Normal Ultrastructure

Abstract

Most electron microscopical studies of the carotid body have been performed on animals. Thus, the normal organ has been examined in several species at sea level as well as in animals exposed to the natural hypoxia of high altitude or the induced hypoxia of simulated altitude in hypobaric chambers. By contrast, with the exception of the chemodectoma, there is scant information on the ultrastructure of either the normal or abnormal human carotid body. This imbalance in our knowledge has come about in part because most physiological studies of the organ have involved animals and it is convenient to compare structure with function in the same species. Another factor is the difficulty in obtaining suitable material for electron microscopy from humans. Grimley and Glenner (1968) obtained fresh specimens of carotid body resected during therapeutic glomectomy in relief of bronchial asthma but most studies must rely on tissue obtained from post-mortem examinations, with all the problems of autolysis and artifact that they bring. Nevertheless, provided that the interval between death and necropsy is less than 12 hours, preservation of cellular detail is sufficiently good to derive much information about the ultrastructure of the carotid body. In this chapter these appearances in the normal human glomus are described, with occasional reference to studies on animals to illustrate similarities and differences between species.