from apical membrane —> Increasing Na2+ reabsorption.
- Balanced by K+ secretion into lumen.
Net effect:
- Reabsorb sodium & water with K+ secretion.
- Aldosterone – Only regulator of external potassium balance.
- Weak regulator of Na2+ & water balance.
- Major regulator of Na2+ & water balance -“Thirst – ADH” mechanism.
3. NATRIURETIC PEPTIDES
- Peptide hormones causing natriuresis (↑ed Na2+ excretion).
- Includes, “Atrial Natriuretic Peptide (ANP) & Brain Natriuretic Peptide (BNP)”.
- Present as granules in atrial muscle cells.
- Released in response to increased plasma Na2+ concentration.
- Effects are physiologically antagonistic to angiotensin II.
Renal effects:
- Causes natriuresis.
– Due to increased GFR, by relaxing glomerular mesangial cells.
- Decreases Na2+ reabsorption from distal tubule & collecting duct.
- Decreases secretion of renin, aldosterone & ADH.
- Relaxes arteriolar & venular smooth muscle lowering BP.
Actions on kidney:
- Major regulating factor for calcium reabsorption.
On Proximal convoluted tubule:
- “Phosphaturic effect” – Inhibits renal phosphate reabsorption.
- Increased urinary cAMP.
- cAMP – 2nd messenger of PTH.
- Production of 1,25-dihydroxycholecalciferol (Calcitriol).;
On Distal convoluted tubule:
- Increases renal Ca2+ reabsorption
Exam Important
1. ANTIDIURETIC HORMONE (ADH):
- Increases water reabsorption.
– By increasing water permeability in late DCT & on cortical and medullary collecting ducts.
- More pronounced effect in medullary collecting duct.
– Because of maximum urinary concentration occurrence.
2. ALDOSTERONE:
- Actions localized to distal tubular & collecting ducts.
- Stimulates basolateral Na2+ – K+ ATPase.
- Major regulator of Na2+ & water balance –“Thirst – ADH” mechanism.
3. Atrial Natriuretic Peptide (ANP):
- Causes natriuresis.
– Due to increased GFR, by relaxing glomerular mesangial cells.
– Decreases Na2+ reabsorption from distal tubule & collecting duct.
- Relaxes arteriolar & venular smooth muscle lowering BP.
Actions on kidney:
- Major regulating factor for calcium reabsorption.
- Production of 1,25-dihydroxycholecalciferol (Calcitriol).
On Proximal convoluted tubule:
- “Phosphaturic effect” – Inhibits renal phosphate reabsorption.
On Distal convoluted tubule:
- Increases renal Ca2+ reabsorption.
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