The mammary glands (commonly referred to as breasts) are structures present on the front (anterior) part of the chest wall in both males and females. Even though they are present in both sexes, the breasts in males are rudimentary when compared to the breasts in females. These glands are modified appendages that are required for milk production in females.
The male breasts are non-functional and do not produce milk. The milk produced by the mammary glands in females play an important role in the nourishment and immunity of babies. The female breasts also have a sexual connotation. Therefore, under-development or removal of the female breasts (as in the case of breast cancer treatment) can cause great emotional turmoil in the affected individuals.
Functions of the Female Breasts
The primary function of the female breasts is production of milk for the baby after childbirth. The milk produced by the female breasts serves as a complete food for the baby in the first six months of its life. The breast milk contains all the essential macronutrients (such as carbohydrate, protein, fat) and micronutrients for the growth of the newborn.
The milk produced by the female breasts in the period immediately after childbirth has a slightly different composition than the milk produced some days later. The initial milk is yellowish in color (rather than white) and is known as colostrum. The colostrum has very little fat content when compared to the white breast milk that is produced later.
Apart from nutrition, the breast milk also serves to provide immune protection to the baby. For this purpose, the breast milk contains chemical mediators, maternal antibodies, enzymes and vitamins. These components of the breast milk boost the immature immune system of the baby and provide protection from infections, allergies, and perhaps, autoimmune diseases.
Read more on benefits of breastfeeding.
Location of the Breast
The breasts are located on the anterior wall of the chest. Typically, the top of the breast lies at the level of the second rib whereas the bottom of the breast lies at the level of the sixth rib. However, there is a large variation in the sizes of breasts, with some larger breasts extending below the sixth rib inferiorly. Suspensory ligaments (also referred to as the suspensory ligaments of Cooper or Cooper’s ligaments) provide support to the core tissue of the breast by attaching it to the overlying skin.
Parts of the Female Breast
Human females have two mammary glands located on the front of their chest wall. The female breast is roughly spherical in shape and differs greatly in size among the members of the female population. The size and shape of the female breasts also change with the stage of life. The breasts are composed of a system of branching tubules, milk-producing glands, and connective tissue (also known as the stroma).
The main tissue of the breast is covered by fat and skin. In the center of each breast, is a darkened, circular area of the skin known as the areola. At the center of the areola lies the nipple through which milk comes out when the baby suckles. The stroma of the breast can be subdivided into lobules. The intralobular stroma constitutes the functional tissue of the breast, whereas the interlobular stroma constitutes the supporting connective tissue that supports the structure of the entire breast.
Internal structure of the female breast
The female mammary gland is structurally subdivided into different lobules, which contain acini or alveolar glands that produce milk. The milk produced by these 15-20 acini is collected by a branched system of ducts that finally open into the nipple. The milk from the acini flows out into the lactiferous ducts, which then drain the milk into the terminal ducts.
The milk from the terminal ducts gets stored in the lactiferous sinus till its release via the nipple. The lobules and the lactiferous ducts are lined by the cells of the luminal epithelium. A layer of smooth muscle known as the myoepithelium lies under the luminal epithelium. Contraction of this myoepithelial layer causes ejection of milk from the nipples.
During puberty, the size of the female breast increases due to accumulation of fat tissue. This is also the period when the glandular tissue of the female breasts starts developing. However, complete development of milk-producing glandular tissue occurs only after pregnancy.
Areola and nipple
The area of the skin that surrounds the nipple is relatively darker than the skin on the rest of the breast. This dark area of the skin is circular in shape, and is referred to as the areola. Multiple sebaceous glands are present in the areola. The skin on the areola and the nipple is prone to chafing during the act of breastfeeding. The sebaceous glands present in the areola secrete an oily sebum, which helps in the lubrication of the chafing-prone areola and nipple.
The nipple is a visible conical projection that is located in the central region of the areola. The nipple is the part of the breast where the infant suckles for milk. The breast milk produced in the acinar glands is relayed to the nipple through a branching network of multiple lactiferous ducts. Suckling stimulates milk flow via the nipples by compression of the smooth muscle layer that envelops the ducts.
Blood Supply to the Breasts
Oxygenated blood supply to the breast tissue is via the branches of internal thoracic artery, axillary artery, and thoracic aorta. The branches of internal thoracic artery that supply the breast tissue include the anterior intercostal and medial mammary branches.
The branches of axillary artery that supply the breast tissue include the lateral thoracic and thoraco-acromial branches. The posterior intercostal arteries from the thoracic aorta also supply the breast tissue. Deoxygenated blood from the breast tissue is drained via the internal thoracic vein and axillary vein.
Lymphatic Drainage from Breasts
The lymphatic drainage from the breast tissue is of great clinical significance due to its role in the spread of breast cancer cells. The lymphatic drainage system of the breast is fairly complex. Most of the lymph from the breast tissue goes through the pectoral or anterior lymph nodes, and drains into the axillary lymph nodes.
Some of the lymph may even drain into the axillary nodes directly. The lymph from the skin on the breast drains indirectly into the parasternal lymph nodes, whereas the lymph from the lobules, areola and nipple drains into the subareolar lymphatic plexus.
Nerve Supply of the Breasts
The lateral and anterior cutaneous branches of the 4th, 5th, and 6th intercostal nerves supply the breast tissues.
Read more on breast pains.