anatomy and physiology of breast pdf

Anatomy And Physiology Of Breast Pdf

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Mammary gland

A mammary gland is an exocrine gland in humans and other mammals that produces milk to feed young offspring. Mammals get their name from the Latin word mamma , "breast". The mammary glands are arranged in organs such as the breasts in primates for example, humans and chimpanzees , the udder in ruminants for example, cows, goats, and deer , and the dugs of other animals for example, dogs and cats. Lactorrhea , the occasional production of milk by the glands, can occur in any mammal, but in most mammals, lactation , the production of enough milk for nursing , occurs only in phenotypic females who have gestated in recent months or years.

It is directed by hormonal guidance from sex steroids. In a few mammalian species, male lactation can occur. With humans, male lactation can occur only under specific circumstances.

The basic components of a mature mammary gland are the alveoli hollow cavities, a few millimeters large lined with milk-secreting cuboidal cells and surrounded by myoepithelial cells. These alveoli join to form groups known as lobules.

Each lobule has a lactiferous duct that drains into openings in the nipple. The myoepithelial cells contract under the stimulation of oxytocin , excreting the milk secreted by alveolar units into the lobule lumen toward the nipple.

All the milk-secreting tissue leading to a single lactiferous duct is called a "simple mammary gland"; in a "complex mammary gland" all the simple mammary glands serve one nipple.

Humans normally have two complex mammary glands, one in each breast, and each complex mammary gland consists of 10—20 simple glands. The presence of more than two nipples is known as polythelia and the presence of more than two complex mammary glands as polymastia.

Maintaining the correct polarized morphology of the lactiferous duct tree requires another essential component — mammary epithelial cells extracellular matrix ECM which, together with adipocytes , fibroblast , inflammatory cells, and others, constitute mammary stroma.

They not only help to support mammary basic structure, but also serve as a communicating bridge between mammary epithelia and their local and global environment throughout this organ's development. A mammary gland is a specific type of apocrine gland specialized for manufacture of colostrum when giving birth. Mammary glands can be identified as apocrine because they exhibit striking "decapitation" secretion.

Many sources assert that mammary glands are modified sweat glands. Mammary glands develop during different growth cycles. They exist in both sexes during embryonic stage, forming only a rudimentary duct tree at birth. In this stage, mammary gland development depends on systemic and maternal hormones, [4] but is also under the local regulation of paracrine communication between neighboring epithelial and mesenchymal cells by parathyroid hormone-related protein PTHrP.

These mesenchymal cells can transform into a dense, mammary-specific mesenchyme, which later develop into connective tissue with fibrous threads, forming blood vessels and the lymph system. These components of the extracellular matrix are strong determinants of duct morphogenesis.

Estrogen and growth hormone GH are essential for the ductal component of mammary gland development, and act synergistically to mediate it. During embryonic development, IGF-1 levels are low, and gradually increase from birth to puberty. Androgens such as testosterone inhibit estrogen-mediated mammary gland development e. Mammary gland development is characterized by the unique process by which the epithelium invades the stroma.

The development of the mammary gland occurs mainly after birth. During puberty , tubule formation is coupled with branching morphogenesis which establishes the basic arboreal network of ducts emanating from the nipple. Developmentally, mammary gland epithelium is constantly produced and maintained by rare epithelial cells, dubbed as mammary progenitors which are ultimately thought to be derived from tissue-resident stem cells.

Embryonic mammary gland development can be divided into a series of specific stages. Initially, the formation of the milk lines that run between the fore and hind limbs bilaterally on each side of the midline occurs around embryonic day The second stage occurs at E This will eventually give rise to the nipple. Lastly, the third stage occurs at E The primitive stem cells are detected in embryo and their numbers increase steadily during development [33]. Postnatally , the mammary ducts elongate into the mammary fat pad.

Then, starting around four weeks of age, mammary ductal growth increases significantly with the ducts invading towards the lymph node. Terminal end buds, the highly proliferative structures found at the tips of the invading ducts, expand and increase greatly during this stage.

This developmental period is characterized by the emergence of the terminal end buds and lasts until an age of about 7—8 weeks. By the pubertal stage, the mammary ducts have invaded to the end of the mammary fat pad. At this point, the terminal end buds become less proliferative and decrease in size. Side branches form from the primary ducts and begin to fill the mammary fat pad.

Ductal development decreases with the arrival of sexual maturity and undergoes estrous cycles proestrus, estrus, metestrus, and diestrus. As a result of estrous cycling, the mammary gland undergoes dynamic changes where cells proliferate and then regress in an ordered fashion. During pregnancy , the ductal systems undergo rapid proliferation and form alveolar structures within the branches to be used for milk production.

After delivery, lactation occurs within the mammary gland; lactation involves the secretion of milk by the luminal cells in the alveoli. Contraction of the myoepithelial cells surrounding the alveoli will cause the milk to be ejected through the ducts and into the nipple for the nursing infant. Upon weaning of the infant, lactation stops and the mammary gland turns in on itself, a process called involution.

This process involves the controlled collapse of mammary epithelial cells where cells begin apoptosis in a controlled manner, reverting the mammary gland back to a pubertal state. During postmenopause , due to much lower levels of estrogen, and due to lower levels of GH and IGF-1, which decrease with age, mammary gland tissue atrophies and the mammary glands become smaller.

Lactiferous duct development occurs in females in response to circulating hormones. First development is frequently seen during pre- and postnatal stages, and later during puberty.

Estrogen promotes branching differentiation, [35] whereas in males testosterone inhibits it. A mature duct tree reaching the limit of the fat pad of the mammary gland comes into being by bifurcation of duct terminal end buds TEB , secondary branches sprouting from primary ducts [5] [36] and proper duct lumen formation.

These processes are tightly modulated by components of mammary epithelial ECM interacting with systemic hormones and local secreting factors. However, for each mechanism the epithelial cells' " niche " can be delicately unique with different membrane receptor profiles and basement membrane thickness from specific branching area to area, so as to regulate cell growth or differentiation sub-locally. Elevated circulating level of growth hormone and estrogen get to multipotent cap cells on TEB tips through a thin, leaky layer of basement membrane.

These hormones promote specific gene expression. Hence cap cells can differentiate into myoepithelial and luminal duct epithelial cells, and the increased amount of activated MMPs can degrade surrounding ECM helping duct buds to reach further in the fat pads. When side branches develop, it is a much more "pushing-forward" working process including extending through myoepithelial cells, degrading basement membrane and then invading into a periductal layer of fibrous stromal tissue.

There is preliminary evidence that soybean intake mildly stimulates the breast glands in pre- and postmenopausal women. Secretory alveoli develop mainly in pregnancy, when rising levels of prolactin , estrogen, and progesterone cause further branching, together with an increase in adipose tissue and a richer blood flow.

In gestation , serum progesterone remains at a stably high concentration so signaling through its receptor is continuously activated. As one of the transcribed genes, Wnts secreted from mammary epithelial cells act paracrinely to induce more neighboring cells' branching. In late pregnancy and for the first few days after giving birth, colostrum is secreted. Milk secretion lactation begins a few days later due to reduction in circulating progesterone and the presence of another important hormone prolactin, which mediates further alveologenesis, milk protein production, and regulates osmotic balance and tight junction function.

Laminin and collagen in myoepithelial basement membrane interacting with beta-1 integrin on epithelial surface again, is essential in this process. In this combined control from ECM and systemic hormones, milk secretion can be reciprocally amplified so as to provide enough nutrition for the baby.

During weaning, decreased prolactin, missing mechanical stimulation baby suckling , and changes in osmotic balance caused by milk stasis and leaking of tight junctions cause cessation of milk production. It is the passive process of a child or animal ceasing to be dependent on the mother for nourishment. In some species there is complete or partial involution of alveolar structures after weaning, in humans there is only partial involution and the level of involution in humans appears to be highly individual.

The glands in the breast do secrete fluid also in nonlactating women. Shrinkage of the mammary duct tree and ECM remodeling by various proteinase is under the control of somatostatin and other growth inhibiting hormones and local factors. But a functional lactiferous duct tree can be formed again when a female is pregnant again. Tumorigenesis in mammary glands can be induced biochemically by abnormal expression level of circulating hormones or local ECM components, [51] or from a mechanical change in the tension of mammary stroma.

Almost all instances of breast cancer originate in the lobules or ducts of the mammary glands. The breasts of the adult human female vary from most other mammals that tend to have less conspicuous mammary glands. The number and positioning of mammary glands varies widely in different mammals. The protruding teats and accompanying glands can be located anywhere along the two milk lines. In general most mammals develop mammary glands in pairs along these lines, with a number approximating the number of young typically birthed at a time.

The number of teats varies from 2 in most primates to 18 in pigs. The Virginia opossum has 13, one of the few mammals with an odd number. Male mammals typically have rudimentary mammary glands and nipples, with a few exceptions: male mice do not have nipples, [57] male marsupials do not have mammary glands, [58] and male horses lack nipples and mammary glands.

Mammary glands are true protein factories [61] , and several labs have constructed transgenic animals , mainly goats and cows , to produce proteins for pharmaceutical use.

There are many theories on how mammary glands evolved. For example, it is thought that the mammary gland is a transformed sweat gland, more closely related to apocrine sweat glands. Many of the current theories are based on comparisons between lines of living mammals— monotremes , marsupials , and eutherians. One theory proposes that mammary glands evolved from glands that were used to keep the eggs of early mammals moist [64] [65] and free from infection [66] [67] monotremes still lay eggs.

Other theories suggest that early secretions were used directly by hatched young, [68] or that the secretions were used by young to help them orient to their mothers.

Lactation is thought to have developed long before the evolution of the mammary gland and mammals; see evolution of lactation. From Wikipedia, the free encyclopedia. For the mountain in Alaska, see Mammary Peak. Cross-section of the human mammary gland. See also: Breast. See also: Breast development.

This article uses anatomical terminology. International Journal of Morphology.

The Breasts

The breast is an organ whose structure reflects its special function: the production of milk for lactation breast feeding. The epithelial component of the tissue consists of lobules , where milk is made, which connect to ducts that lead out to the nipple. Most cancers of the breast arise from the cells which form the lobules and terminal ducts. These lobules and ducts are spread throughout the background fibrous tissue and adipose tissue fat that make up the majority of the breast. The male breast structure is nearly identical to the female breast, except that the male breast tissue lacks the specialized lobules, since there is no physiologic need for milk production by males. Anatomically, the adult breast sits atop the pectoralis muscle the "pec" chest muscle , which is atop the ribcage. The breast tissue extends horizontally side-to-side from the edge of the sternum the firm flat bone in the middle of the chest out to the midaxillary line the center of the axilla , or underarm.

The Who, What, Where, When and Sometimes, Why.

A mammary gland is an exocrine gland in humans and other mammals that produces milk to feed young offspring. Mammals get their name from the Latin word mamma , "breast". The mammary glands are arranged in organs such as the breasts in primates for example, humans and chimpanzees , the udder in ruminants for example, cows, goats, and deer , and the dugs of other animals for example, dogs and cats. Lactorrhea , the occasional production of milk by the glands, can occur in any mammal, but in most mammals, lactation , the production of enough milk for nursing , occurs only in phenotypic females who have gestated in recent months or years.

Lactation is the process by which milk is synthesized and secreted from the mammary glands of the postpartum female breast in response to an infant sucking at the nipple. Breast milk provides ideal nutrition and passive immunity for the infant, encourages mild uterine contractions to return the uterus to its pre-pregnancy size i. Mammary glands are modified sweat glands.

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Anatomy and Physiology of the Breast

The breasts are paired structures located on the anterior thoracic wall, in the pectoral region. They are present in both males and females, yet are more prominent in females following puberty.

Поскольку числовая строка бесконечна, всегда можно заглянуть дальше и найти еще одно простое число. Между 0 и 1 000 000 более 70 000 вариантов. Все зависит оттого, что выбрал Танкадо. Чем больше это число, тем труднее его найти. - Оно будет громадным, - застонал Джабба.

 Мы его не украли, - искренне удивилась Росио.  - Человек умирал, и у него было одно желание. Мы просто исполнили его последнюю волю. Беккер смягчился.

Но не только молодые криптографы научились уважать Стратмора; еще в начале своей карьеры он был замечен начальством как человек, разработавший целый ряд неортодоксальных и в высшей степени успешных разведывательных операций. Продвигаясь по служебной лестнице, Тревор Стратмор прославился умением сжато и одновременно глубоко анализировать сложнейшие ситуации. Он обладал почти сверхъестественной способностью преодолевать моральные затруднения, с которыми нередко бывают связаны сложные решения агентства, и действовать без угрызений совести в интересах всеобщего блага. Ни у кого не вызывало сомнений, что Стратмор любит свою страну.

 Действительно.  - Клушар вздохнул с видом мученика, вынужденного терпеть всякий сброд.

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  1. Gamal R.

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