carotid body
Summary
The carotid body is a small chemoreceptor organ located at the bifurcation of the common carotid artery that detects changes in blood oxygen, carbon dioxide, and pH levels. It plays a crucial role in respiratory and cardiovascular homeostasis by triggering compensatory responses to hypoxemia, hypercapnia, and acidosis.
Detail
The carotid body is a bilateral peripheral chemoreceptor approximately 2-5mm in diameter located at the carotid bifurcation. It contains glomus cells (type I cells) that sense chemical changes in arterial blood, particularly decreased PO2 (<60 mmHg), increased PCO2, decreased pH, and increased temperature. When stimulated, these cells release neurotransmitters (dopamine, acetylcholine, norepinephrine) that activate afferent fibers of the glossopharyngeal nerve (CN IX), which synapse in the nucleus tractus solitarius. This triggers reflexive increases in respiratory rate and depth, as well as cardiovascular responses including increased heart rate and blood pressure. The carotid body is highly vascularized with the highest blood flow per gram of any organ. It serves as the primary peripheral oxygen sensor and becomes hyperplastic in chronic hypoxic conditions like high altitude or chronic lung disease. Carotid body tumors (paragangliomas) are rare but can cause hypertensive crises due to catecholamine release.
Sources
- Guyton and Hall Textbook of Medical Physiology
- West's Respiratory Physiology
- Gray's Anatomy
- Robbins and Cotran Pathologic Basis of Disease
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