THORAX ABDOMEN AND PELVIS

Detailed explanation-1: -Urea recycling is a process in kidneys that involves the reabsorption and secretion of urea several times, which contributes to the high concentration of solutes in the renal medulla and helps to establish and maintain the corticopapillary gradient.

Detailed explanation-2: -Urea absorption in the inner medullary collecting duct provides a mechanism to elevate the concentration of urea in the papillary interstitial fluid and thereby permit the excretion of urea with as little water as possible. Urea reabsorption may have another important effect-to aid in the excretion of potassium (K).

Detailed explanation-3: -Vasopressin (anti-diuretic hormone) is the key hormone regulating the production of concentrated urine. Vasopressin rapidly increases water and urea transport in the terminal inner medullary collecting duct (IMCD).

Detailed explanation-4: -In order to increase the magnitude of the medullary urea gradient, the kidneys recirculate the urea within the renal interstitium. As the concentration of urea in the renal medulla increases, the driving force for passive urea secretion into the medullary sections of the thin Henle also rises.