Mammary glands are the organs that, in mammals, produce milk for the sustenance of their young. These exocrine glands are enlarged and modified sweat glands and give mammals their name. They are rudimentary in both sexes until puberty, when, in response to ovarian hormones, they begin to develop in the female. During pregnancy, they distend further in preparation for nursing the infant. Pregnant women are prevented from lactating (producing milk) by the presence in the blood of high levels of estrogen and progesterone, secreted by the placenta until birth occurs.
After birth, the hormone prolactin (milk-stimulating hormone), is released, and the glands begin producing for the new born infant. Mammary glands are considered Apocrine glands. Apocrine secretion is really a small releasing of itself. The secretory substance collects in a tip of the cell that then breaks off into the duct system, serving up part of the tissue along with the secretion and is found solely in mammary glands.
