EpitheliumEpithelium(epithelial tissue)(epithelial tissue)

Dr. Abdullah AldahmashDr. Abdullah Aldahmash

EpitheliumEpithelium

Epithelial cells are closely packed Epithelial cells are closely packed cells, and form continuous sheetscells, and form continuous sheets..

FunctionFunction

.1.1ProtactionProtaction

.2.2Transcellular transportTranscellular transport

.3.3SecretionSecretion

.4.4AbsorptionAbsorption

.5.5Detection of sensationsDetection of sensations

Special Characteristics Special Characteristics of Epitheliumof Epithelium

Adjacent cells are bound together Adjacent cells are bound together by cell junctionsby cell junctions..

The lower surface of all types of The lower surface of all types of epitheliaepithelia rest on rest on Basement Basement membrane membrane //Basal laminaBasal lamina, a , a structureless material secreted structureless material secreted by the cellsby the cells..

Special Characteristics Special Characteristics of Epitheliumof Epithelium

Epithelial tissues are Epithelial tissues are aavascular (vascular (no no direct blood supplydirect blood supply). Nutrition ). Nutrition depends on diffusion from depends on diffusion from underlying connective tissueunderlying connective tissue..

Epithelial cells regenerate easilyEpithelial cells regenerate easily..

Classification of EpitheliaClassification of Epithelia::

Epithelium is divided into two Epithelium is divided into two typestypes : :

11    .    .Covering & Lining Covering & Lining EpitheliaEpithelia..

22    .    .Glandular EpitheliaGlandular Epithelia . .

Basement Basement MembraneMembrane

Noncellular layer that secures Noncellular layer that secures the overlying tissuesthe overlying tissues

Most epithelial tissues have a Most epithelial tissues have a basement membranebasement membrane

Epithelial Tissue Epithelial Tissue ClassificationsClassifications

Epithelial tissue is classified according Epithelial tissue is classified according to the number of cell layers and the to the number of cell layers and the shape of each epithelial cellshape of each epithelial cell

Epithelial Epithelial Tissue Tissue ClassificationsClassifications

Simple epitheliumSimple epithelium

A single layer of cellsA single layer of cells

Stratified epitheliumStratified epithelium

More than one layer of More than one layer of cellscells

Epithelial Epithelial Tissue Tissue ClassificationsClassifications

Pseudostratified epitheliumPseudostratified epithelium Contains a single layer of cells of varying Contains a single layer of cells of varying heightsheights

All cells attach to the basement membrane, All cells attach to the basement membrane, but some fail to reach the free surface, but some fail to reach the free surface, giving the appearance of multiple layersgiving the appearance of multiple layers

Transitional epitheliumTransitional epithelium Consists of layers of stratified cells that Consists of layers of stratified cells that change shape from cuboidal to squamous change shape from cuboidal to squamous when the organ is stretchedwhen the organ is stretched

Epithelial Epithelial Tissue Tissue ClassificationsClassificationsShape of each epitheliaShape of each epithelia

SquamousFlat sheetsFlat sheets

CuboidalRows of square-shaped cellsRows of square-shaped cells

Columnar Rows of tall, thin cellsRows of tall, thin cells

Epithelia are derived from Epithelia are derived from the three embryonic germ the three embryonic germ layerslayers

Ectoderm:Ectoderm: epidermis and glands of epidermis and glands of skin, cornea, oral and nasal mucosaeskin, cornea, oral and nasal mucosae..

Endoderm:Endoderm: liver, pancreas, lining of liver, pancreas, lining of the GI and respiratorythe GI and respiratory..

Mesoderm:Mesoderm: uriniferous tubules of uriniferous tubules of kidney, lining of male and female kidney, lining of male and female reproductive system, endothelial reproductive system, endothelial lining of circulatory systemlining of circulatory system..

Simple EpitheliaSimple Epithelia

Simple EpitheliaSimple Epithelia

11 ) )Simple Squamous EpitheliumSimple Squamous Epithelium::

Composed of a single layer of Composed of a single layer of flattened cellsflattened cells..

The term ‘squamous’ derives from The term ‘squamous’ derives from the comparison of the cells to the the comparison of the cells to the scales of a fishscales of a fish..

Simple EpitheliaSimple Epithelia

22 ) )Simple Cuboidal EpitheliumSimple Cuboidal Epithelium::

Consists of a single layer of Consists of a single layer of square shaped cells (2D)square shaped cells (2D)..

    Centrally placed nucleusCentrally placed nucleus..

ExampleExample::

Kidney tubulesKidney tubules . .

Simple EpitheliaSimple Epithelia

33 ) )Simple Columnar EpitheliumSimple Columnar Epithelium

Single layer of tall column-like cellsSingle layer of tall column-like cells..

Goblet cells (mucus producing cells) Goblet cells (mucus producing cells) may be seen in this type of may be seen in this type of epitheliumepithelium..

ExamplesExamples::

Stomach and intestinesStomach and intestines . .

Simple EpitheliaSimple Epithelia

44 ) )Pseudostratified Columnar Pseudostratified Columnar EpitheliumEpithelium

Single layer of cells but gives false impression of more Single layer of cells but gives false impression of more than one layer of cells. (stratified)than one layer of cells. (stratified)..

There are tall cells that reach the surface with other There are tall cells that reach the surface with other shorter ones that don’tshorter ones that don’t..

Simple EpitheliaSimple Epithelia

44 ) )Pseudostratified Columnar Pseudostratified Columnar EpitheliumEpithelium

All cells rest on the same basement membraneAll cells rest on the same basement membrane..

The nuclei show different levels of heightThe nuclei show different levels of height..

The higher cells may be ciliatedThe higher cells may be ciliated..

Goblet cells are seen in respiratory epitheliumGoblet cells are seen in respiratory epithelium..

ExamplesExamples::

TracheaTrachea

Stratified EpitheliaStratified Epithelia

Stratified epithelia are described Stratified epithelia are described according to the shape of their according to the shape of their superficial cells.superficial cells.

Consists of two or more cell layers.

Their main function is protection..

Stacked epithelial cells with the surface Stacked epithelial cells with the surface cells being flatcells being flat..

The cells at the base are cuboidal or The cells at the base are cuboidal or columnarcolumnar . .

The intermediate cells are polygonalThe intermediate cells are polygonal..

The basal and intermediate cells maintain The basal and intermediate cells maintain the ability to dividethe ability to divide..

Cells at the surface are dead and lack Cells at the surface are dead and lack nucleinuclei . .

1 )Stratified Squamous Epithelium

(Keratinized & nonkeratinized)

Usually have two cell layers with Usually have two cell layers with surface cells cuboidal or columnarsurface cells cuboidal or columnar..

The basal cells vary in size & shapeThe basal cells vary in size & shape..

ExamplesExamples::

Ducts of the large exocrine glands Ducts of the large exocrine glands such as salivary glands (columnar), such as salivary glands (columnar), sweat glands (cuboidal)sweat glands (cuboidal)..

22 ) )Stratified Cuboidal Stratified Cuboidal & Columnar & Columnar EpitheliumEpithelium::

33 ) )Transitional EpitheliumTransitional Epithelium::

Is a modified type of Is a modified type of Stratified Stratified Squamous epitheliumSquamous epithelium..

Present in the urinary system organsPresent in the urinary system organs..In the relaxed state, it shows 5-8 In the relaxed state, it shows 5-8 layerslayers..

33 ) )Transitional EpitheliumTransitional Epithelium::

Basal cells are cuboidal or columnar, Basal cells are cuboidal or columnar, intermediate cells are polygonal, and intermediate cells are polygonal, and surface cells are roundedsurface cells are rounded..

When the epithelium is stretched, it When the epithelium is stretched, it appears 2-3 layers thick and the appears 2-3 layers thick and the surface cells appear flattenedsurface cells appear flattened..

Junctional Junctional complexecomplexess

Occluding junctions Occluding junctions (tight junction)(tight junction)

Anchoring junctionsAnchoring junctions

Communicating junctionCommunicating junction

Renewal of epithelial Renewal of epithelial cellscells

Skin 28 days

Small intestine 4-6 days

Others renewed periodically until adulthood

Glands Glands

DevelopmentDevelopment

Paranchyma = glandular Paranchyma = glandular epitheliaepithelia

Stroma = connective tissueStroma = connective tissue

Product of epithelial glandsProduct of epithelial glands

Apolypeptide hormonesApolypeptide hormones

e.g. from pitutary glande.g. from pitutary gland

A waxy substanceA waxy substance

e.g. ear canal glande.g. ear canal gland

MucinogenMucinogen

e.g. goblet cellse.g. goblet cells

Milke (protein, lipid and Milke (protein, lipid and carbohydrates)carbohydrates)

Classifications of epithelial Classifications of epithelial glandsglands

11 - -ExocrineExocrine

secrete via ductssecrete via ducts

22 - -Endocrine (Ductless)Endocrine (Ductless)

secrete into blood or lymphatic vesselssecrete into blood or lymphatic vessels

Cytokines and their effectsCytokines and their effects

Autocrine, paracrine and endocrineAutocrine, paracrine and endocrine

ResultsResults::

Constitutive secretory pathwayConstitutive secretory pathway

Regulated secretory pathwayRegulated secretory pathway

ExocrineExocrine

- -Most commonly found in digestive, respiratory Most commonly found in digestive, respiratory and urogenetaland urogenetal

- -can be Unicellular or multicellularcan be Unicellular or multicellular

- -secrete: mucous (e.g. salivary gland), serous (e.g secrete: mucous (e.g. salivary gland), serous (e.g pancreas) or mix (submandibular)pancreas) or mix (submandibular)

- -there are three mechanisms by which they release there are three mechanisms by which they release secretion: merocrine (via exocytosis), apocrine (!!) or secretion: merocrine (via exocytosis), apocrine (!!) or holocrine (secretory cells die and become product)holocrine (secretory cells die and become product)

Exocrine: Exocrine: mechanism of mechanism of

secretionsecretion

- -there are three mechanisms by which there are three mechanisms by which they release secretionthey release secretion : :

- -merocrine (via exocytosis)merocrine (via exocytosis) , ,

- -apocrineapocrine)!!( )!!(

- -or holocrine (secretory cells die and or holocrine (secretory cells die and become product)become product)

Classifications of Classifications of Exocrine Exocrine glandsglands

11--UnicellularUnicellular

e.g. goblet cellse.g. goblet cells

22--MulticellularMulticellular

classified intoclassified into : :

simple (ducts do simple (ducts do not not branch)branch)

compound (ducts do branch- septa)compound (ducts do branch- septa)

further intofurther into::

tubular, acinar (alveolar)or tubuloalveolartubular, acinar (alveolar)or tubuloalveolar