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. Lecture Outlines
Definition
• 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; stroma 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 mammary crests, 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.
A, 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 to F, 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 mammary pit
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 areola, the circular area of skin around the nipple.
The smooth muscle fibers of the nipple and areola differentiate Postnatal Development of Female Breast.
A, Newborn. B, Child. C, Early puberty. D, Late puberty. E, Young adult. F, Pregnant
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.
Postnatal Development
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 and progesterone 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 Gland Structure
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 develop and
As pregnancy progresses, the breasts enlarge as a result of hypertrophy of the glandular parenchyma and engorgement with colostrum,
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.
Inset 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
Gynecomastia
The rudimentary lactiferous ducts in males normally undergo no Gynecomastia (Gr. gyne, 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) have gynecomastia.
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. Supernumerary nipples 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.
Inverted Nipples
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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