820
UNIT FIVE
f
uid that is hypotonic and promotes
the movement oF water into the cells
by osmosis. This is accompanied by the
symptoms oF water intoxication described
in Clinical Application 21.1 on page 816.
2.
High sodium concentration
(
hypernatremia
).
Possible causes oF hypernatremia include
excessive water loss by evaporation and
di±
usion, as may occur during high Fever,
or increased water loss accompanying
diabetes insipidus, in one Form oF which
ADH secretion is insu²
cient to maintain
water conservation by the renal tubules
and collecting ducts. Possible e±
ects oF
hypernatremia include disturbances oF the
central nervous system, such as conFusion,
stupor, and coma.
3.
Low potassium concentration
(
hypokalemia
).
Possible causes oF hypokalemia include
excessive release oF aldosterone by the
adrenal cortex (Cushing syndrome), which
increases renal excretion oF potassium; use
E
xtracellular f
uids usually have high sodium
ion concentrations, and intracellular Fluid
usually has high potassium ion concen-
tration. The renal regulation oF sodium is closely
related to that oF potassium because active
reabsorption oF sodium (under the inFluence oF
aldosterone) is accompanied by secretion (and
excretion) oF potassium. Thus, it is not surprising
that conditions that alter sodium ion balance also
ect potassium ion balance. Such disorders can
be summarized as Follows:
1.
Low sodium concentration
(
hyponatremia
).
Possible causes oF hyponatremia include
prolonged sweating, vomiting, or
diarrhea; renal disease in which sodium is
inadequately reabsorbed; adrenal cortex
disorders in which aldosterone secretion is
insu²
cient to promote the reabsorption oF
sodium (Addison disease); and drinking too
much water.
Possible e±
ects oF hyponatremia
include the development oF extracellular
oF diuretic drugs that promote potassium
excretion; kidney disease; and prolonged
vomiting or diarrhea. Possible e±
ects oF
hypokalemia include muscular weakness or
paralysis, respiratory di²
culty, and severe
cardiac disturbances, such as atrial or
ventricular arrhythmias.
4.
High potassium concentration
(
hyperkalemia
). Possible causes oF
hyperkalemia include renal disease, which
decreases potassium excretion; use oF
drugs that promote renal conservation
oF potassium; insu²
cient secretion oF
aldosterone by the adrenal cortex (Addison
disease); or a shiFt oF potassium From the
intracellular f
uid to the extracellular f
uid,
a change that accompanies an increase
in plasma hydrogen ion concentration
(acidosis). Possible e±
ects oF hyperkalemia
include paralysis oF the skeletal muscles and
severe cardiac disturbances, such as cardiac
arrest.
21.2
CLINICAL APPLICATION
Sodium and Potassium Imbalances
bases. For example, HCO
3
acting as a base combines with
H
+
from the strong acid HCl to form the weak acid carbonic
acid (H
2
CO
3
).
Regulation of Hydrogen Ion Concentration
Either an acid shift or an alkaline (basic) shift in the body fl u-
ids could threaten the internal environment. However, normal
metabolic reactions generally produce more acid than base.
These reactions include cellular metabolism of glucose, fatty
acids, and amino acids. Consequently, the maintenance of
acid-base balance usually eliminates acid. This is accomplished
in three ways: acid-base buffer systems; respiratory excretion
of carbon dioxide; and renal excretion of hydrogen ions.
PRACTICE
20
Explain why the regulation oF hydrogen ion concentration is so
important.
21
What are the major sources oF hydrogen ions in the body?
Acid-Base Buffer Systems
Acid-base buffer systems
are in all body fluids and are
based on chemicals that combine with excess acids or bases.
Buffers are substances that stabilize the pH of a solution,
5.
Breakdown (hydrolysis) of phosphoproteins and
nucleic acids.
Phosphoproteins and nucleic acids
contain phosphorus. Their oxidation produces
phosphoric acid
(H
3
PO
4
), which ionizes to release
hydrogen ions.
The acids resulting from metabolism vary in strength.
Thus, their effects on the hydrogen ion concentration of
body fl
uids vary
(f g. 21.9)
.
Strengths of Acids and Bases
Acids that ionize more completely (release more H
+
) are
strong acids, and those that ionize less completely are weak
acids. For example, the hydrochloric acid (HCl) of gastric
juice is a strong acid and dissociates completely to release
a lot of H
+
, but the carbonic acid (H
2
CO
3
) produced when
carbon dioxide reacts with water is weak and dissociates less
completely to release less H
+
.
Bases release ions, such as hydroxide ions (OH
),
which can combine with hydrogen ions, thereby lowering
their concentration. Thus, sodium hydroxide (NaOH), which
releases hydroxide ions, and sodium bicarbonate (NaHCO
3
),
which releases bicarbonate ions (HCO3
), are bases. Strong
bases dissociate to release more OH
or its equivalent than do
weak bases. Often, the negative ions themselves are called
previous page 850 David Shier Hole's Human Anatomy and Physiology 2010 read online next page 852 David Shier Hole's Human Anatomy and Physiology 2010 read online Home Toggle text on/off