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P A R T 9
Drugs acting on the renal system
Blood supply
The blood flow to the nephron is unique. The renal
arteries come directly off the aorta and enter each
kidney. As a renal artery enters each of the kidneys, it
divides to form interlobar arteries, which become smaller
arcuate (bowed) arteries and then afferent arterioles.
The afferent arterioles branch to form the
glomeru-
lus
inside Bowman’s capsule. The glomerulus is like a
tuft of blood vessels with a capillary-like endothelium
that allows easy passage of fluid and waste products.
The efferent arteriole exits from the glomerulus and
branches into the peritubular capillary system, which
returns fluid and electrolytes that have been reabsorbed
from the tubules to the bloodstream. These capillaries
flow into the vasa recta, which flows into intralobar
veins, which in turn drain into the inferior vena cava.
The two arterioles around the glomerulus work together
to closely regulate the flow of fluid into the glomerulus,
increasing or decreasing pressure on either side of the
glomerulus as needed.
Other structures
A small group of cells, called the juxtaglomerular
apparatus, connects the afferent arteriole to the distal
convoluted tubule. This is where erythropoietin and
renin are produced. Because of their proximity to the
afferent arteriole, these cells are especially sensitive to
the volume and quality of blood flow into the glomer-
ulus. Surrounding the nephrons is an area called the
macula densa, which consists of immune system cells
and chemicals that can respond quickly to any cellular
damage or injury.
Nephron function
The nephrons function by using three basic pro-
cesses: glomerular
filtration
(passage of fluid and small
Afferent
arteriole
Efferent
arteriole
Glomerulus
To renal vein
From renal artery
Collecting
duct
Proximal
convoluted
tubule
Distal
convoluted
tubule
Glomerular (Bowman’s)
capsule
Peritubular
capillaries
Ascending
limb
Descending
limb
Loop of
Henle
Calyx
FIGURE 50.2
The nephron—the functional unit
of the kidneys. Secretion and reabsorption
of water, electrolytes and other solutes in
the various segments of the renal tubule,
the loop of Henle, and the collecting duct
can be influenced by diuretics, other drugs
and endogenous substances, including
certain hormones. In the kidneys, the distal
convoluted tubule wraps around and is
actually next to the afferent arteriole.
