The Breast Overview

Breasts consist mainly of fat and glandular tissue. Nerves, veins, arteries and the connective tissues that help support the breast are also present. A large muscle called the pectoralis is located between the breast and the rib cage.

The tissue that makes up most of the breast is a complicated system of lobules and mammary ducts that look like bunches of grapes on their stems. Each breast contains 15 to 20 lobes in a circular pattern. The fat that covers the lobes gives the breast its size and shape. Each lobe is made up of lobules, and at the end of the lobules are tiny glands, or sacs, where milk is produced when a women is breastfeeding. Up to one million lobules can be found in each breast. Muscle tissue around the lobules serves to push the milk into the ducts.

The ducts carry the milk from the lobules to the nipple. There are usually 5 to 10 ductal systems in each breast, each with its own opening at the nipple. Small muscles in the nipple cause it to become erect in response to sexual stimulation or breastfeeding. Glands on the areola, the darker circle of skin around the nipple, produce small amounts of fluid to lubricate the nipple when a woman is breastfeeding.

Hormones, including estrogen, progesterone and prolactin, affect the breasts in terms of both development and milk-production.  The levels of these hormones change as the result of a woman’s menstrual cycle.