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Renal physiology A/E (AIPG 2009)

A DCT always receive hypo-osmotic solution

B Afferent artery supplies glomerulus

C GFR is controlled by afferent & efferent arteriole

D 5% cardiac output is received by kidney.

Ans. D 5% cardiac output is received by kidney

I. The descending limb of the loop of Henleis permeable to water, but the ascending limb is impermeable.

II. Sodium, potassium and chloride are co-transported out of the thick segment of the ascending limb.

III. Therefore, the fluid in the descending limb of the loop of Henle becomes hypertonic as water moves into the hypertonic interstitium.

IV. In the ascending limb, it becomes more dilute, and when it reaches the top, it is hypotonic to plasma because of the movement of sodium and chloride out to the tubular lumen.

V. Therefore, the fluid that is delivered to the distal convoluted tubule is always hypotonic.

VI. The glomerulus, which is about 200 m in diameter, is formed by the invagination of a tuft of capillaries into the dilated, blind end of the nephron (Bowman's capsule).

VII. The capillaries are supplied by an afferent arteriole and drained by a slightly smaller efferent arteriole.In a resting adult, the kidneys receive 1.2–1.3 L of blood per minute, or just under 25% of the cardiac output.

VIII. The afferent & efferent arteriole control the blood supply as well as the hydrostatic pressure in the glomerulus,thereby controlling the GFR also.

Factors Affecting the GFR.

Changes in renal blood flow

Changes in glomerular capillary hydrostatic pressure

Changes in systemic blood pressure

Afferent or efferent arteriolar constriction

Changes in hydrostatic pressure in Bowman's capsule

Ureteral obstruction

Edema of kidney inside tight renal capsule

Changes in concentration of plasma proteins: dehydration, hypoproteinemia, etc

Changes in Kf

Changes in glomerular capillary permeability

Changes in effective filtration surface area