Question

Why the diameter of the efferent arteriole is less than that of afferent arteriole​

Answer 1

Answer:

The diameter of efferent arteriole is less than that of the afferent arteriole because pressure builds up in the arteriole and some of the fluid is forced to go through the gaps in cells of Bowman's capsule (podocytes). This filters the blood, and this process is called ultrafiltration.

Explanation:

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Answer 2

The afferent arteriole carries blood from the heart to the nephron and therefore the blood flows under pressure. So, to withstand that pressure the walls of the afferent arteriole are thick increasing diameter.

The efferent arteriole carries blood from the nephron to the heart and thus, the blood flows under normal pressure. So, the walls are thinner and diameter is less.