Each breast is made up of 15-25 secretory lobes, embedded in adipose tissue. The mammary gland is like a modified sweat gland. Each of theses lobes is a compound tubular acinar gland. The acini empty into ducts, that are lined by cuboidal, or low columnar epithelial cells, and surrounded by myoepithelial cells. The ducts from each lobule empty into a lactiferous duct that empties onto the surface of the nipple. These ducts are surrounded by smooth muscle in the regon of the nipple, contraction of which makes the nipple become errect.

The lumina become more prominent during the mid point of the menstrual cycle.

This image shows a secretory lobe at low power. Can you identify ducts, the secretory units and the outer dense connective tissue (that around the ducts is loose)?

In pregnant women, the alveolar duct epithelium proliferates, and lots of secretory alveoli form and begins to make a protein rich fluid called colostrum. This magnified image of a mammary gland during pregnancy, shows the large lipid filled acini/alveoli.