The
breast is the upper
ventral region of an animal’s
torso, particularly that of
mammals, including
human
beings. The breasts of a female
primate’s body contain the
mammary glands, which secrete
milk used to feed infants.
Both men and women develop breasts from the same
embryological tissues. However, at puberty female
sex hormones, mainly estrogens, promote breast development, which
does not happen with men. As a result women's breasts become far
more prominent than men's.
Anatomy
Breasts are modified
sudoriferous glands
which produce
milk in women, and in some rare
cases, in men. Each breast has one
nipple
surrounded by the
areola. The areola is
colored from pink to dark brown and has several
sebaceous glands. In women, the larger
mammary glands within the breast
produce the milk. They are distributed throughout the breast, with
two-thirds of the tissue found within 30 mm of the base of the
nipple. These are drained to the nipple by between 4 and 18
lactiferous ducts, where each duct has its own opening.
The network formed by these ducts is complex, like the tangled
roots of a tree. It is not always arranged radially, and branches
close to the nipple. The ducts near the nipple do not act as milk
reservoirs; Ramsay
et al. have shown that conventionally
described
lactiferous sinuses do not, in fact, exist.
Instead, most milk is actually in the back of the breast, and when
suckling occurs, the smooth muscles of the gland push more milk
forward.
The remainder of the breast is composed of
connective tissue (
collagen and
elastin),
adipose tissue (fat), and
Cooper's ligaments. The ratio of glands
to adipose tissues rises from 1:1 in nonlactating women to 2:1 in
lactating women.
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 towards the
axillae and is known as the
tail of Spence. 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. (For further
explanation, see
anatomical
terms of location.)
The
arterial blood supply to the breasts is derived
from the
internal thoracic
artery (formerly called 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. Both sexes have a large concentration of
blood vessels and nerves in their
nipples. The nipples of both women and men can become erect in
response to sexual stimuli, and to cold.
The breast is
innervated
by the anterior and lateral cutaneous branches of the fourth
through sixth intercostal
nerves. The nipple
is supplied by the T4
dermatome.
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
breast cancer is a common cancer and
cancer cells can break away from a
tumour and spread to other parts of the body through
the lymph system by
metastasis.
Shape and support
Breasts vary in size, shape and position on a woman's chest, and
their external appearance is not predictive of their internal
anatomy or lactation potential. The natural shape of a woman's
breasts is primarily dependent on the support provided by the
Cooper's ligaments and the
underlying chest on which they rest (the base). The breast is
attached at its base to the chest wall by the deep fascia over the
pectoral muscles. On its
upper surface it is given some support by the covering skin where
it continues on to the upper chest wall. It is this support which
determines the shape of the breasts. In a small number of women,
the frontal ducts (
ampullae) in the breasts
are not flush with the surrounding breast tissue, which causes the
sinus area to visibly bulge outward.

Relatively round breasts which
protrude almost horizontally.
Some breasts are high and rounded, and protrude almost horizontally
from the chest wall. Such high breasts are common for girls and
women in early stages of development. The protruding or high
breasts are anchored to the chest at the base, and the weight is
distributed evenly over the area of the base of the approximately
dome- or cone-shaped breasts.
In the “low” breast, a proportion of the breasts' weight is
actually supported by the chest against which the lower breast
surface comes to rest, as well as the deep anchorage at the base.
The weight is thus distributed over a larger area, which has the
effect of reducing the strain. In both males and females, the
thoracic cavity slopes progressively
outwards from the thoracic inlet (at the top of the
breastbone) above to the lowest ribs which mark
its lower boundary, allowing it to support the breasts.
The
inframammary fold (or line, or
crease) is an anatomic structure created by adherence between
elements in the skin and underlying connective tissue and
represents the inferior extent of breast anatomy. Some teenagers
may develop breasts whose skin comes into contact with the chest
below the fold at an early age, and some women may never develop
such breasts; both situations are perfectly normal. The
relationship of the nipple position to the fold is described as
ptosis, a term also applied to
other body parts and which refers in general to drooping or
sagging. Due to breast weight and relaxation of support structures,
the nipple-areola complex and breast tissue may eventually hang
below the fold, and in some cases the breasts may extend as far as,
or even beyond, the navel. The length from the nipple to the
sternal notch (central, upper border) in the youthful breast
averages 21 cm and is a common
anthropometric figure used to assess both
breast symmetry and ptosis. Lengthening of both this measurement
and the distance between the nipple and the fold are both
characteristic of advancing grades of ptosis.
The end of the breast, which includes the nipple, may either be
flat (a 180° angle) or angled (angles lower than 180°). Breast ends
are rarely angled sharper than 60°. Angling of the end of the
breast is caused in part by the ligaments that suspend it, such
that the breast ends often have a more obtuse angle when a woman is
lying on her back. Breasts exist in a range of ratios between
length and base diameter, usually ranging from ½ to 1.
Development
Girls develop breasts during
puberty, as a
result of changing
sex hormones, chiefly
estrogen, which also has been demonstrated
to cause the development of woman-like, enlarged breasts in men, a
condition called
gynecomastia.
In most cases, the breasts fold down over the chest wall during
Tanner stage development, as shown in
this
diagram. It is typical for a woman's breasts to
be unequal in size particularly while the breasts are developing.
Statistically it is slightly more common for the left breast to be
the larger. In rare cases, the breasts may be significantly
different in size, or one breast may fail to develop
entirely.
A large 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, 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.
Changes

Breast with visible
stretchmarks.
As breasts are mostly composed of adipose tissue, their size can
change over time. This occurs for a number of reasons, most
obviously when a girl grows during
puberty
and when a woman becomes
pregnant. The
breast size may also change if she gains (or loses)
weight for any other reason. Any rapid increase
in size of the breasts can result in the appearance of
stretchmarks.
It is typical for a number of other changes to occur during
pregnancy: in addition to becoming larger, the breasts generally
become firmer, mainly due to
hypertrophy of the mammary gland in
response to the
hormone prolactin. The size of the nipples may increase
noticeably and their pigmentation may become darker. These changes
may continue during
breastfeeding. The
breasts generally revert to approximately their previous size after
pregnancy, although there may be some increased sagging and
stretchmarks.
The size of a woman's breasts may fluctuate during the
menstrual cycle, particularly with
premenstrual water retention.
An increase in breast size is a common
side effect of use of the
combined oral contraceptive
pill.
Breasts sag if the
ligaments
become elongated, a natural process that can occur over time and is
also influenced by the breast bouncing while exercising. Breasts
can decrease in size at menopause if
estrogen levels decline.
Function
Breastfeeding

An infant breastfeeding
The primary function of
mammary glands
is to nurture young by producing
breast
milk. The production of milk is called
lactation. (While the mammary glands that produce
milk are present in the male, they normally remain undeveloped.)
The orb-like shape of breasts may help limit heat loss, as a fairly
high temperature is required for the production of milk.
Alternatively, one theory states that the shape of the human breast
evolved in order to prevent infants from suffocating while feeding.
Since human infants have a small jaw (not protruding, like other
primates), the infant's nose might be blocked if the mother's chest
was too flat. According to this theory, as the human jaw receded,
the breasts became larger to compensate.
Milk production unrelated to pregnancy can also occur. This
condition, called
galactorrhea, may be
an
adverse effect of some
medicinal drugs (such as some antipsychotic medication), extreme
physical stress or endocrine disorders. If it occurs in men it is
called
male lactation, and is often
classified as a pathological symptom due to its strong correlation
to pituitary disorders. Newborn babies are often capable of
lactation because they receive the hormones
prolactin and
oxytocin via
the mother's bloodstream, filtered through the
placenta. This neonatal liquid is known
colloquially as
witch's milk.
Sexual role
Breasts play an important part in
human sexual behavior; they are also
important female
secondary
sex characteristics. Compared to other primates, human breasts
are proportionately large throughout adult females' lives and may
have evolved as a visual signal of sexual maturity and fertility.
On
sexual arousal breast size
increases,
venous patterns across the breasts
become more visible, and nipples harden. Breasts are sensitive to
touch as they have many nerve endings, and it is common to press or
massage breasts with hands during sexual intercourse (as it is with
other bodily areas representing feminine secondary sex
characteristics as well).
Oral stimulation of nipples and
breasts is also common. Some women can achieve
breast orgasms.
Some people regard exposed breasts to be
aestheticly pleasing and/or
erotic. In the
ancient
Indian work the
Kama Sutra,
marking breasts with nails and biting with teeth are explained as
erotic.
- See also: Mammary
intercourse; Toplessness; Breast fetishism; Cleavage.
Other suggested functions
Zoologists point out that no female
mammal other than the human has breasts of comparable size,
relative to the rest of the body, when not lactating and that
humans are the only
primate that has
permanently swollen breasts. This suggests that the external form
of the breasts is connected to factors other than lactation
alone.
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 while other
primates mate in the
rear-entry
position, humans, because of their upright posture, are more likely
to successfully
copulate by mating face to
face, the so-called
missionary
position. Morris suggested in 1967 that 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 may have helped found a relationship between partners
beyond merely a sexual one. However, this theory has since been
generally disregarded due to the discovery that other primates,
such as
orangutans, routinely mate in the
face-to-face position even though the females do not have prominent
breasts.
The female
gelada monkey in
estrus presents swollen breasts to signal her
reproductive status to the males. Based on that,
evolutionary psychologists suggest
that human female breasts may have evolved to permanently indicate
to human males that the female is apt for reproduction.
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 Venus of Willendorf
, one of many Paleolithic
Venus figurines with ample hips and
bosom. Artifacts such as bowls, rock carvings and sacred
statues with breasts have been recorded from 15,000 BC up to late
antiquity all across Europe, North Africa and the Middle East. 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.
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
Athena, the patron of
Athens who represented heroic endeavor. There were exceptions:
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. Although nude men were depicted standing upright,
most depictions of female nudity in Greek art occurred "usually
with drapery near at hand and with a forward-bending,
self-protecting posture". A popular legend at the time was of the
Amazons, a tribe of fierce female warriors
who socialized only with men for procreation and even removed one
breast to become better warriors. The legend was a popular motif in
art during Greek and Roman antiquity and served as an antithetical
cautionary tale.
Cultural status
In religion
Some religions afford the breast a special status, either in formal
teachings or in symbolism.
Islam forbids
public exposure of the female breasts. 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.
In Silappatikaram, Kannagi tears off her left breast and flings it on
Madurai
, cursing it, causing a devastating
fire.
In practice
Breasts are
secondary sex
characteristics and sexually sensitive. Bare female breasts can
elicit heightened
sexual desires from
men in certain cultures. Cultures that associate the breast
primarily with sex (as opposed to with breastfeeding) tend to
designate bare breasts as
indecent, and they
are not commonly displayed in public, in contrast to male chests.
Other cultures view female
toplessness
as acceptable, and in some countries women have never been
forbidden to bare their chests; in some African cultures, for
example, the thigh is highly sexualised and never exposed in
public, but the breast is not
taboo. Opinion
on the exposure of breasts often depends on the place and context,
and in some
Western societies exposure
of breasts on a beach may be 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 only restricts
exposure of the
nipples.
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 and swimming pools, but these are generally the only public
areas where exposing breasts is acceptable.
When
breastfeeding a
baby in public, legal and social rules regarding
indecent exposure and
dress codes, 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.
Clothing
Since the breasts are flexible, their shape may be affected by
clothing, and
foundation garments
in particular. A
brassiere (bra) may be
worn to give additional support and to alter the shape of the
breasts. There is some debate over whether such support is
desirable. A long term clinical study showed that women with large
breasts can suffer Myalgia, or shoulder pain as a result of bra
straps, although a well fitting bra should support most of the
breasts' weight with proper sized cups and back band rather than on
the shoulders.
Plastic surgery

Bilateral breast reduction
Plastic surgical procedures of the
breast include those for both
cosmetic and
reconstructive surgery indications.
Some women choose these procedures as a result of the high value
placed on
symmetry of the human form, and
because they identify their femininity and sense of self with their
breasts.
After
mastectomy (the surgical removal of
a breast, usually to treat
breast
cancer) some women undergo
breast reconstruction, either with
breast implants or autologous tissue
transfer, using fat and tissues from the abdomen (
TRAM flap) or back (latissiumus muscle
flap).
Breast reduction surgery is a
common procedure which involves removing excess breast tissue, fat,
and skin with repositioning of the nipple-areolar complex (NAC).
Cosmetic procedures include breast lifts (
mastopexy),
breast
augmentation with implants, and procedures that combine both
elements. Implants containing either
silicone gel or
saline are available for augmentation and
reconstructive surgeries. Surgery can repair
inverted nipples by releasing ductal tissues
which are tethering. Breast lift with or without reduction can be
part of upper body lift after massive weight loss body
contouring.
Any surgery of the breast carries with it the potential for
interfering with future breastfeeding, causing alterations in
nipple sensation, and difficulty in interpreting
mammography (xrays of the breast). A number of
studies have demonstrated a similar ability to breastfeed when
breast reduction patients are compared to control groups where the
surgery was performed using a modern pedicle surgical technique.
Plastic surgery organizations have generally discouraged elective
cosmetic breast augmentation surgery for teenage girls as the
volume of their breast tissue may continue to grow significantly as
they mature and because of concerns about understanding long-term
risks and benefits of the procedure. Breast surgery in teens for
reduction of significantly enlarged breasts or surgery to correct
hypoplasia and severe asymmetry is
considered on a case by case basis by most surgeons.
Health
Breast health factors
Factors that appear to be implicated in decreasing the risk of, or
early diagnosis 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.Healthy diet appears
to reduce the risk of breast cancer, and includes limiting dietary
fat, eating a balanced diet that includes plenty of nutrients, and
dietary fibre such as are found in fruits and vegetables, and
restricting intake of alcohol to a maximum of two drinks per day or
less.
Breast disease
Numerous abnormal breast conditions or diseases are documented. A
majority are not cancerous.
See also
Notes
- Introduction to the Human Body, fifth ed. John Wiley
& Sons, Inc.: New York, 2001. 560.
- secondary sex characteristics
- Sir Richard Burton's English translation of Kama
Sutra
- Morris (1967), pp. 64-68.
- Yalom (1998) pp. 9-16; see Eva Keuls (1993), Reign of the
Phallus: Sexual Politics in Ancient Athens for a detailed
study of male-dominant rule in ancient Greece.
- Yalom (1998), p. 18.
- Hollander (1993), p. 6.
- “They shall cover their chests” or “they should draw their
khimar (veils) over their bosoms”, depending on the translation,
Quran (24:31). Available online
- Mctiernan, Anne, M.D., Ph.D., Gralow, Julie.M.D., Talbot, Lisa,
MPH. Breast Fitness: An OptimalExercise and Health Plan for
Reducing Your Risk of Breast Cancer. St Martin's Griffin,
October, 2001. pg 135-137.
References
- Hollander, Anne Seeing through Clothes. University of
California Press, Berkeley. 1993 ISBN 0-52008-231-1
- Morris, Desmond The Naked
Ape: a zoologist's study of the human animal Bantam Books,
Canada. 1967
- Yalom, Marilyn A History of the Breast. Pandora,
London. 1998 ISBN 0-86358-400-4
External links