10.1. Breast: Introduction
The breasts are also known as the mammary glands. They are present in both sexes but in the male remain rudimentary (mainly undeveloped) throughout life. In the female they are underdeveloped in childhood but during pregnancy and lactation they develop considerably. The breast consists of numerous types of tissue: glandular, fibrous and adipose tissues, lymph vessels, blood vessels and nerves.
In a young adult female, the breast forms a rounded elevation LYING IN THE SUPERFICIAL FASCIA on the anterior (and partly lateral) aspect of the thoracic wall. Posterior to the breast lies the deep fascia of the pectoralis major muscle, but note that the breast DOES NOT LIE WITHIN THE DEEP FASCIA. In-between the gland and deep fascia of pectoralis major lies an area of loose areolar tissue in what is called the submammary (or ‘retromammary’) space. The loose tissue here allows some movement of the breast on the deep fascia. From superior to inferior, the breast extends from the second to sixth rib. From medial to lateral, at its widest point, the breast extends from the side of the sternum to a point close to the mid-axillary line.
Subdividing the breast
Medical professionals often subdivide the breast into four quadrants to allow for more accurate examination:
Regulating Secretory Activity
The secretory activity of the breast is mainly regulated by the endocrine system. During pregnancy, two hormones are of particular importance: progesterone (produced by the corpus luteum and placenta) and oestrogen (produced by the ovaries) stimulate the formation of bulbs in the lobules of the breast. After birth, two other hormones are more important: prolactin and growth hormone (GH - both produced by the pituitary gland in the brain) stimulate and maintain fully active milk secretion for five to six months. The lobules shrink when lactation stops.