Cambridge International A Level Biology Revision Guide

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Cambridge International A Level Biology
thousands of tiny tubes, called nephrons, and many
blood vessels. Figure 14.8a shows the position of a single
nephron, and Figure 14.8b shows its structure. One
end of the tube forms a cup-shaped structure called a
Bowman’s capsule, which surrounds a tight network
of capillaries called a glomerulus. The glomeruli and
capsules of all the nephrons are in the cortex of the kidney.
From the capsule, the tube runs towards the centre of the
kidney, first forming a twisted region called the proximal
convoluted tubule, and then a long hairpin loop in the
medulla, the loop of Henle. The tubule then runs back
upwards into the cortex, where it forms another twisted
region called the distal convoluted tubule, before finally
joining a collecting duct that leads down through the
medulla and into the pelvis of the kidney.
Blood vessels are closely associated with the nephrons
(Figure 14.9). Each glomerulus is supplied with blood by
a branch of the renal artery called an afferent arteriole.
The capillaries of the glomerulus rejoin to form an efferent
arteriole. The efferent arteriole leads off to form a network
of capillaries running closely alongside the rest of the
nephron. Blood from these capillaries flows into a branch
of the renal vein.
c
glomerulus
afferent
arteriole
efferent
arteriole
from
renal
artery
to
renal
vein
Figure 14.9 The blood supply associated with a nephron.
306
a
Bowman’s
capsule
proximal convoluted
tubule
distal
convoluted
tubule
b
efferent
arteriole
Bowman’s
capsule
proximal
convoluted
tubule
distal
convoluted
tubule
loop of
Henle
collecting
duct
afferent
arteriole
glomerulus
cortex
ureter
pelvis
cortex
medulla
from renal
artery
descending
limb of loop
of Henle
ascending
limb of loop
of Henle
medulla
collecting
duct
pelvis
Figure 14.8 a Section through the kidney to show the position of a nephron; b a nephron.
c
efferent
arteriole