Encyclopedia
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
male humans also have breasts 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 , extreme physical stress or in endocrine disorders. Oftentimes, newborn babies are capable of
lactation because they receive some amount of prolactin and
oxytocin from their connection to the mother.
Anatomy of the female breasts
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 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 , 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 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 , and spread to other parts of the body through the lymph system by a process known as metastasis.
Function
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 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. 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 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 are considered undesirable by some, and some older women seek cosmetic surgery to raise their busts.
A long term clinical study showed that women with large breasts can suffer shoulder pain as a result of
bra straps , although it should be stated that a well fitting bra should support most of the breasts' weight on the back strap rather than on the shoulders.
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 orb-like shape of breasts help limit heat loss, as a fairly high temperature is required for the production of milk.
In order to support the breasts adequately, a correctly sized bra must be worn and it is for this reason that breast size is typically expressed as a "
bra size". According to the results of the "Size UK" survey
, 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 . 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 larger. In some rare cases, one breast may be significantly larger or smaller than the other, or fail to develop entirely.
Development
The development of a woman's breasts, during puberty, is caused by sex hormones, chiefly
estrogen .
A vast number of medical conditions are known to cause abnormal development of the breasts during puberty. Virginal breast hypertrophy is a condition which involves excessive growth of the breasts during puberty, and in some cases the continued growth beyond the usual pubescent age. Breast hypoplasia is a condition where one or both breasts fail to develop during puberty.
In
Cameroon, some girls are subjected to breast ironing to stunt breast growth in order to make them less sexually attractive and thus become less likely to become a victim of
rape.
Terminology
- For slang terms for the breasts, see
A
brassiere 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
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 many 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.
When
breastfeeding a baby in public, legal and social rules regarding indecent exposure and dress code, as well as inhibitions of the woman, tend to be relaxed. Numerous laws around the world have made public breastfeeding legal and disallow companies from prohibiting it in the workplace. Yet the public reaction at the sight of breastfeeding can make the situation uncomfortable for those involved.
Women in some areas and cultures are approaching the issue of breast exposure as one of sexual equality, since men 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 and Orthodox Judaism forbid public exposure of the female breasts.
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
- 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
- Aberrations of normal development and involution
- cyclical nodularity
- cysts
- fibroadenoma - benign tumor
- Duct ectasia/Periductal masbreastis
- Fibrocystic disease/Fibrocystic changes
- Cysts
- Epithelial hyperplasia
- Epithelial metaplasia
- Papillomas
- Adenosis
- Pregnancy-related
- galactocoele
- puerperal abscess
Malignant breast disease
- Breast cancer
- Carcinoma in situ
- Paget's disease of the nipple, also known as Paget's disease of the breast
References
See also
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External links
