Science Fair Project Encyclopedia
The term breast can refer to the upper ventral region of the human torso. Alternatively the term is used for each of two parts of that, especially for women: the breasts are parts of the female human body that contain the organs that secrete milk used to feed infants. Males also have breasts and are born with the main milk ducts intact, but while the gland that produces milk is present in the male, it normally remains undeveloped. In some situations male breast development does occur, a condition called gynecomastia. Milk production can also occur in both men and women as a rare side-effect of some medicinal drugs (such as some antipsychotic medication). Both sexes have a large concentration of blood vessels and nerves in their nipples.
A woman's 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.
Important parts of the breasts include mammary glands, the axillary tail (tumours frequently occur here), the lobules, Cooper's ligaments, the areola and the nipple. The nipple is supplied by the T4 dermatome.
It is typical for one of a woman's breasts to be larger than the other one; statistically it is more common for the left breast to be the larger. In some rare cases, one breast may be greatly larger or smaller than the other, or fail to develop during puberty.
During puberty, sex hormones, chiefly estrogen, cause the development of a woman's breasts. This hormone has been demonstrated to cause the development of woman-like, enlarged breasts in men, a condition called gynecomastia.
As breasts are mostly composed of adipose tissue, their size can change over time if the woman gains or loses weight. It is typical for them to grow in size during pregnancy, mainly due to hypertrophy of the exocrine gland in response to prolactin.
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.
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 secondary sex characteristics. Some biologists believe that the shape of female breasts evolved as a frontal counterpart to that of the buttocks.
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.
A common misconception is that human female breasts are shaped the way that they are so that they can feed babies by producing milk. The mammary glands that secrete the milk from the breasts make up a relatively small fraction of the overall breast tissue. Most of the human female breast is actually adipose tissue (fat) and connective tissue. Breast size does not make any difference to a woman's ability to nurse a baby.
Because some cultures place a high value on symmetry of the female human form, and because women often identify their femininity and sense of self with their breasts, many women in developed countries undergo breast reconstruction after mastectomy for breast cancer.
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. Topless is the state of having bare breasts. For more on modesty regarding breasts see Nudity.
There are many slang terms for the breasts.
Because the breasts are sexually sensitive in many cases, many cultures view them as private or 'dirty', or interpret their display as sexual (in some cases, even when they are being used for their primary purpose of nursing offspring) -- this has led, in the past, to such events as women being arrested for indecent exposure for breastfeeding their children in public.
Opinions differ as to whether this sexual response on the part of others is the result of breasts, in general, being covered or uncovered; in addition to the above references, see also Naturism.
In a different sort of response, women in some areas and cultures are approaching the issue as one of equality: men may bare their chests, but women are forbidden. In the United States, the Topfree equality movement seeks to redress this imbalance; this movement has won a decision in 1992 in a New York Court of Appeals which seems to substantially support their assertions. A similar movement succeeded in most parts of Canada in the 1990s, and in some countries women have never been forbidden to bare their chests.
Historically, breasts were regarded as fertility symbols due to their association with life-giving milk. Ancient statues of goddesses — 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.
Disorders of the breasts
Infections and inflammations
- 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
- Mondor's disease
- duct ectasia /periductal masbreastis
Benign breast disease
- Aberrations of normal development and involution
- Epithelial hyperplasia *
- puerperal abscess
Malignant breast disease
- breast cancer (mammary carcinoma)
- carcinoma in situ
- Paget's disease of the nipple or Paget's disease of the breast
- La Leche League
- intimate parts
- breast reconstruction
- breast implant
- breast fetishism
- mammary intercourse
- topfree equality
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