ULTRASTRUCTURAL ZONATION OF THE HUMAN ADRENAL CORTEX

Electron microscopic observations of sections from adrenal cortex obtained from a twenty‐four‐year‐old male with hypertension were made. In the zona glomerulosa the cells showed a large nuclear‐cytoplasmic ratio. The mitochondria had a dark matrix and plate‐like inner structure. The agranular endoplasmic reticulum revealed a close association with lipid granules. The Golgi apparatus was prominent and frequently accompanied by centrioles. Free ribosomes were abundant. The zona fasciculata can be subdivided into two layers. In the outer layer the cells are characterized by numerous large lipid granules. Two kinds of mitochondria are discernible; one with a pale matrix and tubulo‐vesicular or vesicular inner structure and the other with a dark matrix and tubulo‐vesicular or lamelllform cristae. In the inner zona fasciculata and reticularis there are two types of cells besides the dark cells. The type 1 cells have a compact cytoplasm, elliptic or irregularly shaped mitochondria with a dark matrix and tubulo‐vesicular or vesicular internal structure. The type 2 cells are large and ovoid, having a clear transparent cytoplasm. The mitochondria are numerous having a clear matrix and almost exclusively vesicular inner elements. Abundance in agranular endoplasmic reticulum, decreased lipid granules, and cytoplasmic incisions are common in both the inner fasciculata and reticularis. In addition the zona reticularis is characterized by increased number of dark cells, numerous pigment bodies, and the appearance of huge mitochondria. On the basis of these observation were discussed the significance of the organelles in steroid biosynthesis, mode of hormone secretion, and cyto‐genesls in the adrenal cortex.