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Semester ii m
Development of Breast:
At the end of lecture the students will able to:
• Describe the stages of development.
• Clinical correlations of developmental anatomy of gland.
• Mammogenesis is the term use to describe the development of the mammary gland.
• The mammary gland is one of a few tissues in mammals, which can repeatedly undergo
growth, functional differentiation, and regression.
Development of Mammary Glands
Are a modified and highly specialized type of apocrine sweat
Consist of parenchyma,
which is formed from ducts, and
Parenchyma derives embryonically from surface ectoderm;
arises from surrounding mesenchyme.
Mammary buds begin to develop during the sixth week as solid
downgrowths of the epidermis into the underlying mesenchyme
These changes occur in response to an inductive influence from the
Mammary buds develop as downgrowths from thickened
, which are thickened strips of ectoderm
extending from the axillary to the inguinal regions
The mammary crests (ridges) appear during the fourth week but
normally persist in humans only in the pectoral area, where the
Each primary bud gives rise to several secondary mammary buds
that develop into lactiferous ducts and their branches
Canalization of these buds is induced by placental sex hormones
entering the fetal circulation. This process continues until late
gestation, and by term, 15 to 19 lactiferous ducts are formed.
The fibrous connective tissue and fat of the mammary gland
develop from the surrounding mesenchyme.
Ventral view of an embryo of approximately 28 days showing the mammary crests. B,
Similar view at 6
weeks showing the remains of these crests. C,
Transverse section of a mammary crest at the site of a developing
mammary gland. D
Similar sections showing successive stages of breast development between the 12th
Development of Nipples and Areola
During the late fetal period, the epidermis at the site of origin of
the mammary gland becomes depressed, forming a shallow
The nipples are poorly formed and depressed in newborn infants.
Soon after birth, the nipples
usually rise from the mammary pits
because of proliferation of the surrounding connective tissue of the
, the circular area of skin around the nipple.
The smooth muscle fibers of the nipple and areola differentiate
Postnatal Development of Female Breast.
Early puberty. D,
Late puberty. E,
Young adult. F,
female. Note that the nipple is inverted at birth (A
). Normally the nipple elevates during
childhood. Failure of this process to occur gives rise to an inverted nipple. At puberty
(12-15 years), the breasts of females enlarge because of development of the mammary
glands and the increased deposition of fat.
The rudimentary mammary glands
of newborn males and females are
Some secretion, often called "witch's milk," may be produced caused by
maternal hormones passing through the placental membrane into the fetal
Newborns breasts contain lactiferous ducts but no alveoli. Before puberty,
In females, the breasts enlarge rapidly during puberty, mainly because of
development of the mammary glands and the accumulation of the fibrous
. Full development occurs at approximately 19-20 years
The lactiferous ducts of male breasts remain rudimentary throughout life.
Embryonic development of the mammary apparatus in humans.
Mammary glands Histogenesis
Consist of 15 to 20 lobes radiating out from the nipple and are
Separated from each other by adipose and collagenous connective tissue.
Secrete milk, a fluid containing proteins, lipids, and lactose as well as
lymphocytes and monocytes, antibodies, minerals, and fat-soluble vitamins
Provide the proper nourishment for the newborn.
Develop in the same manner and are of the same structure in both sexes until
At puberty changes in the hormonal secretions in females cause further
development and structural changes within the glands.
Secretions of estrogen
from the ovaries (and later from
the placenta) and prolactin
from the acidophils of the anterior pituitary
gland initiate development of lobules
and terminal ductules.
Full development of the ductal portion of the breast requires glucocorticoids
and further activation by somatotropin.
Concomittant with these events is an increase in connective tissue and
adipose tissue within the stroma, causing the gland to enlarge.
Full development occurs at about 20 years of age
Minor cyclic changes occur during each menstrual period,
Major changes occur during pregnancy and in lactation.
After age 40 or so, the secretory portions and some of the ducts and
connective tissue elements of the breasts begin to atrophy, and they continue
The glands within the breasts are classified as compound tubuloalveolar glands,
Make 15 to 20 lobes radiating out from the nipple and separated from each other by
adipose and collagenous connective tissue.
Each lobe is drained by its own lactiferous duct leading directly to the nipple, where it
Before reaching the nipple, each of the ducts is dilated to form a lactiferous sinus for milk
storage and then narrows before passing through the nipple
Resting (Non secreting) Mammary Gland
Alveoli are not developed in nonpregnant women
nonpregnant women have the same basic architecture as the lactating
(active) mammary gland, except that they are smaller and without developed
alveoli, which occur only during pregnancy.
Lactating (Active) Mammary Glands
Activated by elevated surges of estrogen and progesterone during pregnancy
to become lactating glands to provide milk for the newborn.
Terminal portions of the ducts branch and grow and the alveoli
As pregnancy progresses, the breasts enlarge as a result of hypertrophy of
the glandular parenchyma and engorgement with colostrum,
is a protein-rich fluid, in preparation for the newborn.
Within a few days after birth, when estrogen and progesterone secretions
have subsided, prolactin, secreted by acidophils of the anterior pituitary
gland, activates the secretion of milk, which replaces the colostrum.
During pregnancy, the terminal portions of the ducts branch and grow and
develop secretory units known as alveoli
shows a longitudinal section of a gland and duct of the active
Alveoles and Alveolar Cells
The alveoli are composed of cuboidal cells partially surrounded by a meshwork of
These secretory cells possess abundant RER and mitochondria, several Golgi complexes,
many lipid droplets, and numerous vesicles containing caseins (milk proteins) and
Not all regions of the alveolus are in the same stage of production, because different acini
display varying degrees of preparation for synthesis of milk substances.
Electron micrograph of an acinar cell
Clinical Developmental Anatomy of Mammary Gland
The rudimentary lactiferous ducts in males normally undergo no
, woman + mastos
, breast) refers to the
development of the rudimentary lactiferous ducts in the male mammary
During midpuberty, approximately two thirds of boys develop varying
degrees of hyperplasia of the breasts. This subareolar hyperplasia may
A decreased ratio of testosterone to estradiol is found
80% of males with Klinefelter syndrome (XXY)
Absence of Nipples (Athelia) or Breasts (Amastia)
Rare congenital anomalies may occur bilaterally or unilaterally.
Result from failure of development or disappearance of the mammary crests.
May also result from failure of mammary buds to form.
More common is hypoplasia of the breast
, often found in association with
gonadal agenesis and Turner syndrome .
Aplasia of Breast
The breasts of a postpubertal female often differ in size. Marked differences
are regarded as anomalies because both glands are exposed to the same
In these cases, there is often associated rudimentary development of muscles
of the thoracic wall, usually the pectoralis major
Supernumerary Breasts and Nipples
An extra breast (polymastia
) or nipple (polythelia
) occurs in approximately
1% of the female population as an inheritable condition.
An extra breast or nipple usually develops just inferior to the normal breast.
are also relatively common in males; often they
Less commonly, supernumerary breasts
or nipples appear in the axillary or
abdominal regions of females developing from extra mammary buds that
develop along the mammary crests. They become more obvious in women
Approximately one third of affected persons have two extra nipples or
Supernumerary mammary tissue
very rarely occurs in a location other
than along the course of the mammary crests. It probably develops from
tissue that was displaced from these crests.
Nipples fail to elevate above the skin surface after birth, remaining in their
May make breast-feeding of an infant difficult
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