.Describe the process of water, nutrient and electrolyte reabsorption in the nep

Question

.Describe the process of water, nutrient and electrolyte reabsorption in the nephron of the kidney. In your answer, make sure to address the following questions: (11 marks total)

a) What molecules are reabsorbed in each tubular element of the nephron? (7 marks)

b) Describe the structure & function of the countercurrent multiplier (exchange) system. (3 marks)

c) What property of the peritubular capillaries facilitates the absorption of materials from the interstitial fluid of the kidneys? (1 mark)

Explanation / Answer

A)In proximal covoluted tubules reabsorption of most ions (sodium, pottacium, chlorine, calcium, phosphate, bicarbonate) glucose, aminoacid occures, urea and water occur from ultrafiltrate to blood stream. Thin descending limb of loop henle allows reabsorption of water, while thin and thick ascending limb reabsorb ions like sodium, chloride, calcium and pottacium. The distal convoluted tubule allows reabsorption of calcium, sodium and chloride. It regulates the pH of urine by secreting proton and reabsorbing bicarbonate. The collecting duct also allows the reabsorption of water and makes the urine more concentrated.

B) The countercurrent mechanism is used to form concentrated urine by nephron. The countercurrent mechanism is formed by flow of filtrate in the two limbs of henle's loop (ascending limb , descending limb in opposit direction, and flow of blood in the vasarecta. The loop of henle acting as counter current multiplier and vasarecta acting as counter current exchanger.

Sodium chloride is transported from ascending limb in to interstitium and produce an osmotic gradient of 200 mosmol at any part of tubule and interstitium. Descending limb of loop of henle transport urea in to interstitium. These produce progressively increasing osmolar gradient in medulla. The vasarecta, countercurrent exchaner maintain the concentration gradient by absorbing excess solutes and water from interstitium.

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