If the glomerular mesangial cells contract, reducing the overall surface area of the glomerulus which of the following is not likely to occur? A Urine output will decrease. B Systemic blood pressure will be lowered. C Glomerular filtration rate will decrease. D Net filtration rate will decrease.

Glomerular capillaries serve to provide a large surface area for glomerular filtration as they are long and extensive. Mesangial cells serve to regulate the available surface area for the process of filtration. When mesangial cells are relaxed, the maximal surface area is available. This results in a very high rate of glomerular filtration. On the other hand, contraction of mesangial cells reduces the available surface area, and thereby, reduces the rate of glomerular filtration.

Systemic blood pressure is the blood pressure in the blood vessels of the systemic pathway. The contraction of heart chambers during the pumping of blood is the source of systemic blood pressure. Therefore, the contraction of glomerular mesangial cells would not lower the systemic blood pressure.