Page 1055 - Fundamentals of anatomy physiology

Clinical Case eat some bad potato salad at the office picnic and
When Treatment Makes You
Worse
Marquis is a 43-year-old office worker who is slightly overweight.
At his annual checkup, his blood pressure measures 150/96,
which is considered moderately high. Marquis feels fine, but his
doctor tells him it is time to treat his hypertension. Marquis’s
doctor advises him to improve his diet and get more exercise. He
also prescribes a new medication, hydrochlorothiazide, or HCTZ,
which he instructs him to take every morning. HCTZ is a diuretic
that is commonly used to lower blood pressure.
Marquis begins taking HCTZ and continues to feel well,
although he notices the medication makes him need to urinate
more frequently. A few weeks later he and a group of coworkers
An Introduction to Fluid, Electrolyte,
and Acid–Base Balance
27 The next time you see a small pond, think about the fish in
it. They live their entire lives totally dependent on the quality
of that isolated environment. Severe water pollution will kill
them, but even subtle changes can have equally grave effects.
Changes in the volume of the pond, for example, can be quite
important. If evaporation removes too much water, the fish be-
come overcrowded. The oxygen and food supplies will run out,
and the fish will suffocate or starve. The ionic concentration of
the water is also crucial. Most of the fish in a freshwater pond
will die if the water becomes too salty. Fish in a saltwater pond
will die if their environment becomes too dilute. The pH of the
pond water, too, is a vital factor. This is another reason that acid (hydrogen ion concentration) of these fluids are as important
rain is such a problem.
Your cells live in a pond whose shores are the exposed
surfaces of your skin. Most of your body weight is water. Water
makes up about 99 percent of the volume of the fluid outside
cells, and it is also an essential ingredient of cytoplasm. All
of a cell’s operations rely on water as a diffusion medium for
the distribution of gases, nutrients, and wastes. If the water
content of the body changes, cellular activities are jeopardized.
For example, when the water content reaches very low levels,
proteins denature, enzymes cease functioning, and cells die.
In this chapter we discuss the homeostatic mechanisms that
regulate ion concentrations, volume, and pH in the fluid sur-
rounding cells.
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come down with food poisoning. After three days
of diarrhea, Marquis feels absolutely horrible. He
is so weak he is barely able to get out of bed. His
muscles ache and his legs and feet cramp a lot.
Worst of all, he feels as if there is a frog jumping
around in his chest. He is often dizzy when this
happens.
After a week in bed, Marquis feels even weaker.
He goes to see his doctor, who sends him to the lab
for some tests. “I know why you feel so terrible,” says his doctor
when he sees the lab results. What is happening to Marquis?
To find out, turn to Clinical Case Wrap-Up on p. 1075.
27-1 Fluid balance, electrolyte
balance, and acid–base balance
are interrelated and essential to
homeostasis
Learning Outcome Explain what is meant by the terms fluid balance,
electrolyte balance, and acid–base balance, and discuss their importance
for homeostasis.
To survive, we must maintain a normal volume and composi-
tion of both the extracellular fluid or ECF (the interstitial
fluid, plasma, and other body fluids) and the intracellular
fluid or ICF (the cytosol). The ionic concentrations and pH
as their absolute quantities. If concentrations of calcium or
potassium ions in the ECF become too high, cardiac arrhyth-
mias develop and death can result. A pH outside the normal
range can also lead to a variety of serious problems. Low pH—
acidity—is especially dangerous, because hydrogen ions break
chemical bonds, change the shapes of complex molecules, dis-
rupt plasma membranes, and impair tissue functions.
&T i p s T r i c k s
The “p” in pH refers to power. Hence, pH refers to the power of
Hydrogen.
In this chapter, we will explore the dynamics of exchange
among the various body fluids, and between the body and the