Question

a)countercurrent exchange mechanisms are important in vertebrate physiology. How does the mechanism work

b)describe 3 specific features of vertebrate animals that depend on countercurrent exchange. ( make sure to include the description of the organs involved and tell how the principle of countercurrent exchange lets animal meet a physiological challenge

Answer 1

(A) The counter current mechanism helps to concentrate the filtrate which occurs in loop of Henle and vasa recta in the medulla region of the kidney.The flow of the filtrate in the two limbs of loop of Henle is in opposite directions and thus form a counter current.The flow of blood in the two limbs of vasa recta is also in opposite directions and therefore form a counter current.

The counter current helps in maintaining an increasing osmolarity towards the inner medullary interstitial fluid i:e from 300mOsmo/ lit in the cortex to about 1200mOsmo/lit in the inner medulla.This gradiant is mainly caused by NaCl and urea.

NaCl is transported by the ascending limb of loop of Henle which is exchange with the descending limb of vasa recta. NaCl is returned to the medullary interstitial fluid by the ascending loop of vasa recta.Similarly ,small amount of urea enter the thin segment of the ascending limb of loop of Henle which is transported back to the medullary interstitial fluid by the collecting duct.

(B)The counter current mechanism helps to maintain a concentration gradient in the medullary interstitial fluid which helps in an easy absorption of water from the filtrate.So that the concentration of the filtrate (urine) is increased.Kidney produces about four times more concentrated urine than the initial filtrate formed.

The permeability of urea found in deeper part of thin ascending loop of Henle and collecting duct that is urea diffuses out of the collecting duct and enters into the thin ascending loop of Henle.Thats why a certain amount of urea is recycled in this way and is trapped in the interstitial fluid that urea called osmolyte ,that maintain the osmolarity or homeostasis of our body.