Breast and milk gland anatomy, illustration. Mammary glands are exocrine glands that secrete milk that is used by mammals to feed their young. The blood supply (arterioles, venules and capillaries) is shown across top. At bottom is a milk duct (lactiferous duct) surrounded by fatty tissue (adipocytes, green). The milk duct is lined with myoepithelial cells, a type of glandular epithelium.