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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