| Mammary Gland |
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Mammary glands are the Organ s that, in the female Mammal , produce Milk for the sustenance of the young. These Exocrine Gland s are enlarged and modified Sweat Gland s and are the characteristic of mammals which gave the class its name. HUMANS Structure The basic components of the mammary gland are the ''alveoli'' (hollow cavities, a few millimetres large) lined with milk-secreting Epithelial Cells and surrounded by Myoepithelial Cell s. These alveoli join up to form groups known as ''lobules'', and each lobule has a ''lactiferous duct'' that drains into openings in the Nipple . The myoepithelial cells can contract, similar to Muscle cells, and thereby push the milk from the alveoli through the lactiferous ducts towards the nipple, where it collects in widenings (''sinuses'') of the ducts. A Suckling baby essentially squeezes the milk out of these sinuses. One distinguishes between a ''simple mammary gland'', which consists of all the milk-secreting tissue leading to a single lactiferous duct, and a ''complex mammary gland'', which consists of all the simple mammary glands serving 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 .) Development and hormonal control The development of mammary glands is controlled by Hormone s. The mammary glands exist in both sexes, but they are rudimentary until Puberty when in response to Ovarian hormones, they begin to develop in the female. Estrogen promotes formation, while Testosterone inhibits it. At the time of Birth , the baby has lactiferous ducts but no alveoli. Little branching occurs before puberty when ovarian estrogens stimulate branching differentiation of the ducts into spherical masses of cells that will become alveoli. True secretory alveoli only develop in Pregnancy , where rising levels of estrogen and Progesterone cause further branching and differentiation of the duct cells, together with an increase in Adipose Tissue and a richer Blood Flow . Colostrum is secreted in late pregnancy and for the first few days after giving birth. True milk secretion ( Lactation ) begins a few days later due to a reduction in circulating progesterone and the presence of the hormone Prolactin . The suckling of the baby causes the release of the hormone Oxytocin which stimulates contraction of the myoepithelial cells. Breast cancer As described above, the cells of mammary glands can easily be induced to grow and multiply by hormones. If this growth runs out of control, Cancer results. Almost all instances of Breast Cancer originate in the lobules or ducts of the mammary glands. OTHER MAMMALS The number of complex and simple mammary glands varies widely in different mammals. The nipples and glands can occur anywhere along the two Milk Line s, two roughly-parallel lines along the front of the body. They are easy to visualize on dogs or cats, where there are from 3 to 5 pairs of nipples following the 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. Male mammals typically have rudimentary mammary glands and nipples, with a few exceptions: male rats and mice don't have nipples, and male horses lack nipples and mammary glands. Mammary glands are true Protein factories, and several companies have constructed Transgenic Animal s, mainly Goat s and Cow s, in order to produce proteins for pharmaceutical use. Complex Glycoprotein s such as Monoclonal Antibodies or Antithrombin cannot be produced by genetically engineered Bacteria , and the production in live mammals is much cheaper than the use of mammalian Cell Culture s. SEE ALSO
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