Secretion of Milk - Pathway IV: Transcytosis. Several...

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1 Secretion of Milk: See: http://mammary.nih.gov/reviews/lactation/Neville001/index.html Model alveolus (a) with subtending duct (d) showing blood supply, adipocyte stroma, myoepithelial cells, and plasma cells (PC). Alveolar Cell from lactating mammary gland. N, nucleus; TJ, tight junction; GJ, gap junction; D, desmosome; SV, secretory vesicle; FDA, fat-depleted adipocyte; PC, Plasma Cell; BM, basement membrane; ME, cross section through process of myoepithelial cell; RER, rough endoplasmic reticulum; MFG, milk fat globular. See text for explanation of secretory pathways I (exocytosis), II (lipid), III (apical transport), IV (transcytosis) and V (paracellular pathway). Pathway I: Exocytosis of proteins (e.g. lactoferrin). Pathway II: Secretion of fat globules by apocrine secretion, although Nelville thinks the terms merocrine, apocrine and holocrine are outdated).
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2 Pathway III: Transport across apical membrane of some small molecules and many drugs.
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Unformatted text preview: Pathway IV: Transcytosis. Several proteins move out of the capillaries, bind to receptors on the basal membrane, enter the alveolar cell by endocytosis, are transported to apical membrane, and secreted into lumen (milk) exocytosis. In the diagrams above, note the plasma cells that make IgA antibodies. These antibodies are transcytosed across the alveolar cells to be secreted into the lumen (milk). (This is the same process that we saw in the parotid gland, GI tract, GU, and respiratory tract: IgA is the mucosal protecting antibody). Pathway V. Paracellular: During lactation, the tight junctions are intact and do not allow paracellular movement except immune cells may move into milk by diapedesis through the intercellular spaces. During involution of the breast following lactation or in the event of mastitis (inflammation), the tight junctions become very leaky....
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This note was uploaded on 11/08/2011 for the course SCIENCE 3254 taught by Professor Dr.shoupe during the Spring '11 term at Fort Valley State University .

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Secretion of Milk - Pathway IV: Transcytosis. Several...

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