The Kidneys and Regulation of Water and Inorganic Ions
525
pumped from one of the patient’s arteries through tubing that
is surrounded by special dialysis fl uid. The tubing then conducts
the blood back into the patient by way of a vein. The dialysis
tubing is generally made of cellophane that is highly perme-
able to most solutes but relatively impermeable to protein and
completely impermeable to blood cells—characteristics quite
similar to those of capillaries. The dialysis fl uid is a salt solu-
tion with ionic concentrations similar to or lower than those
in normal plasma, and it contains no creatinine, urea, or other
substances to be completely removed from the plasma. As blood
fl ows through the tubing, the concentrations of nonprotein
plasma solutes tend to reach diffusion equilibrium with those of
the solutes in the bath fl uid. For example, if the plasma potas-
sium concentration of the patient is above normal, potassium
diffuses out of the blood across the cellophane tubing and into
the dialysis fl uid. Similarly, waste products and excesses of other
substances also diffuse into the dialysis fl
uid and thus are elimi-
nated from the body.
Patients with acute reversible renal failure may require
hemodialysis for only days or weeks. Patients with chronic irre-
versible renal failure require treatment for the rest of their lives,
however, unless they receive a kidney transplant. Such patients
undergo hemodialysis several times a week.
Another way of removing excess substances from the
blood is
peritoneal dialysis,
which uses the lining of the
patient’s own abdominal cavity (peritoneum) as a dialysis
membrane. Fluid is injected, via a needle inserted through the
abdominal wall, into this cavity and allowed to remain there
for hours, during which solutes diffuse into the fl uid from the
person’s blood. The dialysis fl uid is then removed by reinsert-
ing the needle and is replaced with new fl
uid. This procedure
can be performed several times daily by a patient who is simul-
taneously doing normal activities.
The long-term treatment of choice for most patients with
permanent renal failure is kidney transplantation. Rejection
of the transplanted kidney by the recipient’s body is a poten-
tial problem, but great strides have been made in reducing
the frequency of rejection (Chapter 18). Many people who
might benefi t from a transplant, however, do not receive one.
Currently, the major source of kidneys for transplantation is
recently deceased persons. Improved public understanding
should lead to many more individuals giving permission in
advance to have their kidneys and other organs used following
their death. Recently, donation from a living, related donor
has become more common. Because of the large safety factor,
the donor can function quite normally with one kidney.
SECTION D SUMMARY
Diuretics
I. Most diuretics inhibit reabsorption of sodium and water,
thereby enhancing the excretion of these substances. Different
diuretics act on different nephron segments.
Kidney Disease
I. Many of the symptoms of uremia—general renal
malfunction—are due to retention of substances because of
reduced GFR and, in the case of potassium and hydrogen ion,
reduced secretion. Other symptoms are due to inadequate
secretion of erythropoietin and 1,25-dihydroxyvitamin D, and
too much secretion of renin.
II. Either hemodialysis or peritoneal dialysis can be used
chronically to eliminate water, ions, and waste products
retained during uremia.
SECTION D CLINICAL TERMS
congestive heart failure
523
diuretics
523
edema
523
hemodialysis
524
loop diuretic
523
peritoneal dialysis
525
potassium-sparing diuretic
523
renal hypertension
524
uremia
523
SECTION D REVIEW QUESTIONS
1. List the different types of diuretics and briefl y summarize their
mechanisms of action.
2. List several diseases that diuretics can be used to treat.
3. What substances are found in the urine of patients with kidney
disease that are usually not found in the urine of healthy
people?
4. What is uremia?
5. What is the cause of renal hypertension?
6. Briefl y summarize how renal and peritoneal dialysis work.
Chapter 14 Test Questions
(Answers appear in Appendix A.)
1. Which of the following will lead to an increase in glomerular
fl uid fi ltration in the kidney?
a. An increase in the protein concentration in the plasma.
b. An increase in the fl
uid pressure in Bowman’s space.
c. An increase in the glomerular capillary blood pressure.
d. A decrease in the glomerular capillary blood pressure.
e. Constriction of the afferent arteriole.
2. Which of the following is true about renal clearance?
a. It is the amount of a substance excreted per unit time.
b. A substance with clearance >GFR undergoes only fi ltration.
c. A substance with clearance >GFR undergoes fi ltration and
secretion.
d. It can be calculated knowing only the fi ltered load of a
substance and the rate of urine production.
e. Creatinine clearance approximates renal plasma fl ow.
3. Which of the following will
not
lead to a diuresis?
a. excessive sweating
b. central diabetes insipidus
c. nephrogenic diabetes insipidus
d. excessive water intake
e. uncontrolled diabetes mellitus
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