HUMAN BIOLOGY

the UrInary SyStem 233

accumulate in the bloodstream. Patients can suffer nausea,

fatigue, and memory loss. In advanced cases, death may

result. A kidney dialysis machine can restore the proper

solute balances (Figure 12.12A). Like the kidneys, the

machine helps maintain healthy volume and composition

of extracellular fluid by selectively removing and adding

solutes to the patient’s bloodstream.

In a dialysis process, substances in one solution can be

exchanged with those in a chemically different solution by

crossing a permeable membrane. In hemodialysis, a dialysis

machine is connected to an artery or a vein, and then blood

is pumped through tubes made of a material similar to cel-

lophane. The tubes are submerged in warm water that con-

tains a precise mix of salts, glucose, and other substances.

As blood flows through the tubes, the wastes dissolved in it

diffuse out, so solute concentrates return to a normal range.

The cleansed blood then returns to the patient’s body.

Patients usually receive hemodialysis three times a

week, although for some it is a daily need. Patients with

reversible kidney disorders may receive dialysis until they

recover. In chronic cases, the procedure must be used for

the rest of the patient’s life or until a healthy kidney can

be transplanted.

Polycystic kidney disease is an inher-

ited disorder in which cysts (semisolid

masses) form in the kidneys and in many

cases gradually destroy normal kidney tis-

sue (Figure 12.12B). Frequent urinary tract

infections are a common early symptom; in

severe cases, dialysis or a kidney transplant

are the only real options for treatment.

With treatment and the proper diet, many

people with chronic kidney disease are able

to pursue a surprisingly active, close-to-

normal lifestyle.

Many people don’t realize how much good health depends
on normal kidney function. Disorders or injuries that
interfere with it may cause only mild distress, but often the
impact is quite serious.
Kidney stones are deposits of uric acid, calcium salts,
and other substances that have settled out of urine. Smaller
kidney stones usually are eliminated naturally during uri-
nation. Larger ones can become lodged in the renal pelvis
or ureter or even in the bladder or urethra. The blockage
can partially dam urine flow and cause intense pain and
kidney damage. Large kidney stones must be removed
medically or surgically. A procedure called lithotripsy uses
high-energy sound waves to break up the stone into frag-
ments that are small enough to pass out in the urine.
Glomerulonephritis is an umbrella term for several
disorders that can lead to kidney failure. Two major ones
are chronic high blood pressure and diabetes, both of
which damage kidney capillaries. Sometimes the flow of
blood through the glomeruli all but stops.
At any given time, roughly 1 million people in the
United States have kidneys so impaired that they can only
minimally filter the blood and form urine. This loss of
kidney function means that toxic by-products of protein

Kidney Disorders: When Kidneys Fail

dialysis solution

flowing into

abdominal cavity

filter where blood flows

through semipermeable

tubes and exchanges

substances with dialysis

solution

abdominal

cavity, lined

with peritoneum

(green)

patient’s blood

inside tubing

dialysis solution

with unwanted

wastes and

solutes draining

out

Hemodialysis

Tubes carry blood from a

patient’s body through a

filter with dialysis solution

that contains the proper

concentrations of salts.

Wastes diffuse from the

blood into the solution and

cleansed, solute-balanced

blood returns to the body.

Peritoneal dialysis

Dialysis solution is pumped

into a patient’s abdominal

cavity. Wastes diffuse

across the lining of the

cavity into the solution,

which is then drained out.

1

2

Figure 12.12 Animated! Kidney dialysis cleanses the blood of patients with kidney failure. a Two options for dialysis: hemodialysis
and peritoneal dialysis. B The pebbled appearance of a polycystic kidney. (A: © Cengage Learning; B: Arthur Glauberman/Photo Researchers/Getty Images)

a B

12.6

Polycystic kidney

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