Anatomy and Function of the Female Breast
Breast tissue and the generation of milk is a feature of all mammals. Indeed, mammals are creatures where the female initially feeds her young by the generation of milk (a process known as lactation) from special glands called mammary glands. In this, human females are no different from any other mammals. What may surprise you, however, is the information that those milk-generating mammary glands are actually modified sweat glands.
Through the course of evolution these glands have become more numerous and developed to secrete a protein and fat-rich liquid in response to pregnancy. Structurally, each breast contains 15 to 20 lobes arranged in a circular fashion. The fat (subcutaneous adipose tissue) that covers the lobes gives the breast its size and shape. Each lobe is comprised of many lobules, at the end of which are tiny bulb like glands, or sacs, where milk is produced in response to hormonal signals.
In human females the breasts are one of the secondary sexual characteristics and develop in response to the hormonal changes accompanying puberty. The female breast lies on top of the major pectoralis muscles between the second and sixth rib of the chest. Internally the breast is a combination of lactiferous (milk-producing) ducts along with connective tissue, adipose (fatty) tissue and Cooper's ligaments which help support the breast.
The breast is supplied with blood from the internal thoracic artery (previously known as the internal mammary artery). Interestingly both men and women have a large concentration of blood vessels and nerves in their nipples and areolae which means that the nipples of both sexes can become erect and highly-sensitive in response to external stimuli.
Blood and lymph vessels form a network throughout each breast. Breast tissue is drained by lymphatic vessels that lead to axillary nodes (which lie in the axilla) and internal mammary nodes (which lie along each side of the sternum [breast bone]). This is important in terms of breast cancer, as this form of cancer is common and cancer cells can break away from the main tumour and many spread to other parts of the body through the lymphatic system.
During pregnancy and birth the breast is responsive to a complex interplay of hormones that cause the tissue to develop, enlarge and produce milk. The three major hormones affecting the breast being oestrogen, progesterone and prolactin. However, these hormones are also generated during the normal menstrual cycle and cause glandular tissue in the breast and the uterus to change. This is why the breast may feel 'lumpier' during menstruation (and this is entirely normal). But it this change in the breast throughout a woman's life that the cells in the breast are continually being exercised and replaced. This replacement over a woman's lifetime means that errors crop into the cell's DNA and it is the accumulation of these errors that often lead to cancer.
Like most other human features (eg size of feet or hands) the breasts are not uniform in size, with the left breast generally being larger than the right.