Please explain with details about Countercurrent mechanism with a diagram.

Dear student,
The countercurrent mechanism are present in many mammalian organs.The best example is that present in loop of henle in nephron.
‚ÄčThe main function of such mechanism is to create concentration gradient by the expenditure of energy. Descending limb of loop of Henle is permeable to water but ascending limb is permeable to solute like Na+, K+ etc. Solute is actively transported to the medullary space and the filtrate becomes hypotonic in the ascending limb increasing its water potential. The descending limb is permeable to water therefore filtrate becomes hypertonic and the medullary space becomes hypotonic. The interstitium is now hypertonic and will attract water coming from the descending limb into the medullary space. This is the countercurrent mechanism. Mammals and birds have an adaptation that they secrete hyper tonic urine to facilitate the minimal solute and  water loss from body. This is done by the countercurrent mechanism in loop of Henle present in  kidney.
Thus  main purpose of this mechanism is to reduce the water and useful solute volume in urine. It helps in forming a concentrated urine that is a primary adaptation of land dwellers to conserve water.



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