The figure given below shows a part of a nephron. Answer the questions that follow: The figure given below shows a part of a nephron. Answer the questions that follow:
Label the parts numbered 1 to 4.
Topic: Parts of the Malpighian capsule
Answer
1 — EFFERENT ARTERIOLE (carrying blood away from the glomerulus) 2 — AFFERENT ARTERIOLE (bringing blood to the glomerulus) 3 — GLOMERULUS (the knot of blood capillaries) 4 — BOWMAN’S CAPSULE (the double-walled cup surrounding it)
TELL THE TWO ARTERIOLES APART BY THEIR WIDTH, which is drawn deliberately in every such diagram: the AFFERENT is WIDER and the EFFERENT NARROWER.
That difference is not decoration. Blood enters through a wide vessel and can only leave through a narrow one, so it backs up and a HIGH PRESSURE builds inside the glomerulus — and that pressure is what forces the filtrate out. Without the difference in diameter there would be no ultrafiltration at all.
The names give the direction: AFFERENT carries TOWARDS, EFFERENT carries AWAY — the same pair as the sensory and motor neurons of a reflex arc.