Tissues of the body develop from 3 primary germ layers, the first tissues formed in the equine embryo. Generally speaking, germ layers are specialized groups of cells that develop into specific body tissues/organs. a. Ectoderm: gives rise to cells of the epidermis and nervous system b. Mesoderm: gives rise to muscle, connective tissues and certain organs c. Endoderm: gives rise to remaining viscera and the epithelial linings of the GI, respiratory and urinary tracts
Cell Junctions
Cell junctions are contact &/or communication points between the plasma membranes of tissue cells. There are 5 important types: 1. Tight Junctions Consist of web like strands of transmembrane proteins that fuse to outer surfaces of adjacent plasma membranes together to seal off passageways between adjacent cells.
Examples:
2. Adherens Junctions Contain plaque, a dense layer of proteins on the inside of the plasma membrane that attaches both to membrane proteins and to microfilaments of the cytoskeleton. Transmembrane glyoproteins called Cadherins join the cells by inserting into the plaque from the opposite side of the plasma membrane, partially crosses the intracellular space and connects to cadherins of an adjacent cell. Extensive zones of adheren junctions form an Adhesive Belt. They help resist separation of cells of epithelial surfaces during contractile activities.
Examples:
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