Presentation on theme: "Dvt 1102 hISTOLOGY Tissues - collections of similar cells and the substances surrounding them Tissue classification based on structure of cells, composition."— Presentation transcript:
1Dvt 1102 hISTOLOGYTissues - collections of similar cells and the substances surrounding themTissue classification based on structure of cells, composition of noncellular extracellular matrix, and cell functionMajor types of adult tissuesEpithelialConnectiveMuscleNervousHistology: Microscopic Study of TissuesBiopsy: removal of tissues for diagnostic purposesAutopsy: examination of organs of a dead body to determine cause of death
2Embryonic Tissue3 major germ layers that form the embryonic disc (source of stem cells)EndodermInner layerForms lining of digestive tract and derivativesMesodermMiddle layerForms tissues as such muscle, bone, blood vesselsEctodermOuter layerForms skin and neuroectoderm
3I. Epithelial Tissue Cellularity - Consists almost entirely of cells Covers body surfaces, lines hollow organs, and forms glandsOutside surface of the bodyLining of digestive, respiratory and urogenital systemsHeart and blood vesselsLinings of many body cavitiesPolarity - Has apical, basal, and lateral surfacesRests on a basement membraneSpecialized cell contacts bind adjacent cells togetherAvascular - no blood vesselsRegenerative -Replaces lost cells by cell division
4Functions of Epithelia Protecting underlying structures; e.g., epithelium lining the mouthActing as barriers; e.g., skinPermitting the passage of substances; e.g., cells lining air sacs in lungs and nephrons in kidneySecreting substances; e.g., pancreatic cellsAbsorbing substances; e.g., lining of stomach and small intestine
6Classification of Epithelium Number of layers of cellsSimple- one layer of cells. Each extends from basement membrane to the free surfaceStratified- more than one layer.Pseudostratified- tissue appears to be stratified, but all cells contact basement membrane so it is in fact simpleShape of cellsSquamous- flat, scale-likeCuboidal- about equal in height and widthColumnar- taller than wide
18Epithelium: Glandular A gland is one or more cells that makes and secretes an aqueous fluidTwo types of glands formed by infolding of epithelium:Endocrine: no contact with exterior of body; ductless; produce hormones (pituitary, thyroid, adrenals, pancreas)Exocrine: open to exterior of body via ducts (sweat, oil)Exocrine glands classified either by structure or by the method of secretionClassified by structureUnicellular: goblet cellsMulticellular: sweat, oil, pituitary, adrenal
19Multicellular Exocrine Glands Classified on the basis of types of ducts or mode of secretionTypes of ductsSimple: ducts with few branchesCompound: ducts with many branchesIf ducts end in tubules or sac-like structures: acini. PancreasIf ducts end in simple sacs: alveoli. Lungs
20Lateral Surface Features Tight junctionsDesmosomesGap junctions
21Membrane Junctions: Tight Junction Integral proteins of adjacentcells fuse togetherCompletely encircle the celland form an adhesion belt.Form an impermeablejunction.Common near apical region
22Lateral Surface Features – Cell Junctions Desmosomes – two disc-like plaques connected across intercellular spacePlaques of adjoining cells are joined by proteins called cadherinsProteins interdigitate into extracellular spaceIntermediate filaments insert into plaques from cytoplasmic side
23Membrane Junctions: Desmosome Linker proteins extend from plaque like teeth of a zipper.Intermediate filaments extend across width of cell.Common in superficial layers of skin; skinpeels after a sunburnReduces chance of tearing, twisting, stretchingFigure 3.5b
24Membrane Junctions: Gap Junction Connexon proteins are trans-membrane proteins.Present in electrically excitabletissues (heart, smooth muscle)
25Basal Feature: The Basal Lamina Noncellular supporting sheet between the epithelium and the connective tissue deep to it Consists of proteins secreted by the epithelial cells Functions: Acts as a selective filter, determining which molecules from capillaries enter the epithelium Acts as scaffolding along which regenerating epithelial cells can migrate Basal lamina and reticular layers of the underlying connective tissue deep to it form the basement membrane
26Epithelial Surface Features Apical surface featuresMicrovilli – finger-like extensions of plasma membraneAbundant in epithelia of small intestine and kidneyMaximize surface area across which small molecules enter or leaveCilia – whip-like, highly motile extensions of apical surface membranesMovement of cilia – in coordinated waves
27Connective Tissue Most diverse and abundant tissue Main classes Connective tissue properCartilageBone tissueBloodCharacteristicsMesenchyme as their common tissue of origin (mesenchyme derived from mesoderm)Varying degrees of vascularityNonliving extracellular matrix, consisting of ground substance and fibersCells are not as abundant nor as tightly packed together as in epithelium
29Functions of Connective Tissue Enclose organs as a capsule and separate organs into layers. AreolarConnect tissues to one another. Tendons and ligaments.Support and movement. Bones.Storage. Fat.Insulation. Fat.Transport. Blood.Protection. Bone, cells of the immune system.
30Structural Elements of Connective Tissue Ground substance – unstructured material that fills the space between cellsFibers – collagen, elastic, or reticularCells – fibroblasts, chondroblasts, osteoblasts, hematopoietic stem cells, and others
31Connective Tissue Cells Fibroblasts - secrete the proteins needed for fiber synthesis and components of the extracellular matrixAdipose or fat cells (adipocytes). Common in some tissues (dermis of skin); rare in some (cartilage)Mast cells. Common beneath membranes; along small blood vessels. Can release heparin, histamine, and proteolytic enzymes in response to injury.Leukocytes (WBC’s). Respond to injury or infectionMacrophages. Derived from monocytes (a WBC). Phagocytic; provide protectionChondroblasts - form cartilageOsteoblasts - form boneHematopoietic stem cells - form blood cellsUndifferentiated mesenchyme (stem cells). Have potential to differentiate into adult cell types.
32Extracellular Matrix - ECM ECM has 3 major components1. Protein fibers Ground substance FluidProtein fibersCollagen fibers. Composed of the protein collagen. Strong, flexible, inelastic; great tensile strength (i.e. resist stretch). Perfect for tendons, ligamentsElastic fibers. Contain molecules of protein elastin that resemble coiled springs. Returns to its original shape after stretching or compression. Perfect for lungs, large blood vesselsReticular fibers. Formed from fine collagenous fibers; form branching networks (stroma). Fill spaces between tissues and organs.
33Ground SubstanceInterstitial (tissue) fluid within which are one or more of the molecules listed below:Hyaluronic acid: a polysaccharide. Very slippery; serves as a good lubricant for joints. Common in most connective tissues.Proteoglycans: protein and polysaccharide complex. Polysaccharides called glyocosaminoglycans (chondroitin sulfate, keratin sulfate). Protein part attaches to hyaluronic acid. Able to trap large amounts of water.Adhesive molecules: hold proteoglycan aggregates together. Chondronectin in cartilage, osteonectin in bone, fibronectin in fibrous connective tissue.Functions as a molecular sieve through which nutrients diffuse between blood capillaries and cells
34Embryonic Connective Tissue Mesenchyme: source of all adult connective tissue.Derived from mesodermDelicate collagen fibers embedded in semifluid matrixMucus: found only in the umbilical cord. Wharton’s jelly.
40Elastic Connective Tissue Bundles and sheets of collagenous and elastic fibers oriented in multiple directionsIn walls of elastic arteries (aorta), lungs, vocal ligamentsStrong, yet elastic; allows for recoil of tissue after being stretched
41Connective Tissue: Cartilage Composed of chondrocytes (cells) located in matrix-surrounded spaces called lacunae.Type of cartilage determined by components of the matrix.Firm consistency.Ground substance: Proteoglycans and hyaluronic acid complexed together trap large amounts of water (microscopic sponges). Allows tissue to spring back after being compressed.Avascular and no nerve supply. Heals slowly.Perichondrium. Dense irregular connective tissue that surrounds cartilage. Fibroblasts of perichondrium can differentiate into chondroblasts (cartilage-forming cells)Types of cartilageHyalineFibrocartilageElastic
47Muscle Tissue Characteristics Cells are referred to as fibers Contracts or shortens with force when stimulatedMoves entire body and pumps bloodTypesSkeletal:attached to bonesCardiac: muscle of the heart.Smooth: muscle associated with tubular structures and with the skin. Nonstriated and involuntary.
52Tissues and Aging Cells divide more slowly Collagen fibers become more irregular in structure, though they may increase in numberTendons and ligaments become less flexible and more fragileElastic fibers fragment, bind to calcium ions, and become less elasticArterial walls and elastic ligaments become less elasticChanges in collagen and elastin result inAtherosclerosis and reduced blood supply to tissuesWrinkling of the skinIncreased tendency for bones to breakRate of blood cell synthesis declines in the elderlyInjuries don’t heal as readily