Skin In women, the breasts overlie the pectoralis major muscles and usually extend from the level of the second rib to the level of the sixth rib in the front of the human rib cage ; thus, the breasts cover much of the chest area and the chest walls.
At the front of the chest, the breast tissue can extend from the clavicle collarbone to the middle of the sternum breastbone. At the sides of the chest, the breast tissue can extend into the axilla armpit , and can reach as far to the back as the latissimus dorsi muscle , extending from the lower back to the humerus bone the longest bone of the upper arm.
As a mammary gland , the breast is composed of differing layers of tissue , predominantly two types: The suspensory Cooper's ligaments are fibrous-tissue prolongations that radiate from the superficial fascia to the skin envelope. The female adult breast contains 14—18 irregular lactiferous lobes that converge at the nipple. Milk exits the breast through the nipple, which is surrounded by a pigmented area of skin called the areola.
The size of the areola can vary widely among women. The areola contains modified sweat glands known as Montgomery's glands. These glands secrete oily fluid that lubricate and protect the nipple during breastfeeding.
The tissue composition ratios of the breast also vary among women. Some women's breasts have varying proportions of glandular tissue than of adipose or connective tissues. The fat-to-connective-tissue ratio determines the density or firmness of the breast. During a woman's life, her breasts change size, shape, and weight due to hormonal changes during puberty , the menstrual cycle , pregnancy, breastfeeding, and menopause.
The nipple of the breast is surrounded by the areola nipple-areola complex. The areola has many sebaceous glands, and the skin color varies from pink to dark brown.
The basic units of the breast are the terminal duct lobular units TDLUs , which produce the fatty breast milk. They give the breast its offspring-feeding functions as a mammary gland.
They are distributed throughout the body of the breast. The terminal lactiferous ducts drain the milk from TDLUs into 4—18 lactiferous ducts, which drain to the nipple. The milk-glands-to-fat ratio is 2: In addition to the milk glands, the breast is also composed of connective tissues collagen , elastin , white fat, and the suspensory Cooper's ligaments. Sensation in the breast is provided by the peripheral nervous system innervation by means of the front anterior and side lateral cutaneous branches of the fourth-, fifth-, and sixth intercostal nerves.
The T-4 nerve Thoracic spinal nerve 4 , which innervates the dermatomic area , supplies sensation to the nipple-areola complex. The axillary lymph nodes include the pectoral chest , subscapular under the scapula , and humeral humerus-bone area lymph-node groups, which drain to the central axillary lymph nodes and to the apical axillary lymph nodes.
The lymphatic drainage of the breasts is especially relevant to oncology because breast cancer is common to the mammary gland, and cancer cells can metastasize break away from a tumour and be dispersed to other parts of the body by means of the lymphatic system.
Shape, texture, and support The morphologic variations in the size, shape, volume, tissue density, pectoral locale, and spacing of the breasts determine their natural shape, appearance, and position on a woman's chest. Breast size and other characteristics do not predict the fat-to-milk-gland ratio or the potential for the woman to nurse an infant. The size and the shape of the breasts are influenced by normal-life hormonal changes thelarche, menstruation, pregnancy, menopause and medical conditions e.
The suspensory ligaments sustain the breast from the clavicle collarbone and the clavico-pectoral fascia collarbone and chest by traversing and encompassing the fat and milk-gland tissues. The breast is positioned, affixed to, and supported upon the chest wall, while its shape is established and maintained by the skin envelope.
The space between the breast and the pectoralis major muscle, called retromammary space , gives mobility to the breast. The chest thoracic cavity progressively slopes outwards from the thoracic inlet atop the breastbone and above to the lowest ribs that support the breasts. The inframammary fold, where the lower portion of the breast meets the chest, is an anatomic feature created by the adherence of the breast skin and the underlying connective tissues of the chest; the IMF is the lower-most extent of the anatomic breast.
Normal breast tissue typically has a texture that feels nodular or granular, to an extent that varies considerably from woman to woman. Theoretically, as the human jaw receded into the face, the woman's body compensated with round breasts.
Breast development The breasts are principally composed of adipose, glandular , and connective tissues. Puberty Five-stage Tanner Scale The morphological structure of the human breast is identical in males and females until puberty.
For pubescent girls in thelarche the breast-development stage , the female sex hormones principally estrogens in conjunction with growth hormone promote the sprouting, growth, and development of the breasts.
During this time, the mammary glands grow in size and volume and begin resting on the chest. These development stages of secondary sex characteristics breasts, pubic hair, etc. This condition of asymmetry is transitory and statistically normal in female physical and sexual development. Approximately two years after the onset of puberty a girl's first menstrual cycle , estrogen and growth hormone stimulate the development and growth of the glandular fat and suspensory tissues that compose the breast.
This continues for approximately four years until the final shape of the breast size, volume, density is established at about the age of Mammoplasia breast enlargement in girls begins at puberty, unlike all other primates in which breasts enlarge only during lactation.
The breasts become larger, the nipple-areola complex becomes larger and darker, the Montgomery's glands enlarge, and veins sometimes become more visible. Breast tenderness during pregnancy is common, especially during the first trimester. By mid-pregnancy, the breast is physiologically capable of lactation and some women can express colostrum , a form of breast milk.
However, milk production is blocked by the hormones progesterone and estrogen until after delivery, when progesterone and estrogen levels plummet. The breasts can decrease in size when the levels of circulating estrogen decline. The adipose tissue and milk glands also begin to wither.
The breasts can also become enlarged from adverse side effect s of combined oral contraceptive pills. The size of the breasts can also increase and decrease in response to weight fluctuations.
Physical changes to the breasts are often recorded in the stretch marks of the skin envelope; they can serve as historical indicators of the increments and the decrements of the size and volume of a woman's breasts throughout the course of her life.
Breastfeeding The primary function of the breasts, as mammary glands, is the nourishing of an infant with breast milk. Milk is produced in milk-secreting cells in the alveoli. When the breasts are stimulated by the suckling of her baby, the mother's brain secretes oxytocin.
High levels of oxytocin trigger the contraction of muscle cells surrounding the alveoli, causing milk to flow along the ducts that connect the alveoli to the nipple. Clinical significance Main article: Breast disease The breast is susceptible to numerous benign and malignant conditions. The most frequent benign conditions are puerperal mastitis , fibrocystic breast changes and mastalgia. Lactation unrelated to pregnancy is known as galactorrhea.
It can be caused by certain drugs such as antipsychotic medications , extreme physical stress, or endocrine disorders. Lactation in newborns is caused by hormones from the mother that crossed into the baby's bloodstream during pregnancy. Breast cancer Breast cancer is the most common cause of cancer death among women  and it is one of the leading causes of death among women.
Factors that appear to be implicated in decreasing the risk of breast cancer are regular breast examinations by health care professionals, regular mammograms , self-examination of breasts , healthy diet, and exercise to decrease excess body fat. Normally, males produce lower levels of estrogens and higher levels of androgens , namely testosterone , which suppress the effects of estrogens in developing excessive breast tissue.
In boys and men, abnormal breast development is manifested as gynecomastia , the consequence of a biochemical imbalance between the normal levels of estrogen and testosterone in the male body.
Plastic surgery Conventional mastectomy top ; skin sparing mastectomy and latissimus dorsi myocutaneous flap reconstruction, prior to nipple reconstruction and tattooing bottom. Plastic surgery can be performed to augment or reduce the size of breasts, or reconstruct the breast in cases of deformative disease, such as breast cancer. Society and culture General In Christian iconography , some works of art depict women with their breasts in their hands or on a platter, signifying that they died as a martyr by having their breasts severed; one example of this is Saint Agatha of Sicily.
A typical example is the so-called Venus of Willendorf , one of many Paleolithic Venus figurines with ample hips and bosom. Many female deities representing love and fertility were associated with breasts and breast milk.
Figures of the Phoenician goddess Astarte were represented as pillars studded with breasts. Isis , an Egyptian goddess who represented, among many other things, ideal motherhood, was often portrayed as suckling pharaohs , thereby confirming their divine status as rulers. Even certain male deities representing regeneration and fertility were occasionally depicted with breast-like appendices, such as the river god Hapy who was considered to be responsible for the annual overflowing of the Nile. Female breasts were also prominent in the Minoan civilization in the form of the famous Snake Goddess statuettes.
In Ancient Greece there were several cults worshipping the "Kourotrophos", the suckling mother, represented by goddesses such as Gaia , Hera and Artemis. The worship of deities symbolized by the female breast in Greece became less common during the first millennium. The popular adoration of female goddesses decreased significantly during the rise of the Greek city states, a legacy which was passed on to the later Roman Empire.
Women in art were covered in clothing from the neck down, including female goddesses like Athena , the patron of Athens who represented heroic endeavor. Aphrodite , the goddess of love, was more frequently portrayed fully nude, though in postures that were intended to portray shyness or modesty, a portrayal that has been compared to modern pin ups by historian Marilyn Yalom. The legend was a popular motif in art during Greek and Roman antiquity and served as an antithetical cautionary tale.
Body image Many women regard their breasts as important to their sexual attractiveness , as a sign of femininity that is important to their sense of self. Brassiere , Cleavage breasts , Toplessness , Modesty , Naturism , and Exhibitionism As is customary in her culture, a bare-breasted Himba woman of northern Namibia wears a traditional headdress and skirt Because breasts are mostly fatty tissue, their shape can -within limits- be molded by clothing, such as foundation garments.
Some religions ascribe a special status to the female breast, either in formal teachings or through symbolism. Many cultures, including Western cultures in North America, associate breasts with sexuality and tend to regard bare breasts as immodest or indecent. In some cultures, like the Himba in northern Namibia , bare-breasted women are normal. In some African cultures, for example, the thigh is regarded as highly sexualised and never exposed in public, but breast exposure is not taboo.
In a few Western countries and regions female toplessness at a beach is acceptable, although it may not be acceptable in the town center. In many countries, breastfeeding in public is common, legally protected, and generally not regarded as an issue. However, even though the practice may be legal or socially accepted, some mothers may nevertheless be reluctant to expose a breast in public to breastfeed   due to actual or potential objections by other people, negative comments, or harassment.
Mammary intercourse , Breast fetishism , and Stimulation of nipples In some cultures, breasts play a role in human sexual activity. In Western culture, breasts have a " They are sensitive to the touch as they have many nerve endings; and it is common to press or massage them with hands or orally before or during sexual activity. During sexual arousal , breast size increases, venous patterns across the breasts become more visible, and nipples harden.
Compared to other primates, human breasts are proportionately large throughout adult females' lives. Some writers have suggested that they may have evolved as a visual signal of sexual maturity and fertility. In the ancient Indian work the Kama Sutra , light scratching of the breasts with nails and biting with teeth are considered erotic.