Differentiate between Afferent arteriole and Efferent arteriole (diameter).
Topic: Afferent and efferent arterioles
Answer
The AFFERENT arteriole has a WIDER diameter; it carries blood INTO the glomerulus.
The EFFERENT arteriole has a NARROWER diameter; it carries blood AWAY from the glomerulus.
The question specifies DIAMETER, so that difference must be stated plainly: afferent WIDER, efferent NARROWER.
WHY IT MATTERS, and this is what earns the second mark: because blood enters through a wide vessel and can only leave through a narrow one, it backs up and a HIGH HYDROSTATIC PRESSURE builds in the glomerulus. That pressure is what forces the filtrate out through the capillary walls — ULTRAFILTRATION. Without the difference in diameter, filtration could not occur.
It is a neat piece of plumbing, and examiners like it because the structure so obviously serves the function.
The names give the direction: AFFERENT carries towards, EFFERENT carries away — the same pair as the sensory and motor neurons of a reflex arc.
| Point of difference | Afferent arteriole | Efferent arteriole |
|---|---|---|
| Diameter | Wider | Narrower |
| Direction of blood | Into the glomerulus | Out of the glomerulus |
| Effect | Brings blood in faster than it can leave | Restricts outflow, raising pressure inside the glomerulus |