578 Chapter 1616.8 Acid-Base Balance of the Blood 567
A. The normal pH of arterial blood is 7.40, with a range of 7.35
to 7.45.
1. Carbonic acid is formed from carbon dioxide and
contributes to the blood pH. It is referred to as a volatile
acid because it can be eliminated in the exhaled breath.
2. Nonvolatile acids, such as lactic acid and the ketone
bodies, are buffered by bicarbonate.
B. The blood pH is maintained by a proper ratio of carbon
dioxide to bicarbonate.
1. The lungs maintain the correct carbon dioxide
concentration. An increase in carbon dioxide, due to
inadequate ventilation, produces respiratory acidosis.
2. The kidneys maintain the free-bicarbonate
concentration. An abnormally low plasma bicarbonate
concentration produces metabolic acidosis.
C. Ventilation regulates the respiratory component of acid-base
balance.
1. Hypoventilation increases the blood P^ CO 2 , thereby
lowering the plasma pH and producing a respiratory
acidosis.
2. Hyperventilation decreases the plasma P^ CO 2 , decreasing
the formation of carbonic acid, and thereby increasing the
plasma pH to produce a respiratory alkalosis.
3. Because of the action of the chemoreceptors, breathing
is regulated to maintain a proper blood P^ CO 2 and thus a
normal blood pH.16.9 Effect of Exercise and High Altitude on
Respiratory Function 570
A. During exercise there is increased ventilation, or hyperpnea,
which is matched to the increased metabolic rate so that the
arterial blood P^ CO 2 remains normal.
1. This hyperpnea may be caused by proprioceptor
information, cerebral input, and/or changes in arterial
P^ CO 2 and pH.
2. During heavy exercise, the anaerobic threshold may be
reached at 50% to 70% of the maximal oxygen uptake.
At this point, lactic acid is released into the blood by the
muscles.
3. Endurance training enables the muscles to utilize
oxygen more effectively, so that greater levels of
exercise can be performed before the anaerobic
threshold is reached.
B. Acclimatization to a high altitude involves changes that help
to deliver oxygen more effectively to the tissues, despite
reduced arterial P^ O 2.
1. Hyperventilation occurs in response to the low P^ O 2.
2. The red blood cells produce more 2,3-DPG, which
lowers the affinity of hemoglobin for oxygen and
improves the unloading reaction.
3. The kidneys produce the hormone erythropoietin, which
stimulates the bone marrow to increase its production of
red blood cells, so that more oxygen can be carried by
the blood at given values of P^ O 2.Test Your Knowledge- Which of these statements about intrapulmonary pressure
and intrapleural pressure is true?
a. The intrapulmonary pressure is always subatmospheric.
b. The intrapleural pressure is always greater than the
intrapulmonary pressure.
c. The intrapulmonary pressure is greater than the
intrapleural pressure.
d. The intrapleural pressure equals the atmospheric pressure. - If the transpulmonary pressure equals zero,
a. a pneumothorax has probably occurred.
b. the lungs cannot inflate.
c. elastic recoil causes the lungs to collapse.
d. all of these apply. - The maximum amount of air that can be expired after a
maximum inspiration is
a. the tidal volume.
b. the forced expiratory volume.
c. the vital capacity.
d. the maximum expiratory flow rate. - If the blood lacked red blood cells but the lungs were
functioning normally,
a. the arterial P^ O 2 would be normal.
REVIEW ACTIVITIES
b. the oxygen content of arterial blood would be normal.
c. both a and b would apply.
d. neither a nor b would apply.- If a person were to dive with scuba equipment to a depth of
66 feet, which of these statements would be false?
a. The arterial P^ O 2 would be three times normal.
b. The oxygen content of plasma would be three times
normal.
c. The oxygen content of whole blood would be three times
normal. - Which of these would be most affected by a decrease in the
affinity of hemoglobin for oxygen?
a. Arterial P^ O 2
b. Arterial percent oxyhemoglobin saturation
c. Venous oxyhemoglobin saturation
d. Arterial P^ CO 2 - If a person with normal lung function were to hyperventilate
for several seconds, there would be a significant
a. increase in the arterial P^ O 2.
b. decrease in the arterial P^ CO 2.
c. increase in the arterial percent oxyhemoglobin saturation.
d. decrease in the arterial pH.
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