The histology of the adrenal gland of the African elephant, Loxodonta africana

Abstract

The histology, particularly the ultrastructural cytology, of the adrenal gland of the African elephant, Loxodonta africana, is virtually unknown. Tissue from 14 adult male and female elephants was processed for light and transmission electron microscopy. The gland is surrounded by a thick capsule composed of an outer layer of dense connective tissue and an inner layer in which smooth muscle fibres predominate. Below the layer of smooth muscle, a continuous layer of relatively undifferentiated ‘capsular’ cells occur. Where the capsular cells abut on the zona glomerulosa, they appear to be differentiating into glomerulosa cells, as small lipid droplets are present in their cytoplasm. The cortex is divided into three zones as is found in the adrenal glands of other mammals. Large amounts of collagenous and reticular tissue support the secretory cells, which have a marked lipid content. With electron microscopy, the cortical cells show features typical of steroid-producing cells. The medulla is characterized by an outer region of pale-staining chromaffin-positive (adrenaline) cells and an inner region of intensely staining chromaffin-positive (noradrenaline) cells. The latter cells contain granules of different sizes and structure.