Ultrastructure of the mammary gland in lactating Saanen goats

Abstract

The secretory cells of the mammary gland are very diverse in their size, shape, and structure. These are highly specialized cells adapted to the synthesis, accumulation, storage, and excretion of milk. The main feature of glandular cells is the presence of secreted substances. Electron microscopy shows that substances of different secretory cells types have various electron densities. Occasionally, two or more types of secretory granules differing in size and composition can be found in one cell. The material for the morphological study was small (2‐4 mm) tissue samples of goat lactating mammary glands. Pieces were taken from deeper areas of the breast parenchyma. Ultrathin sections with a 50‐70 nm thickness were obtained for electron microscopic analysis using Leica UC7 ultramicrotome. Electron microscopy was performed using a JEOL JEM 1011 microscope. Micrographs were obtained using a Morada camera (Digital Imaging Solutions Inc.). The secretion of the mammary gland occurs according to the apocrine type. Picture of the lactocytes' cytoplasm apical part separation into the lumen of the alveoli is often observed on semi‐thin sections. Thus, numerous droplets of material secreted by lactocytes are found in the lumen of the alveoli. The shape of lactocytes in the lactating mammary gland is close to cubic. The height of the epithelial layer, generally, is 10‐12 microns (µm). The milk ducts, like the alveoli, are dilated. Most of them contain a significant amount of osmiophilic material secreted by the cells of the mammary alveoli. The cells of the epithelium of the single‐layered ducts have a flattened or cuboidal shape. The diameter of the ducts varies noticeably depending on location in the gland parenchyma. The intralobular milk ducts are 10‐20 µm in diameter. At the same time, the larger interlobular ducts reach a diameter of 40‐50 microns and are located in groups in the connective tissue stroma of the mammary gland. Notably, an increase in the mammary alveoli mass in the lactating gland is associated with a decrease in connective tissue volume and the almost complete disappearance of fat cells groups from it. The milk ducts of the teat zone in the lactating gland are strongly expanded, round, or slightly oval‐shaped in cross‐section with a diameter of 30‐60 microns. In contrast to the deeper zones of the mammary gland, we were unable to detect secreted substances in the dilated milk ducts near the teat area. The milk ducts we studied are located close to the most terminal sections of the mammary gland excretory system (gland cistern and teat canal). The milk is inevitably washed out from the ducts during chemical fixation and subsequent stages of objects preparation for histological analysis.