Ultrastructure of the Human Carotid Body

Surgically excised human carotid bodies have been analyzed by electron microscopy. Several ultrastructural features suggest that they are closely related to sympathetic neuroendocrine glands and autonomic ganglia: the chief cells synthesize intensely osmiophilic cytoplasmic granules, occasionally develop neuroid processes, and are intimately associated with neurilemmal sustentacular cells. Other lines of evidence indicate that secretion of the chief cell is norepinephrine or a closely related bioamine-neurotransmitter. The role of chief cells in mediating chemosensation may be explained by modulated release of the bioamine in response to local metabolic conditions. Human chief cells are richly innervated. Recognizable zones of synapse display an efferent type of polarity and sometimes appear adrenergic. Thus, reflexive sympathetic excitation of chief cells may be physiologically significant in man. The anatomic compartmentalization characteristic of carotid body chief cells is discussed in relation to a possible functional significance.