Which of the following factors decreases Glomerular Filtration Rate (GFR)?

Afferent arteriolar constriction leads to a decrease in glomerular filtration rate (GFR) because it reduces the blood flow into the glomeruli, which are the filtering units of the kidneys. When the afferent arterioles constrict, the resistance to inflow increases, causing less blood to enter the glomeruli. This reduction in blood flow results in a decreased hydrostatic pressure within the glomerular capillaries, which is essential for the process of filtration.

In essence, GFR is influenced by the balance between the pressures in the glomerular capillaries and the tubular system. Any factor that reduces blood flow into the glomeruli, such as afferent arteriolar constriction, decreases the filtration pressure, thereby leading to a reduction in GFR. This principle is vital in understanding renal physiology, as the regulation of glomerular pressure is crucial for maintaining proper kidney function and homeostasis in bodily fluids.