Breast

Photograph of a pregnant human female's breasts.

The term breast, also known by the Latin mamma in anatomy, refers to the upper ventral region of an animal's torso, particularly that of mammals, including human beings. In addition, the breasts are parts of a female mammal's body which contain the organs that secrete milk used to feed infants.

This article focuses on human female breasts, but it should be noted that humans also have breasts (although usually less prominent) that are structurally identical and homologous to the female, as they develop embryologically from the same tissues. While the mammary glands that produce milk are present in the male, they normally remain undeveloped. In some situations male breast development does occur, a condition called gynecomastia. Milk production can also occur in both men and women as an adverse effect of some medicinal drugs (such as some antipsychotic medication), extreme physical stress or in endocrine disorders. Often times, newborn babies are capable of lactation because they receive some amount of prolactin and oxytocin (milk hormones) from their connection to the mother.

Anatomy of the female breasts

Cross section of the breast of a human female.

The breasts are covered by skin; each breast has one nipple surrounded by the areola. The areola is colored from pink to dark brown, hairless, and has several sebaceous glands. The larger mammary glands within the breast produce the milk; they consist of several lobules, and each breast has some 10-20 lactiferous ducts that drain milk from the lobules to the nipple, where each duct has its own opening,

Most of the breast is connective tissue, i.e., adipose tissue (fat) and Cooper's ligaments. The breasts sit over the pectoralis major muscle and usually extend from the level of the 2nd rib to the level of the 6th rib anteriorly. The superior lateral quadrant of the breast extends diagonally upwards in an 'axillary tail'. A thin layer of mammary tissue extends from the clavicle above to the seventh or eighth ribs below and from the midline to the edge of the latissimus dorsi posteriorly.

The arterial blood supply to the breasts is derived from the internal thoracic artery (previously referred to as the internal mammary artery), lateral thoracic artery, thoracoacromial artery, and posterior intercostal arteries. The venous drainage of the breast is mainly to the axillary vein, but there is some drainage to the internal thoracic vein and the intercostal veins.

The breast is innervated by the anterior and lateral cutaneous branches of the 4th through 6th intercostal nerves. The nipple is supplied by the T4 dermatome.

Both sexes have a large concentration of blood vessels and nerves in their nipples.

Lymphatic drainage

About 75% of lymph from the breast travels to the ipsilateral axillary lymph nodes. The rest travels to parasternal nodes, to the other breast, or abdominal lymph nodes. The axillary nodes include the pectoral, subscapular, and humeral groups of lymph nodes. These drain to the central axillary lymph nodes, then to the apical axillary lymph nodes. The lymphatic drainage of the breasts is particularly relevant to oncology, since cancer cells can break away from a tumour (breast cancer being a common cancer), and spread to other parts of the body through the lymph system by a process known as metastasis.

Function

breastfeeding

The function of the mammary glands in female breasts is to nurture the young by producing milk, which is secreted by the nipples during lactation. However, zoologists point out that no female mammal other than the human has breasts of comparable size when not lactating and that humans are the only primate that have permanently swollen breasts. This suggests that the external form of the breasts is connected to factors other than lactation alone.

The mammary glands that secrete the milk from the breasts actually make up a relatively small fraction of the overall breast tissue. It is commonly assumed by biologists that the real evolutionary purpose of women having breasts is to attract the male of the species; that, in other words, breasts are sexually dimorphic, or secondary sex characteristics. One theory is based around the fact that, unlike nearly all other primates, human females do not display clear, physical signs of ovulation. This could have plausibly resulted in human males evolving to respond to more subtle signs of ovulation. During ovulation, the increased estrogen present in the female body results in a slight swelling of the breasts, which then males could have evolved to find attractive. In response, there would be evolutionary pressures that would favor females with more swollen breasts who would, in a manner of speaking, appear to males to be the most likely to be ovulating.Some zoologists (notably Desmond Morris) believe that the shape of female breasts evolved as a frontal counterpart to that of the buttocks, the reason being that whilst other primates mate in the typical doggy-style position, humans are more likely to successfully copulate mating face on. A secondary sexual characteristic on a woman's chest would have encouraged this in more primitive incarnations of the human race, and a face on encounter would have helped found a relationship between partners beyond merely a sexual one.

Others believe that the human breast evolved in order to prevent infants from suffocating while feeding[1]. Since human infants do not have a protruding jaw like our ancestors and the other primates, the infant's nose might be blocked by a flat female chest while feeding. According to this theory, as the human jaw became recessed, so the breasts became larger to compensate.

Size, shape and composition

Most of the human female breast is actually adipose tissue (fat) and connective tissue, rather than the mammary glands. There is naturally a great variety in the size and shape of breasts in women, with size being affected by various factors including genetics.

The primary anatomical support for the breasts is thought to be provided by the Cooper's ligaments, with additional support from the skin covering the breasts themselves, and it is this support which determines the shape of the breasts. The breasts naturally sag through aging, as the ligaments become elongated. This process may be accelerated by high impact exercises, and a brassiere may reduce this effect by providing external support, although the health benefits of wearing of a brassiere are not universally accepted. Pendulous breasts (ptosis) are considered undesirable by some, and some older women seek cosmetic surgery to raise their busts.

In a study on shoulder pain treatment in women with large breasts, patients removed the weight from their shoulders for a period of two weeks, either by going braless or by wearing a strapless bra. Only one woman chose a strapless bra and all the others went braless. Quoting the article, "Long-term outcome was presence or absence of muscle pain and tenderness. Seventy-nine percent of patients decided to remove breast weight from the shoulder permanently because it rendered them symptom free."Ryan, EL, Pectoral girdle myalgia in women: a 5-year study in a clinical setting. Clin J Pain. 2000 Dec;16(4):298-303

As breasts are mostly composed of adipose tissue, their size can change over time if the woman gains or loses weight. It is also typical for them to grow in size during pregnancy and while breastfeeding, mainly due to hypertrophy of the mammary gland in response to the hormone prolactin. The size of a woman's breasts usually fluctuates during the menstrual cycle, particularly with premenstrual water retention. An increase in breast size is also a common side effect of use of the contraceptive pill.

There is no relationship between breast size and ability to breastfeed, and it is a common belief that human female breasts are shaped the way they are so that they can feed babies by producing milk. However, their shape is also thought to have evolved due to sexual attraction, as described above.

The size of a woman's breasts is typically expressed as a "bra size". According to the results of the "Size UK" survey ^[2], the average bra size in the UK has increased from a 34B in the 1950s to a 36C today, and the average size for US women is a 34B as of 2005 by the CDC. Women with exceptionally large breasts may experience back pain. In some societies there is a belief amongst some that small breasts make a woman less sexually attractive. Some women suffer from insecurity about their breasts, and in some cultures a number of women who are unhappy with their size seek surgery either to artificially reduce or enlarge their breasts. The American Society for Aesthetic Plastic Surgery found that 334,052 breast augmentation procedures were performed in 2004 [3]. Some women undergo breast reconstruction after mastectomy for breast cancer, a result of the high value placed on symmetry of the female human form in those cultures, and because women often identify their femininity and sense of self with their breasts.

It is typical for a woman's breasts to be unequal in size, particularly whilst the breasts are developing during puberty. Statistically it is slightly more common for the left breast to be the largerFor slang terms for the breasts, see WikiSaurus:breasts

A brassiere (from French, lit: arm-holder) or 'bra' is an item of women's underwear consisting of two cups that totally or partially cover the breasts for support and modesty.

Being 'topless' is the state of baring breasts.

Cultural status

Edouard Manet, "Blonde Woman With Bare Breasts"

Historically, breasts were regarded as fertility symbols, because they are the source of life-giving milk. Certain prehistoric female statuettes - so-called Venus figurines - often emphasised the breasts, as in the example of the Venus of Willendorf. In historic times, goddesses such as Ishtar were shown with multiple breasts, alluding to their role as goddesses of childbirth.

Breasts are considered as secondary sex characteristics, and are sexually sensitive in many cases. Bare female breasts can elicit heightened sexual desires from men and women. Since they are associated with sex, in many cultures bare breasts are considered indecent, and they are not commonly displayed in public, in contrast to male chests. Other cultures view the baring of breasts as acceptable, and in some countries women have never been forbidden to bare their chests. Opinions on the exposure of breasts is often dependent on the place and context, and in some Western societies exposure of breasts on a beach may be considered acceptable, although in town centres, for example, it is usually considered indecent. In some areas, the prohibition against the display of a woman's breasts generally only restricts exposure of the nipples.

Certain types of work may also require that a woman expose her breasts, and in these contexts it is considered acceptable even if it would not be in another context. Female university students working as art models for fine arts classes generally have to work bare-breasted, if not completely nude. Actresses sometimes need to go bare-breasted for particular scenes. Strippers also typically make their living by showing off their breasts. Many women have bared their breasts (and other body parts) on the Internet, and such displays are generally considered legal and acceptable.

In some other situations, their display may be interpreted as indecent, even when they are being used for their primary purpose of nursing offspring. This has led, in several cases, to women being arrested for indecent exposure for breastfeeding their children in public.A number of US states have since passed corrective laws, specifically permitting breastfeeding in public.

Women in some areas and cultures are approaching the issue of breast exposure as one of sexual equality, since men (and pre-pubescent children) may bare their chests, but women and teenage girls are forbidden. In the United States, the Topfree equality movement seeks to redress this imbalance. This movement won a decision in 1992 in the New York State Court of Appeals- People v. Santorelli , where the court ruled that the state's indecent exposure laws do not ban women from being barebreasted. A similar movement succeeded in most parts of Canada in the 1990s. In Australia and much of Europe it is acceptable for women and teenage girls to sunbathe topless on some public beaches, but these are generally the only public areas where exposing breasts is acceptable.

Some religions require that women always keep their breasts covered. For example, Islam forbids public exposure of the female breasts except when breastfeeding. Orthodox Judaism has rules prohibiting exposure.

In addition to the above references, see also modesty, nudism and exhibitionism.

In some paintings women are sometimes shown 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.

Disorders of the breasts

Infections and inflammations

A 1930 Soviet poster promoting breast care.

*Mastitis
** bacterial mastitis
** mastitis from milk engorgement
** mastitis of mumps
** subareolar mastitis
*Other infections
** chronic intramammary abscess
** chronic subareolar abscess
** tuberculosis of the breast
** syphilis of the breast
** retromammary abscess
** actinomycosis of the breast
*Inflammations
** Mondor's disease
** duct ectasia = periductal masbreastis
** Breast engorgement

Benign breast disease

*Congenital disorders
** inverted nipple
** supernumerary nipples/supernumerary breasts/duplicated nipples
*Aberrations of normal development and involution
** cyclical nodularity
** cysts
** fibroadenoma - benign tumor
*Duct ectasia/Periductal masbreastis
** nipple discharge
** abscesses
** mammary fistula
*Fibrocystic disease/Fibrocystic changes
**Cysts
**Epithelial hyperplasia
**Epithelial metaplasia
**Papillomas
**Adenosis
*Pregnancy-related
** galactocoele
** puerperal abscess