Fine structure of the carotid body of normal and anoxic cats

Certain modifications and clarifications of current concepts of the fine structure of the carotid body are described. The two principal cell types are here designated “enclosing” and “enclosed” to emphasize the enveloping nature of the former. The enclosed cells have numerous processes, contain lysosome‐like bodies which are sometimes related to crystals with a period of about 100Å. In addition to the typical dark‐cored vesicles, a few with lighter content are always present. The enclosing cells are in most respects similar in their contents to the enclosed, even to the presence of occasional dark‐cored vesicles. The fenestrations of the blood vessels apparently are closed by thin diaphragms. In addition to the type of nerve endings previously described, there is a second type which extensively surrounds the enclosed cells, in the manner of a basket, and differs from the first type in having relatively empty cytoplasm with few synaptic vesicles or mitochondria. It is postulated that this is the afferent ending, while the former may be efferent. Severe anoxia rendered both cell types more dense than normal. In contrast to previous reports, the dark‐cored vesicles of the enclosed cells did not disappear but rather increased in relative number, and their mitochondria were less opaque. No comparable changes were noted in control anoxic tissues of liver, kidney or adrenal medulla. The possibility is discussed that the enclosing cell has more than a simple supportive function, as the usual name “sustentacular” seems to imply.