Question

describe and explain the teo major countercurrent mechanisms present in the kidney

whats the major significant feature for each one that contributes to its job?

how is the countercurrent mechanism utilized for water conservation?

Answer 1

Major countercurrent mechanisms in kidney are Long loop of Henle which establishes a vertical osmotic medullary gradient( countercurrent multipliers) and vasa recta which preserves the gradient while providing blood to renal medulla and maintaining the solute circulation. (Countercurrent exchangers).

The collecting ducts of all the nephrons use this gradient with the support of vasopressin hormone and produces urine of different concentrations .All these mechanisms together known as medullary counter current system.

Loop of Henle is the U shaped portion of the tubule that conducts urine within each nephrons of kidneys.

In loop of Henle, Thick ascending limb plays a role in active transport of Na and Cl .It is impermeable to water and solute reabsorption occurs here.continued inflow of sodium chloride occurs from the proximal convoluted tubule into the loop of Henle.Thin ascending limb is passively permeable to solutes.Thin descending limb has a high permeability to water and impermeable to solutes.

The magnitude in Loop of Henle depends on rate of fluid flow, strength of the single effect and length of loop of Henle.

In vasa recta , descending limb gains solutes and loses water ( solutes diffuse into vessels) and ascending limb gains water and loses solutes ( solutes diffuse out of the vessels) and thus maintaining the solute recirculation.

In collecting ducts , by its permeability to urea and water ,it acts as a osmotic equilibrating device. The renal medullary interstitium around the collecting ducts are hyperosmotic.

Countercurrent mechanism help in conserving water by excreting concentrated urine.It continues to excrete solutes while increasing water reabsorption and also because of the high osmolarity of renal medullary interstitial fluid.