Whats the difference between the efferent arteriole and afferent?
The afferent arteriole brings blood to the glomerulus and the efferent arteriole carries blood away from the glomerulus.
The afferent arteriole is the arteriole that brings blood to the glomerulus. It is larger in diameter than the efferent arteriole.
The efferent arteriole is the arteriole that carries blood away from the glomerulus. It is smaller in diameter than the afferent arteriole.
Why is the afferent arteriole larger in diameter than the efferent arteriole?
This is to provide for the increased blood pressure in the glomerulus for ultrafiltration to take place. When the afferent arteriole is larger, more blood would flow into the efferent arteriole, which is of a smaller diameter, resulting in increased blood pressure in the glomerulus. The high hydrostatic pressure forces small molecules such as water, urea, uric acid, creatinine, amino acids, mineral salts through the glomerulus to the Bowman's capsule and into the nephron, resulting in ultrafiltration.