Either 1 of the 2 mammary glands, which, in women, provide milk to nourish a baby and are secondary sexual characteristics. In males, the breast is an immature version of the female breast. At puberty, a girl’s breasts begin to develop: the areola (the circular area of pigmented skin around the nipple) swells and the nipple enlarges. This is followed by an increase in glandular tissue and fat. The adult female breast consists of 15–20 lobes of milk-secreting glands embedded in fatty tissue. The ducts of these glands have their outlet in the nipple. Bands of fine ligaments determine the breast’s height and shape. The areolar skin contains sweat glands, sebaceous glands, and hair follicles. The size and shape and general appearance of the breasts may vary during the menstrual cycle, during pregnancy and lactation, and after the menopause. During pregnancy, oestrogen and progesterone, secreted by the ovary and placenta, cause the milkproducing glands to develop and become active and the nipple to become larger. Just before and after childbirth, the glands in the breast produce a watery fluid known as colostrum. This fluid is replaced by milk a few days later. Milk production and its release is stimulated by the hormone prolactin.


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