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Aging changes in the breast

Learn More. Mammalia are so named based on the presence of the mammary gland in the breast. The mammary gland is an epidermal appendage, derived from the apocrine glands. The human breast consists of the parenchyma and stroma, originating from ectodermal and mesodermal elements, respectively. Development of the human breast is distinctive for several reasons. The human breast houses the mammary gland that produces and delivers milk through development of an extensive tree-like network of branched ducts.

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It is also characterized by cellular plasticity, with extensive remodeling in adulthood, a factor that increases its susceptibility to carcinogenesis. Also, breast development occurs in distinct stages via complex epithelial—mesenchymal interactions, orchestrated by aling pathways under the regulation of systemic hormones. Congenital and acquired disorders of the breast often have a basis in development, making its study essential to understanding breast pathology.

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The human breast consists of parenchymal and stromal elements. The parenchyma forms a system of branching ducts eventually leading to secretory acini development and the stroma consists mainly of adipose tissue, providing the environment for development of the parenchyma. The process of development of the ductal system and acini is termed branching morphogenesis and although it commences in the fetus, it halts in early childhood until puberty when hormonal stimulation triggers further differentiation. Prenatal breast development can be classified into two main processes; formation of a primary mammary bud and development of a rudimentary mammary gland.

Most knowledge of morphological changes in the fetal breast comes from studies on rodents. The successive, distinct stages of intrauterine breast development described below correlate loosely with gestational age and ificant variations at similar stages can be seen.

As early as 4 to 6 weeks of gestation, mammary-specific progenitor cells may be seen.

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These discrete areas of proliferation extend in a line between the fetal axilla and inguinal region and form two ridges called the mammary crests or milk lines Fig. Development of the mammary gland. A Ventral view of an embryo at days gestation showing mammary crests.

B Similar view at 6-week gestation showing the remains of the mammary crests. C Transverse section of a mammary crest at the site of the developing mammary gland. D—F Similar sections showing successive stages of breast development between the 12 th week of gestation and birth.

Most of the mammary crest atrophies except for paired solid epithelial masses in the pectoral region at the fourth intercostal space, which form the primary mammary buds. Toward the end of the first trimester 21 the primary mammary buds begin to grow downwards into the underlying mesenchyme, under an inductive influence of regulatory factors secreted by the mesenchyme. At the end of the first trimester of pregnancy, a well-defined mammary bud penetrating into the upper dermis can be observed.

Breast ironing / flattening – advice for practitioners

Secondary epithelial buds appear from the indentations on the main mammary bud. By 6 months of gestational age, the basic framework of the gland is established. A well-defined tubular architecture in a bed of dense fibroconnective tissue stroma is noted at this stage. Repeated branching of the secondary epithelial buds and canalization occur in the third trimester. Although most sources agree these secondary processes end in rudimentary lobular structures or end buds, 3623 some argue that the breast at birth does not contain any evidence of lobules, only ductal structures with surrounding stroma.

The epidermis in the region of the future nipple becomes depressed, forming the mammary pit during the third trimester Fig. The nipple is created with smooth muscle fibers aligned in a circular and longitudinal fashion. During the final weeks of gestation, the loose fibroconnective tissue stroma increases in vascularity. Due to a complex interplay between fetal, placental, and maternal hormones that has not yet been elucidated, 14 limited secretory activity in the late-term fetus and newborn infant may occur.

At term, approximately 15 to 20 lobes of glandular tissue have formed, each containing a lactiferous duct that opens onto the breast surface through the mammary pit.

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Both the surrounding skin and the fibrous suspensory ligaments of Cooper that anchor the breast to the pectoralis major fascia provide support to the breast. The first 2 years of life are a critical period for some aspects of breast maturation as well as involution. Soon after birth, the nipples become everted from proliferation of the underlying mesoderm, 13 and the areolae increase in pigmentation.

Overview of the breast

Development of erectile tissue in the nipple areolar complex increases response of the nipple to stimulation. Nipples that remain inverted until puberty are not uncommon.

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An increase in vascularity of the gland stroma soon after birth causes a visible difference between the light periductal connective tissue and the denser supporting stroma. The most well-accepted morphological and functional maturation stages from birth to 2 years have been described by Anzbagahan et al. Human breast development. J Mammary Gland Biol Neoplasia ;5 2 — The morphological changes begin in the immediate postnatal period and do not follow a linear progression. The functional changes from birth to 2 years follow a more linear progression than do the morphological changes.

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Many combinations of morphological type and functional stage can occur due to the wide variations in infant breast development. The time taken for the glands to regress to this stage of quiescence varies. Sexually dimorphic development of the breast first begins at puberty and unlike the preceding stages of development, pubertal changes are heavily under the influence of sex hormones, in particular estrogen.

Tanner described the most well-accepted macroscopic stages of development in the breast at puberty Fig. At this point, there is no additional development of the stroma or parenchyma beyond what has occurred in infancy. Breast development is generally the first secondary sexual characteristic to develop, preceding pubic hair development by about 6 months.

No breast development by 14 years of age in girls should prompt further investigation. Tanner stages of breast development. Variations in pattern of pubertal changes in girls.

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Arch Dis Child ;— Copyright BMJ Publishing. Tanner stage 2 involves formation of the breast bud with elevation of the nipple as well as a small mound of breast tissue along with enlargement of the diameter of the areola. ificant variations in breast development occur in individuals at the same age based on level of pubertal maturation, ethnicity, 36 and hormonal concentrations. Clinically, Tanner stage 2 of breast development correlates with the entity of thelarche.

Tanner stage 3, attained at an average age of No separation of the contours is noted at this time. During Tanner stage 4, at the average age of 13 to 14 years, there is enlargement of the nipple and areola, leading to the formation of a secondary mound on the breast. Menarche tends to occur between Tanner stage 3 and Tanner stage 4. Tanner stage 5 is characterized by the recession of the areola on to the breast with resulting loss of the separation of contours. This stage is attained by an average age of 15 years.

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Also, the breast bud stage can persist from 6 months to 2 years before advancing to Tanner stage 3. After or during these stages of development, breast shrinkage may occur if there is weight loss due to decrease in adipose tissue. ificant development of the nipple also occurs during puberty. Underlying the extensive tissue remodeling that occurs at puberty is a mammary cell hierarchy composed of multipotent stem and lineage-restricted progenitor cells.

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Following a period of stromal changes, ductal elongation and dichotomous branching occurs, with both these events being under the influence of estrogen. During puberty, the epithelium forms into a branching, bilayered ductal structure, consisting of an outer basal myoepithelial layer of cells and an inner luminal cell layer that can be divided further into ductal luminal cells, lining the inside of the ducts, and alveolar luminal cells, which secrete milk during lactation Fig. Pubertal breast development. A Carmine-stained whole-mount preparation of the advancing edge arrow of the parenchyma from a year-old girl.

B Hematoxylin- and eosin-stained developing breast of year-old girl showing solid end bud-like structures denoted teb and lateral buds arrows. C Coronal section of breast of year-old girl. D Higher power view of panel C, arrows indicate ducts and unfilled arrowhe indicate duct termini. E Histology section of the peripheral region of parenchyma seen in C. F Carmine-stained whole mount preparation of breast from year-old nulliparous woman.

Dense breasts: answers to commonly asked questions

A segmental duct divides into two subsegmental ducts sswhich then lead to the terminal duct lobular units tdlu. G Electron micrograph of a normal adult subsegmental duct. The bilayered histology with paler luminal cells ldarker basal myoepithelial cells m is evident.

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An intraepithelial lymphocyte arrow is also seen. H Electron micrograph of a terminal duct lobular unit showing two basal clear cells.

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