Essentials of Anatomy and Physiology

446 Fluid–Electrolyte and Acid–Base Balance

Some of the major imbalances of electrolyte levels
are described in Box 19–2: Electrolyte Imbalances.

ACID–BASE BALANCE

You have already learned quite a bit about the regula-
tion of the pH of body fluids in the chapters on chem-
istry (see Chapter 2 for the pH scale), the respiratory
system, and the urinary system. In this section, we will
put all of that information together.
The normal pH range of blood is 7.35 to 7.45. The
pH of tissue fluid is similar but can vary slightly above
or below this range. The intracellular fluid has a pH
range of 6.8 to 7.0. Notice that these ranges of pH are
quite narrow; they must be maintained in order for
enzymatic reactions and other processes to proceed
normally.

Maintenance of acid–base homeostasis is accom-

plished by the buffer systems in body fluids, the rate

and depth of respiration, and the kidneys.

BUFFER SYSTEMS

The purpose of a buffer systemis to prevent drastic

changes in the pH of body fluids by chemically react-

ing with strong acids or bases that would otherwise

greatly change the pH. A buffer system consists of a

weak acid and a weak base. These molecules react with

strong acids or bases that may be produced and change

them to substances that do not have a great effect on

pH.

Bicarbonate Buffer System

The two components of this buffer system are carbonic

acid (H 2 CO 3 ), a weak acid, and sodium bicarbonate

Figure 19–3. Electrolyte concentrations in intracellular fluid, tissue fluid, and plasma.

Concentrations are expressed in milliequivalents per liter. See text for summary of major

differences among these fluids.

QUESTION:Tissue fluid is most like which of the other fluids? Why did you already know

this?