Everything about Mammary Gland totally explained
Mammary glands are the
organs that, in
mammals, produce
milk for the sustenance of the young. These
exocrine glands are enlarged and modified
sweat glands and give mammals their name. The mammary glands of domestic mammals containing more than two breasts are called
dugs.
Humans
Structure
The basic components of the mammary gland are the
alveoli (hollow cavities, a few millimetres large) lined with milk-secreting
cuboidal cells and surrounded by
myoepithelial cells. 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 toward the nipple, where it collects in widenings (
sinuses) of the ducts. As the infant begins to suck, the hormonally mediated "let down reflex" ensues and the mother's milk is secreted into – not sucked from the gland by – the baby's mouth.
All the milk-secreting tissue leading to a single lactiferous duct is called a "simple mammary gland"; a "complex mammary gland" is 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
Mammary glands exist in both sexes, but are rudimentary until
puberty when, in females, they begin to develop in response to
ovarian hormones.
Estrogen promotes formation, whereas
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 and positioning of complex and simple mammary glands varies widely in different mammals. The nipples and glands can occur anywhere along the two
milk lines, two roughly-parallel lines along the
ventral aspect of the body. 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 nipples varies from 2 (in most primates) to 16 (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 glands normally found in a range of mammals:
Male mammals typically have rudimentary mammary glands and nipples, with a few exceptions: male mice don't have nipples, and male horses lack nipples and mammary glands. The male Dyak fruit bat has lactating mammary glands.
Mammary glands are true
protein factories, and several companies have constructed
transgenic animals, mainly
goats and
cows, in order to produce proteins for pharmaceutical use. Complex
glycoproteins such as
monoclonal antibodies or
antithrombin can't be produced by genetically engineered
bacteria, and the production in live mammals is much cheaper than the use of mammalian
cell cultures.
Evolution
It is believed that the mammary gland is a transformed sweat gland, more closely related to
Apocrine sweat glands. There are many theories of how they evolved, but since they don't fossilize well, supporting such theories presents a major difficulty for the researcher. One theory proposes that mammary glands evolved from glands that were used to keep the eggs of early mammals moist.
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Gallery
Image:Bezerro mamando REFON .jpg|Cow
Image:White Cat Nursing Four Kittens HQ.jpg|Cat
Image:Piglets1.jpg|Pig
Image:Baby sheep feeding.JPG|Sheep
Image:Kid feeding on mothers milk.jpg|Goat
Image:Elephant_breastfeading.jpg|Elephant
Image:Mousesuckling.jpg|Mouse
Image:Breastfeeding_infant.jpg|Human
Further Information
Get more info on 'Mammary Gland'.
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