Chapter 4 OutlineEpithelial Tissue Connective Tissue Muscle Tissue Nervous TissueTissue Change and Aging
IntroductionThe body is composed of trillions of cells, which are organized into more complex units called tissuesA tissue is a group of similar cells and extracellular products that perform a common function
IntroductionFour types of tissue in the body:Epithelial tissueConnective tissueMuscle tissueNervous tissue
Epithelial TissueEpithelial tissue lines every body surface and all body cavitiesOrgans are lined on the outside and inside by epithelial tissueThe majority of glands are derived from epithelial tissueEpithelial tissue possesses little to no extracellular matrix
Characteristics of Epithelial TissueAll epithelia share several characteristics:Junctions: Cells are bound together by several types of intercellular junctionsPolarity: Epithelial cells have an apical (top) surface and a basal (bottom) surface where they attach to underlying cells
Characteristics of Epithelial TissueAttachment: Basal surface is attached to a thin basement membrane, which is an acellular structure produced by both epithelial and underlying connective tissue cellsAvascularity: All epithelial tissues lack blood vessels; the cells receive their nutrients by diffusion from underlying tissues
Characteristics of Epithelial TissueInnervation: Epithelia are richly innervatedHigh regeneration capacity: Because the apical surface is constantly exposed to the environment, epithelial cells are frequently damaged or die; they are replaced as quickly as they are lost
Polarity and Intercellular Junctions in an EpitheliumFigure 4.1aCopyright McGraw-Hill Education. Permission required for reproduction or display.Apical (free) surfaceLateral surfaceBasal surfaceEpitheliumBasement membraneConnective tissueBlood vessel(a) Epitheliumconnective tissue junction
Functions of Epithelial TissuePhysical protection: From dehydration and abrasion, as well as physical, chemical, and biological agentsSelective permeability: Regulate the passage of certain molecules in or out of certain regions of the bodySecretion: Some epithelial cells called exocrine cells produce secretions such as sweat or oilSensation: Possess nerve endings that can detect light, taste, sound, smell, and hearing
Basement membrane
Specialized StructuresThe basement membrane is found between the epithelium and underlying connective tissueProvides anchoring of epithelial tissueActs as a barrier to regulate passage of large molecules between epithelium and underlying connective tissue
Cell junctionsNot restricted to epithelial cells, however, they are found in large number in epithelial tissue.Tight junction (zonula occludens)Adherent junction = desmosomeGap junction
Polarity and Intercellular Junctions in an EpitheliumFigure 4.1Copyright McGraw-Hill Education. Permission required for reproduction or display.Apical (free) surfaceLateral surfaceBasal surfaceEpitheliumBasement membraneConnective tissueBlood vessel(a) Epitheliumconnective tissue junctionGap junctionPoreConnexonIntercellular spacePlasma membraneIntermediate filamentsHemidesmosomeDesmosomeProtein filamentsProtein plaque(b) Types of intercellular junctionsTight junctionAdhering junctionMembrane proteinPlasma membraneMicrofilamentIntercellular spaceAdjacent plasmamembranes
Tight JunctionsEncircle cells near their apical surfacePrevent molecules from traveling between epithelial cells, therefore molecules must go through the epithelial cells rather than in between themGatekeepers between an external and internal environment
Adhering Junctions (desmosomes)Belt desmosome (zonula adherens)Spot desmosome (macula adherens)hemidesmososme
Belt Desmosome
keeps tissues from separating as they stretch and contract.
Belt DesmosomeFormed completely around the cell deep to the tight junction Microfilaments act like a purse string to stabilize the apical surface of the epithelial cell
Spot Desmosome
Spot DesmosomesLike a button or snap between adjacent cells Appear at locations of mechanical stress between cells sharing this type of junction Consist of a thickened protein plaque on each of the apposed cell membranes with a fine network of proteins spanning the intercellular space between the plaquesOn the cytoplasmic side, intermediate filaments attach to the plaques and provide support and stability to this structure that is shared between the two apposed cells
Hemidesmosomesjoins the basal surface cell to basal lamina rather than to another cell
Membrane Junctions- Gap Junction
Gap JunctionsFluid-filled channels that directly connect the cytoplasms of apposed cells sharing these structuresAllow adjacent cells to communicate with each other by the flow of ions and other small molecular messengers
Classification of Epithelial TissueMany different types of epithelial tissueClassified according to two criteria:Number of layers of cellsShape of the cells
Classification by Number of Cell LayersSimple epithelium: A single layer of cells with all cells having an apical surface and attached to the basement membraneStratified epithelium: Two or more layers of cells; not all cells have an apical surface nor do all cells attach to the basement membranePseudostratified epithelium: Cell nuclei give the appearance of a multilayered epithelium, but not all cells reach the apical surface
Classification of EpitheliaFigure 4.2a
Classification by Cell ShapeSquamous: Flat, wide, and somewhat irregular in shapeCuboidal: About the same size on all sides; the nucleus is usually centrally locatedColumnar: Taller than they are wide; nucleus is oval and located in the basal region of the cell
Classification of EpitheliaFigure 4.2b
Types of Epithelium
Simple Squamous EpitheliumSingle layer of flat cells
Simple Cuboidal EpitheliumSingle layer of cells as tall as they are wide
Nonciliated Simple Columnar EpitheliumSingle layer of cells that are taller than they are wideNo cilia present
Ciliated Simple Columnar EpitheliumColumnar epithelial cells; some have cilia on their apical surface
Nonkeratinized Stratified Squamous EpitheliumMultiple layers of cellsApical cells are squamous
Keratinized Stratified Squamous EpitheliumMultiple layers of cellsApical cells are squamousSuperficial layers of cells contain keratin
Stratified Cuboidal EpitheliumMultiple layers of cellsApical cells are cuboidal
Stratified Columnar EpitheliumMultiple layers of cellsApical cells are columnar
Pseudostratified Columnar EpitheliumSingle layer of columnar epithelial cells, but layered appearance of nuclei suggests multiple layers of cells
Transitional EpitheliumApical cell shape changes depending on whether the tissue is stretched or relaxed
GlandsIndividual cells or multicellular organsThey produce mucin, hormones, enzymes, and waste productsGlands fall into two categories:Endocrine glands do not possess ducts and secrete directly into the interstitial fluid or the bloodstreamExocrine glands possess ducts and their cells secrete their products into their ducts
General Structure of Exocrine GlandsFigure 4.4
Structural Classification of Multicellular Exocrine GlandsFigure 4.5
Unicellular Exocrine GlandsThe only important unicellular gland is the goblet cellsecrete mucin Mucin, a complex glycoprotein, which dissolve in water mucus (for protection and lubrication)
Figure 4.4(b)(a)MicrovilliSecretoryvesiclescontainingmucinGolgiapparatusRough ERNucleus
Modes of SecretionApocrine:Merocrine Holocrine
ApocrineSecretes intact vesicle along with some cytoplasm. Secretion process results in some damage to cells plasma membrane Ex: mammary glands
Merocrine
Products are secreted by exocytosis (e.g., pancreas, sweat and salivary glands)Most numerous gland typeEx: digestive enzymes from pancreatic acinar cells and insulin
Holocrinethe whole cell is released. Cells may be viable (oocyte or sperm) Cell may rupture: Sebaceous gland is the only example (cells are replaced by rapid division of stem cells.)
Connective TissueMost diverse, abundant, widely distributed, and structurally varied of all four tissue typesConnective tissue is the glue and filler of the bodyExamples include tendons, ligaments, fat, bones, cartilage, and blood
Characteristics ofConnective TissueCells: Different cells for different types of connective tissueExamples include fibroblasts, osteocytes, and adipocytesProtein fibers: Elastic fibers, collagen, reticular fibersGround substance: A mixture of proteins and carbohydrates with variable amounts of salts and waterProtein fibers and ground substance comprise the extracellular matrix
Ground substanceComponents:Interstitial fluid (mostly water)Fibronectin: adhesion proteins (glue) attaches the ECM to the plasma membraneProteoglycansProtein core + large polysaccharides (chrondroitin sulfate and hyaluronic acid)Trap water in varying amounts, affecting the viscosity of the ground substance
Connective Tissue Components and OrganizationFigure 4.7
Functions of Connective TissuePhysical protectionSupport and structural frameworkBinding of structuresStorageTransportImmune protection
Development of Connective TissueArises from mesodermTwo types of embryonic CT:Mesenchyme: The source of all adult connective tissueMucous: Found in umbilical cord
Embryonic Connective Tissue
Classification of Connective TissueTypes present after birth can be classified into three broad categories:Connective tissue properSupporting connective tissueFluid connective tissue
Connective Tissue ClassificationFigure 4.8
Connective Tissue ProperThere are two groups of cells in connective tissue proper:Resident cells: Include fibroblasts, adipocytes, fixed macrophages, and mesenchymal cellsWandering cells: Include mast cells, plasma cells, free macrophages, and other leukocytes
Cells of Connective Tissue Proper
Fibers of Connective Tissue ProperThere are three general types of protein fibers produced by CT cells and secreted into the extracellular matrix:Collagen fibers: long, unbranching, strong, flexible, and resistant to stretching. They make up 25% of all protein in the human body, making collagen the most abundant protein.
Fibers of Connective Tissue ProperElastic fibers: Thinner than collagen, stretch easily, branch, and rejoinThese fibers allow structures such as blood vessels to stretch and relaxReticular fibers: Thinner than collagen fibers; form a branching, woven frameworkFound in the stroma of organs with abundant spaces such as liver, lymph nodes, and spleen
Ground Substance of Connective Tissue ProperA combination of proteins and carbohydratesTexture is usually gelatinousAdditional content such as water and salts can result in a texture anywhere from semi-fluid (adipose) to hard (bone)
Categories of Connective Tissue ProperClassified into two categories:Loose connective tissue: Serves as the bodys packing material, found in spaces around organsTypes include areolar, adipose, and reticularDense connective tissue: Strong, has fibers (mostly collagen) packed tightly togetherTypes include dense regular, dense irregular, and elastic
Connective Tissue Proper
Areolar Connective TissueOne of the most widely distributed of all tissuesSeveral kinds of cells present: fibroblasts and macrophages, mast cells, plasma cells, fat cells, and some white blood cells Function: stretch, flexible connection
Adipose Connective TissueProduces the hormone leptin, which signals the brain how much fat is stored Leptin inhibits NPY synthesis (appetite stimulator)
Reticular Connective TissueForms framework of spleen, lymph nodes, and bone marrowFunctions: defense against microorganisms and other injurious substancesContains reticular fibers, fibroblasts, and leukocytes
Dense Regular Connective TissueCollagen fibers aligned parallel to applied force
Dense Irregular Connective TissueBundles of collagen fibers extending in many directions
Elastic Connective TissueElastic fibers provide ability to stretch and recoil
Supporting Connective TissueTwo types of supporting connective tissue:CartilageBone
CartilageFirm, gel-like extracellular matrix composed of protein and ground substanceCells are called chondrocytesChondrocytes occupy small spaces enclosed by their extracellular matrix called lacunaeSupport and withstand deformation
Types of CartilageThere are three types of cartilage:Hyaline cartilageFibrocartilageElastic cartilage
Hyaline CartilageMost common type, but also the weakestGlassy matrix
FibrocartilageDensely interwoven collagen fibers contribute to the durability
Elastic CartilageAbundant elastic fibers
BoneCells are called osteocytesExtracellular matrix is a mixture of collagen and calcium saltsThis mixture provides flexibility from the organic components and compressional strength from the inorganic components
BoneCalcified matrix arranged in osteons
Fluid Connective TissueRefers to the bloodComposed of the following components:Plasma: A watery ground substance containing protein fibersErythrocytes: Red blood cellsLeukocytes: White blood cellsPlatelets: Fragments of blood cells involved in blood clotting
Fluid Connective TissueContains erythrocytes, leukocytes, and plateletsPlasma contains soluble proteins
Epithelial Membranes Majority of the organs are composed of all 4 tissues.Epithelial membranes are the simplest organs, which is composed of mainly Epithelial tissue and connective tissue.1. Cutaneous membrane (skin)
Cutaneousmembrane(skin)(a) Cutaneous membrane (the skin) covers the body surface.
Epithelial Membranes2. Mucous membranes (Mucosae)Line body cavities open to the exterior (e.g., digestive and respiratory tracts)Epithelial tissue can be:stratified squamous epitheliasimple columnar epithelia. The epithelial sheet is directly underlain by a layer of loose CT called the lamina propria
Figure 4.11bMucosa ofnasal cavityMucosa oflung bronchiMucosa ofmouthEsophaguslining(b) Mucous membranes line body cavities open to the exterior.
Mucus membrane
Epithelial Membranes3. Serous Membranes (Serosae):Membranes in a closed ventral body cavityParietal serosae line internal body wallsVisceral serosae cover internal organsEpithelial and connective tissues are:simple squamous epithelium (a mesothelium) a thin layer of areolar tissueIt is named according to their sites (pleura, pericardium, peritoneum)
Figure 4.11cParietalpericardiumVisceralpericardium(c) Serous membranes line body cavities closed to the exterior.ParietalperitoneumVisceralperitoneumParietalpleuraVisceralpleura
Muscle TissueComprised of cells called fibersWhen stimulated by the nervous system, fibers shortenThe result of shortening is movementExamples: Movement of bones, blood, food, and sperm
Classification of Muscle TissueThree histological types of muscle in the body:Skeletal muscle tissueCardiac muscle tissueSmooth muscle tissue
Skeletal Muscle TissueCells (muscle fibers) are:Cylindrical and long (some as long as whole muscle)MultinucleatedStriated (striped internal appearance) and voluntaryAttached to bones of skeleton and sometimes skin
Skeletal Muscle TissueLong, cylindrical fibersStriated, parallel, and unbranchedLong, cylindrical fibersStriated, parallel, and unbranched
Cardiac Muscle TissueFound only in the wall of the heart (myocardium)Cells are:Branched, Y-shaped, and shorter than skeletal fiber cellsStriatedInvoluntaryAttached end-to-end by strong gap junctions at intercalated discs that allow rapid passage of electrical current from one cell to the next during each heartbeatContraction causes movement of blood
Cardiac Muscle TissueCells are short, striated, and branchingIntercalated discs at cell junctions
Smooth Muscle TissueFound in walls of most internal organsExamples: Stomach, intestines, urinary bladderCells are:Relatively short, wide in the middle, and tapered at the ends (fusiform)Involuntary with no striationsContraction causes movement of food, blood, sperm
Smooth Muscle TissueCells are fusiform, short, and nonstriated
Nervous TissueContains two types of cells:Neurons: Nerve cells that are capable of initiating and conducting electrical activity throughout the bodyGlial cells: Cells that support and protect neuronsFunction is communication and control of body functionsFound in brain, spinal cord, and nerves
Nervous TissueNeurons containing cell processes called axons and dendritesGlial cells lack these processes
Tissue Change and AgingTissues can undergo change in form, size, or number during the aging process:Metaplasia: Epithelia lining the respiratory airways of people who smoke change from pseudostratified ciliated to stratified squamousHypertrophy: An increase in the size of existing cellsHyperplasia: An increase in number of cells in a tissueNeoplasia: Out-of-control growth, which forms a tumorAtrophy: Shrinkage of tissue by cell size or number
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