Organ Hist, Unit 1 - Chapter 1 Epithelium Introduction...

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Organ Histology Unit 1 Chapter 1: Epithelium Introduction: Generalized Functions: protection diffusion (filtration) secretion absorption movement of surface materials and specializations which assist neural functions Divided into 2 categories  – based upon arrangement: glandular Histogenesis : can develop from any of the 3 original germ layers affects the name of the tissue but not function or appearance mesothelia   mesoderm (CV system, serous cavities) epithelia  [epithelium = generic term]    ectoderm (skin) endothelia   endoderm (gut, respiratory tract) Functional Characteristics: Adjacent cells   little or no intercellular space and/or fluid form a barrier separating 2 different environments   acidic contents of the stomach and highly vascular connective tissue Well developed cell junctions to maintain the barrier: zonula = structure that completely encircles a cell macula = spot – attaches 2 points fascia = incomplete zonula 4 types of junctions: zonula occludens  (tight junction or occluding junction)    attaches and seals the intercellular space 2 cells share intrinsic cell membrane proteins 2 functions: adhesion – attachment between cells zonula adherens    provides poor cell to cell attachment but attaches components of the cytoskeleton to the inside of the cell  membrane
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2 functions: provide weak attachment provides stability for cell structure macula adherens  (desosome)    provides strong attachment between cells; “spot weld” – characteristic of epithelia junctional complex :  when the 3 junctions occur together – in this order  gap junction    “pipeline” between cells functions: communication between cells strong attachment between cells structure: permanent fusion of 6  connexons  (proteins) from adjacent cells that form a macromolecular passageway between cells – there is  an opening in the cylinder more specialized junctions may include:  hemidesmosomes, fascia occludens, and fascia adherens No intervening blood or lymph vessels rely upon nutrition by diffusion Always associated with vascular connective tissue connective tissue provides: nutrition by diffusion   from blood supply within the connective tissue Separated from the connective tissue by a complete or partial basement membrane complete basement membrane  consists of: basal lamina 
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Organ Hist, Unit 1 - Chapter 1 Epithelium Introduction...

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