Y khoa, y dược - Tissue: the living fabric: Part A

4 Tissue: The Living Fabric: Part ATissuesGroups of cells similar in structure and functionTypes of tissuesEpithelial tissueConnective tissueMuscle tissueNerve tissueFigure 4.1Nervous tissue: Internal communication• Brain, spinal cord, and nervesMuscle tissue: Contracts to cause movement• Muscles attached to bones (skeletal)• Muscles of heart (cardiac)• Muscles of walls of hollow organs (smooth)Epithelial tissue: Forms boundaries between different environments, protects, secretes, absorbs, filters• Skin surface (epidermis)• Lining of GI tract organs and other hollow organsConnective tissue: Supports, protects, bindsother tissues together• Bones• Tendons• Fat and other soft padding tissueEpithelial Tissue (Epithelium)Two main types (by location):Covering and lining epitheliaOn external and internal surfaces Glandular epitheliaSecretory tissue in glandsCharacteristics of Epithelial TissueCells have polarity—apical (upper, free) and basal (lower, attached) surfacesApical surfaces may bear microvilli (e.g., brush border of intestinal lining) or cilia (e.g., lining of trachea)Noncellular basal lamina of glycoprotein and collagen lies adjacent to basal surfaceCharacteristics of Epithelial TissueAre composed of closely packed cellsContinuous sheets held together by tight junctions and desmosomesSupported by a connective tissue reticular lamina (under the basal lamina)Avascular but innervated High rate of regenerationClassification of EpitheliaAsk two questions:How many layers? 1 = simple epithelium>1 = stratified epitheliumFigure 4.2aStratifiedSimpleApical surfaceBasal surfaceApical surfaceBasal surface(a) Classification based on number of cell layers.Classification of EpitheliaWhat type of cell?SquamousCuboidalColumnar (If stratified, name according to apical layer of cells)Figure 4.2bSquamousCuboidalColumnar(b) Classification based on cell shape.Overview of Epithelial TissuesFor each of the following types of epithelia, note:DescriptionFunctionLocationFigure 4.3a(a) Simple squamous epitheliumDescription: Single layer of flattenedcells with disc-shaped central nucleiand sparse cytoplasm; the simplestof the epithelia.Function: Allows passage ofmaterials by diffusion and filtrationin sites where protection is notimportant; secretes lubricatingsubstances in serosae.Location: Kidney glomeruli; air sacsof lungs; lining of heart, bloodvessels, and lymphatic vessels; liningof ventral body cavity (serosae).Photomicrograph: Simple squamous epitheliumforming part of the alveolar (air sac) walls (125x).Air sacs oflung tissueNuclei ofsquamousepithelialcellsEpithelia: Simple SquamousTwo other locationsEndotheliumThe lining of lymphatic vessels, blood vessels, and heartMesotheliumThe epithelium of serous membranes in the ventral body cavityFigure 4.3b(b) Simple cuboidal epitheliumDescription: Single layer ofcubelike cells with large,spherical central nuclei.Function: Secretion andabsorption.Location: Kidney tubules;ducts and secretory portionsof small glands; ovary surface.Photomicrograph: Simple cuboidalepithelium in kidney tubules (430x).BasementmembraneConnectivetissueSimplecuboidalepithelialcellsFigure 4.3c(c) Simple columnar epitheliumDescription: Single layer of tall cells with round to oval nuclei; some cells bear cilia; layer may contain mucus-secreting unicellular glands (goblet cells).Function: Absorption; secretion of mucus, enzymes, and other substances; ciliated type propels mucus (or reproductive cells) by ciliary action.Location: Nonciliated type lines most of the digestive tract (stomach to anal canal),gallbladder, and excretory ducts of someglands; ciliated variety lines small bronchi, uterine tubes, and some regionsof the uterus.Photomicrograph: Simple columnar epitheliumof the stomach mucosa (860X).SimplecolumnarepithelialcellBasementmembraneFigure 4.3d(d) Pseudostratified columnar epitheliumDescription: Single layer of cells ofdiffering heights, some not reachingthe free surface; nuclei seen atdifferent levels; may contain mucus-secreting cells and bear cilia.Function: Secretion, particularly ofmucus; propulsion of mucus byciliary action.Location: Nonciliated type in male’ssperm-carrying ducts and ducts oflarge glands; ciliated variety linesthe trachea, most of the upperrespiratory tract.Photomicrograph: Pseudostratified ciliatedcolumnar epithelium lining the human trachea (570x).TracheaCiliaPseudo-stratifiedepitheliallayerBasementmembraneMucus ofmucous cellFigure 4.3e(e) Stratified squamous epitheliumDescription: Thick membranecomposed of several cell layers;basal cells are cuboidal or columnarand metabolically active; surfacecells are flattened (squamous); in thekeratinized type, the surface cells arefull of keratin and dead; basal cellsare active in mitosis and produce thecells of the more superficial layers.Function: Protects underlyingtissues in areas subjected to abrasion.Location: Nonkeratinized type formsthe moist linings of the esophagus,mouth, and vagina; keratinized varietyforms the epidermis of the skin, a drymembrane.Photomicrograph: Stratified squamous epitheliumlining the esophagus (285x).StratifiedsquamousepitheliumNucleiBasementmembraneConnectivetissueEpithelia: Stratified Cuboidal Quite rare in bodyFound in some sweat and mammary glandsTypically two cell layers thickEpithelia: Stratified ColumnarLimited distribution in bodySmall amounts in pharynx, male urethra, and lining some glandular ductsAlso occurs at transition areas between two other types of epitheliaFigure 4.3f(f) Transitional epitheliumDescription: Resembles both stratified squamous and stratified cuboidal; basal cells cuboidal or columnar; surface cells domeshaped or squamouslike, depending on degree of organ stretch.Function: Stretches readily and permits distension of urinary organ by contained urine.Location: Lines the ureters, urinary bladder, and part of the urethra.Photomicrograph: Transitional epithelium lining the urinary bladder, relaxed state (360X); note the bulbous, or rounded, appearance of the cells at the surface; these cells flatten and become elongated when the bladder is filled with urine.BasementmembraneConnectivetissueTransitionalepitheliumGlandular Epithelia A gland is one or more cells that makes and secretes an aqueous fluidClassified by:Site of product release—endocrine or exocrineRelative number of cells forming the gland—unicellular (e.g., goblet cells) or multicellularEndocrine Glands Ductless glands Secrete hormones that travel through lymph or blood to target organsExocrine GlandsMore numerous than endocrine glandsSecrete products into ductsSecretions released onto body surfaces (skin) or into body cavitiesExamples include mucous, sweat, oil, and salivary glandsUnicellular Exocrine GlandsThe only important unicellular gland is the goblet cellFigure 4.4(b)(a)MicrovilliSecretoryvesiclescontainingmucinGolgiapparatusRough ERNucleusMulticellular Exocrine GlandsMulticellular exocrine glands are composed of a duct and a secretory unitClassified according to:Duct type (simple or compound) Structure of their secretory units (tubular, alveolar, or tubuloalveolar)Figure 4.5Compound duct structure(duct branches)Simple tubularExampleIntestinal glandsSimple branchedtubularExampleStomach (gastric)glandsCompound tubularExampleDuodenal glands of small intestineCompound alveolarExampleMammary glandsSimplealveolarExampleNo importantexample in humansSimple branchedalveolarExampleSebaceous (oil)glandsCompoundtubuloalveolarExampleSalivary glandsTubularsecretorystructureAlveolarsecretorystructureSurface epitheliumDuctSecretory epitheliumSimple duct structure(duct does not branch)Modes of SecretionMerocrine Products are secreted by exocytosis (e.g., pancreas, sweat and salivary glands)HolocrineProducts are secreted by rupture of gland cells (e.g., sebaceous glands)Figure 4.5Compound duct structure(duct branches)Simple tubularExampleIntestinal glandsSimple branchedtubularExampleStomach (gastric)glandsCompound tubularExampleDuodenal glands of small intestineCompound alveolarExampleMammary glandsSimplealveolarExampleNo importantexample in humansSimple branchedalveolarExampleSebaceous (oil)glandsCompoundtubuloalveolarExampleSalivary glandsTubularsecretorystructureAlveolarsecretorystructureSurface epitheliumDuctSecretory epitheliumSimple duct structure(duct does not branch)