Histology Study of cells, tissues and organs as seen with the help of microscope - PowerPoint Presentation

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Histology

Study of cells, tissues and organs as seen with the help of microscope

Study

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Histology

Often called Microscopic AnatomyGreek word – Histos

= tissue

Logia=science/studyCells work together in functionally related groups called tissues

4 basic type of tissues:

Epithelial

– lining and covering

Connective

– support

Muscle

– movement

Nervous

– control

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Epithelial Tissue

or Epithelium

Consist of sheets of cells

Covers

a external surface of the bodyMay line the internal cavities and the organsForms most organs & glands

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Special Characteristics of Epithelia

Cellularitycells are in close contact with each other with little or no intercellular space between them

Specialized

contacts:

Junctional Complexesmay have junctions for both attachment and communication

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Special Characteristics of Epithelia

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

Avascular..No blood vessel, no lymphaticsnutrients must diffuse

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Special Characteristics of

EpitInnervated

Regeneration

epithelial tissues have a high capacity for regeneration

Invaginates and grows in the underlying CT..specializing as glandsApical surface shows modification: presence of cilia or

microvilli

Nuclear shape corresponds

to the cell shape: oval in

columnar,round

in

cuboidal

or polyhedral and flat in

squamous

cells

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Functions

Functions of epitheliumProtectionAbsorption,

May secrete material and ion transport

Filtration

Forms slippery surfacesFunction as sensory surfaces

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Embryologically

Epithelia are derived from all the 3 germ layers:Ectoderm Epithelium of skinEndoderm Epithelium of gutMesoderm Epithelium of pericardial, peritoneal and pleural cavities

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Basement Membrane

All cells rest on it.Thin, non-cellularSeparates epithelium from underlying connective tissueEasily seen with light microscope

Made up of:

Basal Lamina-Amorphous, product of epithelium Reticular Lamina-Reticular fibres, product of CT

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Basement Membrane

The epithelial cells lie on the reticular lamina

(collagen – CT)

Reticular lamina is bound to another CT called

areolar CT. Together this structure is called the "basement

membrane

”

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Basal 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

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Intercellular Junctions OR

Junctional ComplexesZonula

occludens

(Tight Junctions)Zonula adherensMacula adherens (Desmosome) and hemidesmosome

Gap junction (Nexus)

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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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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…..Serves as a SELECTIVE BARRIER, giving it a sealing effect.

Example- Intestine and urinary bladder

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Adherens

junctions (zonula adherens) – anchoring junction

Transmembrane

linker proteins attach to actin microfilaments of the cytoskeleton and bind adjacent

cells

Along with tight junctions, form the tight

junctional

complex around apical lateral borders of epithelial

tissues

Present just below the tight junctions

Provides Rigidity to the apex of the cell.

Presence of dense plaque – like material on the

cytoplasmic

surface of the plasma membranes of the junction.

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Desmosomes

(Macula Adherens) Hemidesmosomes

Gap of 30nm

Transmembrane

ProteinsElectron dense plaqueAttachment to Intermediate

Filaments

FIRM ADHESION between cells

Subjected to friction,

Epidermis of skin.

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Desmosomes

Desmosomes – two disc-like plaques connected across intercellular spacePlaques of adjoining cells are joined by proteins called cadherins Proteins interdigitate

into extracellular space

Intermediate filaments insert into plaques from

cytoplasmic side

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Desmosomes

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Gap junctions (Nexus)

passageway between two adjacent cellsLet small molecules move directly between neighboring cells

Cells are connected by hollow cylinders of

protein

Passage of inorganic ionsExchange of chemical messengers in cell recognition and differentiation.

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Gap Junction

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Tight Junctions

In the apical Band or beltBarrier device

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Surface Modifications

Glycocalyx-rich in polysaccharides Concentrates ions prior to absorption

Act as receptor sites for hormones and enzymes.

Microvilli

- minute finger like projectionsIncrease absorptive surface Stereocilia –

Long thick

Microvilli

, Non motile, may show branching, Increase surface area(

Epididimis

), helps perception of stimuli (Internal Ear)

Cilia-

long, hair like projections of plasma membrane

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Microvilli and Cilia

NonmotileContain MicrofilamentsFunction-AbsorptionIntestinal epithelium, proximal convoluted tubules of the kidney

Motile

Contain 9+2 pattern of microtubules

Driving the entangled particles, transport in one dcirectionExamples: Respirastory

tract,uterine

tube and

ependyma

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Epithelial Tissues

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According to the number of cell layers

First name of tissue indicates number of layersSimple – one layer of cells

Stratified – more than one

layer of cells

Classifications & Naming of Epithelia

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Classification & Naming of Epithelia

Last name of tissue describes shape of cellsSquamous – cells wider than tall (plate or “scale” like)

Cuboidal – cells are as wide

as tall, as in cubes

Columnar – cells are taller than they are wide, like columns

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Naming Epithelia

Naming the epithelia includes both the layers (first) and the shape of the cells (second)i.e. stratified cuboidal epitheliumThe name may also include any accessory structures

Goblet cells

Cilia

KeratinSpecial epithelial tissues (don’t follow naming convention)PsuedostratifiedTransitional

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Simple Squamous

EpitheliumDescription single layer of flat cells with disc-shaped nucleiSpecial types Endothelium (inner covering)

slick lining of hollow organs

Mesothelium (middle covering)

Lines peritoneal, pleural, and pericardial cavities Covers visceral organs of those cavities

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Simple Squamous

EpitheliumFunction Passage of materials by passive diffusion and filtration

Secretes lubricating substances in serosae

Location

Renal corpusclesAlveoli of lungs Lining of heart, blood and lymphatic vessels

Lining of ventral body cavity (serosae)

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Simple Squamous Epithelium

Simple squamous lining the walls of the capillary

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Simple Cuboidal Epithelium

Descriptionsingle layer of cube-like cells with large, spherical central nucleiFunction secretion and absorption

Location

kidney tubules, secretory

portions of small glands, ovary & thyroid follicles

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Simple Columnar Epithelium

Description single layer of column-shaped (rectangular) cells with oval nucleiSome bear cilia at their apical surface

May 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 glandsCiliated form

Lines small bronchi,

uterine tubes, uterus

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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

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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

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Stratified Squamous Epithelium

DescriptionMany layers of cells – squamous in shapeDeeper layers of cells appear cuboidal or columnar Thickest epithelial tissue – adapted for protection

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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

Function

Protects underlying tissues in areas subject to abrasionLocation Keratinized – forms epidermisNon-keratinized – forms lining of esophagus, mouth, and vagina

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Transitional Epithelium

Description Basal cells usually cuboidal or columnarSuperficial cells dome-shaped or squamousFunctionstretches and permits distension of urinary bladder

Location

Lines ureters, urinary bladder and part of urethra

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Introduction

Histology

There are (4) types of tissue:

1. Epithelial

2. Connective

3. Muscle

4. Nervous

Similarities

between tissue types:

1. All contain cells

2. Cells that make up tissues have similar functions

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Epithelial Structure

Apical

Basement Membrane

Apical

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Basement Membrane

The epithelial cells lie on the reticular lamina

(collagen – CT)

Reticular lamina is bound to another CT called

areolar CT. Together this structure is called the "basement

membrane

”

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Classification and Examples

1. Simple Epithelium

Single layer

All cells anchored to basement membrane

2. Simple SquamousKidney – filtration

3.

Simple

Cuboidal

Kidney tubules

Filtration; secretion, absorption

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Simple Epithelia

4. Simple Columnar

Tall, thin cells

Absorptive cells (small intestine)

Goblet Cells 5. Pseudostratified ‘Ciliated

’

Columnar

Epithelium

“

Pseudostratified

” ?

Trachea

Goblet Cells and Mucus

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Stratified Epithelium

Characteristics2+ layers

Stratified

SquamousSkin – outer layer hardened by ‘keratin’ 4 to 5 layers thick

3.

Stratified

Cuboidal

Ducts of sweat glands

This type + stratified columnar are rare!

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MCQ

Transitional epithelium is found inUterusUreterGall bladder

vagina

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MCQ

Stomach is lined bySimple columnar epitheliumStraified squamous epithelium

Simple

cuboidal

epitheliumPseudostratified columnar epithelium

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MCQ

Simple Squamous epithelium is seen inAlveoli of lungsStomach

Urinary bladder

Tongue

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MCG

Glycocalyx coat present in the absorptive surface of small intestine1.Increases the surface area2.Transports the absorbed material3.Concentrates ions prior to absorption

4.Participates in the digestion of carbohydrates

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MCQ

Pseudostratified Epithelium is seen in1. Ureter2.Skin3.Trachea

4.Kidney

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Simple

squamous epithelium lining of serous membrane is called………..Basement membrane is made up of how many layers….What are Microvilli?Desmosomes

?