Anatomy – Cell Junctions

definition of “cell junctions”
contact points between the plasma membranes of tissue cells (how cells are held together to form tissues)

name the 5 main types of cell junctions
1. tight junctions; 2. adherens junctions; 3. desmosomes; 4. hemidesmosomes; and, 5. gap junctions

tight junctions
form tight seals between cells with weblike strands of transmembrane proteins that fuse together the outer surfaces of adjacent plasma membranes); prevents passage of substances between cells (i.e., tissues that line the stomach, intestines, and urinary bladder have many tight junctions)

adherens junctions
contain plaque, a dense layer of proteins on the inside layer of the plasma membrane that attaches both to membrane proteins AND to microfilaments of the cytoskeleton; transmembrane glycoproteins called CADHERINS join the cells; in epitheleal cells, adherens junctions often form extensive zones called “adhesion belts” that encircle the cell; (help epitheleal surfaces resist separation during various contractile activities like when food moves through the intestines)

contain plaque and transmembrane glycoproteins (cadherin). Plaque attaches to intermediate filament (keratin) which extends from desmosomes on one side of the cell across cytoplasm to a desmosomes on the opposite side of the cell. (prevent epidermal cells from separating under tension and cardiac muscle cells from pulling apart during contraction)

strongly anchor cells to an underlying basement membrane NOT to other cells; transmembrane glycoproteins are INTEGRINS

gap junctions
membrane proteins called CONNEXINS form tiny fluid-filled tunnels called connexons that connect neighboring calls; connexons allow ions and small molecules to diffuse from the cytosol of one cell to another; allow cells to communicate with one another; enable nerve or muscle impulses to spread rapidly among cells; found in nervous system, cardiac muscle and gastrointentinal tract

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CH 4 Anatomy & Physiology 1

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