When the kidneys fail to regulate body fluid composition, nitrogenous waste accumulates in the blood — a condition called uremia. NEET questions on this topic test whether you can distinguish the regulatory hormones (ADH, aldosterone, ANF), locate their targets precisely, and connect renal failure to its clinical consequence.
Regulation of kidney function. The hypothalamus monitors blood osmolarity. When osmolarity rises (dehydration), the posterior pituitary releases antidiuretic hormone (ADH), which increases water reabsorption in the distal convoluted tubule (DCT) and collecting duct by inserting aquaporin channels. Result: concentrated urine, reduced volume. When osmolarity falls, ADH secretion drops — dilute urine is produced.
Aldosterone, released from the adrenal cortex (zona glomerulosa), acts on the DCT to increase Na⁺ and water reabsorption. It is stimulated by the renin-angiotensin pathway when blood pressure or blood volume drops.
Atrial natriuretic factor (ANF) is released by the atrial wall when blood volume rises. ANF inhibits renin secretion and NaCl reabsorption, promoting Na⁺ and water excretion — opposing aldosterone's effect.
Uremia and dialysis. When GFR drops severely (chronic kidney disease), urea, creatinine, and other wastes accumulate — uremia. Symptoms include nausea, fatigue, and altered mental status. Haemodialysis removes wastes by passing blood through a semipermeable membrane against a dialysing fluid (contains glucose, salts at normal plasma concentration but zero urea — urea moves down its concentration gradient). This is an artificial substitute for glomerular filtration, not tubular function.
Renal transplant is the permanent correction; the transplanted kidney is placed in the iliac fossa and connected to iliac vessels. NCERT Class 11 Biology Chapter 16, page 214) covers these regulatory and disorder facts.
Two named kidney disorders. Renal calculi (kidney stones) are stones or insoluble masses of crystallised salts — such as oxalates — formed within the kidney. Glomerulonephritis is inflammation of the glomeruli of the kidney (NCERT Class 11 Biology, Chapter 16, page 214). Both sit alongside uremia and renal failure in NEET's disorders list, and NEET distractors sometimes confuse the two: renal calculi is a crystallised obstruction, glomerulonephritis is an inflammatory disorder of the filtering unit itself, not a stone.
Watch-out: NEET distractors commonly swap ADH's target (DCT + collecting duct) with aldosterone's target (DCT only for Na⁺), or confuse ANF's origin (atrial wall) with its action site (kidney).
Select an option to see the explanation. Wrong answers show why your choice was tempting — and name the exact trap it exploits.
Which hormone increases water reabsorption in the collecting duct by promoting aquaporin insertion?
Answer: D. ADH (vasopressin), released by the posterior pituitary, acts on the DCT and collecting duct to insert aquaporin channels, increasing water reabsorption. NCERT Class 11 Biology Chapter 16, page 212.
Why A is wrong: A is wrong because aldosterone primarily increases Na⁺ reabsorption in the DCT; water follows passively, but aldosterone does not act via aquaporin insertion in the collecting duct.
Why B is wrong: B is wrong because renin is an enzyme (not a hormone acting on tubules) that converts angiotensinogen to angiotensin I; it does not directly act on the collecting duct.
Why C is wrong: C is wrong because ANF promotes sodium and water excretion (natriuresis/diuresis) — it opposes water reabsorption, not promotes it.
Atrial natriuretic factor (ANF) is released from the:
Answer: B. ANF is secreted by cardiac atrial cells when blood volume/pressure increases, and it acts on the kidney to promote Na⁺ and water loss. NCERT Class 11 Biology Chapter 16, page 212.
Why A is wrong: A is wrong because the juxtaglomerular apparatus secretes renin, not ANF.
Why C is wrong: C is wrong because the adrenal cortex secretes aldosterone (and cortisol/androgens), not ANF.
Why D is wrong: D is wrong because the posterior pituitary releases ADH (vasopressin) and oxytocin, not ANF.
Uremia refers to the accumulation of which substance in the blood due to kidney failure?
Answer: B. Uremia is defined as the accumulation of urea and other nitrogenous waste products (creatinine, uric acid) in the blood when kidneys fail to excrete them adequately. NCERT Class 11 Biology Chapter 16, page 213.
Why A is wrong: A is wrong because glucose accumulation in blood is hyperglycaemia (a diabetes feature), not uremia.
Why C is wrong: C is wrong because bilirubin accumulation causes jaundice (a liver/bile duct disorder), not uremia.
Why D is wrong: D is wrong because lactic acid accumulation occurs in anaerobic conditions (e.g., intense exercise or shock); it is not the defining feature of uremia.
A patient's blood osmolarity drops below normal. Which is the expected hormonal response?
Answer: A. Low blood osmolarity signals overhydration. The hypothalamus detects this and reduces ADH release from the posterior pituitary, so less water is reabsorbed in the DCT/collecting duct, producing dilute urine to restore normal osmolarity. NCERT Class 11 Biology Chapter 16, page 212.
Why B is wrong: B is wrong because increased ADH would retain more water and further dilute the blood — this is the opposite of the needed correction for low osmolarity.
Why C is wrong: C is wrong because aldosterone is primarily stimulated by low blood pressure/volume via the renin-angiotensin system, not by low osmolarity directly; additionally, retaining Na⁺ would worsen the dilution.
Why D is wrong: D is wrong because ANF is released in response to high blood volume/pressure (atrial stretch), not directly to low osmolarity; while ANF would excrete sodium, the primary regulator here is ADH suppression.
During haemodialysis, urea moves from the patient's blood into the dialysing fluid. Which principle drives this movement?
Answer: C. The dialysing fluid contains zero urea while the patient's blood has elevated urea. Urea diffuses across the semipermeable dialysis membrane from high concentration (blood) to low concentration (dialysate). NCERT Class 11 Biology Chapter 16, page 213.
Why A is wrong: A is wrong because haemodialysis relies on passive diffusion across a semipermeable membrane, not ATP-dependent active transport.
Why B is wrong: B is wrong because osmosis refers specifically to water movement across a semipermeable membrane; urea is a solute and moves by diffusion, not osmosis.
Why D is wrong: D is wrong because hydrostatic pressure-driven filtration describes glomerular filtration in the kidney (ultrafiltration), not the mechanism in a dialysis machine where concentration gradients drive solute removal.
Aldosterone secretion increases when blood pressure drops. Which pathway mediates this response?
Answer: D. Low blood pressure is detected by juxtaglomerular cells, which release renin. Renin converts angiotensinogen to angiotensin I, which is converted to angiotensin II. Angiotensin II stimulates the adrenal cortex (zona glomerulosa) to secrete aldosterone. NCERT Class 11 Biology Chapter 16, page 212.
Why A is wrong: A is wrong because the hypothalamus-posterior pituitary axis releases ADH (for water reabsorption in response to high osmolarity), not aldosterone.
Why B is wrong: B is wrong because while ACTH from the anterior pituitary can modestly stimulate the adrenal cortex, the primary regulator of aldosterone in response to blood pressure drop is the renin-angiotensin system, not the hypothalamic-pituitary axis.
Why C is wrong: C is wrong because ANF opposes aldosterone action (promotes Na⁺ excretion) and is released when blood volume is high, not low; ANF does not stimulate aldosterone secretion.
A student claims: "ANF and aldosterone both act on the kidney, so they have similar effects." What is incorrect about this claim?
Answer: C. Although both hormones act on the kidney, their effects are opposite. Aldosterone promotes Na⁺ (and consequent water) reabsorption in the DCT, conserving fluid. ANF inhibits NaCl reabsorption and renin secretion, promoting Na⁺ and water excretion. They are functional antagonists. NCERT Class 11 Biology Chapter 16, page 212.
Why A is wrong: A is wrong because both ANF and aldosterone do act on the kidney — ANF promotes renal Na⁺ excretion. ANF is released from the heart (atrial wall) but acts on the kidney.
Why B is wrong: B is wrong because ANF is released from the atrial wall of the heart, not the adrenal cortex. Aldosterone is from the adrenal cortex. Their sources are different.
Why D is wrong: D is wrong because while ANF may modestly increase GFR, the key distinction is their opposing effect on Na⁺ handling (excretion vs. reabsorption), not a direct GFR increase/decrease comparison; aldosterone does not primarily decrease GFR.
A person drinks 2 litres of water rapidly. Arrange the correct sequence of regulatory events:
1. Blood osmolarity decreases
2. ADH secretion from posterior pituitary decreases
3. Water reabsorption in collecting duct decreases
4. Dilute urine is produced
5. Osmoreceptors in hypothalamus detect the change
Answer: A. Excess water intake first dilutes blood (1 — osmolarity drops). Osmoreceptors in the hypothalamus detect this (5). In response, ADH secretion from the posterior pituitary decreases (2). With less ADH, fewer aquaporins are inserted in the collecting duct, so water reabsorption decreases (3). The final result is production of dilute, high-volume urine (4). NCERT Class 11 Biology Chapter 16, page 212.
Why B is wrong: B is wrong because osmoreceptors cannot detect the change (step 5) before the change occurs (step 1 — osmolarity must drop first after water intake); also, dilute urine (4) cannot precede decreased water reabsorption (3) since reduced reabsorption is the cause of dilute urine.
Why C is wrong: C is wrong because ADH secretion cannot decrease (step 2) before the hypothalamic osmoreceptors detect the change (step 5); the hypothalamus is the sensor that triggers the ADH response.
Why D is wrong: D is wrong because this sequence has osmoreceptors detecting a change (5) before osmolarity has actually decreased (1), which reverses cause and effect; also places urine production (4) before decreased reabsorption (3).
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Given
Four statements about hormonal regulation of kidney function. One is correct.
Required
Identify the correct statement.
Concept
Renal regulation involves three hormones (ADH, aldosterone, ANF) and one enzyme (renin), each with a specific source, target, and action. NEET distractors swap sources and targets between these.
Formula
No mathematical formula applies. This is a recall + concept-verification question.
Substitution (verification of each option)
• (A) ADH source: posterior pituitary (not adrenal cortex). ADH increases water reabsorption (not specifically Na⁺). Two errors — reject.• (B) ANF source: atrial wall ✓. ANF action: inhibits NaCl reabsorption (promotes excretion) ✓. Both facts correct.• (C) Aldosterone source: adrenal cortex (not posterior pituitary). Target: DCT for Na⁺ reabsorption (collecting duct is primarily ADH's target for water). Source wrong — reject.• (D) Renin source: juxtaglomerular cells (not DCT). Renin converts angiotensinogen to angiotensin I (not angiotensin II to I — that reverses the direction). Two errors — reject.
Calculation
Not applicable (conceptual verification).
Final answer
(B) — ANF is released from the atrial wall and inhibits NaCl reabsorption.
Common trap
The most frequent distractor swap in this question type is mixing ADH's source (posterior pituitary) with aldosterone's source (adrenal cortex), or confusing renin's source (JGA) with its substrate direction. Option (A) and (C) each contain a deliberate source-swap.
Similar NEET-style question
"Assertion: When blood volume increases, more Na⁺ is excreted by the kidney. Reason: ANF released from the atrial wall inhibits renin secretion." — Evaluate both A and R, and determine if R correctly explains A.
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ADH (vasopressin): water reabsorption in CD. Aldosterone: Na+ reabsorption. Renin-angiotensin system: BP regulation. Disorders: uremia, glomerulonephritis, renal calculi. Treatment: haemodialysis, transplant.
-- NCERT Class 11 Biology, Chapter 16, p. 212More in Human Physiology: 33 exam traps and mistakes · 2 formulas · 1 question pattern from its other lessons.
2 questions from NEET 2023. Answers verified against NTA official keys.
Page numbers are the ones printed in the current NCERT textbook (2023 rationalised edition), unless marked pre-2023. The books are free at ncert.nic.in.
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