a fraction of a second, but have the least capacity to
prevent pH changes.- Bicarbonate buffer system—see text for reactions;
important in both blood and tissue fluid; base to
acid ratio is 20 to 1. - Phosphate buffer system—see Fig. 19–4 and text
for reactions; important in ICF and in the kidneys. - Protein buffer system—amino acids may act as
either acids or bases. See text for reactions; impor-
tant in ICF.
Respiratory Mechanisms
- The respiratory system affects pH because it regu-
lates the amount of CO 2 in body fluids. - May be the cause of a pH change or help compen-
sate for a metabolic pH change—see Table 19–3. - Respiratory compensation is rapidly effective
(within a few minutes), but limited in capacity if the
pH imbalance is ongoing.
Renal Mechanisms- The kidneys have the greatest capacity to buffer
pH changes, but they may take several hours to
days to become effective (see Table 19–3). - Reactions: see Figs. 18–6 and 19–4.
- Summary of reactions: in response to acidosis, the
kidneys will excrete Hions and retain Naions
and HCO 3 ions; in response to alkalosis, the kid-
neys will retain Hions and excrete Naions and
HCO 3 ions.
Effects of pH Changes- Acidosis—depresses synaptic transmission in the
CNS; result is confusion, coma, and death. - Alkalosis—increases synaptic transmission in the
CNS and PNS; result is irritability, muscle spasms,
and convulsions.
452 Fluid–Electrolyte and Acid–Base Balance
REVIEW QUESTIONS
- Name the major water compartments and the
name for water in each of them. Name three spe-
cialized body fluids and state the location of each.
(p. 442) - Explain how water moves between compartments;
name the processes. (p. 442) - Describe the three sources of water for the body
and the relative amounts of each. (p. 443) - Describe the pathways of water output. Which is
the most important? What kinds of variations are
possible in water output? (p. 443) - Name the hormones that affect fluid volume, and
state the function of each. (pp. 444) - Define electrolyte, cation, anion, osmosis, and
osmolarity. (pp. 444, 445) - Name the major electrolytes in plasma, tissue fluid,
and intracellular fluid, and state their functions.
(pp. 445, 447)
8. Explain how the bicarbonate buffer system will
react to buffer a strong acid. (p. 448)
9. Explain how the phosphate buffer system will
react to buffer a strong acid. (p. 448) - Explain why an amino acid may act as either an
acid or a base. (p. 448) - Describe the respiratory compensation for
metabolic acidosis and for metabolic alkalosis.
(pp. 449–450) - If the body fluids are becoming too acidic, what
ions will the kidneys excrete? What ions will the
kidneys return to the blood? (p. 450) - Which of the pH regulatory mechanisms works
most rapidly? Most slowly? Which of these mech-
anisms has the greatest capacity to buffer an
ongoing pH change? Which mechanism has the
least capacity? (pp. 448, 450) - Describe the effects of acidosis and alkalosis.
(p. 450)