Section X. THE PULMONARY NAVL
7-38. NERVOUS CONTROL OF BREATHING
As we have seen, breathing is a combination of many factors. These factors are
integrated and controlled by the nervous system.
a. Respiratory reflexes are controlled by the respiratory center found in the
medullary portion of the hindbrainstem. ( See lesson 12). The level of carbon dioxide
(CO2) in the circulating blood is one of the major influences upon the respiratory reflex.
b. The individual intercostal nerves innervate the intercostal muscles.
c. The muscles attached to and moving the rib cage are innervated by their
appropriate nerves. (Ultimately, almost every muscle in the body may be mobilized to
assist in breathing.)
d. The diaphragm is innervated by its own individual pair of phrenic nerves.
7-39. FUNCTIONAL BLOOD SUPPLY
There are essentially two blood supplies for the lungs--nutrient blood and
functional blood. Nutrient blood is carried by the bronchial arteries from the thoracic
aorta. Nutrient blood provides nourishment and oxygen to the tissues of the lung.
Functional blood is actually involved in the respiratory exchange of gases between the
alveoli and the capillaries. Functional blood is brought to and from the lungs by the
pulmonary cycle of the cardiovascular system.
a. The pulmonary cycle originates in the right ventricle of the heart. Contraction
of the right ventricle forces the blood into the pulmonary arch, which divides into the
right and left pulmonary arteries to their respective lungs. Paralleling the branching of
the respiratory tree, the arteries divide and subdivide within the lungs. These arteries
lead to capillaries in the vicinity of the alveoli. The walls of these capillaries are thin
enough to accommodate the passage of gases to and from the alveolus.
b. The blood, now saturated with oxygen, is collected by the pulmonary venous
system. The blood is deposited ultimately into the left atrium of the heart.