epithelial tissue. general features of epithelium consists of packed cells with little extracellular...
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General Features of General Features of EpitheliumEpithelium• Consists of packed cells with little Consists of packed cells with little
extracellular material between themextracellular material between them• Cells are arranged in continuous sheets, in Cells are arranged in continuous sheets, in
either single or multiple layerseither single or multiple layers• Have a free surface and a basal surfaceHave a free surface and a basal surface• Are Are avascular : a- avascular : a- without without vascular-vascular- blood blood
vesselsvessels• Have nerve supplyHave nerve supply• High capacity for renewal by cell divisionHigh capacity for renewal by cell division
Covering and Lining Covering and Lining EpitheliumEpithelium
Classification by shapeClassification by shape
• Squamous - flatSquamous - flat
• Cuboidal – cubes or hexagonsCuboidal – cubes or hexagons
• Columnar – tall, rectangular and Columnar – tall, rectangular and cylindricalcylindrical
• Transitional – range in shape from flat Transitional – range in shape from flat to columnar and often change shapeto columnar and often change shape
Classification by Arrangement of LayersClassification by Arrangement of Layers
• Simple – single layer in areas of diffusion, Simple – single layer in areas of diffusion, osmosis, filtration, secretion and osmosis, filtration, secretion and absorptionabsorption
• Stratified – two or more layers used for Stratified – two or more layers used for protecting underlying tissuesprotecting underlying tissues
• Pseudostratified columnar – contains one Pseudostratified columnar – contains one layer, appears to have several layers but layer, appears to have several layers but not all cells reach the surface, ciliated or not all cells reach the surface, ciliated or secrete mucoussecrete mucous
Simple Squamous Simple Squamous EpitheliumEpithelium
Single layer, flat cells, central nucleusSingle layer, flat cells, central nucleus
Lines the heart, blood vessels, lymphatic Lines the heart, blood vessels, lymphatic vessels, alveoli, glomerular capsules, and vessels, alveoli, glomerular capsules, and
forms the epithelial layer of serous forms the epithelial layer of serous membranesmembranes
Function: filtration, diffusion, osmosis, Function: filtration, diffusion, osmosis, secretion in serous membranessecretion in serous membranes
Simple Cuboidal EpitheliumSimple Cuboidal Epithelium
Single layer, cube shaped, central Single layer, cube shaped, central nucleusnucleus
Lines the tubes and smaller ducts of Lines the tubes and smaller ducts of the kidneysthe kidneys
Function: secretion and absorptionFunction: secretion and absorption
Nonciliated Simple Columnar Nonciliated Simple Columnar EpitheliumEpithelium
Single layer, nonciliated, rectangular, Single layer, nonciliated, rectangular, cylindrical cells, nucleus at base, contain cylindrical cells, nucleus at base, contain goblet cells, some have microvilligoblet cells, some have microvilli
Lines GI, respiratory, reproductive and Lines GI, respiratory, reproductive and urinary tractsurinary tracts
Function: secretion and absorptionFunction: secretion and absorption
Stratified Squamous Stratified Squamous EpitheliumEpitheliumSeveral layers, cuboidal or columnar deep, Several layers, cuboidal or columnar deep,
squamous superficial, basal cells replace squamous superficial, basal cells replace surface cellssurface cells
Keratinized epidermis, nonkeratinized lines Keratinized epidermis, nonkeratinized lines the mouth, esophagus, vagina and tonguethe mouth, esophagus, vagina and tongue
Function: protectionFunction: protection
Transitional EpitheliumTransitional Epithelium
Variable cell shapes, superficial cells Variable cell shapes, superficial cells squamous when stretched, cuboidal squamous when stretched, cuboidal when relaxedwhen relaxed
Lines urinary bladder and portions of Lines urinary bladder and portions of ureters and urethraureters and urethra
Function: permits organs to stretch Function: permits organs to stretch without rupturingwithout rupturing
Pseudostratified Columnar Pseudostratified Columnar EpitheliumEpithelium
Not true stratified tissue, cells at different Not true stratified tissue, cells at different layers, all cells attached to basement layers, all cells attached to basement membrane, only some reach surfacemembrane, only some reach surface
Ciliated lines airways of most of the upper Ciliated lines airways of most of the upper respiratory tract (trachea)respiratory tract (trachea)
Function: secretion and movement of mucusFunction: secretion and movement of mucus