Anatomy and physiology of the
Women and men both have breasts, but women have more breast tissue than men.
Each breast lies over a muscle of the chest called the pectoral muscle. The female
breast covers a fairly large area. It extends from just below the collarbone
(clavicle), to the armpit (axilla) and across to the breastbone (sternum).
The breast is a mass of glandular, fatty and connective tissue. The breast is made
lobules – glands that produce milk
ducts – tubes that carry milk from the lobules to the nipple
fatty and connective tissue – surrounds and protects the ducts and
lobules and gives shape to the breast
areola – the pink or brown, circular area around the nipple that contains
small sweat glands, which release (secrete) moisture as a lubricant during
nipple – the area at the centre of the areola where the milk comes out
Ligaments support the breast. They run from the skin through the breast and
attach to muscles on the chest.
There are several major nerves in the breast area, including nerves in the chest and
arm. There are also sensory nerves in the skin of the chest and axilla.
The lymphatic system of the breast
The breast has many blood vessels and lymph vessels. Lymph vessels are thin
tubes similar to blood vessels. They collect and move lymph fluid away from the
breast into small bean-shaped masses of lymphatic tissue, called lymph nodes, in
the area around the breast. The lymph vessels and lymph nodes are part of
the lymphatic system, which helps fight infections.
The breast lymph nodes include:
supraclavicular nodes – above the collarbone
infraclavicular (or subclavicular) nodes – below the collarbone
axillary nodes – in the armpit (axilla)
internal mammary nodes – inside the chest around the breastbone
Axillary lymph nodes
There are about 30–50 lymph nodes in the axilla. The number varies from woman
The axillary lymph nodes are divided into 3 levels according to how close they are
to the pectoral muscle on the chest:
level I (low axilla) – located in the lower or bottom part of the armpit,
along the outside border of the pectoral muscle
level II (mid axilla) – located in the middle part of the armpit, beneath
the pectoral muscle
level III (high axilla) – located below and near the centre of the
collarbone, above the breast area and along the inside border of the
When breast cancer spreads, it usually goes to level I lymph nodes first, to level II
next and then to level III.
Breast tissue changes at different times during a woman’s life. It changes during
puberty, during the menstrual cycle, during pregnancy and after menopause.
Female breasts do not begin growing until puberty (around 10–12 years of age). At
this time, the breasts respond to hormonal changes (mostly increased estrogen and
progesterone) in the body and begin to develop. During puberty, the breast ducts
and milk glands grow. The breast skin stretches as the breasts grow, creating a
rounded appearance. Young women tend to have denser breasts (more glandular
tissue) than older women.
In older women, much of the glandular and ductal tissue is replaced with fatty
tissue and breasts become less dense. Ligaments also lose their elasticity when
women age, causing the breasts to sag.
The size and shape of women’s breasts vary considerably. Some women have a
large amount of breast tissue and have larger breasts. Others have a smaller
amount of tissue with little breast fat. A woman’s breasts are rarely the same size.
Often one breast is slightly larger or smaller, higher or lower or shaped differently
than the other.
Hormones and the breast
Estrogen is the main female hormone. It influences female sexual characteristics,
such as breast development, and it is necessary for reproduction. Most of the
estrogen in a woman’s body is made by the ovaries, though a small amount is
made by the adrenal glands.
Progesterone is the other female sex hormone made in the ovaries. Its role is to
prepare the uterus (womb) for pregnancy and the breasts for producing milk for
The breast tissues are exposed to monthly cycles of estrogen and progesterone
throughout a woman’s childbearing years.
In the first part of the menstrual cycle, estrogen stimulates the growth of
the milk ducts.
Progesterone takes over in the second part of a woman’s menstrual cycle,
stimulating the lobules.
After menopause, the monthly cycle of estrogen and progesterone end. However,
the adrenal glands continue to produce estrogen so that a woman keeps her sexual
The breast’s main function is to produce, store and release milk to feed a baby. Milk
is produced in lobules throughout the breast when they are stimulated by hormones
in a woman’s body after giving birth. The ducts carry the milk to the nipple. Milk
passes from the nipple to the baby during breast-feeding.
Anatomy and Physiology of the Breast
Although both men and women have breasts, it is in the female that the breast
becomes prominent and a vital component of her persona. In the male, the
breast is rudimentary.
The female breast is a symbol of womanhood and femininity but, at the same
time, it has an important function. It is an organ that, with appropriate
stimulation, will produce milk. Breast milk comes from tiny glands within the
breast that resemble bunches of grapes. Breast milk is essential for the
sustenance and growth of the newborn baby.The breast is in fact a modified
sweat gland. But, while a sweat gland secretes sweat (perspiration), the
breast / mammary gland secretes milk.
The anatomy of the breast is quite simple. It is made up of about eighteen
lobules of glandular tissue. These lobules resemble bunches of grapes and
each grape represents the secreting unit, called alveolus (pleural: alveoli). The
alveolus consists of cells, which line the unit and produce the milk.
Blood supply to the breast
The main blood supply comes from the internal mammary artery, that comes
off the subclavian artery, which supplies the arm. This is one of the main
branches of the arch of the aorta. Additional supplies come from branches of
the axillary artery and from the intercostal arteries of the pectoralis major
muscle overlying the breast. The venous drainage corresponds with the
The physiology of the breast is directly dependent on parts of the body's
endocrine system. This system is essential in controlling the function of the
human body. This is done by the production of hormones by these endocrine
glands. These hormones are chemical messengers that circulate in the blood
stream and act on organs remote from their organ of primary secretion.
Gland Hormone Physiology
With regard to breast function, at birth the breast is just a little nipple bud with
essentially no function. At puberty, the breasts begin to enlarge, under the
influence of the hormones oestrogen and progesterone.The hormonal flux
associated with the menstrual cycle is dependent on oestrogen and
During pregnancy, the pituitary secretes the hormone prolactin (luteotrophic
hormone) which initiates and stimulates milk production (lactogenesis). This
prolactin hormone is stimulated by oestrogen and inhibited by progesterone.
Post Pregnancy: With the disappearance of the corpus luteum of pregnancy
and the expulsion of the placenta, the levels of progesterone drop
precipitously. Thus the unopposed action of oestrogen stimulates prolactin
production, which in turn stimulates the formation of milk. The feeding baby,
by its sucking action on the nipple, expresses milk from the breast ducts, but it
cannot get at the milk lying deep within the aveoli. Here again another
hormone, called oxytocin, comes into action. Stimulation of the nipples by
sucking sends nerve impulses to the brain (hypothalamus). The brain in turn
activates the pituitary to produce oxytocin, which reaches the breast via the
The woman's monthly "periods" are again harmoniously controlled. The
breasts also enlarge premenstrually and occasionally become painful. This is
called cyclical mastalgia. This pain disappears with the onset of menstruation,
as the breast contracts.
Shape and form
The shape and form of the breast is basically determined by the genes and is
thus inherited. The factors that determine the appearance of the breasts are:
• The amount of fat in the breast. The glandular tissue is similar in small and
large breasts. It is mainly the fat that determines size. Thus losing weight by
diet and exercise will probably decrease the size of the breasts to a certain
• The shape of the breast is strongly influenced by the triangle of skin, which
extends from the chin to fan out over the breast. This triangle of skin is
supported by the fan shaped platysma muscle. This skin triangle together with
its supporting fan shape platysma muscle is sometimes referrd to as the
"natural bra". By exposing her lower teeth, the women contracts the platysma
muscle, and this will lift the breast upwards (the natural bra effect).
• Coopers ligaments also contribute to breast firmness.Thus by looking after
the skin with a good skin oil or cream, and by doing the correct exercises
(push ups and swimming are excellent breast toners), and finally by eating a
healthy diet, the condition of the breasts can be maintained to a certain extent.