What would happen to the glomerular capillary pressure and filtration rate?

Question

What would happen to the glomerular capillary pressure and filtration rate if you increase the diameter of the afferent arteriole?

If, experimentally, the solute concentration of the medullary interstitial fluid of the kidney is increased; what would happen to the urine volume and concentration?

Answer 1

Increasing the diameter of the afferent arteriole allows more blood to enter the capillary bed of the glomerulus. If there is not a corresponding increase in diameter of the efferent arteriole, the influx of blood will create a "back-up" or increase in pressure. When the pressure in the capillaries increases, more fluid is pushed through the capillary walls, resulting in an increase in filtration rate.

Increasing the concentration of solute in the medullary interstitial fluid will increase the osmotic gradient in the descending limb of the loop of Henle. This will cause more water to be drawn out of the filtrate and into the medulla via osmosis. Since water is being removed from the filtrate, the volume of urine will decrease. When the volume of urine decreases but the amount of solute stays the same, the concentration of the urine will increase.