WHAT A HEALTH
1. What functions of the kidney cannot be replaced
2. A dialysis patient's blood has an NaCl concentration of 150 mEq/L.
What should the NaCl composition of the dialysis fluid be to remove
excess NaCl and return the blood to normal NaCl concentration?
Renal Failure and Dialysis
idney diseases such as
n e p h r it is
(inflammation of the
g lo m e r u lo n e p h r it is
(inflammation of the
glomeruli) can interfere with the blood supply to the kid-
ney and lead to renal failure. Renal failure may also occur
as a complication of diabetes mellitus or from exposure to
toxins such as heavy metals.
When the kidneys fail, meta-
bolic wastes build up, and the
normal blood composition
goes awry. Without treatment,
renal failure can quickly cause
death. To treat renal failure, pa-
tients must undergo dialysis.
There are two types of dialysis
In hemodialysis, the patient's blood is pumped
through a machine, where the blood is dialyzed through
an artificial membrane against a prepared solution. Dur-
ing this process, wastes are removed from the blood, and
plasma components are either prevented from passing
through the membrane or are added back into the blood
after the process has occurred. The cleansed blood
is passed through a detector to remove air and then
returned to the body. Hemodialysis often destroys fragile
red blood cells as they pass through tubes and mem-
branes under pressure.
In contrast, peritoneal dialysis uses the peritoneum
of the abdominal cavity as a dialyzing membrane to filter
the blood. The peritoneum has a large surface area and
numerous blood vessels and is a very effective filter. An
artificial dialyzing solution is infused directly into the
person's peritoneal cavity, where the solution exchanges
components with the plasma flowing through the blood
vessels in the peritoneum. After a predetermined amount
of time, the solution is removed, discarded, and replaced
with fresh solution.
Regardless of the type, dialysis must be performed
frequently. Most people on hemodialysis require about
6-12 hours a week, typically divided into three sessions.
Peritoneal dialysis is done multiple times per day. Dialysis
is only a temporary solution; ultimately, a kidney trans-
plant is the only permanent treatment for renal failure.
The removal of waste
products from blood
by diffusion through
a selectively perme-
able membrane. The
verb form of dialysis is
d ia ly z e
462 CHAPTER 15
The Urinary System and Fluid, Electrolyte, and Acid-Base Balance