Question

The process of countercurrent multiplication involves?

Select one:

a. Osmosis of water out of the ascending Loop of Henle

b. Removal of excess tubular salt by the vasa recta

c. Removal of water from the medullary interstitium by the vasa recta

d. Active transport of sodium and chloride from the descending Loop of Henle

Answer 1

Answers :

C. Removal of water from the medullary interstitium by the vasa recta.

A countercurrent mechanism that expends energy to create a concentration gradient. The mechanism of countercurrent multiplication works together with the vasa recta's countercurrent exchange to prevent the wash out of salts and maintain a high osmolarity at the inner medulla.

The countercurrent flow within the descending and ascending limb creates an osmotic pressure drawing water from the descending limb into the hyperosmolar medullary space. making the filtrate hypertonic. The countercurrent flow within the descending and ascending limb thus increases , or multiplies the osmotic gradient between tubular fluid and interstitial space.

The descending limb of the loop of Henle is permeable to water but impermeable to solutes, due to the presence of aquaporin1 in its tubular wall. Thus, water moves across the tubular wall into the medullary space, making the filtrate hypertonic. This is the filtrate that is continues to the ascending limb.

The ascending limb is impermeable to the water because of a lack of aquaporin , a common trasporter protein for water channels in all cells except the walls of the ascending limb of the loop of Henle but permeable to solutes but here Na+ ,Cl- , and K+  are actively transported into the medullary space making the filtrate hypotonic.