Question

Urine is hypotonic in
a. PCT
b. Loop of Henle
c. DCT
d. Collecting duct

Answer 1

Hint: The structural and functional unit of the kidney is the nephron. Its body is divided into the different structural parts which filter out the urine. A hypotonic solution has a lower solute concentration than the inside of the cells (solute concentration in the cell is high).

Complete answer:
> The DCT has a laminar construction in its walls. These perform a variety of functions, all of which are important for the filtration of urine. The proximal wall of the distal convoluted tubule helps in maintaining homeostasis of the calcium level in the bloodstream and the distal wall plays an important part in maintaining the homeostasis of sodium and potassium for the body. The ascending limb of the loop of Henle passes filtrate into DCT. Hence urine is hypotonic to DCT. So option C is correct.

> PCT is lined with cuboidal epithelium with a brush border. It increases the surface area for absorption. Almost all essential nutrients and 70-80 % of electrolytes and water are reabsorbed by PCT with small changes in luminal osmolarity. Hence urine is isotonic in the proximal convoluted tubule. So, option A is wrong.

> The ascending limb of Henle's loop is impermeable to water and permeable to electrolytes. So option B is wrong.

> The collecting duct is the area where urine is collected. So the option D is wrong.

Hence, The correct answer is option (C).

Note: Urine is created within the kidneys via the nephrons, the smallest structural unit within the kidney. It is then transported to the bladder for storage. It is through the nephron and its series of components that allow the water, salt, and wastes to be extracted and exchanged from the blood to form urine. The hypotonic urine is generally present in the distal consolidated tubules of the nephrons.