Question

Why diameter of afferent arterial is bigger than efferent
arteriole

Answer 1

Afferent arterioles carry blood to the glomerulus, whereas Efferent arterioles take the blood away from the glomerulus.

Blood flows through a great pressure in glomerulus because the afferent arteriole which delivers the blood to the glomerulus has little vascular resistance because it is short & wide.

Therefore if the resistance is low the pressure of blood is high.

Hope it helps you :)

Answer 2

The efferent arteriole carries blood away from the glomerulus. Because it has a smaller diameter than the afferent arteriole, it creates some resistance to blood flow, producing the back-up of blood in the glomerulus which creates higher pressure in the glomerular cavity.