Breasts | Research & Encyclopedia Articles

Breasts

Breasts are located on the anterior aspect of the chest and are composed of glandular tissue, adipose tissue, and ligamentous tissue. In women, breasts function to produce and secrete milk after childbirth, a process called lactation. The accessory reproductive glands, or mammary glands, are actually modified sweat glands responsible for lactation in women; they are present in men, but tend to be underdeveloped.

Supportive fibrous tissue, called Cooper's ligaments, is found throughout the breasts. These ligaments partially cover the lobes of glandular tissue, helping to bind the breasts together and give them shape. The nipples are externally located and serve as a passage for the milk to the environment. Each nipple is innervated by many nerves and contains smooth muscle. The nerves cause the nipples to be sensitive to external stimuli while the muscle fibers allow the nipples to become erect. A pigmented area called areola surrounds each nipple. The areola have small, raised bumps that contain oil-producing glands, called Montgomery's glands that help to lubricate the nipples during breast-feeding.

The breasts also contain a network of lymphatic vessels that rid the body of foreign materials and waste products. The lymphatic vessels in the breasts connect to the axillary nodes in the armpits and the internal mammary nodes behind the sternum. The fluid in the lymphatic vessels, called lymph, consists of lymphocytes that function as part of the body's immune system.

Many hormones are responsible for the growth, development, and function of the mammary glands. Estrogen encourages the proliferation of the mammary glands and progesterone is necessary for the development of the mammary glands. Besides the sex hormones, cortisol, insulin, growth hormone, and thyroid hormones also have an active role in the growth of breasts during puberty. Two pituitary hormones are necessary for the production and secretion of milk following pregnancy. Prolactin stimulates production of milk, while oxytocin causes contraction of the smooth muscle in the ducts that release milk from the breast in response to suckling.

Mammary tissue begins to develop in human embryos even before the development of the distinguishing reproductive organs of males and females. Human embryos, like all mammals, have similar developmental patterns regardless of whether they become male or female. All human embryos are morphologically female until the sixth week of development when gender is determined. If the Y chromosome is present, testosterone is released, resulting in the development of male characteristics. During childhood, the breasts of females and males are underdeveloped and very much the same. Occasionally breast development does occur in men, a condition known as gynecomastia. This condition is often due to a change in hormone levels, but does have other causes.

Before puberty, the female's breasts remain underdeveloped. This is because the ovaries have not yet begun to secrete the sex hormones estrogen and progesterone. Once puberty begins, breast growth and development result from hormonal influence and an increase in fat deposition. Additionally, the ducts of the mammary glands begin to grow and branch out. During menstruation, the breasts may swell and become sensitive to the touch; however, this does not occur in all women. During pregnancy, the breasts tend to increase in size due to the enlargement of the ducts and glandular tissue. The nipples also increase in size and the areola become darker. After menopause, hormonal activity decreases, the mammary glands are replaced with fat, and breasts begin to sag under the influence of gravity and deteriorating musculo-ligamental support.

Mammography is the use of x-ray imagery specially designed for examining breasts. Mammography screens for any abnormalities in the breast tissue and is a diagnostic tool for the early detection of breast cancer. Two types of mammography exist; they are classified based on the invasiveness of the procedure. Screening mammography is used to detect breast cancer while lumps are still too small to be felt. Usually women receive screenings once they reach the age of 40. Diagnostic mammography is a more in depth procedure utilized once an abnormality has been determined.

Most lumps found in the breasts are noncancerous cysts filled with fluid or benign tumors called fibroadenomas. The most common type of breast cancer, ductal carcinoma, occurs in the milk ducts of the mammary glands. A carcinoma is a malignant tumor found in epithelial cells. Another carcinoma of the breast, lobular carcinoma, grows in the lobes of the mammary glands. Other types of breast cancer include inflammatory carcinoma characterized by red, swollen breasts with a rash. Paget's disease is a cancer of the nipple and areola. Most types of breast cancer are infiltrating, meaning they spread to other tissue.