Fig. 3.

Internal structure of mammary gland and mammary alveolus. The mammary gland is composed of lobes that comprise lobules containing 150–220 alveoli. Mammary alveoli are fundamental constituents that produce milk components. The mammary alveolus consists of parenchymal and stromal compartments based on the basement membrane. The parenchyma is constructed of inner milk secretory epithelial cells that surround a central lumen and outer myoepithelial cells that attach to the base of the mammary epithelium. In addition, the stroma is constituted of adipocytes and extracellular matrix