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

4 Tissue: The Living Fabric: Part BConnective TissueMost abundant and widely distributed tissue typeFour classesConnective tissue properCartilageBone tissueBloodTable 4.1Major Functions of Connective TissueBinding and supportProtectionInsulationTransportation (blood)Characteristics of Connective TissueConnective tissues have:Mesenchyme as their common tissue of originVarying degrees of vascularityCells separated by nonliving extracellular matrix (ground substance and fibers) Structural Elements of Connective TissueGround substanceMedium through which solutes diffuse between blood capillaries and cellsComponents:Interstitial fluidAdhesion proteins (“glue”) ProteoglycansProtein core + large polysaccharides (chrondroitin sulfate and hyaluronic acid)Trap water in varying amounts, affecting the viscosity of the ground substanceStructural Elements of Connective TissueThree types of fibersCollagen (white fibers)Strongest and most abundant typeProvides high tensile strengthElasticNetworks of long, thin, elastin fibers that allow for stretchReticular Short, fine, highly branched collagenous fibers Structural Elements of Connective TissueCellsMitotically active and secretory cells = “blasts”Mature cells = “cytes”Fibroblasts in connective tissue properChondroblasts and chondrocytes in cartilage Osteoblasts and osteocytes in boneHematopoietic stem cells in bone marrowFat cells, white blood cells, mast cells, and macrophages Figure 4.7MacrophageFibroblastLymphocyteFat cellMast cellNeutrophilCapillaryCell typesExtracellularmatrixFibers• Collagen fiber• Elastic fiber• Reticular fiberGround substanceConnective Tissue: EmbryonicMesenchyme—embryonic connective tissueGives rise to all other connective tissues Gel-like ground substance with fibers and star-shaped mesenchymal cellsOverview of Connective TissuesFor each of the following examples of connective tissue, note:DescriptionFunctionLocationConnective Tissue ProperTypes:Loose connective tissueAreolarAdiposeReticular Dense connective tissueDense regularDense irregularElastic(a) Connective tissue proper: loose connective tissue, areolarDescription: Gel-like matrix with allthree fiber types; cells: fibroblasts,macrophages, mast cells, and somewhite blood cells.Function: Wraps and cushionsorgans; its macrophages phagocytizebacteria; plays important role ininflammation; holds and conveystissue fluid.Location: Widely distributed underepithelia of body, e.g., forms laminapropria of mucous membranes;packages organs; surroundscapillaries.Photomicrograph: Areolar connective tissue, asoft packaging tissue of the body (300x).EpitheliumLaminapropriaFibroblastnucleiElasticfibers Collagenfibers Figure 4.8aFigure 4.8b(b) Connective tissue proper: loose connective tissue, adiposeDescription: Matrix as in areolar,but very sparse; closely packedadipocytes, or fat cells, havenucleus pushed to the side by largefat droplet.Function: Provides reserve foodfuel; insulates against heat loss;supports and protects organs.Location: Under skin in thehypodermis; around kidneys andeyeballs; within abdomen; in breasts.Photomicrograph: Adipose tissue from thesubcutaneous layer under the skin (350x).Nucleus offat cellVacuolecontainingfat dropletAdiposetissueMammaryglandsFigure 4.8c(c) Connective tissue proper: loose connective tissue, reticularDescription: Network of reticularfibers in a typical loose groundsubstance; reticular cells lie on thenetwork.Function: Fibers form a soft internalskeleton (stroma) that supports othercell types including white blood cells,mast cells, and macrophages.Location: Lymphoid organs (lymphnodes, bone marrow, and spleen).Photomicrograph: Dark-staining network of reticularconnective tissue fibers forming the internal skeletonof the spleen (350x).SpleenWhite bloodcell(lymphocyte)ReticularfibersFigure 4.8d(d) Connective tissue proper: dense connective tissue, dense regular Description: Primarily parallelcollagen fibers; a few elastic fibers;major cell type is the fibroblast.Function: Attaches muscles tobones or to muscles; attaches bonesto bones; withstands great tensilestress when pulling force is appliedin one direction.Location: Tendons, mostligaments, aponeuroses.Photomicrograph: Dense regular connectivetissue from a tendon (500x).ShoulderjointLigamentTendonCollagenfibersNuclei offibroblastsFigure 4.8e(e) Connective tissue proper: dense connective tissue, dense irregular Description: Primarilyirregularly arranged collagenfibers; some elastic fibers;major cell type is the fibroblast.Function: Able to withstandtension exerted in manydirections; provides structuralstrength.Location: Fibrous capsules oforgans and of joints; dermis ofthe skin; submucosa ofdigestive tract.Photomicrograph: Dense irregularconnective tissue from the dermis of theskin (400x).CollagenfibersNuclei offibroblastsFibrousjointcapsuleFigure 4.8f(f) Connective tissue proper: dense connective tissue, elasticDescription: Dense regularconnective tissue containing a highproportion of elastic fibers.Function: Allows recoil of tissuefollowing stretching; maintainspulsatile flow of blood througharteries; aids passive recoil of lungsfollowing inspiration.Location: Walls of large arteries;within certain ligaments associatedwith the vertebral column; within thewalls of the bronchial tubes.Elastic fibersAortaHeartPhotomicrograph: Elastic connective tissue inthe wall of the aorta (250x).Connective Tissue: CartilageThree types of cartilage:Hyaline cartilageElastic cartilageFibrocartilageFigure 4.8g(g) Cartilage: hyalineDescription: Amorphous but firmmatrix; collagen fibers form animperceptible network; chondroblastsproduce the matrix and when mature(chondrocytes) lie in lacunae.Function: Supports and reinforces;has resilient cushioning properties;resists compressive stress.Location: Forms most of theembryonic skeleton; covers the endsof long bones in joint cavities; formscostal cartilages of the ribs; cartilagesof the nose, trachea, and larynx.Photomicrograph: Hyaline cartilage from thetrachea (750x).CostalcartilagesChondrocytein lacunaMatrixFigure 4.8h(h) Cartilage: elasticDescription: Similar to hyalinecartilage, but more elastic fibersin matrix.Function: Maintains the shapeof a structure while allowinggreat flexibility.Location: Supports the externalear (pinna); epiglottis.Photomicrograph: Elastic cartilage fromthe human ear pinna; forms the flexibleskeleton of the ear (800x).Chondrocytein lacunaMatrixFigure 4.8i(i) Cartilage: fibrocartilageDescription: Matrix similar tobut less firm than that in hyalinecartilage; thick collagen fiberspredominate.Function: Tensile strengthwith the ability to absorbcompressive shock.Location: Intervertebral discs;pubic symphysis; discs of kneejoint.Photomicrograph: Fibrocartilage of anintervertebral disc (125x). Special stainingproduced the blue color seen.IntervertebraldiscsChondrocytesin lacunaeCollagenfiberFigure 4.8j(j) Others: bone (osseous tissue)Description: Hard, calcifiedmatrix containing many collagenfibers; osteocytes lie in lacunae.Very well vascularized.Function: Bone supports andprotects (by enclosing);provides levers for the musclesto act on; stores calcium andother minerals and fat; marrowinside bones is the site for bloodcell formation (hematopoiesis).Location: BonesPhotomicrograph: Cross-sectional viewof bone (125x).LacunaeLamellaCentralcanalFigure 4.8k(k) Others: bloodDescription: Red and whiteblood cells in a fluid matrix(plasma).Function: Transport ofrespiratory gases, nutrients,wastes, and other substances.Location: Contained withinblood vessels.Photomicrograph: Smear of human blood (1860x); twowhite blood cells (neutrophil in upper left and lymphocytein lower right) are seen surrounded by red blood cells.NeutrophilRed bloodcellsLymphocytePlasmaNervous TissueNervous system (more detail with the Nervous System, Chapter 11)Figure 4.9Photomicrograph: Neurons (350x)Function: Transmit electricalsignals from sensory receptorsand to effectors (muscles andglands) which control their activity.Location: Brain, spinalcord, and nerves.Description: Neurons arebranching cells; cell processesthat may be quite long extend fromthe nucleus-containing cell body;also contributing to nervous tissueare nonirritable supporting cells(not illustrated).DendritesNeuron processesCell bodyAxonNuclei ofsupportingcellsCell bodyof a neuronNeuronprocessesNervous tissueMuscle TissueSkeletal muscle (more detail with the Muscular System, Chapter 10)Figure 4.10a(a) Skeletal muscleDescription: Long, cylindrical,multinucleate cells; obviousstriations.Function: Voluntary movement;locomotion; manipulation of theenvironment; facial expression;voluntary control.Location: In skeletal musclesattached to bones oroccasionally to skin.Photomicrograph: Skeletal muscle (approx. 460x).Notice the obvious banding pattern and thefact that these large cells are multinucleate.NucleiStriationsPart ofmuscle fiber (cell)Muscle TissueCardiac muscle (more detail with the Cardiovascular System, Chapters 18 and 19)Figure 4.10b(b) Cardiac muscleDescription: Branching, striated, generally uninucleate cells that interdigitate atspecialized junctions (intercalated discs).Function: As it contracts, it propels blood into the circulation; involuntary control.Location: The walls of the heart.Photomicrograph: Cardiac muscle (500X);notice the striations, branching of cells, andthe intercalated discs.IntercalateddiscsStriationsNucleusMuscle TissueSmooth muscle Figure 4.10c(c) Smooth muscleDescription: Spindle-shapedcells with central nuclei; nostriations; cells arranged closely to form sheets.Function: Propels substancesor objects (foodstuffs, urine,a baby) along internal passage-ways; involuntary control.Location: Mostly in the wallsof hollow organs.Photomicrograph: Sheet of smooth muscle (200x).SmoothmusclecellNucleiEpithelial Membranes Cutaneous membrane (skin) (More detail with the Integumentary System, Chapter 5)Figure 4.11aCutaneousmembrane(skin)(a) Cutaneous membrane (the skin)covers the body surface. Epithelial MembranesMucous membranesMucosaeLine body cavities open to the exterior (e.g., digestive and respiratory tracts)Figure 4.11bMucosa ofnasal cavityMucosa oflung bronchiMucosa ofmouthEsophaguslining(b) Mucous membranes line body cavitiesopen to the exterior.Epithelial MembranesSerous MembranesSerosae—membranes (mesothelium + areolar tissue) in a closed ventral body cavityParietal serosae line internal body wallsVisceral serosae cover internal organsFigure 4.11cParietalpericardiumVisceralpericardium(c) Serous membranes line body cavitiesclosed to the exterior.ParietalperitoneumVisceralperitoneumParietalpleuraVisceralpleuraSteps in Tissue RepairInflammationRelease of inflammatory chemicalsDilation of blood vesselsIncrease in vessel permeabilityClotting occursFigure 4.12, step 1ScabBlood clot inincised woundEpidermisVeinInflammatorychemicalsInflammation sets the stage:• Severed blood vessels bleed and inflammatory chemicals arereleased.• Local blood vessels become more permeable, allowing whiteblood cells, fluid, clotting proteins and other plasma proteinsto seep into the injured area.• Clotting occurs; surface dries and forms a scab.Migrating whiteblood cellArtery1Steps in Tissue RepairOrganization and restored blood supplyThe blood clot is replaced with granulation tissueEpithelium begins to regenerateFibroblasts produce collagen fibers to bridge the gapDebris is phagocytizedFigure 4.12, step 2RegeneratingepitheliumArea ofgranulationtissueingrowth FibroblastMacrophageOrganization restores the blood supply:• The clot is replaced by granulation tissue, which restoresthe vascular supply.• Fibroblasts produce collagen fibers that bridge the gap.• Macrophages phagocytize cell debris.• Surface epithelial cells multiply and migrate over thegranulation tissue.2Steps in Tissue RepairRegeneration and fibrosisThe scab detachesFibrous tissue matures; epithelium thickens and begins to resemble adjacent tissueResults in a fully regenerated epithelium with underlying scar tissue Figure 4.12, step 3RegeneratedepitheliumFibrosedareaRegeneration and fibrosis effect permanent repair:• The fibrosed area matures and contracts; the epitheliumthickens.• A fully regenerated epithelium with an underlying area ofscar tissue results.3Developmental AspectsPrimary germ layers: ectoderm, mesoderm, and endodermFormed early in embryonic developmentSpecialize to form the four primary tissuesNerve tissue arises from ectodermMuscle and connective tissues arise from mesodermEpithelial tissues arise from all three germ layersFigure 4.13MesodermEndoderm16-day-old embryo(dorsal surface view)EpitheliumNervous tissue(from ectoderm)Muscle and connectivetissue (mostly frommesoderm)EctodermTissues: Study GuideTissues- Types of muscle tissues