TISSUETISSUE•An association of cells and An association of cells and

intercellular materials intercellular materials morphologically and morphologically and physiologically integrated physiologically integrated for the performance of for the performance of specific functionsspecific functions

EPITHELIUMEPITHELIUMA tissue A tissue

consisting consisting almost totally almost totally of an of an aggregation of aggregation of cells in cells in apposition, apposition, specialized for specialized for absorptive, absorptive, secretory, secretory, excretory, or excretory, or protective protective functions, functions, and and resting on a resting on a basement basement membrane.membrane.

An example of epithelium

CHARACTERISTICS OF CHARACTERISTICS OF EPITHELIA: SEPARATIONEPITHELIA: SEPARATION

• True True epithelia epithelia are are separated separated from the from the underlying underlying CT CT – ““EpithelioidEpithelioid” ”

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

– BL usually BL usually PAS+PAS+

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

reactionreaction

BASEMENT MEMBRANEBASEMENT MEMBRANE

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

same but close enough

• A definitive characteristic– Isolates

epithelium from underlying CT

– All true epithelia have it

BASEMENT MEMBRANEBASEMENT MEMBRANE

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

same but close enough

• A definitive characteristic– Isolates

epithelium from underlying CT

– All true epithelia have it

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

• Neatly classifiableNeatly classifiable• Lines hollow organs and forms sheets: Lines hollow organs and forms sheets: Epidermis Epidermis

of skin, Lining of glandular ducts, Lining of blood vesselsof skin, Lining of glandular ducts, Lining of blood vessels

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

• Forms solid masses– Usually

secretory• Not neatly

classified– Exocrine &

endocrine glands

Pancreas: an example of glandular epithelium

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

Cells Cells short-short-livedlived: : typically typically days to days to weeks. weeks.

Most epithelia Most epithelia also have also have significant significant regeneration regeneration capability.capability.

Right: Proliferating Right: Proliferating cells in intestine, cells in intestine, BRDU stainBRDU stain

CHARACTERISTICS OF CHARACTERISTICS OF EPITHELIA: POLARITYEPITHELIA: POLARITY

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

• Most obvious in epithelial sheets– True of most

epithelia

CHARACTERISTICS OF CHARACTERISTICS OF EPITHELIA: POLARITYEPITHELIA: POLARITY

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

• Most obvious in epithelial sheets– True of most

epithelia

APICALAPICAL

BASALLATERALLATERAL

CHARACTERISTICS OF CHARACTERISTICS OF EPITHELIA: VASCULARITYEPITHELIA: VASCULARITY

– Epithelial Epithelial sheetssheets (“C&L”) are (“C&L”) are AVASCULARAVASCULAR• Nourished by diffusion onlyNourished by diffusion only

– The reason for rapid loss The reason for rapid loss & replacement& replacement

CHARACTERISTICS OF CHARACTERISTICS OF EPITHELIA: VASCULARITYEPITHELIA: VASCULARITY

• EPITHELIAL EPITHELIAL MASSES MASSES (Secretory (Secretory epithelium) epithelium) AREARE VASCULARVASCULAR– All cells All cells

near a BV!near a BV!

CHARACTERISTICS OF CHARACTERISTICS OF EPITHELIA: VASCULARITYEPITHELIA: VASCULARITY

• EPITHELIAL EPITHELIAL MASSES MASSES (Secretory (Secretory epithelium) epithelium) AREARE VASCULARVASCULAR– All cells All cells

near a BV!near a BV!

FUNCTIONS OF EPITHELIAFUNCTIONS OF EPITHELIA• 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!Secretes mucinous Secretes mucinous materialmaterial

FUNCTIONS OF EPITHELIAFUNCTIONS OF EPITHELIA

• InterchangInterchange with the e with the environmeenvironment: nt: Gas Gas exchangeexchange– Nutrient Nutrient

absorptionabsorption– 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:

– Chemotactic sensations: olfaction and gustationChemotactic sensations: olfaction and gustation

TASTE BUDS IN TONGUETASTE BUDS IN TONGUEOLFACTORY EPITHELIUMOLFACTORY EPITHELIUM

CLASSIFICATION CLASSIFICATION OF C&L OF C&L

EPITHELIAEPITHELIA

• ONLY TWO ONLY TWO CRITERIACRITERIA– SHAPE of SHAPE of

cells in the cells in the TOP layerTOP layer

– NUMBER of NUMBER of layerslayers

1 = “simple”1 = “simple”

>1 = >1 = “stratified”“stratified”

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

BY SHAPEBY SHAPE

SQUAMOUSSQUAMOUS• Cells have a Cells have a

“Fried Egg” “Fried Egg” shape; shape; irregular irregular outlinesoutlines

• EXAMPLES: EXAMPLES: Lining of blood Lining of blood vesselsvessels

MesotheliumMesothelium covering internal covering internal organsorgans

SIMPLE SIMPLE SQUAMOUSSQUAMOUS

Single Layer of Single Layer of CellsCellsSquamous Squamous shapeshapeExample: Example: Lining of a Lining of a blood vessel blood vessel

SIMPLE SQUAMOUSSIMPLE SQUAMOUS EPITHELIUM EPITHELIUM

SIMPLE SQUAMOUSSIMPLE SQUAMOUS EPITHELIUM EPITHELIUM

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 wide.wide.

– EXAMPLES:EXAMPLES:– Lining of gland Lining of gland

ductsducts– Walls of Walls of

thyroid gland folliclesthyroid gland follicles

SIMPLE SIMPLE CUBOIDALCUBOIDAL

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

BY SHAPE BY SHAPE

COLUMNARCOLUMNAR• Cells are Cells are

distinctly distinctly taller than taller than they are they are widewide– EXAMPLES:EXAMPLES:– Lining of Lining of

intestineintestine– Some large Some large

gland ductsgland ducts

STRATIFIED STRATIFIED SQUAMOUSSQUAMOUS• More than one

layer!– TOP layer is

squamous• Very common

– Epidermis of the skin

– Lining of bodily orifices

• Often found in regions of heavy wear– May be

hardened or cornified (keratinized)

STRATIFIED STRATIFIED CUBOIDALCUBOIDAL

OROR COLUMNARCOLUMNAR

Lining of Lining of larger gland larger gland ductsducts

Repro tract in Repro tract in some animalssome animals

SPECIAL TYPES: SPECIAL TYPES: PSEUDOPSEUDOSTRATIFIEDSTRATIFIED

• Principally in Principally in respiratory respiratory tract, but also tract, but also in other in other locationslocations

• Not all cells Not all cells reach free reach free surfacesurface

• All cells reach All cells reach basement basement membranemembrane

• Truly a Truly a “simple” type“simple” type

• NOT “always NOT “always ciliated”!ciliated”!

SPECIAL SPECIAL TYPES: TYPES:

URINARY URINARY

• Found only Found only in urinary in urinary passagespassages

• A “tight” A “tight” epithelium epithelium with many with many occluding occluding junctionsjunctions

• A truly A truly stratified stratified typetype

SPECIAL TYPES: CONJUNCTIVASPECIAL TYPES: CONJUNCTIVA

• A variant A variant form of form of stratified stratified columnarcolumnar– Contains Contains

goblet goblet cellscells

• Found Found inside inside eyelids eyelids and on and on surface of surface of eyeeye

CiliaCilia

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

What kind of epithelium is this?

MicrovilliMicrovilli• Found on Found on

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

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

• ““Brush Brush border” or border” or “striated “striated border” in border” in LMLM

““EPITHELIALORGANSEPITHELIALORGANS

””• PrimarilyPrimarily epithelial epithelial

tissuetissue– But ALL organs have more But ALL organs have more

than one tissue type!than one tissue type!• 3-dimensional masses of 3-dimensional masses of

cellscells– ExcludesExcludes epithelial sheets epithelial sheets

• Not normally capable of Not normally capable of autonomous functionautonomous function

– Well vascularizedWell vascularized– Set off from CT by a basal Set off from CT by a basal

laminalamina– Usually capable of Usually capable of

considerable regenerationconsiderable regeneration– Always Always have some other have some other

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

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

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

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

• Not confined to glands: epithelial sheets can Not confined to glands: epithelial sheets can be secretorybe secretory

SECRETIONSECRETION

GLANDSGLANDS

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

GLANDSGLANDS

CHARACTERISTICS OF SECRETORY CHARACTERISTICS OF SECRETORY CELL TYPESCELL TYPES

• 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• Prominent nucleolus & Golgi apparatusProminent nucleolus & Golgi apparatus• May show granularity in cytoplasmMay show granularity in cytoplasm

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

• NO loss of NO loss of cytoplasm in cytoplasm in processprocess

• Cells typically Cells typically cuboidal to cuboidal to columnarcolumnar

• Used by Used by MOST MOST exocrine and exocrine and ALL endocrine ALL endocrine glandsglands

MODES OF SECRETION: MODES OF SECRETION: APOCRINEAPOCRINE

• Loss of SOME Loss of SOME cytoplasm in cytoplasm in processprocess

• Apical region Apical region pinches off & pinches off & degeneratesdegenerates

• 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 SIMPLE EXOCRINE GLANDSGLANDS

• Duct is NOT divided• Secretory Region MAY be

divided = “Branched”

COMPOUND EXOCRINE GLANDSCOMPOUND EXOCRINE GLANDS

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