| Normal
Breast Development
What
is normal breast development?
Breast development is a vital part of reproduction in the human female.
Unlike other mammals, however, human females are the only ones who develop
full breasts long before they are needed to nurse their offspring.
Breast development
occurs in distinct stages throughout a woman’s life, first before birth,
and again at puberty and during the childbearing years. Changes also
occur to the breasts during menstruation and when a woman reaches menopause.
The development
and kinds of breast changes that take place are directly related to
age. There three phases of development: lobule development, which takes
place between the ages of 10 and 25; glandular development, which is
under the influence of menstrual hormones and occurs between the ages
of about 13 and 45, and involution, or shrinkage of the milk ducts,
which begins from about age 35 on.
When does
breast development begin?
This first stage of development begins at about six weeks of fetal development
with a thickening called the mammary ridge or the milk line. By six
months of development this extends all the way down to the groin, but
then regresses. At this time, solid columns of cells form from each
breast bud, with each column becoming a separate sweat gland. Each of
these has its own separate duct leading to the nipple. By the final
months of fetal development, these columns have become hollow, and by
the time a female infant is born, a nipple and the beginnings of the
milk-duct system have formed.
What breast
changes happen at puberty?
As a girl approaches adolescence, the first outward signs of breast
development begin to appear. When the ovaries start to secrete estrogen,
fat in the connective tissue begins to accumulate causing the breasts
to enlarge. The duct system also begins to grow. Usually the onset of
these breast changes is also accompanied by the appearance of pubic
hair and hair under the arms.
Once ovulation and
menstruation begin, the maturing of the breasts begins with the formation
of secretory glands at the end of the milk ducts. The breasts and duct
system continue to grow and mature, with the development of many glands
and lobules. The rate at which breasts grow varies greatly and is different
for each young woman.
What cyclical
changes occur to the breasts during menstruation?
Each month, women experience fluctuations in hormones that make up the
normal menstrual cycle. Estrogen, which is produced by the ovaries in
the first half of the menstrual cycle, stimulates the growth of milk
ducts in the breasts. The increasing level of estrogen leads to ovulation
halfway through the cycle, and then the hormone progesterone takes over
in the second half of the cycle, stimulating the formation of the milk
glands. These hormones are believed to be responsible for the cyclical
changes such as the swelling, pain, and tenderness that many women experience
in their breasts just before menstruation.
During menstruation,
many women also experience changes in breast texture, with breasts feeling
particularly lumpy. These are the glands in the breast enlarging to
prepare for a possible pregnancy. If pregnancy does not occur, the breasts
return to normal size. Once menstruation begins, the cycle begins again.
What happens
to the breasts during pregnancy and lactation?
Many physicians believe the breasts are not fully mature until a woman
has given birth and produced milk. Breast changes are one of the earliest
signs of pregnancy -
a result of the pregnancy hormone, progesterone. In addition, the areolas
(the dark areas of skin that surround the nipples of the breasts) begin
to swell followed by the rapid swelling of the breasts themselves. Most
pregnant women experience tenderness down the sides of the breasts and
tingling or soreness of the nipples because of the growth of the milk
duct system and the formation of the many more lobules.
By the fifth or
sixth month of pregnancy, the breasts are fully capable of producing
milk. As in puberty, estrogen controls the growth of the ducts and progesterone
controls the growth of the glandular buds. Many other hormones, such
as follicle stimulating hormone (FSH), luteinizing hormone (LH), prolactin,
oxytocin, and human placental lactogen (HPL) also play vital roles in
milk production.
Other physical changes,
such as the prominence of the blood vessels in the breast and the enlargement
and darkening of the areola occur. All of these changes are in preparation
for breastfeeding the baby after birth.
What happens
to the breasts at menopause?
By the time a woman reaches her late 40s and early 50s, menopause is
beginning or is well underway. At this time, the levels of estrogen
and progesterone begin to fluctuate, with levels of estrogen dramatically
decreasing. This leads to many of the symptoms commonly associated with
menopause. With this reduction in the stimulation by estrogen to all
tissues of the body, including the breast tissue, there is a reduction
in the glandular tissue of the breasts. Without estrogen, the connective
tissue of the breast becomes dehydrated and inelastic, and the breast
tissue, which was prepared to make milk, shrinks and loses shape. This
leads to the "sagging" of the breasts often associated with
women of this age.
Women who are on
hormone replacement therapy may experience some of the premenstrual
breast symptoms that they experienced while they were still menstruating,
which can even include tenderness and swelling. However, if there was
sagging of the breasts before menopause, this is not reversed with hormone
replacement therapy.
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