Page 382 - Anatomy and Physiology of Farm Animals, 8th Edition

The Respiratory System / 367

Erythrocyte
VetBooks.ir

CO 2 dissolved in plasma
(7%)
Carbaminohemoglobin
(23%)

CO 2 from cellular
H 2 O + CO 2 CO 2 metabolism
Carbonic anhydrase
Hemoglobin
H 2 CO 3

– +
HCO 3 H

–
HCO 3
dissolved in
plasma (70%)
Figure 19-16. Gas exchange in systemic tissues and transport of carbon dioxide in the blood.
Percentages reflect the different modes by which carbon dioxide is transported from systemic tissues to
the lungs.

important neural input is from central reduced. The low blood carbon dioxide
chemoreceptors in the medulla of the concentration means that the primary
brainstem. These receptors respond to stimulus for normal ventilation is lost.
hydrogen ion concentration changes in the These animals may undergo a period of
interstitial fluid of the brain and stimulate apnea (cessation of breathing) until
the inspiratory center to increase ventila- blood carbon dioxide levels are restored
tion when the hydrogen ion concentration by metabolism.
increases. Carbon dioxide from the blood Another group of chemoreceptors, the
readily diffuses into the interstitial fluids of carotid and aortic bodies, also provide
the brain, and in body fluids is in equilib- neural input to the respiratory center.
rium with carbonic acid; therefore, an These peripheral chemoreceptors detect
increase in blood carbon dioxide increases changes in arterial blood hydrogen ion
the hydrogen ion concentration in the concentration and oxygen content.
brain and stimulates ventilation. The Increases in hydrogen ion concentration or
effects of changes in blood carbon dioxide reductions in blood O content initiate
2
on ventilation are so pronounced that neural inputs to increase ventilation.
blood carbon dioxide is considered to be However, the effects of these peripheral
the most important regulator of ventilation chemoreceptors are less pronounced than
in most conditions. those of the central chemoreceptors, so
During general anesthesia, mechani- changes in blood hydrogen ion concentra-
cal hyperventilation often occurs during tion or oxygen content must be severe to
induction of anesthesia as the anesthe- override the effect of blood carbon
tist attempts to fill the patient’s lungs dioxide.
with anesthetic gas. As a result of this Further regulating the respiratory center
hyperventilation, the patient’s blood and breathing rhythmicity is a reflex arc
carbon dioxide may be significantly involving stretch receptors in the lung