The breasts are one of the most prominent superficial features in women. They are present in the pectoral region of the anterior thoracic wall, and consist of mammary glands, overlying skin, and supporting fibrous tissue embedded in a fatty matrix, together with blood vessels, nerves, and lymphatics. Both men and women have breasts, but normally they are only well developed in the latter.
Anatomy of the female breast
The mammary glands are modified sweat glands that overlie the pectoralis major and minor muscles, as well as the anterior thoracic wall. They are comprised of a series of ducts and associated secretory lobules, which converge into 15 to 20 lactiferous ducts that open immediately to the nipple. The nipple is comprised of smooth muscle fibers arranged in a circular pattern. These fibers compress the lactiferous ducts during lactation, and erect the nipples in response to stimulation. The nipple is surrounded by a circular pigmented area of skin termed the areola, and forms the greatest prominence of the breast. The areola contains numerous oil-secreting sebaceous glands that enlarge and lubricate the areola and nipple during pregnancy, preventing chaffing.
The mammary glands, ducts, and lobules mentioned previously are surrounded by a well-developed tissue stroma. In certain areas, the stroma condenses to form the suspensory ligaments supporting the breast. The mammary glands are accessory to female reproduction, unlike in men, where they are rudimentary and functionless, consisting only of a few small ducts. Glandular tissue is more predominant in lactating women, while fat comprises most of the breast in non-lactating women. The amount of fat present in a female breast determines its size. The breast normally enlarges during puberty, mainly due to increased fat deposition and partly due to glandular development. The breast size and shape is determined by various factors that include genetics, ethnicity, and diet. Fat in the male breast is similar to the subcutaneous tissue elsewhere.
The breast rests on a bed of deep fascia formed by the pectoralis major and other surrounding muscles. The retromammary space is a loose layer of subcutaneous tissue that separates the breast from the deep fascia, providing a degree of motility over the underlying structures. The attached surface of the breast extends transversely from the lateral border of the sternum up till as far as the mid axillary line, and vertically from ribs II to VI.
The vasculature of the breasts involves many routes. Laterally, they are supplied by branches from the axillary artery, including the: superior thoracic, thoracoacromial, lateral thoracic and subscapular arteries. Anterior intercostal branches from the internal thoracic artery, and medial mammary branches from the perforating branches, supply the breasts medially. Other vessels supplying the breasts include branches of the second to fourth intercostal arteries. They perforate the thoracic wall and the overlying muscles. The venous drainage is parallel to the arteries of the breasts, and its veins bare their names. The anterior and lateral cutaneous branches of the fourth to sixth intercostal nerves provide sensory innervation to the skin of the breasts, and sympathetic fibers to their blood vessels and smooth muscles. The nipples are innervated by the fourth intercostal nerves only.