779
CHAPTER TWENTY
Urinary System
rated rapidly. When it appeared that most of his
kidney function had been lost (end-stage renal
disease, or ESRD), he was oF
ered arti±
cial kidney
treatments (hemodialysis).
To prepare Charles for hemodialysis, a vas-
cular surgeon created a ±
stula in his left forearm
by surgically connecting an artery to a vein. The
greater pressure of the blood in the artery that
now flowed directly into the vein swelled the
vein, making it more accessible.
During hemodialysis treatment, a hollow
needle was inserted into the vein of the fistula
near its arterial connection. This allowed the
blood to flow, with the aid of a blood pump,
through a tube leading to the blood compart-
ment of a dialysis machine. In this compartment,
the blood passed over a selectively permeable
membrane. On the opposite side of the mem-
brane was a dialysate solution with a controlled
composition. Negative pressure on the dialysate
side of the membrane, created by a vacuum
pump, increased the movement of ²
uid through
the membrane. At the same time, waste and
excess electrolytes diffused from the blood
C
harles B., a forty-three-year-old construc-
tion worker, had been feeling unusually
tired for several weeks, with occasional diz-
ziness and di³
culty sleeping. More recently he had
noticed a burning pain in his lower back, just below
his rib cage, and his urine had darkened. In addi-
tion, his feet, ankles, and face were swollen. His wife
suggested that he consult their family physician.
Charles had elevated blood pressure (hyper-
tension) and the regions of his kidneys were
sensitive to pressure. His urine had excess pro-
tein (proteinuria) and blood (hematuria), and his
blood had elevated blood urea nitrogen (BUN),
elevated serum creatinine, and decreased serum
protein (hypoproteinemia) concentrations.
Charles likely had
chronic glomerulonephritis,
an inflammation of the capillaries in the glom-
eruli of the nephrons. It is a progressive degen-
eration with no direct treatment, although drugs
can help to control blood pressure. Microscopic
examination of a small sample of kidney tissue
(biopsy) con±
rmed the diagnosis.
Despite antihypertensive drugs and careful
attention to his diet, Charles’s condition deterio-
through the membrane and entered the dialysate
solution. The blood was then returned through a
tube to the vein of the ±
stula.
To maintain favorable blood concentrations
of waste, electrolytes, and water, Charles had to
undergo hemodialysis three times per week, with
each treatment lasting three to four hours. During
the treatments, he was given an anticoagulant to
prevent blood clotting, an antibiotic drug to con-
trol infections, and an antihypertensive drug.
Charles was advised to carefully control his
intake of water, sodium, potassium, proteins, and
total calories between treatments. He was also
asked to consider a kidney transplant, which could
free him from dependence on hemodialysis.
In a transplant, a kidney from a living donor
or a cadaver, whose tissues are antigenically simi-
lar (histocompatible) to those of the recipient, is
placed in the depression on the medial surface of
the right or left ilium (iliac fossa). The renal artery
and vein of the donor kidney are connected to
the recipient’s iliac artery and vein, respectively,
and the kidney’s ureter is attached to the dome of
the recipient’s urinary bladder.
20.1
CLINICAL APPLICATION
Chronic Kidney Failure
cal radiate arteries
(interlobular arteries)
.
The f nal branches
oF the cortical radiate arteries, called
afferent arterioles
(aF
er-ent ar-te
re-o
ˉlz), lead to the nephrons, the Functional
units oF the kidneys.
Venous blood returns through a series oF vessels that
generally correspond to the arterial pathways. ±or example,
the venous blood passes through cortical radiate, arcuate,
interlobar, and renal veins. The
renal vein
then joins the
inFerior vena cava as it courses through the abdominal cav-
ity. (
Figs. 20.6
and
20.7
show branches oF the renal arteries
and veins.)
Nephrons
Structure of a Nephron
Some organs can be broken down into subunits, each oF
which perForms the Functions oF the organ as a whole. Each
kidney contains about 1 million such Functional units, the
nephrons
(neF
ronz). Each nephron in turn consists oF a
renal corpuscle
(re
nal kor
pusl) and a
renal tubule
(re
nal
tu
bu
¯l) (see f g. 20.4).
A renal corpuscle consists oF a f ltering unit composed oF
a tangled cluster oF blood capillaries called a
glomerulus
(glo-
mer
u-lus) and a surrounding thin-walled, saclike structure
About two in every ten patients with renal failure can use a procedure
that can be done at home called
continuous ambulatory peritoneal
dialysis
instead of hemodialysis. The patient infuses a solution into
the abdominal cavity through a permanently implanted tube. The
solution stays in for four to eight hours, while it takes up substances
that would normally be excreted into urine. Then the patient drains
the waste-laden solution out of the tube, replacing it with clean ²
uid.
Infection is a risk associated with this procedure.
Renal Blood Vessels
The
renal arteries,
which arise From the abdominal aorta,
transport a large volume oF blood to the kidneys (f g. 20.5).
When a person is at rest, the renal arteries usually carry From
15% to 30% oF the total cardiac output into the kidneys,
although the kidneys account For only 1% oF body weight.
A renal artery enters a kidney through the hilum and
gives oFF several branches, called the
interlobar arteries,
which pass between the renal pyramids. At the junction
between the medulla and the cortex, the interlobar arteries
branch to Form a series oF incomplete arches, the
arcuate
arteries
(arciForm arteries), which, in turn, give rise to
corti-
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