Breast
Breast | |
---|---|
Details | |
Artery | Internal thoracic artery |
Vein | Internal thoracic vein |
Identifiers | |
Latin | mamma (mammalis 'of the breast')[1] |
MeSH | D001940 |
TA98 | A16.0.02.001 |
TA2 | 7097 |
FMA | 9601 |
Anatomical terminology |
The breast is one of two prominences located on the upper
In females, it serves as the
Humans are the only animals with permanent breasts. At
Etymology and terminology
The English word breast derives from the
A large number of colloquial terms for breasts are used in English, ranging from fairly polite terms to vulgar or slang.[7] Some vulgar slang expressions may be considered to be derogatory or sexist to women.[8]
Evolutionary development
Humans are the only mammals whose breasts become permanently enlarged after sexual maturity (known in humans as puberty). The reason for this evolutionary change is unknown.[9] Several hypotheses have been put forward:
A link has been proposed to processes for synthesizing the
It has been suggested by zoologists Avishag and Amotz Zahavi that the size of the human breasts can be explained by the handicap theory of sexual dimorphism. This would see the explanation for larger breasts as them being an honest display of the women's health and ability to grow and carry them in her life. Prospective mates can then evaluate the genes of a potential mate for their ability to sustain her health even with the additional energy demanding burden she is carrying.[13][14]
The zoologist Desmond Morris describes a sociobiological approach in his science book The Naked Ape. He suggests, by making comparisons with the other primates, that breasts evolved to replace swelling buttocks as a sex signal of ovulation. He notes how humans have, relatively speaking, large penises as well as large breasts. Furthermore, early humans adopted bipedalism and face-to-face coitus. He therefore suggested enlarged sexual signals helped maintain the bond between a mated male and female even though they performed different duties and therefore were separated for lengths of time.[15][14][16]
The study The evolution of the human breast (2001) proposed that the rounded shape of a woman's breast evolved to prevent the sucking infant offspring from suffocating while feeding at the teat; that is, because of the human infant's small jaw, which did not project from the face to reach the nipple, they might block the
Ashley Montague (1965) proposed that breasts came about as an adaptation for infant feeding for a different reason, as early human ancestors adopted bipedalism and the loss of body hair. Human upright stance meant infants must be carried at the hip or shoulder instead of on the back as in the apes. This gives the infant less opportunity to find the nipple or the purchase to cling on to the mother's body hair. The mobility of the nipple on a large breast in most human females gives the infant more ability to find it, grasp it and feed.[12]
Other suggestions include simply that permanent breasts attracted mates, that "pendulous" breasts gave infants something to cling to, or that permanent breasts shared the function of a camel's hump, to store fat as an energy reserve.[9]
Structure
In women, the breasts overlie the
The dimensions and weight of the breast vary widely among women. A small-to-medium-sized breast weighs 500 grams (1.1 pounds) or less, and a large breast can weigh approximately 750 to 1,000 grams (1.7 to 2.2 pounds) or more. In terms of composition, the breasts are about 80 to 90%
Glandular structure
The breast is an
Lymphatic drainage
Approximately 75% of the
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.g.
While it is a common belief that breastfeeding causes breasts to sag,
The base of each breast is attached to the chest by the deep fascia over the pectoralis major muscles. The space between the breast and the pectoralis major muscle, called retromammary space, gives mobility to the breast. The chest (
Development
The breasts are principally composed of adipose,
their sizes and volumes fluctuate according to the hormonal changes particular to thelarche (sprouting of breasts), menstruation (egg production), pregnancy (reproduction), lactation (feeding of offspring), and menopause (end of menstruation).Puberty
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.) are illustrated in the five-stage Tanner scale.[37]
During
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 21. Mammoplasia (breast enlargement) in girls begins at puberty, unlike all other primates in which breasts enlarge only during lactation.[20]
Changes during the menstrual cycle
During the menstrual cycle, the breasts are enlarged by premenstrual water retention and temporary growth.[39]
Pregnancy and breastfeeding
The breasts reach full maturity only when a woman's first pregnancy occurs.
Pregnancy causes elevated levels of the hormone prolactin, which has a key role in the production of milk. However, milk production is blocked by the hormones progesterone and estrogen until after delivery, when progesterone and estrogen levels plummet.[42]
Menopause
At menopause, breast atrophy occurs. 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
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.[42]
Full-term newborns have an instinct and a need to suck on a nipple, and breastfed babies nurse for both nutrition and for comfort.[43] Breast milk provides all necessary nutrients for the first six months of life, and then remains an important source of nutrition, alongside solid foods, until at least one or two years of age.
Clinical significance
The breast is susceptible to numerous benign and malignant conditions. The most frequent benign conditions are
Breast cancer
Breast cancer is the most common cause of cancer death among women
Male breasts
Both females and males develop breasts from the same embryological tissues. Anatomically, male breasts do not normally contain lobules and acini that are present in females. In rare instances, it is possible for very few lobules to be present, this makes it possible for some men to develop lobular carcinoma of the breast.[47] 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.[48] Around 70% of boys temporarily develop breast tissue during adolescence.[32] The condition usually resolves by itself within two years.[32] When male lactation occurs, it is considered a symptom of a disorder of the pituitary gland.
Plastic surgery
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.[49] Breast augmentation and breast lift (mastopexy) procedures are done only for cosmetic reasons, whereas breast reduction is sometimes medically indicated.[19] In cases where a woman's breasts are severely asymmetrical, surgery can be performed to either enlarge the smaller breast, reduce the size of the larger breast, or both.[19]
Breast augmentation surgery generally does not interfere with future ability to breastfeed.[50] Breast reduction surgery more frequently leads to decreased sensation in the nipple-areola complex, and to low milk supply in women who choose to breastfeed.[50] Implants can interfere with mammography (breast x-rays images).
Society and culture
General
In
There is a long history of female breasts being used by comedians as a subject for comedy fodder (e.g., British comic Benny Hill's burlesque/slapstick routines).[57]
Art history
In European pre-historic societies, sculptures of female figures with pronounced or highly exaggerated breasts were common. A typical example is the so-called
Many female deities representing love and fertility were associated with breasts and breast milk. Figures of the Phoenician goddess
Female breasts were also prominent in
During the middle of the first millennium BC, Greek culture experienced a gradual change in the perception of female breasts. Women in art were covered in clothing from the neck down, including female goddesses like
Body image
Many women regard their breasts as important to their
Clothing
Because breasts are mostly fatty tissue, their shape can—within limits—be molded by clothing, such as foundation garments. Bras are commonly worn by about 90% of Western women,[62][63][64] and are often worn for support.[65] The social norm in most Western cultures is to cover breasts in public, though the extent of coverage varies depending on the social context. Some religions ascribe a special status to the female breast, either in formal teachings or through symbolism.[66] Islam forbids free women from exposing their breasts in public.
Many cultures, including Western cultures in North America, associate breasts with sexuality and tend to regard bare breasts as
Social attitudes and laws regarding breastfeeding in public vary widely. 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[67][68] due to actual or potential objections by other people, negative comments, or harassment.[69] It is estimated that around 63% of mothers across the world have publicly breast-fed.[70] Bare-breasted women are legal and culturally acceptable at public beaches in Australia and much of Europe.[citation needed] Filmmaker Lina Esco made a film entitled Free the Nipple, which is about "...laws against female toplessness or restrictions on images of female, but not male, nipples", which Esco states is an example of sexism in society.[57]
Sexual characteristic
In some cultures, breasts play a role in
Many people regard bare female breasts to be aesthetically pleasing or
Research conducted at the Victoria University of Wellington showed that breasts are often the first thing men look at, and for a longer time than other body parts.[75] The writers of the study had initially speculated that the reason for this is due to endocrinology with larger breasts indicating higher levels of estrogen and a sign of greater fertility,[75][76] but the researchers said that "Men may be looking more often at the breasts because they are simply aesthetically pleasing, regardless of the size."[75]
Some women report achieving an orgasm from nipple stimulation, but this is rare.[77][78] Research suggests that the orgasms are genital orgasms, and may also be directly linked to "the genital area of the brain". In these cases, it seems that sensation from the nipples travels to the same part of the brain as sensations from the vagina, clitoris and cervix. Nipple stimulation may trigger uterine contractions, which then produce a sensation in the genital area of the brain.[79][80][81]
Anthropomorphic geography
There are many mountains named after the breast because they resemble it in appearance and so are objects of religious and ancestral veneration as a fertility symbol and of well-being. In Asia, there was "Breast Mountain", which had a cave where the
Measurement
The
See also
References
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There are some females who appear to find no erotic satisfaction in having their breasts manipulated; perhaps half of them derive some distinct satisfaction, but not more than a very small percentage ever respond intensely enough to reach orgasm as a result of such stimulation (Chapter 5). [...] Records of females reaching orgasm from breast stimulation alone are rare.
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- Hollander, Anne (1993). Seeing through clothes. Berkeley: University of California Press. ISBN 978-0-520-08231-1.
- Morris, Desmond The Naked Ape: a zoologist's study of the human animal Bantam Books, Canada. 1967
- Yalom, Marilyn (1998). A history of the breast. London: Pandora. ISBN 978-0-86358-400-8.
- Venes, Donald (2013). Taber's cyclopedic medical dictionary. Philadelphia: F.A. Davis. ISBN 978-0-8036-2977-6.
- Lawrence, Ruth (2016). Breastfeeding : a guide for the medical profession, 8th edition. Philadelphia, PA: Elsevier. ISBN 978-0-323-35776-0.
External links
- "Are Women Evolutionary Sex Objects?: Why Women Have Breasts". Archived from the original on 2 December 2011.