Excretory Products and Their Elimination — NEET UG practice

1. Understand the trigger for this pathway: The renin-angiotensin mechanism is activated when blood flow to the kidney drops.

Given a drop in blood volume or pressure, the glomerular filtration rate falls, which corresponds to event C.

2. Identify the kidney's response to low GFR: The juxtaglomerular (JG) cells sense this fall and release the enzyme renin, which converts angiotensinogen (from blood) into angiotensin I, and this is further converted into angiotensin II.

So, this step corresponds to event E.

3. Determine the action of angiotensin II: Angiotensin II is a powerful vasoconstrictor and also stimulates the adrenal cortex to release aldosterone.

Hence, this matches event D.

4. Follow the effect of aldosterone: Aldosterone acts on the distal parts of the nephron tubule, causing reabsorption of $\mathrm{Na}^+$ and water back into the blood.

Therefore, this corresponds to event B.

5. Conclude the final outcome: This reabsorption of sodium and water restores blood volume, raising both blood pressure and the glomerular filtration rate.

So, the final event is A.

6. Final sequence: Putting these steps together gives the order C, E, D, B, A.

Hence, the correct answer is Option D.

1. Recall the location of the JGA: The Juxtaglomerular Apparatus (JGA) is formed at the point of contact between a tubular part of the nephron and a blood vessel supplying that same nephron.

2. Identify which tubule is involved: The tubular part involved is the distal convoluted tubule (DCT), since it lies close to the afferent arteriole as the nephron loops back near the glomerulus.

3. Identify which arteriole is involved: The vessel involved is the afferent arteriole, which carries blood into the glomerulus and is sensitive to changes in blood pressure and filtrate composition.

4. Combine both structures: Since JGA is formed by cellular modification in the distal convoluted tubule and afferent arteriole at their point of contact.

Hence, the correct answer is Option D: Distal convoluted tubule and afferent renal arteriole.

1. Check statement (a): The descending limb of the loop of Henle is permeable to water but almost impermeable to electrolytes.

Given this is a known structural property of the descending limb, statement (a) is true.

2. Check statement (b): As the filtrate moves down the descending limb, water leaves into the medullary interstitium, which is hyperosmotic due to the countercurrent mechanism.

So, the filtrate becomes progressively concentrated, making statement (b) true.

3. Check statement (c): Sodium ions and water are indeed reabsorbed as the filtrate passes through the loop of Henle — water in the descending limb and $\mathrm{Na}^+$ in the ascending limb.

Hence, statement (c) is also true.

4. Check statement (d): The ascending limb actively pumps out $\mathrm{Na}^+$ and $\mathrm{Cl}^-$, while some transport also occurs passively depending on the segment (thin vs thick ascending limb).

Therefore, statement (d) is true as well.