Conclusion - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 802

Table 14.2. Hering-Breuer reflex.

Inspiratory center ⊕−→ Phrenic and intercostal nerves,

⊕−→ inspiratory muscles,

⊕−→ lung inflation

Pulmonary stretch receptors ⊕−→ vagus nerve,

−→ inspiratory center

Chemicals such as oxygen, carbon dioxide, and hydrogen ion influence the
body's respiration. Chemical concentrations are monitored by chemoreceptors
located centrally in the medulla oblongata and peripherally at the bifurcation of the
carotid arteries and aortic arch. The peripheral chemoreceptors augment afferent
inputs to the respiratory centers in the brainstem when perfused with hypoxemic,
hypercapnic, and acidotic arterial blood. The central chemoreceptors are sensitive
to brain hypercapnia and acidosis.
Other influence factors of the body's respiration include voluntary control, i.e.,
the cerebral cortex, emotions driven by the hypothalamus and limbic system, body
temperature, and mechanically and chemically gated receptors.
Baroreceptors are pressure sensors of the carotid sinuses and aortic arch.
Proprioceptors localize to skeletal muscles, tendons, and joints that sense body
movements. During exercise, these receptors transmit signals to the respiratory
centers that increase breathing frequency and amplitude.
Cutaneous thermoreceptors can also send signals to the cerebral cortex, which, in
turn, activates respiratory centers, causing hyperventilation. Pain receptors operates
similarly to provoke hyperventilation.
In addition, juxtacapillary (J) receptors in alveolar walls are innervated by fibers
of the vagus nerve. Irritant receptors are sensory terminals of myelinated afferent
fibers that reside in bronchial and bronchiolar walls. Irritant receptors respond to
smoke and dust; they are stimulated by histamine, serotonine, and prostaglandins,
as well as inflation, deflation, and acute congestion of blood capillaries [ 1622 ]. Their
stimulation causes prolonged inspiratory duration and excitatory responses, such as
cough and gasp. Juxtacapillary receptors, or unmyelinated C-fiber endings, reside
in alveolar walls, close to capillaries of pulmonary circulation (hence their name),
as well as in bronchial walls, near capillaries of the bronchial (systemic) circulation.
They are stimulated by hyperinflation, lung injury, and edema (especially alveolar
J receptors), and by exposure to chemicals, such as histamine and serotonine
(especially bronchial J receptors) [ 1622 ]. Their acute and strong stimulation can
cause apnea and a fall in systemic vascular resistance. Afferent, unmyelinated
C fibers of the somatic sensory system innervate both pulmonary capillary bed
and airways, thereby yielding vagal inputs with different properties from these two
neighboring structures.
The human body uses two major ventilatory control systems to maintain the
content of oxygen, carbon dioxide, and protons: the chemical and behavioral control