number 8 A. Glomerular filtration, tubular reabsorption and secretion B. Tubular

Question

number 8

A. Glomerular filtration, tubular reabsorption and secretion B. Tubular reabsorption and secretion, Glomerular filtration C. Sodium reabsorption, water reabsorption D Glucose reabsorption, sodium reabsorption Which one of the following two nephron types is critical in the establishment of the medullary osmotic gradient? A. Cortical nephrons B. Juxtamedullary nephrons Under normal circumstances which of the following is the primary mechanism for water loss by the body? A. Water lost via respiratory action B. Water lost via feces C. Water lost via urine D. Water lost via sweat When arterial blood pressure declines below normal, which of the following compensatory changes in renal function occur as a result of sympathetic nervous system activation? A. Afferent arteriolar vasoconstriction B. Afferent arteriolar vasodilation C. Decreased Renin secretion D. Decreased ADH secretion E. None of the above

Explanation / Answer

Solution 8

The correct option is Option B - Juxtamedullary Nephrons

The kidneys contain two types of nephrons, superficial cortical nephrons (70-80%) and juxtamedullary nephrons (20-30%). Now, kidneys have a remarkable mechanism for reabsorbing water from the tubular fluid, called countercurrent multiplication. Countercurrent multiplication in the kidneys is the process of using energy to generate an osmotic gradient that enables to reabsorb water from the tubular fluid and produce concentrated urine.

A juxtamedullary nephron is a type of nephron, found only in birds and mammals.t is these nephrons which are responsible for the development of the osmotic gradients in the renal medulla, which are used to concentrate urine.

Medullary osmotic gradient is produced by-

Active sodium transport by thick ascending limb from lumen into interstitium
Low blood flow countercurrent mechanism
Recycling of urea between medullary collecting ducts and deep portions of loop of Henle

Final concentration of urine in the collecting ducts rely on the medullary osmotic gradient

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