Breast

Breast, front of the chest; especially in female mammals, the modified cutaneous, glandular structure it bears—the mamma or mammary gland. In humans, each breast consists of 15 to 20 branching ducts surrounded by connective tissue that acts as a supporting framework. The larger partitions between the lobes form strands that extend from the skin to the underlying deep fascia. At puberty in the female, fat accumulates in the connective tissue of the breast and the overlying skin. The skin of the areola, the disk-shaped area surrounding the nipple, contains modified sweat glands and sebaceous glands. The breasts usually secrete a small quantity of fluid, or colostrum, from early pregnancy onwards, and for 2–3 days after childbirth. Milk begins about 3 days after childbirth, increasing to an average rate of about 28 fl oz (850 ml) per day. The principal constituents of breast milk are water, lactose, fat, and protein. The ejection of milk is stimulated by sucking and by the release of the pituitary hormone oxytocin.

See also: Mammary glands.