If the diameter of the afferent arteriole decreases to less than that of efferent arteriole

The afferent arteriole is a fine branch of the renal artery which has ha wider lumen than the efferent arteriole which carries blood away from the glomerulus. If the afferent arteriole diameter is less than the efferent arteriole, then glomerular hydrostatic pressure will decrease due to which net filtration pressure will decrease, and hence glomerular filtration will decrease.