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HistologyHistology
Study of TissuesStudy of Tissues Epithelial TissueEpithelial Tissue Connective TissueConnective Tissue Nervous and Muscular Tissue Nervous and Muscular Tissue Intercellular Junctions, Glands and Intercellular Junctions, Glands and
MembranesMembranes Tissue Growth, Development, Death and Tissue Growth, Development, Death and
RepairRepair
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The Study of TissuesThe Study of Tissues 200 Different cell types200 Different cell types Four primary tissue classesFour primary tissue classes
epithelial tissueepithelial tissue connective tissueconnective tissue muscular tissuemuscular tissue nervous tissuenervous tissue
Histology (microscopic anatomy)Histology (microscopic anatomy) study of tissues organ formationstudy of tissues organ formation
Organ = structure with discrete boundariesOrgan = structure with discrete boundaries composed of 2 or more tissue typescomposed of 2 or more tissue types
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Features of Tissue ClassesFeatures of Tissue Classes Tissue = similar cells and cell productsTissue = similar cells and cell products
arose from same region of embryoarose from same region of embryo Differences between tissue classesDifferences between tissue classes
types and functions of cellstypes and functions of cells characteristics of matrix (extracellular material)characteristics of matrix (extracellular material)
• fibrous proteins fibrous proteins • ground substanceground substance
clear gels (ECF, tissue fluid, interstitial fluid, tissue gel)clear gels (ECF, tissue fluid, interstitial fluid, tissue gel) rubbery or stony in cartilage or bonerubbery or stony in cartilage or bone
space occupied by cells versus matrixspace occupied by cells versus matrix• connective tissue cells are widely separated connective tissue cells are widely separated • little matrix between epithelial and muscle cellslittle matrix between epithelial and muscle cells
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Tissue Techniques and SectioningTissue Techniques and Sectioning
Preparation of histological specimensPreparation of histological specimens fixative prevents decay (formalin)fixative prevents decay (formalin) sliced into thin sections 1 or 2 cells thicksliced into thin sections 1 or 2 cells thick mounted on slides and colored with mounted on slides and colored with
histological stainhistological stain• stains bind to different cellular componentsstains bind to different cellular components
Sectioning reduces 3-dimensional Sectioning reduces 3-dimensional structure to 2-dimensional slicestructure to 2-dimensional slice
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Sectioning Solid ObjectsSectioning Solid Objects
Sectioning a cell Sectioning a cell with a centrally with a centrally located nucleuslocated nucleus
Some slices Some slices miss the cell miss the cell nucleusnucleus
In some the In some the nucleus is nucleus is smaller smaller
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Sectioning Hollow StructuresSectioning Hollow Structures
Cross section of Cross section of blood vessel, gut, blood vessel, gut, or other tubular or other tubular organ.organ.
Longitudinal Longitudinal section of a sweat section of a sweat gland. Notice gland. Notice what a single slice what a single slice could look like.could look like.
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Types of Tissue SectionsTypes of Tissue Sections
Longitudinal sectionLongitudinal section tissue cut along tissue cut along
longest direction of longest direction of organorgan
Cross sectionCross section tissue cut tissue cut
perpendicular to length perpendicular to length of organof organ
Oblique sectionOblique section tissue cut at angle tissue cut at angle
between cross and between cross and longitudinal sectionlongitudinal section
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Epithelial TissueEpithelial Tissue
Layers of closely adhering cellsLayers of closely adhering cells Flat sheet with upper surface exposed to the Flat sheet with upper surface exposed to the
environment or an internal body cavityenvironment or an internal body cavity No blood vesselsNo blood vessels
underlying connective tissue supplies oxygenunderlying connective tissue supplies oxygen
Rests on basement membraneRests on basement membrane thin layer of collagen and adhesive proteinsthin layer of collagen and adhesive proteins anchors epithelium to connective tissueanchors epithelium to connective tissue
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Simple Versus Stratified Simple Versus Stratified EpitheliaEpithelia
Simple epitheliumSimple epithelium contains one layer of cellscontains one layer of cells named by shape of cellsnamed by shape of cells
• Stratified epithelium– contains more than one layer– named by shape of apical cells
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Simple Squamous EpitheliumSimple Squamous Epithelium
Single row of flat cellsSingle row of flat cells Permits diffusion of substancesPermits diffusion of substances Secretes serous fluidSecretes serous fluid Alveoli, glomeruli, endothelium, and serosaAlveoli, glomeruli, endothelium, and serosa
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Simple Cuboidal EpitheliumSimple Cuboidal Epithelium
Single row cube-shaped cells with microvilliSingle row cube-shaped cells with microvilli Absorption and secretion, mucus productionAbsorption and secretion, mucus production Liver, thyroid, mammary and salivary glands, Liver, thyroid, mammary and salivary glands,
bronchioles, and kidney tubulesbronchioles, and kidney tubules
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Simple Columnar EpitheliumSimple Columnar Epithelium
Single row tall, narrow cellsSingle row tall, narrow cells oval nuclei in basal half of celloval nuclei in basal half of cell
Absorption and secretion; mucus secretion Absorption and secretion; mucus secretion Lining of GI tract, uterus, kidney and uterine tubesLining of GI tract, uterus, kidney and uterine tubes
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Pseudostratified EpitheliumPseudostratified Epithelium
Single row of cells some not reaching free Single row of cells some not reaching free surfacesurface nuclei give layer stratified looknuclei give layer stratified look
Secretes and propels respiratory mucus Secretes and propels respiratory mucus
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Stratified EpitheliaStratified Epithelia
More than one layer of cells More than one layer of cells Named for shape of surface cellsNamed for shape of surface cells
exception is transitional epitheliumexception is transitional epithelium Deepest cells on basement membraneDeepest cells on basement membrane VariationsVariations
keratinized epithelium has surface layer of dead keratinized epithelium has surface layer of dead cellscells
nonkeratinized epithelium lacks the layer of nonkeratinized epithelium lacks the layer of dead cellsdead cells
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Keratinized Stratified SquamousKeratinized Stratified Squamous
Multilayered epithelium covered with dead squamous Multilayered epithelium covered with dead squamous cells, packed with keratincells, packed with keratin
epidermal layer of skinepidermal layer of skin
Retards water loss and barrier to organismsRetards water loss and barrier to organisms
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Nonkeratinized Stratified SquamousNonkeratinized Stratified Squamous
Multilayered surface epithelium forming moist, Multilayered surface epithelium forming moist, slippery layerslippery layer
Tongue, oral mucosa, esophagus and vaginaTongue, oral mucosa, esophagus and vagina
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Stratified Cuboidal EpitheliumStratified Cuboidal Epithelium
Two or more cell layers; surface cells square Two or more cell layers; surface cells square Secretes sweat; produces sperm and hormonesSecretes sweat; produces sperm and hormones Sweat gland ducts; ovarian follicles and seminiferous Sweat gland ducts; ovarian follicles and seminiferous
tubulestubules
1818
Transitional EpitheliumTransitional Epithelium
Multilayered epithelium surface cells that change Multilayered epithelium surface cells that change from round to flat when stretchedfrom round to flat when stretched allows for filling of urinary tractallows for filling of urinary tract ureter and bladderureter and bladder
1919
Connective TissueConnective Tissue
Widely spaced cells separated by fibers and Widely spaced cells separated by fibers and ground substanceground substance
Most abundant and variable tissue typeMost abundant and variable tissue type FunctionsFunctions
connects organsconnects organs gives support and protection (physical and gives support and protection (physical and
immune)immune) stores energy and produces heatstores energy and produces heat movement and transport of materialsmovement and transport of materials
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Cells of Connective TissueCells of Connective Tissue
Fibroblasts produce fibers and ground substanceFibroblasts produce fibers and ground substance Macrophages phagocytize foreign material and Macrophages phagocytize foreign material and
activate immune systemactivate immune system arise from monocytes (WBCs)arise from monocytes (WBCs)
Neutrophils wander in search of bacteriaNeutrophils wander in search of bacteria Plasma cells synthesize antibodiesPlasma cells synthesize antibodies
arise from WBCsarise from WBCs Mast cells secrete Mast cells secrete
heparin inhibits clottingheparin inhibits clotting histamine that dilates blood vesselshistamine that dilates blood vessels
Adipocytes store triglyceridesAdipocytes store triglycerides
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Fibers of Connective TissueFibers of Connective Tissue Collagen fibers (white fibers)Collagen fibers (white fibers)
tough, stretch resistant, yet flexibletough, stretch resistant, yet flexible tendons, ligaments and deep layer of the skintendons, ligaments and deep layer of the skin
Reticular fibersReticular fibers thin, collagen fibers coated with glycoproteinthin, collagen fibers coated with glycoprotein framework in spleen, lymph nodes, marrowframework in spleen, lymph nodes, marrow
Elastic fibers (yellow fibers)Elastic fibers (yellow fibers) thin branching fibers of elastin proteinthin branching fibers of elastin protein stretch and recoil like rubberband (elasticity)stretch and recoil like rubberband (elasticity) skin, lungs and arteries stretch and recoilskin, lungs and arteries stretch and recoil
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Connective Tissue Ground SubstanceConnective Tissue Ground Substance
Gelatinous material between cells Gelatinous material between cells absorbs compressive forcesabsorbs compressive forces
Consists of 3 classes of large moleculesConsists of 3 classes of large molecules glycosaminoglycans – chondroitin sulfateglycosaminoglycans – chondroitin sulfate
• disaccharides that attract sodium and hold waterdisaccharides that attract sodium and hold water• role in regulating water and electrolyte balancerole in regulating water and electrolyte balance
Proteoglycan (bottlebrush-shaped molecule) Proteoglycan (bottlebrush-shaped molecule) • create bonds with cells or extracellular create bonds with cells or extracellular
macromoleculesmacromolecules adhesive glycoproteinsadhesive glycoproteins
• protein-carbohydrate complexes bind cell membrane protein-carbohydrate complexes bind cell membrane to collagen outside the cellsto collagen outside the cells
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Fibrous Connective Tissue TypesFibrous Connective Tissue Types
Loose connective tissueLoose connective tissue gel-like ground substance between cellsgel-like ground substance between cells typestypes
• areolarareolar• reticularreticular• adiposeadipose
Dense connective tissueDense connective tissue fibers fill spaces between cellsfibers fill spaces between cells types vary in fiber orientationtypes vary in fiber orientation
• dense regular connective tissuedense regular connective tissue• dense irregular connective tissuedense irregular connective tissue
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Areolar TissueAreolar Tissue
Loose arrangement of fibers and cells in abundant Loose arrangement of fibers and cells in abundant ground substanceground substance
Underlies all epithelia, between muscles, Underlies all epithelia, between muscles, passageways for nerves and blood vesselspassageways for nerves and blood vessels
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Reticular TissueReticular Tissue
Loose network of reticular fibers and cellsLoose network of reticular fibers and cells Forms supportive stroma (framework) for Forms supportive stroma (framework) for
lymphatic organslymphatic organs Found in lymph nodes, spleen, thymus and bone Found in lymph nodes, spleen, thymus and bone
marrowmarrow
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Adipose TissueAdipose Tissue
Empty-looking cells with thin margins; nucleus pressed Empty-looking cells with thin margins; nucleus pressed against cell membraneagainst cell membrane
Energy storage, insulation, cushioningEnergy storage, insulation, cushioning subcutaneous fat and organ packingsubcutaneous fat and organ packing brown fat (hibernating animals) produces heatbrown fat (hibernating animals) produces heat
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Dense Regular Connective TissueDense Regular Connective Tissue
Densely, packed, parallel collagen fibersDensely, packed, parallel collagen fibers compressed fibroblast nuclei compressed fibroblast nuclei
Tendons and ligaments hold bones together and Tendons and ligaments hold bones together and attach muscles to bonesattach muscles to bones
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Dense Irregular Connective TissueDense Irregular Connective Tissue
Densely packed, randomly arranged, collagen Densely packed, randomly arranged, collagen fibers and few visible cellsfibers and few visible cells withstands stresses applied in different directions withstands stresses applied in different directions deeper layer of skin; capsules around organsdeeper layer of skin; capsules around organs
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CartilageCartilage
Supportive connective tissue with rubbery Supportive connective tissue with rubbery matrixmatrix
Chondroblasts produce matrixChondroblasts produce matrix called chondrocytes once surroundedcalled chondrocytes once surrounded
No blood vesselsNo blood vessels diffusion brings nutrients and removes wastesdiffusion brings nutrients and removes wastes heals slowlyheals slowly
Types of cartilage vary with fiber typesTypes of cartilage vary with fiber types hyaline, fibrocartilage and elastic cartilagehyaline, fibrocartilage and elastic cartilage
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Hyaline CartilageHyaline Cartilage
Rubbery matrix; dispersed collagen fibers; clustered Rubbery matrix; dispersed collagen fibers; clustered chondrocytes in lacunaechondrocytes in lacunae supports airway, eases joint movements supports airway, eases joint movements
Ends of bones at movable joints; sternal ends of ribs; Ends of bones at movable joints; sternal ends of ribs; supportive material in larynx, trachea, bronchi and fetal supportive material in larynx, trachea, bronchi and fetal skeletonskeleton
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Elastic CartilageElastic Cartilage
Hyaline cartilage with elastic fibers Hyaline cartilage with elastic fibers Provides flexible, elastic supportProvides flexible, elastic support
external ear and epiglottisexternal ear and epiglottis
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FibrocartilageFibrocartilage
Hyaline cartilage with extensive collagen fibers (never has Hyaline cartilage with extensive collagen fibers (never has perichondrium)perichondrium)
Resists compression and absorbs shockResists compression and absorbs shock pubic symphysis, meniscus and intervertebral discspubic symphysis, meniscus and intervertebral discs
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BoneBone
Spongy bone - spongy in appearanceSpongy bone - spongy in appearance delicate struts of bonedelicate struts of bone covered by compact bone covered by compact bone found in heads of long bonesfound in heads of long bones
Compact bone - solid in appearanceCompact bone - solid in appearance more complex arrangementmore complex arrangement cells and matrix surround vertically oriented cells and matrix surround vertically oriented
blood vessels in long bonesblood vessels in long bones
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Bone Tissue (compact bone)Bone Tissue (compact bone)
Calcified matrix in lamellae around central canalCalcified matrix in lamellae around central canal Osteocytes in lacunae between lamellae Osteocytes in lacunae between lamellae Skeletal support; leverage for muscles; mineral Skeletal support; leverage for muscles; mineral
storagestorage
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BloodBlood
Variety of cells and cell fragments; some Variety of cells and cell fragments; some with nuclei and some withoutwith nuclei and some without
Nonnucleated pale pink cells or nucleated Nonnucleated pale pink cells or nucleated white blood cellswhite blood cells
Found in heart and blood vesselsFound in heart and blood vessels
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Nerve TissueNerve Tissue Large cells with long cell processesLarge cells with long cell processes
surrounded by smaller glial cells lacking processessurrounded by smaller glial cells lacking processes
Internal communication between cellsInternal communication between cells in brain, spinal cord, nerves and gangliain brain, spinal cord, nerves and ganglia
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Muscle TissueMuscle Tissue
Elongated cells stimulated to contractElongated cells stimulated to contract Exert physical force on other tissuesExert physical force on other tissues
move limbsmove limbs push blood through a vesselpush blood through a vessel expel urineexpel urine
Source of body heatSource of body heat 3 histological types of muscle3 histological types of muscle
skeletal, cardiac and smoothskeletal, cardiac and smooth
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Skeletal MuscleSkeletal Muscle Long, cylindrical, unbranched cells with striations Long, cylindrical, unbranched cells with striations
and multiple peripheral nucleiand multiple peripheral nuclei movement, facial expression, posture, breathing, movement, facial expression, posture, breathing,
speech, swallowing and excretionspeech, swallowing and excretion
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Cardiac MuscleCardiac Muscle Short branched cells with striations and Short branched cells with striations and
intercalated discsintercalated discs one central nuclei per cellone central nuclei per cell
Pumping of blood by cardiac (heart) musclePumping of blood by cardiac (heart) muscle
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Smooth MuscleSmooth Muscle
Short fusiform cells; nonstriated with only one central nucleusShort fusiform cells; nonstriated with only one central nucleus sheets of muscle in viscera; iris; hair follicles and sheets of muscle in viscera; iris; hair follicles and
sphincters sphincters swallowing, GI tract functions, labor contractions, control of swallowing, GI tract functions, labor contractions, control of
airflow, erection of hairs and control of pupilairflow, erection of hairs and control of pupil
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Intercellular JunctionsIntercellular Junctions
All cells (except blood) anchored to each other All cells (except blood) anchored to each other or their matrix by intercellular junctionsor their matrix by intercellular junctions
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Tight JunctionsTight Junctions Encircle the cell joining it to surrounding cellsEncircle the cell joining it to surrounding cells
zipperlike complementary grooves and ridgeszipperlike complementary grooves and ridges Prevents passage between cellsPrevents passage between cells
GI and urinary tracts GI and urinary tracts
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DesmosomesDesmosomes Patch between cells holding them together Patch between cells holding them together
cells spanned by filaments terminating on protein plaquecells spanned by filaments terminating on protein plaque• cytoplasmic intermediate filaments also attach to plaquecytoplasmic intermediate filaments also attach to plaque
Uterus, heart and epidermisUterus, heart and epidermis
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Gap JunctionsGap Junctions Ring of transmembrane proteins form a water-filled channelRing of transmembrane proteins form a water-filled channel
small solutes pass directly from cell to cell small solutes pass directly from cell to cell
in embryos, cardiac and smooth musclein embryos, cardiac and smooth muscle
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Endocrine and Exocrine GlandsEndocrine and Exocrine Glands
Secrete substances Secrete substances composed of epithelial tissuecomposed of epithelial tissue
Exocrine glands connect to surface with a Exocrine glands connect to surface with a duct (epithelial tube)duct (epithelial tube)
Endocrine glands secrete (hormones) directly Endocrine glands secrete (hormones) directly into bloodstream into bloodstream
Mixed organs do both Mixed organs do both liver, gonads, pancreasliver, gonads, pancreas
Unicellular glands – endo or exocrineUnicellular glands – endo or exocrine goblet or intrinsic cells of stomach wallgoblet or intrinsic cells of stomach wall
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Exocrine Gland StructureExocrine Gland Structure
Stroma = capsule and septa divide gland into lobes and Stroma = capsule and septa divide gland into lobes and lobuleslobules
Parenchyma = cells that secreteParenchyma = cells that secrete Acinus = cluster of cells surrounding the duct draining Acinus = cluster of cells surrounding the duct draining
those cellsthose cells
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Types of Exocrine GlandsTypes of Exocrine Glands
Simple glands - unbranched ductSimple glands - unbranched duct Compound glands - branched ductCompound glands - branched duct Shape of glandShape of gland
acinar - secretory cells form dilated sac acinar - secretory cells form dilated sac tubuloacinar - both tube and sacstubuloacinar - both tube and sacs
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Types of SecretionsTypes of Secretions
Serous glandsSerous glands produce thin, watery secretionsproduce thin, watery secretions
• sweat, milk, tears and digestive juicessweat, milk, tears and digestive juices
Mucous glandsMucous glands produce mucin that absorbs water to form a sticky produce mucin that absorbs water to form a sticky
secretion called mucussecretion called mucus Mixed glands contain both cell typesMixed glands contain both cell types Cytogenic glands release whole cells Cytogenic glands release whole cells
sperm and egg cellssperm and egg cells
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Holocrine GlandHolocrine Gland
Secretory cells disintegrate to deliver their Secretory cells disintegrate to deliver their accumulated productaccumulated product oil-producing glands of the scalpoil-producing glands of the scalp
5050
Merocrine and Apocrine SecretionMerocrine and Apocrine Secretion
Merocrine glands release their Merocrine glands release their product by exocytosisproduct by exocytosis tears, gastric glands, tears, gastric glands,
pancreas, etc.pancreas, etc. Apocrine glands are merocrine Apocrine glands are merocrine
glands with confusing glands with confusing appearance (apical cytoplasm appearance (apical cytoplasm not lost)not lost) mammary and armpit sweat mammary and armpit sweat
glandsglands
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Mucous MembranesMucous Membranes
Epithelium, lamina propria and muscularis mucosaeEpithelium, lamina propria and muscularis mucosae Lines passageways that open to the exterior: reproductive, Lines passageways that open to the exterior: reproductive,
respiratory, urinary and digestiverespiratory, urinary and digestive Mucous (movement of cilia) trap and remove foreign particles and Mucous (movement of cilia) trap and remove foreign particles and
bacteria from internal body surfacesbacteria from internal body surfaces
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Membrane TypesMembrane Types
Cutaneous membrane = skinCutaneous membrane = skin stratified squamous epithelium over connective tissuestratified squamous epithelium over connective tissue relatively dry layer serves protective functionrelatively dry layer serves protective function
Synovial membrane lines joint cavitiesSynovial membrane lines joint cavities connective tissue layer only, secretes synovial fluid connective tissue layer only, secretes synovial fluid
Serous membrane (serosa) –internal membraneSerous membrane (serosa) –internal membrane simple squamous epithelium over areolar tissue, simple squamous epithelium over areolar tissue,
produces serous fluidproduces serous fluid covers organs and lines walls of body cavities covers organs and lines walls of body cavities
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Tissue GrowthTissue Growth
Hyperplasia = tissue growth through cell Hyperplasia = tissue growth through cell multiplicationmultiplication
Hypertrophy = enlargement of preexisting Hypertrophy = enlargement of preexisting cellscells muscle grow through exercisemuscle grow through exercise
Neoplasia = growth of a tumor (benign or Neoplasia = growth of a tumor (benign or malignant) through growth of abnormal malignant) through growth of abnormal tissuetissue
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Tissue RepairTissue Repair
RegenerationRegeneration replacement of damaged cells with original cellsreplacement of damaged cells with original cells skin injuries and liver regenerate skin injuries and liver regenerate
FibrosisFibrosis replacement of damaged cells with scar tissue replacement of damaged cells with scar tissue
• function is not restoredfunction is not restored healing muscle injuries, scarring of lung tissue in TB or healing muscle injuries, scarring of lung tissue in TB or
healing of severe cuts and burns of the skinhealing of severe cuts and burns of the skin
keloid is healing with excessive fibrosis (raised keloid is healing with excessive fibrosis (raised shiny scars)shiny scars)
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Wound Healing of a LacerationWound Healing of a Laceration
Damaged vessels leak bloodDamaged vessels leak blood Damaged cells and mast Damaged cells and mast
cells leak histaminecells leak histamine dilates blood vesselsdilates blood vessels increases blood flowincreases blood flow increases capillary increases capillary
permeabilitypermeability Plasma carries antibodies, Plasma carries antibodies,
clotting factors and WBCs clotting factors and WBCs into woundinto wound
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Wound Healing of a LacerationWound Healing of a Laceration
Clot formsClot forms Scab forms on Scab forms on
surfacesurface Macrophages Macrophages
start to clean up start to clean up debrisdebris
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Wound Healing of a LacerationWound Healing of a Laceration
New capillaries grow New capillaries grow into woundinto wound
Fibroblasts deposit Fibroblasts deposit new collagen to new collagen to replace old materialreplace old material
Fibroblastic phase Fibroblastic phase begins in 3-4 days begins in 3-4 days and lasts up to 2 and lasts up to 2 weeksweeks
5858
Wound Healing of a LacerationWound Healing of a Laceration
Epithelial cells Epithelial cells multiply and spread multiply and spread beneath scabbeneath scab
Scab falls offScab falls off Epithelium thickensEpithelium thickens Connective tissue Connective tissue
forms only scar forms only scar tissue (fibrosis)tissue (fibrosis)
Remodeling phase Remodeling phase may last 2 yearsmay last 2 years
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