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Originating from the neural crest, the carotid body is an important anatomical structure that helps the body achieve homeostasis. It is also called glomus caroticum or carotid glomus. This structure can detect changes in the partial pressures of oxygen and carbon dioxide. It can also sense potenz hydrogen (pH) and temperature changes.
When the neck is dissected, the carotid body looks like a red or brown ovoid tissue. This color can be attributed to the fact that it is a highly vascular tissue, which means that it has a lot of capillaries. Its vascularity is related to its function of detecting the blood's concentration of important substances.
The carotid body can be found where the common carotid artery bifurcates or divides into the internal and external carotid arteries. A person has two carotid bodies, one on each side of the neck. Each is supplied by the carotid sinus nerve, a branch of the glossopharyngeal nerve. It is also partially supplied by the vagus nerve.
The main components of the carotid body are chemoreceptors with accompanying supporting cells. Therefore, it is very similar to the aortic body, which is also a collection of chemoreceptors located near the aortic arch. The aortic body also contains baroreceptors, which detect changes in pressure and are more intricately linked with the cardiovascular system.
The chemoreceptors of the carotid body are called chief cells. As cells derived from the neuroectoderm, chief cells are able to release neurotransmitters, such as acetylcholine, dopamine and adenosine triphosphate (ATP), which trigger excitatory postsynaptic potentials (EPSPs). These neurotransmitters reach the respiratory center to regulate breathing.
The supporting cells are called sustentacular cells. These cells are similar to the glial cells of the nervous system. They provide structural and nutritional support to the chief cells.
By virtue of having chemoreceptors, the carotid body detects changes in the concentrations of several substances. Therefore, both carotid bodies act as peripheral chemoreceptors, and they are primarily stimulated by a change in the partial pressure of oxygen. At oxygen partial pressures greater than 100 millimeters of mercury, the carotid body activity is low. When the oxygen partial pressure falls below this level, a condition called hypoxia occurs, wherein the carotid body activity increases. Similarly, when there is an increase in the carbon dioxide content of the blood, it becomes more active.
Once there is a fall in oxygen levels or a rise in carbon dioxide levels, signals in the form of action potentials are sent to the respiratory center in the medulla oblongata. The respiratory center then sends back signals to the respiratory system in order to induce adaptive responses. The primary adaptive response is an increase in the rate of breathing. By increasing the rate or breathing, more oxygen is taken into the lungs, and more carbon dioxide is eliminated from the body.
Concerning the carotid body: Is it possible that high blood pressure may actually be a result of the signaling of the carotid body in an attempt to bring more blood flow to the brain to increase oxygen?
A pretty good overview but it's worth noting carotid chemoreceptors are not active in hypoxia until PaO2 has dropped below 60mmHg. This eliminates the possibilities of hypoxic stimulation in moderate exercise and puts the focus on changes in breath by breath fluctuations of PaCO2 without changing the mean and causing hypercapnia.