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

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Unit 4 The Tissue Level of OrganizationCell Junctions-Cell junctions = contact points between the plasma membranes of tissue cells-Tight Junctions =weblike strands of transmembrane proteins that fuse together the outersurfaces of adjacent plasma membranes to seal off passageways between adjacent cellsoEx. The lining of the stomach, intestines, urinary bladder-Adherens Junctions = contain plaque inside the plasma membrane that attaches to bothmembrane proteins and microfilaments of the cytoskeleton; cadherins (transmembraneglycoproteins) joint the cellsoHelp epithelial surfaces resist separation during various contractile activities (foodmoving through the intestines-Desmosomes = contains plaque and have transmembrane proteins; do not attach tomicrofilaments – instead attach to elements of the cytoskeleton (intermediate filament- proteinkeratin)oPrevent epithelial cells from separating under tension and cardia muscle cells frompulling apart during contractionoEx. Common among the cells that make the epidermis, cardiac muscle cells-Hemidesmosomes = do not like adjacent cells; transmembrane glycoproteins inhemidesmosomes are integrins rather than cadherinsoAnchor cells not to each other but to the basement membrane-Gap Junctions = connexins (membrane protein) form tiny fluid filled tunnels called connexonsthat connect neighboring cellsoPlasm membrane of gap junctions are separated by a narrow intercellular gapoAllow cells in tissue to communicate to one anotheroEx. Allow nerve or muscle impulses to spread rapidly among cellsComparison between Epithelial and Connective Tissue-Epithelial = cells are tightly packed with no extracellular matrix, has no blood vessels-Connective = large amount of extracellular matrix, has blood vesselsEpithelial Tissue-Cells in a continuous sheet, single or multiple layers-Forms coverings and linings throughout the body-Has its own nerve supply but is avascular; relies on other blood vessels of adjacent connectivetissues to bring nutrients and remove wastes (through diffusion)-Forms boundaries between the bodys organs or between the body and external environment-Constantly renew and repair itself-Roles in the body; filtration, protection, secretion, absorption and excretion-3 Major FunctionsoSelective barrier that limits or aids the transfer of substances into and out of the bodyoSecretory surface that releases products produced but the cells into free surfaces
oProtective surface that resists the abrasive influences of the environment-Apical (free) Surface = faces the body surface, contain cilia or microvilli; internal organ or tubularduct-Lateral Surfaces = face the adjacent cells on the other side; tight junctions, adherens junctions,desmosomes and/or gap juctions-

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Term
Spring
Professor
NA
Tags
Classification of Connective Tissue, embryonic connective tissue, Epithelial and Connective Tissue

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