A mammary gland is an exocrine gland in mammals that produce milk to feed young children. Mammals get their name from the Latin mamma , "breast". Milk glands are arranged in organs such as breasts in primates (eg, humans and chimpanzees), udder in ruminant animals (eg, cows, goats, and deer), and other animal waste (eg, dogs and dogs). cat). Laktorea, occasional milk production by glands, can occur in any mammal, but in most lactation mammals, the production of milk sufficient for breastfeeding occurs only in phenotypic women who have given birth within the last few months or years. This is directed by hormonal guidance of sex steroids. In some mammalian species, male lactation may occur.
Video Mammary gland
Structure
The basic components of mature mammary glands are the alveoli (hollow cavity, several millimeters large) covered with cube cells secreted by milk and surrounded by myoepithelial cells. The alveoli combine to form a group known as lobules. Each lobule has a lacterous channel that flows into the hole in the nipple. Myoepithelial cells contract under the stimulation of oxytocin, secreting milk secreted by the alveolar units to the lumen of the lobule to the nipple. As the infant begins to suck, mediated with oxytocin-mediated "let-down reflex" words and breast milk is removed - not sucked from the gland - into the baby's mouth.
All milk-secreting tissues that lead to a single lactiferous channel are called "simple milk glands"; in "complex mammary glands" all simple milk glands serve one nipple. Humans usually have two complex milk glands, one in each breast, and each complex milk gland composed of 10-20 simple glands. The presence of more than two nipples is known as polythelia and the presence of more than two complex milk glands as polymastia.
Maintaining true polarized morphology of lactiferous channel trees requires another important component - matrix extracellular breast epithelial cells (ECM) that together with adipocytes, fibroblasts, inflammatory cells, etc., are mammae stroma. Mammary epithelial ECM mainly contains myoepithelial basal membrane and connective tissue. They not only help support the basic structure of mammas, but also serve as a communication bridge between the mammary epithelium and their local and global environment throughout the development of this organ.
Histology
The mammary gland is a specialized apocrine gland to produce colostrum during childbirth. The mammary glands can be identified as apocrine because they exhibit a striking "head-bearing" secretion. Many sources state that the mammary gland is a modified sweat gland. Some authors have denied it and argue that they are sebaceous glands.
Maps Mammary gland
Development
The milk glands grow during different growth cycles. They exist in both sexes during the embryonic stage, forming only the imperfect ducts at birth. At this stage, the development of the mammary glands depends on the systemic (and mother) hormones, but also under the (local) regulation of paracrine communication between the elder and adjacent epithelial cells with parathyroid hormone-related proteins (PTHrP). This locally secreted factor gives rise to a series of external and internal positive feedbacks between the two types of cells, so that the epithelial cells of the mammal shoots can proliferate and sprout into the mesenchyme layer until they reach the fat pad to begin the first round of branched. At the same time, embryonic mesenchymal cells around the epithelial bud receive a PTHrP-activated secreting factor, such as BMP4. These mesenchymal cells can turn into a specific, mamary-specific mesenchyme, which then develops into connective tissue with fibrous yarn, forming blood vessels and lymph systems. Basic membranes, especially those containing laminins and collagen, which are formed thereafter by different mioepithelial cells, maintain the polarity of this main duct. These extracellular matrix components are a strong determinant of ductal morphogenesis.
Biochemistry
Estrogen and growth hormone (GH) are essential for the ductal component of the development of the mammary gland, and act synergistically to mediate it. Neither estrogen nor GH are capable of promoting ductal development without others. The role of GH in ductal development has been found to be largely mediated by the induction of insulin secretion as growth factor 1 (IGF-1), which occurs both systemically (mainly liver) and locally on milk fat. pad through growth hormone receptor activation (GHR). However, GH itself also acts independently of IGF-1 to stimulate ductal development by increasing expression of estrogen (ER) receptors in the mammary gland tissue, which is a downstream effect of GHR activation of the mammary gland. However, unlike IGF-1, GH itself is not essential for the development of the mammary gland, and IGF-1 in association with estrogen can induce normal glandular development without the presence of GH. In addition to IGF-1, other paracrine growth factors such as epidermal growth factor (EGF), altering growth factor beta (TGF-?), Amphiregulin, fibroblast growth factor (FGF), and hepatocyte growth factor (HGF) are involved in breast development as a downstream mediator to sex hormones and GH/IGF-1.
During embryonic development, IGF-1 levels are low, and gradually increase from birth to puberty. At puberty, GH and IGF-1 levels reach the highest levels in life and estrogen begins to be secreted in high numbers in women, which when ductal development occurs mostly. Under the influence of estrogen, stromal and fatty tissues around the ductal system in the mammary gland also grow. After puberty, GH and IGF-1 levels decrease, limiting further development to pregnancy, if that happens. During pregnancy, progesterone and prolactin are essential for mediating lobuloalveolar development in mammary estrogen tissue, which occurs in lactation and breastfeeding preparations.
Androgens such as testosterone inhibit estrogen-mediated milk growth gland (eg, by reducing local ER expression) by activation of androgen receptors expressed in the mammary gland tissue, and along with relatively low estrogen levels, are the cause of the lack of developed milk glands. in men.
Timeline
Before birth
The development of the mammary gland is characterized by the unique process by which the epithelium attacks the stroma. The development of the mammary gland occurs mainly after birth. During puberty, the formation of the tubules is accompanied by branched morphogenesis that forms the basic ductal base tissue originating from the nipple.
Growth epithelial epithelial is constantly produced and maintained by rare epithelial cells, dubbed the mammae progenitor which is ultimately thought to originate from tissue stem cells.
The development of the embryonic gland can be divided into a series of special stages. Initially, the formation of milk lines running between the front and rear members bilaterally on each side of the midline occurs around the day of the embryo 10.5 (E10.5). The second stage occurs in E11.5 when placode formation begins along the milk milk line. This will eventually cause the nipple. Finally, the third stage occurs in E12.5 and involves invaginating cells in the placode to mesenchyme, leading to anlage mammae (biology).
The primitive cells (stems) are detected in the embryo and the number continues to increase during development
Growth
Postnatal, the milk ducts extend into the fatty mammary pad. Then, starting around the age of four weeks, the growth of the mammary ducts increases significantly with the channel striking toward the lymph nodes. The tip end of the terminal, a highly proliferative structure found at the end of the invasive channel, is enlarged and greatly increased during this stage. This developmental period is characterized by the appearance of the end terminals and lasts until the age of about 7-8 weeks.
At the puberty stage, the milk ducts have invaded the ends of the fatty mammary pad. At this point, the terminal end term becomes less proliferative and decreases in size. The side branches are formed from the main channel and begin filling the fatty mammae pad. The development of the duct decreases with the arrival of sexual maturity and undergoes an estrous cycle (proestrus, estrus, metestrus, and diestrus). As a result of the estrous cycle, the mammary glands undergo a dynamic change in which cells proliferate and then retreat regularly.
Pregnancy
During pregnancy, the ductal system undergoes rapid proliferation and forms an alveolar structure in the branches to be used for milk production. After delivery, lactation occurs inside the mammary gland; lactation involves the secretion of milk by luminal cells in the alveoli. The contraction of the myoepithelial cells surrounding the alveoli will cause milk to be released through the ducts and to the nipples for breastfed babies. After weaning the baby, lactation stops and the mammary gland changes by itself, a process called involution . This process involves controlled collapse of mammary epithelial cells where the cells initiate apoptosis in a controlled manner, returning the mammary gland back to puberty state.
Postmenopausal
During postmenopausal, because of the much lower estrogen levels, and because of lower levels of GH and IGF-1, which decrease with age, mammary glandular and mammary gland atrophy becomes smaller.
Physiology
Hormonal control
The development of lactiferous channels occurs in women in response to circulating hormones. The first development is often seen during the pre- and postnatal stages, and then during puberty. Estrogen promotes branching differentiation, whereas in men testosterone inhibits it. An adult channel tree reaches the fat pad of the mammary gland comes into existence by the bifurcation of the terminal end of the sediment channel (TEB), the secondary branch grows from the primary duct and the formation of the proper lumen duct. These processes are strictly modulated by the epithelial epithelial mammary components interacting with the systemic hormones and local secreting factors. However, for each of the mechanisms of the 'epithelial cell' niche 'can be very unique with different membrane receptor profiles and basal membrane thicknesses from specific branching areas to the region, so as to regulate cell growth or sub-local differentiation. Important players include beta-1 integrins, epidermal growth factor receptors (EGFR), laminin-1/5, collagen-IV, metalloproteinase matrices (MMPs), heparan sulfate proteoglycans, and others. Increased levels of growth hormone and estrogen are increased until multipotent cap cells at the tip of the TEB through a thin and leaky basal membrane layer. These hormones promote specific gene expression. Therefore cell caps can differentiate into mioepithelial and luminal epithelial cells (ducts), and an increased number of activated MMPs may decrease the surrounding ECM that helps shoots the channel to reach further on the fat pads. On the other hand, the basement membrane along the adult mammary ducts is thicker, with strong adhesion to epithelial cells through binding to integrin and non-integrin receptors. When the side branch develops, it is much more "push-forward" work processes including expanding through the myoepithelial cells, lowering the basement membrane and then attacking to the periduct layer of the fibrous stromal tissue. Degraded basement membrane fragments (laminin-5) to lead the way migration of mammary epithelial cells. Whereas, laminin-1 interacts with a negative non-integrin dystroglycan receptor regulating this side bending process in case of cancer. This complex "Yin-yang" balances the crosstalks between the ECM mammma and epithelial cells "instructs" the development of healthy to adult mammary glands.
There is early evidence that intake of soy slightly stimulates breast glands in pre- and postmenopausal women.
Pregnancy
Secretory alveoli develop mainly in pregnancy, when elevated levels of prolactin, estrogen, and progesterone lead to further branching, along with enhanced adipose tissue and richer blood flow. In pregnancy, serum progesterone remains at a stable high concentration so that the signal through the receptor continues to be activated. As one of the genes transcribed, the secreted Wnts of the mammary epithelial cells act in paracetel to induce more adjacent cell branches. When the lactiferous duct is almost ready, the "leaves" of the alveoli are distinguished from the luminal epithelial cells and added to the end of each branch. In late pregnancy and during the first few days after delivery, colostrum is secreted. Milk secretion (lactation) begins a few days later due to reduced circulating progesterone and the presence of other important prolactin hormones, which mediate further alveologenesis, milk protein production, and regulate osmotic balance and tight connection function. Laminin and collagen in myoepithelial basal membranes interact with beta-1 integrins on the surface of the epithelium again, are essential in this process. Its binding ensures proper placement of prolactin receptors on the lateral side of the basal cell of alveoli and the directional secretion of milk to the lactiferous ducts. Surging the baby causes the release of the hormone oxytocin, which stimulates the contraction of the myoepithelial cells. In the combined control of ECM and systemic hormones, the secretion of milk can be reinforced reciprocally so as to provide adequate nutrition for the baby.
Wean
During weaning, decreased prolactin, missing mechanical stimuli (breastfed infants), and changes in osmotic balance caused by milk stasis and leakage of tight intersections lead to cessation of breast milk production. This is the process (passive) of a child or animal stops dependent on the mother for food. In some species there is an intact involution or partial alveolar structure after weaning, in humans there is only partial involution and the level of involution in humans seems highly individualized. The glands in the breast do remove fluid also in women who are not breastfeeding. In some other species (such as cattle), all alveoli and secretory channel structures collapse by programmed cell death (apoptosis) and autophagy due to a lack of growth-enhancing factors from either ECM or circulating hormones. At the same time, apoptosis of blood-capillary endothelial cells accelerates bed-ductal lactation regression. The shrinkage of mammary duct trees and ECM remodeling by various proteases is under the control of somatostatin and growth inhibiting hormone and other local factors. This major structural change causes loose fatty tissue to fill in the empty space afterwards. But the functioning lactiferous ducts can re-form when a woman becomes pregnant again.
Clinical interests
Tumorigenesis in the mammary gland can be induced biochemically by the level of abnormal expression of circulating hormones or local ECM components, or from mechanical changes in the tension of the mammae stroma. Under either of these two conditions, the mammary epithelial cells will grow out of control and eventually produce cancer. Almost all cases of breast cancer come from the lobules or ducts of the mammary gland.
Other mammals
General
The breasts of adult human women vary from most other mammals that tend to have a less conspicuous milk gland. The number and position of the mammary glands varies greatly in different mammals. Prominent nipples and accompanying glands can be found anywhere along the two milk lines. In general, most mammals develop mammary glands in pairs along these lines, with numbers close to the number of young people who are usually born at a time. The number of nipples varies from 2 (in most primates) to 18 (in pigs). The Virginia Opossum has 13, one of the few mammals with an odd number. The following table lists the number and position of pacifiers and glands found in various mammals:
Male mammals usually have mammary glands and nipples that are not perfect, with some exceptions: male rats have no nipples, and stallions have no nipples and mammary glands. Male Dayak bats have mammary glands. Male lactation is rare in a few species, including humans.
The mammary gland is a true protein plant, and some laboratories have built transgenic animals, especially goats and cows, to produce proteins for pharmaceutical purposes. Complex glycoproteins such as monoclonal or antithrombin antibodies can not be produced by genetically engineered bacteria, and production in living mammals is much cheaper than the use of mammalian cell cultures.
Evolution
Evolution of the mammary gland is difficult to explain; this is because the mammary glands are usually required by mammals to feed their children. There are many theories about how the mammary gland evolves. For example, it is thought that the mammary gland is a changed sweat gland, more closely related to apocrine sweat glands. Because the milk glands do not fossil well, supporting such a theory with fossil evidence is difficult. Many of today's theories are based on the comparison between living mammalian lines - monotremes, marsupials, and eutherians. One theory suggests that the mammary gland evolved from the glands used to keep the early mammal eggs moist and free of infection (monotrem still laying eggs). Other theories suggest that early secretions are used directly by newly hatched babies, or that secretions are used by children to help them orient their mothers.
Lactation is thought to have developed long before the evolution of mammary glands and mammals; see lactation evolution.
Additional images
See also
- Breastfeeding
- Breast tumor
- Mammaglobin
- Gynecomastia
- The hypothalamic-pituitary-prolactin axis
- Shrimp
- Milk wizards
- The milk line
- List of human body glands # Skin
References
Bibliography
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Ackerman, A. Bernard; Almut BÃÆ'¶er; Bruce Bennin; Geoffrey J. Gottlieb (2005). Histology Diagnosis of Inflammatory Skin Disease Algorithm Method Based Pattern Analysis . ISBN 978-1-893357-25-9. Archived from the original on April 21, 2011. - Moore, Keith L. et al. (2010) Clinical-Oriented Anatomy 6th Ed
External links
- Comparison of Mammary Gland Anatomy by W. L. Hurley
- In the anatomy of the breast by Sir Astley Paston Cooper (1840). Many images, in the public domain.
Source of the article : Wikipedia
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