Morphology of the rat carotid body

The carotid body (CB) is the main peripheral arterial chemoreceptor that registers the levels of pO2, pCO2 and pH in the blood and responds to their changes by regulating breathing. It is strategically located in the bifurcation region of each common carotid artery. The organ consists of "glomera" composed of two cell types, glomus and sustentacular cells, interspersed by blood vessels and nerve bundles, and separated by connective tissue. The neuron-like glomus or type I cells contain numerous cytoplasmic organelles and dense-cored vesicles that store and release neurotransmitters. They form both conventional chemical and electrical synapses between each other and are contacted by peripheral nerve endings of petrosal ganglion afferent neurons. The glial-like sustentacular or type II cells sustain physiologic neurogenesis in the adult CB and are thus supposed to be progenitor cells. This new source of adult stem cells may be potentially useful for tissue repair after injury or for cell therapy against neurodegenerative diseases. The CB is a highly vascularized organ and its intraorgan hemodynamics possibly plays a role in the process of chemoreception. There is also evidence that chronic hypoxia induces marked morphological and neurochemical changes within the CB but the detailed molecular mechanisms by which these affect the hypoxic chemosensitivity still remain to be elucidated. Dysregulation of the CB function is implicated in various physiological and pathophysiological conditions, including ventilatory altitude acclimatization and sleep-disordered breathing. Knowledge of the morphological and functional aspects of the CB will contribute to our better understanding of respiratory homeostasis in health and disease.Biomedical Reviews 2011; 22: 41-55