Chapter 26
Fluid, Electrolyte, and Acid-Base Balance
1015
26
8.
Acidosis activates the respiratory center to increase respiratory
rate and depth, which eliminates more CO
2
and causes blood pH
to rise. Alkalosis depresses the respiratory center, resulting in CO
2
retention and a fall in blood pH.
Fluid, Electrolyte, and Acid/Base Balance; Topic:
Acid/Base Homeostasis, pp. 27–28.
Renal Mechanisms of Acid-Base Balance
(pp. 1006–1009)
9.
Te kidneys provide the major long-term mechanism for
controlling acid-base balance by maintaining stable HCO
3
2
levels
in the ECF. Nonvolatile acids (organic acids other than carbonic
acid) can be eliminated from the body only by the kidneys.
10.
Secreted hydrogen ions come from the dissociation of carbonic
acid generated within the tubule cells.
11.
±ubule cells are impermeable to bicarbonate in the filtrate,
but they can conserve filtered bicarbonate ions indirectly by
absorbing HCO
3
2
generated within them (by dissociation of
carbonic acid to HCO
3
2
and H
1
). For each HCO
3
2
(and Na
1
)
reabsorbed, one H
1
is secreted into the filtrate, where it combines
with HCO
3
2
.
12.
±o generate and add new HCO
3
2
to plasma to counteract
acidosis, either of two mechanisms may be used:
Secreted H
1
, buffered by bases other than HCO
3
2
, is excreted
from the body in urine (the major urine buffer is the phosphate
buffer system).
NH
4
1
(derived from glutamine catabolism) is excreted in
urine.
13.
±o counteract alkalosis, bicarbonate ion is secreted into the
filtrate and H
1
is reabsorbed.
Fluid, Electrolyte, and Acid/Base Balance; Topic:
Acid/Base Homeostasis, pp. 29–37.
Abnormalities of Acid-Base Balance
(pp. 1009–1012)
14.
Acid-base imbalances can be classified as metabolic or respiratory
based on their cause.
15.
Respiratory acidosis results from carbon dioxide retention.
Respiratory alkalosis occurs when carbon dioxide is eliminated
faster than it is produced.
16.
Metabolic acidosis occurs when nonvolatile acids (lactic acid,
ketone bodies, and others) accumulate in the blood or when
bicarbonate is lost from the body. Metabolic alkalosis occurs
when bicarbonate levels are excessive.
17.
Extremes of pH for life are 6.8 and 7.8.
18.
Compensations occur when the respiratory system or kidneys
counteract acid-base imbalances resulting from abnormal or
inadequate functioning of the alternate system. Respiratory
compensations involve changes in respiratory rate and depth.
Renal compensations modify blood levels of HCO
3
2
.
Fluid, Electrolyte, and Acid/Base Balance; Topic:
Acid/Base Homeostasis, pp. 38–59.
Developmental Aspects of Fluid, Electrolyte,
and Acid-Base Balance
(p. 1012)
1.
Infants have a higher risk of dehydration and acidosis because
of their low lung residual volume, high rate of fluid intake and
output, high metabolic rate, relatively large body surface area, and
functionally immature kidneys at birth.
2.
Te elderly are at risk for dehydration because of their low
percentage of body water and insensitivity to thirst cues. Diseases
that promote fluid and acid-base imbalances (cardiovascular disease,
diabetes mellitus, and others) are most common in the aged.
9.
Cardiovascular system baroreceptors sense changing arterial
blood pressure, prompting changes in sympathetic vasomotor
activity. Rising arterial pressure leads to vasodilation and
enhanced Na
1
and water loss in urine. Falling arterial pressure
promotes vasoconstriction and conserves Na
1
and water.
Regulation of Potassium Balance
(pp. 1000–1003)
10.
Te more proximal regions of the nephrons reabsorb about 90%
of filtered potassium.
11.
Te main thrust of renal regulation of K
1
is to excrete it.
Aldosterone and increased plasma K
1
content enhance
potassium ion secretion by the principal cells of the collecting
ducts. ±ype A intercalated cells of the collecting duct reabsorb
small amounts of K
1
during K
1
deficit.
Regulation of Calcium and Phosphate Balance
(pp. 1003–1004)
12.
Calcium balance is regulated primarily by parathyroid hormone
(P±H), which enhances blood Ca
2
1
levels by targeting the bones,
kidneys, and intestine. P±H-regulated reabsorption occurs
primarily in the DC±.
13.
P±H decreases renal reabsorption of phosphate ions.
Regulation of Anions
(p. 1004)
14.
When blood pH is normal or slightly high, chloride is the
major anion accompanying sodium reabsorption. In acidosis,
bicarbonate replaces chloride.
15.
Reabsorption of most other anions is regulated by their transport
maximums (±
m
).
Fluid, Electrolyte, and Acid/Base Balance; Topic:
Electrolyte Homeostasis, pp. 1–38.
Acid-Base Balance
(pp. 1004–1012)
1.
Te homeostatic pH range of arterial blood is 7.35 to 7.45. A
higher pH represents alkalosis; a lower pH reflects acidosis.
2.
Some acids enter the body in foods, but most are generated
by breakdown of phosphorus-containing proteins, incomplete
oxidation of fats or glucose, and the loading and transport of
carbon dioxide in the blood.
3.
Acid-base balance is achieved by chemical buffers, respiratory
regulation, and in the long term by renal regulation of bicarbonate
ion (hence, hydrogen ion) concentration of body fluids.
Fluid, Electrolyte, and Acid/Base Balance;
Topic: Acid/Base Homeostasis, pp. 1–15.
Chemical Buffer Systems
(pp. 1004–1006)
4.
Acids are proton (H
1
) donors; bases are proton acceptors. Acids
that dissociate completely in solution are strong acids; those that
dissociate incompletely are weak acids. Strong bases are more
effective proton acceptors than are weak bases.
5.
Chemical buffers are single or paired sets (a weak acid and its
salt) of molecules that act rapidly to resist excessive shi²s in pH
by releasing or binding H
1
.
6.
Chemical buffers of the body include the bicarbonate, phosphate,
and protein buffer systems.
Fluid, Electrolyte, and Acid/Base Balance; Topic:
Acid/Base Homeostasis, pp. 16–26.
Respiratory Regulation of H
1
(p. 1006)
7.
Respiratory regulation of acid-base balance of the blood utilizes
the bicarbonate buffer system and the fact that CO
2
and H
2
O are
in reversible equilibrium with H
2
CO
3
.
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