Carotid Body Chemotransduction
Organisms have a fundamental dependence on their environment for continued survival. Most organisms can do without solid and liquid nutrition for several hours, sometimes days or even weeks. However, the other substrate needed to convert nutrition into biological energy is oxygen. Virtually all aerobic organisms cannot survive without environmental oxygen for longer than a few minutes. Diving mammals seem to be an exception to this dependence. In the course of evolution part of the machinery which these organisms have developed for delivering environmental oxygen to their tissues is the pulmonary and cardiovascular systems. Essentially each involves a pump, a series of collapsible tubes through which a fluid flows, and a gas exchanging surface. The control of these systems in the face of a challenge such as exercise or an unfavorable environment is of critical importance. The pumps might have to beat faster, the tubes may have to alter their resistance in general or regionally to redistribute the flow to various organs or parts of organs. The cardiopulmonary system may have to change overall or regional compliances to facilitate flow. These mechanical variables are controlled by local, humoral, and neural input. The neural control of the cardiopulmonary system is frequently described as the input/output of Receptors-Afferent Pathways-Central Nervous System-Efferent Pathways-Effectors. The carotid body is one of the Receptors in this model. Sampling the arterial blood, it increases its neural input into the nucleus tractus solitarius when the partial pressure of oxygen in the arterial blood falls, the carbon dioxide partial pressure or hydrogen ion concentration rises. Presently it is unclear how the carotid body converts hypoxia, hypercapnia, or acidosis into increased neural activity; that is, how it chemotransduces.
KeywordsCarotid Body Excitatory Neurotransmitter Nucleus Tractus Solitarius Neural Input Carbon Dioxide Partial Pressure
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