Epithelium 2008

TISSUETISSUETISSUETISSUE•• An association of cells and An association of cells and

intercellular materials intercellular materials intercellular materials intercellular materials morphologically and morphologically and physiologically integrated for physiologically integrated for the performance of specific the performance of specific the performance of specific the performance of specific functionsfunctions

EPITHELIUMEPITHELIUMA tissue consisting A tissue consisting

almost totally of an almost totally of an yyaggregation of aggregation of cells cells in apposition, in apposition,

i li d f i li d f specialized for specialized for absorptive, absorptive, secretory secretory secretory, secretory, excretory, or excretory, or protective protective ppfunctions, functions, and and resting on a resting on a basement basement membrane.membrane. An example of epithelium

CHARACTERISTICS OF EPITHELIA: CHARACTERISTICS OF EPITHELIA: SEPARATIONSEPARATIONSEPARATIONSEPARATION

•• True True i h li i h li epithelia are epithelia are

separated separated from the from the from the from the underlying CT underlying CT –– ““EpithelioidEpithelioid” ”

tissue lacks the tissue lacks the BL but is BL but is similarsimilar

–– BL usually BL usually PAS+PAS+

The periodic acid/Schiff (PAS) reactionThe periodic acid/Schiff (PAS) reaction

BASEMENT MEMBRANEBASEMENT MEMBRANE

• Sometimes also called “basal lamina”– Not exactly the

same but close same but close enough

• A definitive characteristic– Isolates epithelium

from underlying from underlying CT– All true epithelia

h ithave it

BASEMENT MEMBRANEBASEMENT MEMBRANE

• Sometimes also called “basal lamina”– Not exactly the

same but close same but close enough

• A definitive characteristic– Isolates epithelium

from underlying from underlying CT– All true epithelia

h ithave it

CATEGORIES OF EPITHELIA: “COVERING & CATEGORIES OF EPITHELIA: “COVERING & LINING”LINING”

•• Neatly classifiableNeatly classifiableyy•• Lines hollow organs and forms sheets: Lines hollow organs and forms sheets: Epidermis of skin, Epidermis of skin,

Lining of glandular ducts, Lining of blood vesselsLining of glandular ducts, Lining of blood vessels

CATEGORIES OF EPITHELIA: CATEGORIES OF EPITHELIA: “GLANDULAR” OR “SECRETORY”“GLANDULAR” OR “SECRETORY”GLANDULAR OR SECRETORYGLANDULAR OR SECRETORY

• Forms solid massesmasses– Usually

secretory • Not neatly

classified– Exocrine & – Exocrine &

endocrine glands

Pancreas: an example of glandular epithelium

CHARACTERISTICS OF EPITHELIA:CHARACTERISTICS OF EPITHELIA:PROLIFERATION & HIGH TURNOVERPROLIFERATION & HIGH TURNOVER

C ll C ll hh li dli d Cells Cells shortshort--livedlived: : typically days to typically days to weeks. weeks.

M t ith li M t ith li Most epithelia Most epithelia also have also have significant significant regeneration regeneration regeneration regeneration capability.capability.

Right: Proliferating cells in Right: Proliferating cells in g gg gintestine, BRDU stainintestine, BRDU stain

CHARACTERISTICS OF EPITHELIA: CHARACTERISTICS OF EPITHELIA: POLARITYPOLARITYPOLARITYPOLARITY

Cells ha e a • Cells have a “top” and “bottom” i.e.,different activities take place at place at different places.

• Most obvious in i h li l hepithelial sheets– True of most

epithelia

CHARACTERISTICS OF EPITHELIA: CHARACTERISTICS OF EPITHELIA: POLARITYPOLARITYPOLARITYPOLARITY

Cells ha e a

APICALAPICAL

• Cells have a “top” and “bottom” i.e.,

BASALLATERALLATERAL

different activities take place at place at different places.

• Most obvious in i h li l hepithelial sheets– True of most

epithelia

CHARACTERISTICS OF EPITHELIA: CHARACTERISTICS OF EPITHELIA: VASCULARITYVASCULARITYVASCULARITYVASCULARITY

–– Epithelial Epithelial sheetssheets (“C&L”) (“C&L”) are AVASCULARare AVASCULAR

N i h d b diff i lN i h d b diff i l•• Nourished by diffusion onlyNourished by diffusion only–– The reason for rapid loss The reason for rapid loss

& replacement& replacement

CHARACTERISTICS OF EPITHELIA: CHARACTERISTICS OF EPITHELIA: VASCULARITYVASCULARITY

•• EPITHELIAL EPITHELIAL MASSES MASSES (Secretory (Secretory epithelium) epithelium) epithelium) epithelium) AREAREVASCULARVASCULAR–– All cells All cells

near a BV!near a BV!

CHARACTERISTICS OF EPITHELIA: CHARACTERISTICS OF EPITHELIA: VASCULARITYVASCULARITY

•• EPITHELIAL EPITHELIAL MASSES MASSES (Secretory (Secretory epithelium) epithelium) epithelium) epithelium) AREAREVASCULARVASCULAR–– All cells All cells

near a BV!near a BV!

FUNCTIONS OF EPITHELIAFUNCTIONS OF EPITHELIAS ti M i l l d l b t C&L f b • Secretion: Mainly glandular but C&L forms can be secretory– Secretory sheets found in reproductive tract, conjunctiva & GI tract

GOBLET CELLSGOBLET CELLS

Common in many Common in many epithelial sheets!epithelial sheets!epithelial sheets!epithelial sheets!Secretes mucinous Secretes mucinous materialmaterial

FUNCTIONS OF EPITHELIAFUNCTIONS OF EPITHELIA

•• Interchange Interchange •• Interchange Interchange with the with the environmentenvironment: : Gas exchangeGas exchange–– Nutrient Nutrient

absorptionabsorptionabsorptionabsorption–– Skin Skin

functionsfunctions

FUNCTIONS OF EPITHELIAFUNCTIONS OF EPITHELIA•• Protection:Protection:–– UV barrierUV barrier–– Physical barrier to infectionPhysical barrier to infection–– Pigmentation/camouflagePigmentation/camouflage

FUNCTIONS OF EPITHELIAFUNCTIONS OF EPITHELIA

•• Excretion:Excretion:–– Disposal of nitrogenous waste by sweatingDisposal of nitrogenous waste by sweating

FUNCTIONS OF EPITHELIAFUNCTIONS OF EPITHELIA•• Stimulus Reception:Stimulus Reception:•• Stimulus Reception:Stimulus Reception:–– Chemotactic sensations: olfaction and gustationChemotactic sensations: olfaction and gustation

TASTE BUDS IN TONGUETASTE BUDS IN TONGUEOLFACTORY EPITHELIUMOLFACTORY EPITHELIUM

CLASSIFICATION CLASSIFICATION OF C&L EPITHELIAOF C&L EPITHELIAOF C&L EPITHELIAOF C&L EPITHELIA

•• ONLY TWO ONLY TWO CRITERIACRITERIA–– SHAPE of cells SHAPE of cells

in the TOP in the TOP layerlayer–– NUMBER of NUMBER of

layerslayers1 = “simple”1 = “simple”

>1 = “stratified”>1 = “stratified”

CLASSIFICATION OF CLASSIFICATION OF C&L EPITHELIA BY C&L EPITHELIA BY C&L EPITHELIA BY C&L EPITHELIA BY

SHAPESHAPE

SQUAMOUSSQUAMOUSSQUAMOUSSQUAMOUS•• Cells have a Cells have a

“Fried Egg” “Fried Egg” Fried Egg Fried Egg shape; irregular shape; irregular outlinesoutlines•• EXAMPLES: EXAMPLES:

Lining of blood Lining of blood vesselsvessels

MesotheliumMesotheliumi i t l i i t l covering internal covering internal

organsorgans

SIMPLE SIMPLE SQUAMOUSSQUAMOUS

Single Layer of Single Layer of CellsCellsS S hhSquamous Squamous shapeshapeExampleExample: Lining of : Lining of a blood vessel a blood vessel a blood vessel a blood vessel

SIMPLE SQUAMOUSSIMPLE SQUAMOUSSIMPLE SQUAMOUSSIMPLE SQUAMOUSEPITHELIUMEPITHELIUM

SIMPLE SQUAMOUSSIMPLE SQUAMOUSSIMPLE SQUAMOUSSIMPLE SQUAMOUSEPITHELIUMEPITHELIUM

CLASSIFICATION CLASSIFICATION OF C& L OF C& L

EPITHELIA BY EPITHELIA BY SHAPESHAPE

•• CUBOIDALCUBOIDAL–– Cells are Cells are

APPROXIMATELY APPROXIMATELY as tall as they are as tall as they are as tall as they are as tall as they are wide.wide.–– EXAMPLES:EXAMPLES:–– Lining of gland ductsLining of gland ducts–– Walls of thyroid gland Walls of thyroid gland

folliclesfollicles

SIMPLE SIMPLE SIMPLE SIMPLE CUBOIDALCUBOIDAL

CLASSIFICATION CLASSIFICATION OF C&L EPITHELIA OF C&L EPITHELIA

BY SHAPE BY SHAPE

COLUMNARCOLUMNARCOLUMNARCOLUMNAR•• Cells are Cells are

distinctly distinctly distinctly distinctly taller than taller than they are they are t ey a e t ey a e widewide–– EXAMPLES:EXAMPLES:–– Lining of Lining of

intestineintestine–– Some large Some large Some large Some large

gland ductsgland ducts

STRATIFIED STRATIFIED SQUAMOUSSQUAMOUSSQUAMOUSSQUAMOUS• More than one

l !layer!– TOP layer is

squamous• Very common– Epidermis of the

skinskin– Lining of bodily

orifices • Often found in • Often found in

regions of heavy wear

M b h d d – May be hardened or cornified (keratinized)

STRATIFIED STRATIFIED CUBOIDALCUBOIDALCU OCU O

OROR

COLUMNARCOLUMNARCOLUMNARCOLUMNAR

Lining ofLining ofLining of Lining of larger gland larger gland ductsductsductsducts

Repro tract inRepro tract inRepro tract in Repro tract in some some animalsanimals

SPECIAL TYPES: SPECIAL TYPES: PSEUDOPSEUDOSTRATIFIEDSTRATIFIEDPSEUDOPSEUDOSTRATIFIEDSTRATIFIED

•• Principally in Principally in respiratory tract respiratory tract respiratory tract, respiratory tract, but also in other but also in other locationslocations•• Not all cells reach Not all cells reach

free surfacefree surface•• All cells reach All cells reach All cells reach All cells reach

basement basement membranemembraneT l “ i l ” T l “ i l ” •• Truly a “simple” Truly a “simple” typetype•• NOT “always NOT “always yy

ciliated”!ciliated”!

SPECIAL SPECIAL TYPES: TYPES: TYPES: TYPES:

URINARY URINARY

•• Found only in Found only in urinary urinary yypassagespassages

•• A “tight” A “tight” ith li ith li epithelium epithelium

with many with many occluding occluding junctionsjunctions

•• A truly A truly stratified typestratified typestratified typestratified type

SPECIAL TYPES: CONJUNCTIVASPECIAL TYPES: CONJUNCTIVAJJ

•• A variant A variant form of form of stratified stratified

llcolumnarcolumnar–– Contains Contains

goblet cellsgoblet cells

•• Found Found inside inside eyelids and eyelids and on surface on surface of eyeof eyeof eyeof eye

CiliaCiliaWhat kind What kind of epithelium is this?

•• Frequently associated with epithelial sheetsFrequently associated with epithelial sheetsFrequently associated with epithelial sheetsFrequently associated with epithelial sheets•• Associated with transport/protection functionsAssociated with transport/protection functions

MicrovilliMicrovilli•• Found on many Found on many

cell types; often cell types; often on epithelial on epithelial sheetssheets

•• Associated with Associated with secretion or secretion or absorption absorption functionfunction

•• “Brush border” “Brush border” or “striated or “striated border” in LMborder” in LMborder in LMborder in LM

“EPITHELIALORGANS“EPITHELIALORGANS””•• PrimarilyPrimarily epithelial tissueepithelial tissue–– But ALL organs have more But ALL organs have more

than one tissue type!than one tissue type!•• 33--dimensional masses of cellsdimensional masses of cells–– ExcludesExcludes epithelial sheetsepithelial sheets•• Not normally capable of Not normally capable of

t f tit f tiautonomous functionautonomous function–– Well vascularizedWell vascularized–– Set off from CT by a basal Set off from CT by a basal

laminalamina–– Usually capable of considerable Usually capable of considerable

regenerationregeneration–– Always Always have some other tissue have some other tissue

present (usually CT)present (usually CT)present (usually CT)present (usually CT)

•• Examples:Examples:–– Glands of various typesGlands of various types

LiLi–– LiverLiver–– KidneyKidney

SECRETIONSECRETION

•• DEFINITION: The process by which cells take up DEFINITION: The process by which cells take up small molecules from the blood, and transform small molecules from the blood, and transform ,,them into more complex materials that are then them into more complex materials that are then released from the cells.released from the cells.

•• Secretion is an active process that always requires Secretion is an active process that always requires •• Secretion is an active process that always requires Secretion is an active process that always requires energy. energy. Excretion is usually a passive process.Excretion is usually a passive process.

•• Not confined to glands: epithelial sheets can be Not confined to glands: epithelial sheets can be ttsecretorysecretory

GLANDSGLANDSGLANDSGLANDSGLANDSGLANDS

••Epithelial organs specialized for secretionEpithelial organs specialized for secretion••Exocrine and endocrine types: Exocrine and endocrine types: bothboth are classic examples are classic examples of epithelial of epithelial organsorgans

CHARACTERISTICS OF SECRETORY CHARACTERISTICS OF SECRETORY CELL TYPESCELL TYPESCELL TYPESCELL TYPES

•• Basophilic cytoplasm Basophilic cytoplasm if secretion is a peptideif secretion is a peptide•• Basophilic cytoplasm Basophilic cytoplasm if secretion is a peptideif secretion is a peptide•• Nucleus is “vesicular” Nucleus is “vesicular” –– Large amounts of Large amounts of heterochromatinheterochromatin

P i t l l & G l i pp tP i t l l & G l i pp t•• Prominent nucleolus & Golgi apparatusProminent nucleolus & Golgi apparatus•• May show granularity in cytoplasmMay show granularity in cytoplasm

MODES OF SECRETION: MODES OF SECRETION: CC ( OC )CC ( OC )ECCRINE (MEROCRINE)ECCRINE (MEROCRINE)

•• NO loss of NO loss of cytoplasm in cytoplasm in processprocessprocessprocess•• Cells typically Cells typically

cuboidal to cuboidal to cuboidal to cuboidal to columnarcolumnar•• Used by MOST Used by MOST Used by MOST Used by MOST

exocrine and exocrine and ALL endocrine ALL endocrine glandsglands

MODES OF SECRETION: APOCRINEMODES OF SECRETION: APOCRINE

•• Loss of SOME Loss of SOME cytoplasm in cytoplasm in processprocessprocessprocess•• Apical region Apical region

pinches off & pinches off & pinches off & pinches off & degeneratesdegenerates•• Used by some Used by some Used by some Used by some

sweat glandssweat glands–– No other No other

examples in examples in mammalsmammals

MODES OF SECRETION: HOLOCRINEMODES OF SECRETION: HOLOCRINE

• One example in mammals: Sebaceous glands

• ENTIRE CELL dies, forms secretion by degeneration

STRUCTURAL CLASSIFICATION OF STRUCTURAL CLASSIFICATION OF EXOCRINE (DUCTED) GLANDSEXOCRINE (DUCTED) GLANDS

•• BASED ON TWO BASED ON TWO CRITERIACRITERIA–– SHAPE OF SHAPE OF

SECRETORY SECRETORY REGIONREGION•• TubularTubular•• Coiled tubularCoiled tubular•• Acinar/alveolarAcinar/alveolar•• TubuloacinarTubuloacinar

–– DEGREE OF DEGREE OF DIVISION OF DIVISION OF DUCTWORKDUCTWORK•• SimpleSimple•• CompoundCompound•• “Compound” is “Compound” is

NOT = NOT = “Branched”“Branched”

SIMPLE EXOCRINE GLANDSSIMPLE EXOCRINE GLANDS• Duct is NOT divided

S t R i MAY b di id d = • Secretory Region MAY be divided = “Branched”

COMPOUND EXOCRINE GLANDSCOMPOUND EXOCRINE GLANDS

• DUCT is divided = “Compound”• Secretory region usually divided• Secretory region usually divided