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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

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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

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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

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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