Question

The high osmolarity of the renal medulla is maintained by all of the following except

(A) active transport of salt from the upper region of the ascending limb.

(B) the spatial arrangement of juxtamedullary nephrons.

(C) diffusion of urea from the collecting duct.

(D) diffusion of salt from the descending limb of the loop of Henle.

Short answer

(A) The statement “active transport of salt from the upper region of the ascending limb” is false.

(B) The statement “the spatial arrangement of juxtamedullary nephrons” is false.

(C) The statement “diffusion of urea from the collecting duct” is false.

(D) The statement “diffusion of salt from the descending limb of the loop of Henle” is true.

Step-by-step solution

Kidney

Osmoregulation and excretion are maintained by the special organs called kidneys. Either side of the dorsal aorta comprises kidneys. The outer renal cortex, renal medulla, and renal pelvis are the crucial parts of the kidney. Mesomere of the embryo gives rise to kidneys.

Explanation of option (A)

The renal medulla is impermeable to water which results in increased osmolarity. However, active transportation occurs in ascending limbs which helps to regulate the osmolarity.

Therefore, the active transport of salts helps the renal medulla to maintain high osmolarity.

Thus, the given statement is false.

Explanation of option (B)

The juxtamedullary nephrons participate in the dilution or concentration of urine depending on the quantity of water.

Therefore, the high osmolarity of the renal medulla is regulated by juxtamedullary nephrons.

Thus, the given statement is false.

Explanation of option (C)

In the collecting ducts, the homeostasis feedback mechanism acts and thereby stimulates the anti-diuretic hormone. This hormone activates the aquaporin channel insertion, which results in the recovery of water.

Therefore, the diffusion of urea from the collecting duct regulates the high osmolarity in the renal medulla.

Thus, the given statement is false.

Explanation of option (D)

Recovery of salt and water takes place in the loop of Henle. The movement of liquid through the ascending limb leads to the diffusion of salts to the surrounding medium. Salt reabsorption indices high solute concentration and increases the osmolarity of the renal medulla.

Therefore, diffusion from ascending loop of Henle does not decrease the high osmolarity of the renal medulla.

Thus, the given statement is true.