Excretion – Mechanism of Concentration of the Filtrate: NEET MCQs with Answers

14 free questions on Excretion – Mechanism of Concentration of the Filtrate for NEET (UG), starting with previous-year NEET and AIPMT questions. Try each one, then tap Show answer for the answer and a short explanation.

Syllabus covered: Mechanism of Concentration of the Filtrate

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Question 1

Previous-year question
Two statements are given below. Choose the most appropriate option. [Re-NEET 2024]
Statement I: Concentrated urine is formed due to the counter current mechanism in the nephron.
Statement II: The counter current mechanism helps to maintain an osmotic gradient in the medullary interstitium.
  1. Statement I is correct but Statement II is incorrect.
  2. Statement I is incorrect but Statement II is correct.
  3. Both Statement I and Statement II are correct.
  4. Both Statement I and Statement II are incorrect.
Show answer
Answer: (C) Both Statement I and Statement II are correct.
Explanation: Both statements are correct. The counter current mechanism operating in Henle's loop and vasa recta maintains an increasing osmotic gradient in the medullary interstitium (300 to about 1200 mOsmol L⁻¹), and this gradient allows water to leave the collecting tubule so that concentrated urine is formed.

Question 2

Previous-year question
Angiotensinogen is a protein produced and secreted by [AIPMT 2006]
  1. macula densa cells
  2. endothelial cells (cells lining the blood vessels)
  3. liver cells
  4. Juxtaglomerular (JG) cells
Show answer
Answer: (C) liver cells
Explanation: Angiotensinogen is a plasma protein produced and secreted by the liver cells. Renin, secreted from the juxtaglomerular cells, acts enzymatically on angiotensinogen to release the 10-amino-acid peptide angiotensin-I. (The macula densa is a plaque in the wall at the end of the thick ascending limb of the nephron.)

Question 3

Previous-year question
Which one of the following statements is correct with respect to kidney function regulation? [AIPMT 2011]
  1. Exposure to cold temperature stimulates ADH release
  2. An increase in glomerular blood flow stimulates the formation of angiotensin-II
  3. During summer, when the body loses a lot of water by evaporation, the release of ADH is suppressed
  4. When someone drinks a lot of water, ADH release is stopped
Show answer
Answer: (D) When someone drinks a lot of water, ADH release is stopped
Explanation: When a person drinks a large amount of water that the body does not require, the osmolarity of the blood decreases. This fall in osmolarity inhibits the release of ADH, so less water is reabsorbed and the excess is excreted as dilute urine.

Question 4

Previous-year question
A fall in Glomerular Filtration Rate (GFR) activates [AIPMT 2012]
  1. juxtaglomerular cells to release renin
  2. adrenal cortex to release aldosterone
  3. adrenal medulla to release adrenaline
  4. posterior pituitary to release vasopressin
Show answer
Answer: (A) juxtaglomerular cells to release renin
Explanation: A fall in glomerular blood flow, blood pressure or GFR activates the juxtaglomerular cells to release renin, which converts angiotensinogen to angiotensin I and then to angiotensin II. Angiotensin II constricts blood vessels and raises glomerular blood pressure, restoring GFR.

Question 5

Previous-year question
Which of the following causes an increase in sodium reabsorption in the distal convoluted tubule? [AIPMT 2014]
  1. Increase in aldosterone levels
  2. Increase in antidiuretic hormone levels
  3. Decrease in aldosterone levels
  4. Decrease in antidiuretic hormone levels
Show answer
Answer: (A) Increase in aldosterone levels
Explanation: An increase in aldosterone levels increases sodium reabsorption in the DCT. Aldosterone is secreted by the outer layer of the adrenal gland, and when it is present all the Na⁺ ions in the filtrate are reabsorbed. Retaining Na⁺ raises the osmotic pressure of the blood and reduces water loss from the body.

Question 6

Previous-year question
A decrease in blood pressure/volume will NOT cause the release of [NEET 2017]
  1. renin
  2. atrial natriuretic factor
  3. aldosterone
  4. ADH
Show answer
Answer: (B) atrial natriuretic factor
Explanation: A decrease in blood pressure or volume stimulates the hypothalamus to release ADH and the JGA cells to release renin, and the renin-angiotensin mechanism then activates the adrenal cortex to release aldosterone. Atrial Natriuretic Factor, by contrast, is produced by the atria of the heart in response to increased blood pressure or volume; it causes vasodilation and lowers blood pressure.

Question 7

Previous-year question
Which of the following would help in the prevention of diuresis? [NEET (Sep.) 2020]
  1. Reabsorption of Na⁺ and water from renal tubules due to aldosterone
  2. Atrial natriuretic factor causes vasoconstriction
  3. Decrease in the secretion of renin by JG cells
  4. More water reabsorption due to undersecretion of ADH
Show answer
Answer: (A) Reabsorption of Na⁺ and water from renal tubules due to aldosterone
Explanation: The adrenal cortex secretes mineralocorticoids, chiefly aldosterone, which increase the reabsorption of Na⁺ and water from the renal tubules and thereby prevent diuresis (the production of a large amount of dilute urine). Renin production would need to increase, not decrease, and ADH prevents diuresis when secreted in adequate — not reduced — amounts.
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Question 8

Previous-year question
Select the correct statement. [NEET (Oct.) 2020]
  1. Atrial Natriuretic Factor increases the blood pressure
  2. Angiotensin-II is a powerful vasodilator
  3. Counter-current pattern of blood flow is not observed in vasa recta
  4. Reduction in Glomerular Filtration Rate (GFR) activates JG cells to release renin
Show answer
Answer: (D) Reduction in Glomerular Filtration Rate (GFR) activates JG cells to release renin
Explanation: A fall in glomerular filtration rate activates the juxtaglomerular cells to release renin, which converts angiotensinogen in the blood to angiotensin-I. The other statements are wrong: ANF causes vasodilation and thereby decreases blood pressure; angiotensin-II is a powerful vasoconstrictor that raises GFR; and a counter-current pattern of blood flow is observed in the vasa recta.

Question 9

Previous-year question
The ability of vertebrates to produce concentrated (hyperosmotic) urine usually depends upon the [AIPMT 2000]
  1. area of Bowman's capsule epithelium
  2. length of Henle's loop
  3. length of the proximal convoluted tubule
  4. capillary network forming the glomerulus
Show answer
Answer: (B) length of Henle's loop
Explanation: Henle's loop and the vasa recta form a counter-current system that builds an increasing osmolarity towards the inner medulla, and a longer loop creates a steeper gradient. This gradient lets water leave the collecting duct, so animals with long loops produce more concentrated urine.

Question 10

Previous-year question
Which of the following factors is responsible for the formation of concentrated urine? [NEET (National) 2019]
  1. Maintaining hyperosmolarity towards the inner medullary interstitium in the kidneys
  2. Secretion of erythropoietin by juxtaglomerular complex
  3. Hydrostatic pressure during glomerular filtration
  4. Low levels of antidiuretic hormone
Show answer
Answer: (A) Maintaining hyperosmolarity towards the inner medullary interstitium in the kidneys
Explanation: Maintaining hyperosmolarity towards the inner medullary interstitium is the factor responsible for concentrating the urine, because it provides the concentration gradient necessary for water reabsorption in the renal tubules. Erythropoietin secretion relates to red blood cell production, and low ADH levels would result in dilute urine.

Question 11

Previous-year question
The increase in osmolarity from the outer to the inner medullary interstitium is maintained due to I. close proximity between Henle's loop and vasa recta II. counter-current mechanism III. selective secretion of HCO₃⁻ and hydrogen ions in PCT IV. higher blood pressure in glomerular capillaries [NEET (Oct.) 2020]
  1. Only II
  2. III and IV
  3. I, II and III
  4. I and II
Show answer
Answer: (D) I and II
Explanation: The close proximity of Henle's loop and the vasa recta, together with the counter-current flow in them, maintains an increasing osmolarity towards the inner medullary interstitium — from about 300 mOsmol L⁻¹ in the cortex to about 1200 mOsmol L⁻¹ in the inner medulla. Statements III and IV concern acid–base balance and filtration pressure, not medullary osmolarity.

Question 12

Previous-year question
If the loop of Henle were absent from the mammalian nephron, which of the following would be expected? [2000]
  1. There would be hardly any change in the quality and quantity of the urine
  2. The urine would be more dilute
  3. The urine would be more concentrated
  4. There would be no urine formation
Show answer
Answer: (B) The urine would be more dilute
Explanation: Without the loop no medullary osmotic gradient could be built, so the collecting duct would have no osmotic force to draw water out of the filtrate. Urine could still be formed by filtration and proximal reabsorption, but it would be copious and dilute, as it is in amphibians, which lack the loop.

Question 13

Previous-year question
The formation of concentrated, hyperosmotic urine in vertebrates generally depends on [2003]
  1. the area of the Bowman's capsule epithelium
  2. the length of the proximal convoluted tubule
  3. the capillary network forming the glomerulus
  4. the length of the loop of Henle
Show answer
Answer: (D) the length of the loop of Henle
Explanation: The loop of Henle establishes a gradient of increasing osmolarity from the cortex to the inner medulla by countercurrent multiplication, and the collecting duct passing through that gradient can then withdraw water from the filtrate. The longer the loop, the steeper the gradient and the more concentrated the urine, which is why desert mammals have exceptionally long loops.

Question 14

Previous-year question
Which of the following statements is correct? [NEET, 2017]
  1. The descending limb of loop of Henle is impermeable to water
  2. The ascending limb of loop of Henle is permeable to water
  3. The descending limb of loop of Henle is permeable to electrolytes
  4. The ascending limb of loop of Henle is impermeable to water
Show answer
Answer: (D) The ascending limb of loop of Henle is impermeable to water
Explanation: The ascending limb is impermeable to water but transports electrolytes out; the descending limb is permeable to water.

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