Describe the forces involved in glomerular filtration and explain how it is regulated by the sympathetic system
What will be an ideal response?
Net filtration pressure in the glomerulus is the net force pushing fluid out of the glomerulus and into the Bowman's capsule. It is a specialized capillary exchange, but general rules of bulk flow across the capillary bed apply. The force pushing fluid out of the glomerulus is capillary blood pressure. The two forces pushing fluid back into the glomerulus are plasma-colloid osmotic pressure and Bowman's capsule hydrostatic pressure. The net result favors filtration of fluid out of the glomerulus. Average GFR, glomerular filtration rate, is 125ml/min or 180l/day.
Controlled changes in the GFR are brought about by the sympathetic nervous system, which adjusts glomerular blood flow by regulating the caliber of the afferent arterioles. GFR is reduced by baroreceptor reflex in response to drop in blood pressure. During the reflex, sympathetic activity directed at the afferent arteriole causes vasoconstriction and a decrease in blood flow into the glomerulus. This lowers glomerular pressure and decreases GFR.
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