3. Desmosomes Like adheren junctions, desmosomes also have plaque and cadherins to connect adjacent cells. However, the plaque of desmosomes does not attach to microfilaments. Instead, the plaque attaches to intermediate filaments that consist of the protein keratin . Keratin from one desmosome extends across the cytosol to desmosomes on the opposite side of the cell. This contributes to the stability of the cells and tissues.
Examples:
4. Hemidesmosomes These types resemble desmosomes but do not join adjacent cells. The transmembrane proteins are Integrins rather than cadherins. Integrins on the inside of the plasma membrane attach to intermediate filaments (keratin). On the outside of the plasma membrane the integrins attach to the protein-based Laminin which is present in the Basement Membrane. Therefore, hemidesmosomes anchor cells to the basement membrane. 5. Gap Junctions Membrane proteins called Connexins form tiny fluid-filled tunnels call Connexons that connect neighbouring cells. Through the connexons, ions and other small molecules can diffuse from the cytosol of one cell to another. Gap junctions actually may help cells communicate such as in the developing embryo where chemical and electrical signals that regulate growth travel.
Examples include:
A. Epithelial Tissue
Epithelial tissue is the type of tissue found on the surface of the body (skin) and on the surfaces of body cavities & hollow organs. This tissue forms coverings and linings throughout our body. Epithelial cells are arranged in sheets and can consist of one single layer or many tightly packed layers. They are held together by many cell junctions. It is never covered by another tissue, so it ALWAYS has a free surface.
Functions : Protection, Absorption, Filtration, Secretion, Excretion, Sensation
1. Selective barriers that limit or aid the transfer of substances into and out of the body. 2. Secretory surfaces that release products produced by cells onto their free surfaces. 3. Protective surfaces that resist the abrasive influences of the environment.
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