Mammary glands


Mammary glands are located inside the breasts of sexually mature female body. They are in actuality modified sweat glands which are in fact comprised of secretory mammary alveoli and the appropriate ducts. Mammory glands are considered to be part of the integumentary system rather than the reproductive system. The glands are associated with the female reproductive system in part due to their assistance in attracting a mate as well as their role in nourishing a baby. Size and shape of the female breast are different for every human body and factors such as race, age, body fat, and pregnancy can make a large difference in these variations.

The release of estrogen during puberty releases hormones that stimulate the growth of the breasts and the functions of the mammary glands. Pregnant women as well as nursing women experience hypotrophy of the breasts while it is not uncommon for atrophy of the breasts to occur after menopause.


Breasts are situated over ribs 2 through 6 and overlap the pectoral muscle as well as some portions of the oblique muscles. The lateral margin of the sternum creates an unintentional margin for the edge of each breast. Each breast also follows the anterior margin of the respective axilla. Coming within very close proximity to the axillary vessels, the breasts upward and laterally toward the axilla, which contributes to the high incidence of breast cancer due to the axillary process’ lymphatic drainage.

15 to 20 lobes compose the mammary gland, and each lobe is equipped with its own duct to the outside of the body. Adipose tissue in varying amounts segregates each lobe. While this tissue controls the size and shape that the breast takes, there is no determination by this tissue when it comes to the woman’s ability to suckle her young. Lobules are subdivisions of each lobe. These subdivisions contain mammary alveoli. The milk of a lactating female are produced within the mammary alveoli. Suspensory ligaments support the breasts which are attached between the lobules and run deep into the fascia which overlap the pectoral muscles. Breast milk is secreted into a network of mammary ducts which receive the milk from the clusters of mammary alveoli. These mammary ducts converge to form lactiferous ducts. Near the nipple, each lactiferous duct expands into the lumen to allow for outward flow of milk. The lactiferous sinuses store the milk before the suckling action, or additional pressure, releases it from the body. The milk leaves the body from the tip of the nipple.


Mammary glands
Image: Mammary Glands

The nipple contains some erectile tissue that protrudes into a cylindrical projection. The circular area around the nipple that contrasts in color is the areola. Sebaceous areolar glands create a bumpy surface around the areola which reside just under the surface of the areola’s skin. These glands secrete fluids during lactation as well as when a woman is not lactating, which keep the nipple supple. The complexion of the areola is based on the complexion of the skin that covers the rest of the body, varying in pigments and tints. During gestation most areola surfaces darken. It also becomes larger in most cases. This is thought to be more obvious for a nursing infant to find.


Branches of the internal thoracic artery are responsible for supplying blood flow to the nipple as well as the rest of the breast and mammary glands. Between the second, third, and forth intercostal spaces these braches of the thoracic artery enter the mammary glands. These spaces are positioned laterally to the sternum and offer entry to the mammary artery, which only supplies supportive blood. The return veins run alongside the initial arteries which supply the blood. During pregnancy and lactation, and sometimes during other periods, a superficial venous plexus can be seen through the surface of the skin.

The fourth, fifth, and sixth thoracic nerves innervate the breast principally through sensory somatic neurons. These neurons are derivative of the anterior and lateral branches of the thoracic nerves. The release of milk is dependant upon the sensory innervation as stimulus is the only natural release an infant can provide to be nourished.
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