A&P Chapter IV.docx - Chapter 4 Tissue Level of...

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Chapter 4: Tissue Level of Organization I. Tissues of the Body Cells Differentiation allows the cells to perform a restricted range of functions 200 types of cells in the body and the cell types combine to form tissues Type of Tissues Epithelial: covers exposed surfaces; lines internal passageways and chambers; produces glandular secretions Connective: fills internal spaces, provides structural support; stores energy Muscle: contracts to produce active movement Neural: conducts electrical impulses; carries information II. Epithelial Tissue Epithelial tissue consists almost entirely of cells Epithelial Tissue Epithelia (layers of cells that cover internal and external surfaces) Glandular epithelia composed of fluid-secreting cells from the epithelia Characteristics of Epithelial tissue Cells bound closely together Free (apical) surface Attached to underlying connective tissue by basement membrane Avascular (lacks blood vessels); because of lack of vessels, these cells must get their nutrients across their attached surface from deeper tissues or from their exposed surfaces Continual replacement or regeneration of cells Locations o Cover external and internal body surfaces (ex. Skin, internal passageways – digestive, urinary, respiratory, reproductive tracts) that form selective barriers o Line internal cavities and passageways (ex. Cavities around lungs, heart) and prevent friction, Functions Provide physical protection: prevents surfaces from abrasions, dehydration and destruction Control permeability Provide sensation: through touch receptors (corpuscles) Produce specialized secretions (glandular epithelium with gland cells) o Exocrine: secretions to surface of epithelium Ex. Perspiration on skin, milk from mammary gland o Endocrine: secretions to surrounding tissue fluid and blood (hormones) Ex. Come from thyroid, pancreas and pituitary glands Intercellular Connections To be effective in protecting tissues, the epithelial cells have to be firmly attached to the basement membrane CAMs: cell adhesion molecules that are transmembrane proteins and interconnect opposing plasma membranes o CAMs bind to each other and extracellular materials by a layer of proteoglycans Cell Junctions: other specialized attachment sites for cell-to-cell attachment or attachment to extracellular materials
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o Tight junction: lipid layers of adjacent plasma membranes are bound together by interlocking membrane proteins Below tight junctions lie an adhesion belt which goes around cells and binds them to their neighbors (bands are connected to actin filaments) Prevent water and solutes passage between cells Location: between epithelial cells exposed to harsh/powerful enzymes Ex. Digestive tract lining o Gap junction: two cells held together by embedded membrane proteins (connexons). The connexons create small passageways for small molecules to pass through
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  • Winter '08
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  •  Glandular epithelia

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