Tissues Lecture Handouts.pdfSupport by connective tissue at the basal surface, both the epithelial...
Transcript of Tissues Lecture Handouts.pdfSupport by connective tissue at the basal surface, both the epithelial...
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Tissues
Tissues
Cells work together in functionally related groups called tissues
How is this done?Attachmentscommunication
Types of tissues:1. Epithelial – lining and covering2. Connective – support 3. Muscle – movement4. Nervous – control
Lateral Surface Features
Factors holding epithelial cells togetherAdhesion proteins link plasma membranes of adjacent cellsContours of adjacent cell membranes Special cell junctions
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Lateral Surface Features – Cell Junctions
Tight junctions (zona occludens) – close off intercellular space
Found at apical region of most epithelial typesSome proteins in plasma membrane of adjacent cells are fusedPrevent molecules from passing between cells of epithelial tissue
Tight Junction
Lateral Surface Features – Cell Junctions
Adherens junctions (zonula adherens) –anchoring junction
Transmembrane linker proteins attach to actin microfilaments of the cytoskeleton and bind adjacent cellsAlong with tight junctions, form the tight junctional complex around apical lateral borders of epithelial tissues
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Zonula Adherens (Belt Desmosome)
Lateral Surface Features – Cell Junctions
Desmosomes (macula adherens) – two disc‐like plaques connected across intercellular space
Plaques of adjoining cells are joined by proteins called cadherins Proteins interdigitate into extra‐cellular spaceIntermediate filaments insert into plaques from cytoplasmic side
CDH1 - E-cadherin (epithelial) CDH2 - N-cadherin (neural) CDH12 - cadherin 12, type 2 (N-cadherin 2) CDH3 - P-cadherin (placental) CDH4 - R-cadherin (retinal) CDH5 - VE-cadherin (vascular endothelial) CDH6 - K-cadherin (kidney) CDH7 - cadherin 7, type 2 CDH8 - cadherin 8, type 2 CDH9 - cadherin 9, type 2 (T1-cadherin) CDH10 - cadherin 10, type 2 (T2-cadherin) CDH11 - OB-cadherin (osteoblast) CDH13 - T-cadherin - H-cadherin (heart) CDH15 - M-cadherin (myotubule) CDH16 - KSP-cadherin CDH17 - LI cadherin (liver-intestine) CDH18 - cadherin 18, type 2 CDH19 - cadherin 19, type 2 CDH20 - cadherin 20, type 2 CDH23 - cadherin 23, (neurosensory epithelium)
Desmosome
Figure 4.7b
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Desmosome Detail
Lateral Surface Features – Cell Junctions
Gap junctions – passageway between two adjacent cells
Let small molecules move directly between neighboring cellsCells are connected by hollow cylinders of protein
Gap Junction
Figure 4.7c
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Epithelial Tissue –General Characteristics & Functions
Covers a body surface or lines a body cavity Forms most glandsFunctions of epithelium
ProtectionAbsorption, secretion, and ion transportFiltrationForms slippery surfaces
Special Characteristics of Epithelia
Cellularitycells are in close contact with each other with little or no intercellular space between them
Specialized contactsmay have junctions for both attachment and communication
Polarityepithelial tissues always have an apical and basal surface
Support by connective tissue at the basal surface, both the epithelial tissue and the connective tissue contribute to the basement membrane
Avascularnutrients must diffuse
InnervatedRegenerative
epithelial tissues have a high capacity for regeneration
Special Characteristics of Epithelia
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First name of tissue indicates number of layers
Simple – one layer of cells
Stratified – more than one layer of cells
Classifications of Epithelia
Classifications of EpitheliaLast name of tissue describes shape of cells
Squamous – cells wider than tall (plate or “scale” like)
Cuboidal – cells are as wide as tall, as in cubes
Columnar – cells are taller thanthey are wide, like columns
Naming Epithelia
Naming the epithelia includes both the layers (first) and the shape of the cells (second)
i.e. stratified cuboidal epithelium
The name may also include any accessory structuresGoblet cellsCiliaKeratin
Special epithelial tissues (don’t follow naming convention)
PsuedostratifiedTransitional
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Simple Squamous Epithelium
Description single layer of flat cells with disc‐shaped nuclei
Special types Endothelium (inner covering)
slick lining of hollow organs
Mesothelium (middle covering) Lines peritoneal, pleural, and pericardial cavities Covers visceral organs of those cavities
Simple Squamous EpitheliumFunction
Passage of materials by passive diffusion and filtration
Secretes lubricating substances in serous membranes
Location Renal corpuscles
Alveoli of lungs
Lining of heart, blood and lymphatic vessels
Lining of ventral body cavity (serosae/serous memb.)
Simple Squamous Epithelium
Simple squamous lining the walls of
the capillary
If it’s from a mesothelial lining
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Simple Cuboidal Epithelium
Descriptionsingle layer of cube‐like cells with large, spherical central nuclei
Function secretion and absorption
Location kidney tubules, secretory portions of small glands, ovary surface
Simple Cuboidal Epithelium
Simple Columnar Epithelium
Description single layer of column‐shaped (rectangular) cells with oval nuclei
Some bear cilia at their apical surfaceMay contain goblet cells
Function Absorption; secretion of mucus, enzymes, and other substancesCiliated type propels mucus or reproductive cells by ciliary action
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Simple Columnar Epithelium
Location Non‐ciliated form
Lines digestive tract, gallbladder, ducts of some glands
Ciliated form Lines small bronchi, uterine tubes, and uterus
Pseudostratified Columnar Epithelium
DescriptionAll cells originate at basement membraneOnly tall cells reach the apical surfaceMay contain goblet cells and bear ciliaNuclei lie at varying heights within cells
Gives false impression of stratification
Function secretion of mucus; propulsion of mucus by cilia
Pseudostratified Columnar Epithelium
LocationsNon‐ciliated type
Ducts of male reproductive tubes Ducts of large glands
Ciliated variety Lines trachea and most of upper respiratory tract
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Stratified Epithelia
Contain two or more layers of cellsRegenerate from belowMajor role is protectionAre named according to the shape of cells at apical layer
Stratified Squamous Epithelium
DescriptionMany layers of cells – squamous in shapeDeeper layers of cells appear cuboidal or columnar Thickest epithelial tissue – adapted for protection
Stratified Squamous EpitheliumSpecific types
Keratinized – contain the protective protein keratinSurface cells are dead and full of keratin
Non‐keratinized – forms moist lining of body openings
FunctionProtects underlying tissues in areas subject to abrasion
Location Keratinized – forms epidermisNon‐keratinized – forms lining of esophagus, mouth, and vagina
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Stratified Squamous Epithelium
Non-keratinized vs. Keratinized
Stratified Cuboidal Epithelium
Descriptiongenerally two layers of cube‐shaped cells
Functionprotection
LocationForms largest ducts of sweat glandsForms ducts of mammary glands and salivary glands
Stratified Columnar Epithelium
Descriptionseveral layers; basal cells usually cuboidal; superficial cells elongated
Functionprotection and secretion
Location Rare tissue typeFound in male urethra and vas deferens, largest ducts of salivary glands, nasopharynx
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Transitional Epithelium
Description Basal cells usually cuboidal or columnarSuperficial cells dome‐shaped or squamous
Functionstretches and permits distension of urinary bladder
Location Lines ureters, urinary bladder and part of urethra
Transitional EpitheliumRelaxed state
Stretched state
Glandular Epithelium
Ducts carry products of exocrine glands to epithelial surfaceInclude the following diverse glands
Mucus‐secreting glands Sweat and oil glandsSalivary glandsLiver and pancreas
May be: unicellular or multicellular
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Unicellular Exocrine Glands (The Goblet Cell)
Goblet cells produce mucin Mucin + water mucusProtects and lubricates many internal body surfaces
Multicellular Exocrine Glands
Have two basic partsEpithelium‐walled ductSecretory unit
Classified by structure of ductSimpleCompound
Categorized by secretory unitTubularAlveolarTubuloalveolar
Types of Multicellular Exocrine Glands
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Exocrine Vs. Endocrine Glands
Endocrine Gland Characteristics:Ductless glandsSecrete substances directly into bloodstream Produce molecules called hormones
Which is Which?
Basal Feature: The Basal LaminaNoncellular 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 form the basement membraneHemidesmosomal junctions… holding it all down!
Epithelial Surface Features
Apical surface features Microvilli – finger‐like extensions of plasma membrane
Abundant in epithelia of small intestine and kidneyMaximize surface area across which small molecules enter or leaveAct as stiff knobs that resist abrasion
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Epithelial Surface Features
Apical surface featuresCilia – whip‐like, highly motile extensions of apical surface membranes
Contains a core of nine pairs of microtubules encircling one middle pairAxoneme – a set of microtubulesEach pair of microtubules – arranged in a doublet Microtubules in cilia – arranged similarly to cytoplasmic organelles called centriolesMovement of cilia – in coordinated waves
A Cilium
Connective TissueMost diverse and abundant tissueMain classes
Connective tissue properCartilageBone tissueBlood
Components of connective tissue:Cells (varies according to tissue)Matrix
Fibers (varies according to tissue)Ground substance (varies according to tissue)
dermatin sulfate, hyaluronic acid, keratin sulfate, chondroitin sulfate…
Common embryonic origin – mesenchyme
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Classes of Connective Tissue
Connective Tissue Model Areolar connective tissue
Underlies epithelial tissueSurrounds small nerves and blood vesselsHas structures and functions shared by other connective tissues Borders all other tissues in the body
Structures within areolar connective tissue allow:Support and binding of other tissuesHolding body fluidsDefending body against infectionStoring nutrients as fat
Connective Tissue Proper
Loose Connective TissueAreolarReticularAdipose
Dense Connective TissueRegularIrregularElastic
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Areolar Connective TissueDescription
Gel‐like matrix with:all three fiber types (collagen, reticular, elastic) for supportGround substance is made up by glycoproteins also made and screted by the fibroblasts.
Cells – fibroblasts, macrophages, mast cells, white blood cellsFunction
Wraps and cushions organsHolds and conveys tissue fluidImportant role in inflammation Main battlefield in fight against infection
Defenders gather at infection sitesMacrophagesPlasma cellsMast cellsNeutrophils, lymphocytes, and eosinophils
Areolar Connective Tissue
Location Widely distributed under epitheliaPackages organsSurrounds capillaries
Adipose Tissue
Description Closely packed adipocytes Have nucleus pushed to one side by fat droplet FunctionProvides reserve food fuelInsulates against heat lossSupports and protects organs
LocationUnder skin Around kidneys Behind eyeballs, within abdomen and in breasts
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Reticular Connective Tissue
Description – network of reticular fibers in loose ground substanceFunction – form a soft, internal skeleton (stroma) – supports other cell typesLocation – lymphoid organs
Lymph nodes, bone marrow, and spleen
Dense Irregular Connective Tissue
Description Primarily irregularly arranged collagen fibersSome elastic fibers and fibroblasts
Function Withstands tensionProvides structural strength
LocationDermis of skinSubmucosa of digestive tractFibrous capsules of joints and organs
Dense Regular Connective TissueDescription
Primarily parallel collagen fibersFibroblasts and some elastic fibersPoorly vascularized
FunctionAttaches muscle to boneAttaches bone to boneWithstands great stress in one direction
LocationTendons and ligamentsAponeuroses Fascia around muscles
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CartilageCharacteristics:
Firm, flexible tissueContains no blood vessels or nervesMatrix contains up to 80% waterCell type – chondrocyte
Types:HyalineElasticFibrocartilage
Hyaline Cartilage
DescriptionImperceptible collagen fibers (hyaline = glassy)Chodroblasts produce matrixChondrocytes lie in lacunae
FunctionSupports and reinforcesResilient cushionResists repetitive stress
Hyaline Cartilage
LocationFetal skeletonEnds of long bonesCostal cartilage of ribsCartilages of nose, trachea, and larynx
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Elastic CartilageDescription
Similar to hyaline cartilageMore elastic fibers in matrix
Function Maintains shape of structureAllows great flexibility
LocationSupports external earEpiglottis
Fibrocartilage
DescriptionMatrix similar, but less firm than hyaline cartilageThick collagen fibers predominate
FunctionTensile strength and ability to absorb compressive shock
LocationIntervertebral discsPubic symphysisDiscs of knee joint
Bone Tissue
FunctionSupports and protects organsProvides levers and attachment site for musclesStores calcium and other mineralsStores fatMarrow is site for blood cell formation
Location Bones
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Blood TissueDescription
red and white blood cells in a fluid matrix
Functiontransport of respiratory gases, nutrients, and wastes
Locationwithin blood vessels
CharacteristicsAn atypical connective tissueDevelops from mesenchymeConsists of cells surrounded by nonliving matrix
Covering and Lining Membranes
Combine epithelial tissues and connective tissuesCover broad areas within bodyConsist of epithelial sheet plus underlying connective tissue
Three Types of MembranesCutaneous membrane – skin Mucous membrane
Lines hollow organs that open to surface of bodyAn epithelial sheet underlain with layer of lamina propria
Serous membrane – slippery membranesSimple squamous epithelium lying on areolar connective tissueLine closed cavities
Pleural, peritoneal, and pericardial cavities
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Covering and Lining Membranes
Covering and Lining Membranes
Muscle Tissue
TypesSkeletal muscle tissueCardiac muscle tissue Smooth muscle tissue
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Skeletal Muscle Tissue
CharacteristicsLong, cylindrical cellsMultinucleateObvious striations
Function Voluntary movementManipulation of environmentFacial expression
LocationSkeletal muscles attached to bones (occasionally to skin)
Cardiac Muscle Tissue
FunctionContracts to propel blood into circulatory system
CharacteristicsBranching cellsUninucleateIntercalated discs
LocationOccurs in walls of heart
Smooth Muscle Tissue
CharacteristicsSpindle‐shaped cells withcentral nucleiArranged closely to form sheetsNo striations
FunctionPropels substances along internal passagewaysInvoluntary control
LocationMostly walls of hollow organs
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Nervous Tissue
FunctionTransmit electrical signals from sensory receptors to effectors
LocationBrain, spinal cord, and nerves
DescriptionMain components are brain, spinal cord, and nervesContains two types of cells
Neurons – excitatory cellsSupporting cells (neuroglial cells)
Tissue Response to Injury
Inflammatory response – non‐specific, local response
Limits damage to injury site
Immune response – takes longer to develop and very specific
Destroys particular microorganisms at site of infection
The Tissues Throughout Life
At the end of second month of development:Primary tissue types have appearedMajor organs are in place
AdulthoodOnly a few tissues regenerateMany tissues still retain populations of stem cells
With increasing age:Epithelia thin Collagen decreasesBones, muscles, and nervous tissue begin to atrophyPoor nutrition and poor circulation – poor health of tissues