The mammary gland is a gland located in the breasts of females that is responsible for lactating, also known as producing milk. Both males and females have glandular tissue within the breasts, however, after puberty the glandular tissue begins to develop in response to estrogen release in females. Mammary glands only produce milk after childbirth. During pregnancy, the hormones progesterone and prolactin are released. The progesterone interferes with prolactin, preventing the mammary glands from lactating. During this time, small amounts of a pre-milk substance are produced, which is called colostrum. This liquid is rich in antibodies and nutrients to sustain an infant for the first few days of life. After childbirth, progesterone levels decrease and the levels of prolactin remain raised. This signals the mammary glands to begin lactating. Each time a baby is breastfed, the milk is emptied from the breast. After which, the mammary glands are signaled to continue producing milk. As a woman approaches menopause, the time when menstruation stops, the tissues of the ductile system become fibrous and degenerate. This causes involution of the mammary gland and decreases the ability to produce milk.
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In Depth: Mammary gland