Independent Study |
Mammary Macro-structure |
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Secretory tissue in the interior of the gland is made up of:
The relative amount of connective and secretory tissue varies from animal to animal.
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Secretory tissue in the udder is organized into lobes, with each lobe made up of many lobules. Each lobule contains 150-220 microscopic alveoli. Lobules and alveoli are covered in more detail in the Micro-Structure section of this lab. Lobe - Groups of lobules are surrounded by a connective tissue sheath and comprise a lobe. Each mammary gland is made of numerous lobes. Lobules - Clusters of 150-220 alveoli are encapsulated by a connective tissue sheath and are organized as a lobule (~.7-.8 mm dia.). Alveoli - (acini) Alveoli are sack-like structures where milk is synthesized and secreted. An alveolus is the discrete milk producing unit. It is estimated to hold ~1/5 of a drop of milk. The lumen of the alveolus is lined by a single layer of secretory epithelial cells. The epithelial lining is surrounded by contractile myoepithelial cells. Myoepithelial cells contract in response to the hormone oxytocin, resulting in milk being squeezed out of the alveolar lumen and into the small ducts. Outside of the myoepithelial cells the alveolus is surrounded by a connective tissue basement membrane. The capillary bed on the outside of the alveolus is part of the stromal tissue (connective tissue) between alveoli. A group of alveoli can be visualized as a clump of grapes, with the stems acting as the small ducts leading from the alveoli. |
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Mammary Structure
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