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Chapter 4.docx - Chapter 4 The Tissue Level of Organization...

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Chapter 4The Tissue Level of OrganizationObjectivesAfter completing this chapter, you should be able to1.define the termtissue, and classify the tissues of the body into four major types.
2.describe the structure and functions of the five principal types of cell junctions.
Cells of epithelial tissue that lines the stomach, intestines, and urinary bladder havemany tight junctions. They inhibit the passage of substances between cells andprevent the contents of these organs from leaking into the blood or surroundingtissues.2.Adherens junctions: containplaque, a dense layer of proteins on the inside of theplasma membrane that attaches both to membrane proteins and to microfilaments ofthe cytoskeleton.Transmembrane glycoproteins calledcadherinsjoin the cells. Each cadherin insertsinto the plaque from the opposite side of the plasma membrane, partially crosses theintercellular space, and connects to cadherins of an adjacent cell.In epithelial cells, adherens junctions often form extensive zones calledadhesionbeltsbecause they encircle the cell similar to the way a belt encircles your waist.Adherens junctions help epithelial surfaces resist separation during various contractileactivities, as when food moves through the intestines.3.Desmosomes: like adherens junctions, desmosomes contain plaque and havetransmembrane glycoproteins (cadherins) that extend into the intercellular spacebetween adjacent cells membranes and attach to one another.However, unlike adherens junctions, the plaque of desmosomes does not attach tomicrofilaments. Instead, a desmosome plaque attaches to elements of the cytoskeletonknown as intermediate filaments, which consist of the protein keratin.

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Term
Fall
Professor
Allan Kew

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