The functional morphology of chromaffin cells.

Based on classical and up-to-date literature, the most important morphological and histochemical characteristics of chromaffin cells are summarized. Chromaffinoblasts begin to migrate into the cortex of the adrenal in the second month of the human embryo. In adults, the polygonal cells of the medulla appear as rounded islands as well as shorter or longer cords beside sinusoidal vessels. A high variety in form of chromaffin granules was registered in the human adreno-medullary cells but author stressed that the fixation process itself can influence the shape of secretory granules. A well-developed Golgi apparatus, abundant rough-surfaced endoplasmic reticulum, a large number of mitochondria and lipofuscin pigments can be seen in the chromaffin cells. These organelles participate actively in the genesis and ultimate fate of chromaffin granules. Although exocytosis seems to be the most probable hormone-liberation process in the hamster adrenal medulla, the general validity of this process has not convincingly been proved in other species of vertebrates. The physiological effects of adreno-medullary hormones and the innervation of the gland are thoroughly discussed.