Chapter 2Chapter 2

EpitheliumEpithelium

1.General feature:1.General feature:1) contain more cells and less extracellular ground substan1) contain more cells and less extracellular ground substan

cece2) Polarisaton2) Polarisaton:: ---free outer surface: face the surface of the body or the l---free outer surface: face the surface of the body or the l

umen of an organ or glandumen of an organ or gland ---basal surface: face underlying connective tissue---basal surface: face underlying connective tissue3)  Avascularity, but innervation3)  Avascularity, but innervation: : ---no blood vessels---no blood vessels ---rich in nerve terminals---rich in nerve terminals4) 4) Having functions ofHaving functions of protection, secretion, protection, secretion, absorptionabsorptionand sensory receptionand sensory reception

2.Classification of Epithelium2.Classification of Epithelium

1)1)    Covering epithelium:Covering epithelium: the epithelium which cover body the epithelium which cover body surface or line the inner surface of body cavities, tubes surface or line the inner surface of body cavities, tubes and sac.and sac.

2)2)    Glandular epithelium:Glandular epithelium: the epithelium which main the epithelium which main function is secretion.function is secretion.

3)3)    Sensory epithelium:Sensory epithelium: the epithelium which has special the epithelium which has special sensory function.sensory function.

3. Classification of covering epithelium3. Classification of covering epithelium: :

According to the number of layer and shape of cellAccording to the number of layer and shape of cellss

Simple epi.:Simple epi.: --- ---simple squamous epi.simple squamous epi.

---simple cuboidal epi.---simple cuboidal epi.

---simple columnar epi.---simple columnar epi.

---pseudostratified ciliated columnar epi.---pseudostratified ciliated columnar epi.

Stratified epi.:Stratified epi.: ---stratified squamous epi.---stratified squamous epi.

---stratified columnar epi.---stratified columnar epi.

---transitional epi.---transitional epi.

1)1)            simple squamous epi:simple squamous epi:

---structural feature:---structural feature:

/one layer flattened cells, cell border are interdigitate closely/one layer flattened cells, cell border are interdigitate closely

/with flattened ellipsoid nucleus/with flattened ellipsoid nucleus

---distribution: ---distribution: • mesothelium:mesothelium: the simple squamous epi. which l the simple squamous epi. which l

ine the inner surface of body cavities such as ine the inner surface of body cavities such as thorthoracic, pericardiac and abdominal cavitiesacic, pericardiac and abdominal cavities..

• endothelium:endothelium: the simple squamous epi. which li the simple squamous epi. which line the inner surface of cardiovascular and lymphne the inner surface of cardiovascular and lymphatic system.atic system.

• other placeother place:: alveoli, parietal layers of renal caps alveoli, parietal layers of renal capsule.ule.

---function:---function: a) transport of materials a) transport of materials b) facilitates movement of viscerab) facilitates movement of viscera

Vascular Vascular endotheliumendothelium

Mesothelium on Mesothelium on abdominal cavityabdominal cavity

2)2)            simple cuboidal epi.:simple cuboidal epi.:

---structural feature:---structural feature: • one layer of cells, with same height and width , hexagonal one layer of cells, with same height and width , hexagonal

in shape.in shape.• spherical centrally-located nucleusspherical centrally-located nucleus

---distribution:---distribution: /the renal tubule /the renal tubule

/thyroid/thyroid

/the some ducts of glands/the some ducts of glands

---function:---function: covering and secretion covering and secretion

thyroidrenal tubule

3)3)            simple columnar epi.:simple columnar epi.:

----structural features:--structural features: • one layer of columnar cells, with basally located ovoione layer of columnar cells, with basally located ovoi

d nucleusd nucleus

---distribution:---distribution: gastrointestinal tract gastrointestinal tract gall bladdergall bladder uterusuterus---function:---function: secretion and absorption secretion and absorption

goblet cell: scattered, secreting granules-mucusgoblet cell: scattered, secreting granules-mucus

goblet cellsimple columnar epi

4)4)            pseudostratified ciliated columnar epi.:pseudostratified ciliated columnar epi.:

---Structural feature:---Structural feature: 1, Four types of cells1, Four types of cellscolumnar cell (ciliated); goblet cellcolumnar cell (ciliated); goblet cellfusiform cell; basal cell: pyramid-shapedfusiform cell; basal cell: pyramid-shaped

2, Every cell locate on basement membrane: 2, Every cell locate on basement membrane: Simple epi.Simple epi.

four types of cells

---distribution:---distribution:

inner surface of large inner surface of large duct of respiratory passagesduct of respiratory passages

tracheatrachea

bronchibronchi

The epithelium of trachea

5)5)            stratified squamous epi.:stratified squamous epi.:

---structural features:---structural features: • deepest (basal) cells: deepest (basal) cells: one layer of cuboidal cellsone layer of cuboidal cells• the cells in intermediate regions: the cells in intermediate regions: several layers of polseveral layers of pol

ygonal –shaped cells ygonal –shaped cells • to the surface: to the surface: more and more flattened cellsmore and more flattened cells

---distributon:---distributon:

• non-karatinised:non-karatinised: mouth, pharynx, oesophagus, mouth, pharynx, oesophagus, urethra and vaginaurethra and vagina

• karatinised:karatinised: the surface of body, make up the ski the surface of body, make up the skinn

non-karatinised karatinised

6)6)    transitional epithelium:transitional epithelium:

• flexible qualitiesflexible qualities

-including the number of layers and shape of -including the number of layers and shape of cellscells

---distribution: bladder---distribution: bladder

in the distended bladder: in the distended bladder: there are there are two to three layers of cells. The cells two to three layers of cells. The cells become flattened.become flattened.

in the contracted bladder: there are six to sevethere are six to seven layers of cells. n layers of cells. The surface cells are very large and cuboida The surface cells are very large and cuboidal in shape, covering several deep cells.l in shape, covering several deep cells.

4. Epithelial specializations4. Epithelial specializations

1)1)            Specializations of free surfaceSpecializations of free surface

①①        microvilli:microvilli: ---definition:---definition: delicate finger-liked projections of cell-membra delicate finger-liked projections of cell-membra

ne and cytoplasm protruding from the free surfacene and cytoplasm protruding from the free surface

---structure:---structure: • 0.1um in diameter, with different longth.0.1um in diameter, with different longth.• surface: cell membrane with cell coatsurface: cell membrane with cell coat• core: longitudinal microfilament-actin filament fixcore: longitudinal microfilament-actin filament fix

ed on terminal webed on terminal web• terminal web: made up of transverse-arranged filaterminal web: made up of transverse-arranged fila

ment at the apical side of cellsment at the apical side of cells

---function:---function: increase the surface areas, thus aid in the increase the surface areas, thus aid in the processes of secretion and absorption.processes of secretion and absorption.

---distribution:---distribution: /striated border: intestinal epi. cell /striated border: intestinal epi. cell

/brush border: proximal renal tubule/brush border: proximal renal tubule

Striated borderStriated border

②② cell coat:cell coat:

---definition:---definition: a thick layer of extracellular glycoproteina thick layer of extracellular glycoprotein

---function:---function: adherence, supporting, protection, exchange of material and recognizeadherence, supporting, protection, exchange of material and recognize

     ③     ③ cilia:cilia:---definition:---definition: elongated, mobile projections of cell m elongated, mobile projections of cell m

embrane and cytoplasm protruding from free surfaembrane and cytoplasm protruding from free surfacece

---structure:---structure:

• 5-10um long, 300-500nm in diameter5-10um long, 300-500nm in diameter

• surface: cell membranesurface: cell membrane

• core: microtubules, 9X2+2core: microtubules, 9X2+2

• basal body: basal body:

centrioles-connected with microtubules of ciliacentrioles-connected with microtubules of cilia

---function:---function: beat in a rhythmical manner and produce a beat in a rhythmical manner and produce a forward-moving wave forward-moving wave

---distribution:---distribution: epithelial cells of respiratory tract epithelial cells of respiratory tract

respiratory tract

2)2)    specializations specializations of the lateral surfaceof the lateral surface

---intercellular connection of adjacent cells: ---intercellular connection of adjacent cells:

• non-special manner: the minute space and adherent molenon-special manner: the minute space and adherent molecules (glycoproteins, proteoglycans)cules (glycoproteins, proteoglycans)

• Special manner: junctional structuresSpecial manner: junctional structures

①①  Tight junction (zonula occludens):Tight junction (zonula occludens):

---structure:---structure: • apical partapical part

• point-liked fused between adjacent point-liked fused between adjacent cellscells• arranged in 2-4 thread-likedarranged in 2-4 thread-liked structuresstructures• form anastomosing networkform anastomosing network

---function:---function: seal the space between cellsseal the space between cells

 ② ② intermediate junction (zonula adintermediate junction (zonula adherens):herens):

---structure: ---structure:

• below the tight junctionbelow the tight junction• a gap of 15-20nm in width with media gap of 15-20nm in width with medi

um electron-density filament materialum electron-density filament material• plaque of electron-dense materials, plaque of electron-dense materials,

with attached microfilament-make up with attached microfilament-make up of terminal webof terminal web

---function:---function: /adherens/adherens /keep the cell shape/keep the cell shape /transfer cell contract force/transfer cell contract force

③③ desmosome (macula adherens):desmosome (macula adherens):

---structure:---structure:

• plate or spot-shapedplate or spot-shaped

• a gap of 20-30 nm, witha gap of 20-30 nm, with

low electron-density filaments interdilow electron-density filaments interdigitategitate

• Many tonofilaments are inserted into aMany tonofilaments are inserted into attachment plaque, each filament make ttachment plaque, each filament make a hairpin loop and then passes back inta hairpin loop and then passes back into the cytoplasmo the cytoplasm

• ---function:---function:

firmly connectionfirmly connection

④④ gap junction (communicgap junction (communicating junction):ating junction):

---structure:---structure: • the smallest gap of 2-3 nmthe smallest gap of 2-3 nm• connexons:connexons: -consist of protein-consist of protein -7~9nm in diameter-7~9nm in diameter -composed of 6-subunits of prot-composed of 6-subunits of prot

eins- connexineins- connexin -2nm channel: electron-lucid ce-2nm channel: electron-lucid ce

ntral channelntral channel---function:---function: provide a ions and small molecules provide a ions and small molecules

pathway between cellspathway between cells

junctional complex:junctional complex:

at least two types of junctional structures get toat least two types of junctional structures get together.gether.

3)3)            specialization of basal surfacespecialization of basal surface

①①    basement membrane:basement membrane:---definition:---definition: a sheet of membrane-liked amorphous m a sheet of membrane-liked amorphous m

aterial interposed between epithelium cells and undaterial interposed between epithelium cells and underlying CT.erlying CT.

---structure:---structure:

• HE: pink colour, hard to seeHE: pink colour, hard to see

• PAS +PAS +

• EM: two layersEM: two layers ----basal lamina: 20-300 nm, electron-dense, basal lamina: 20-300 nm, electron-dense,

thread-liked and amorphous ground substance, thread-liked and amorphous ground substance, produced by epithelium Cellproduced by epithelium Cell

--reticular lamina: RT+ground substance, --reticular lamina: RT+ground substance, produced by CTproduced by CT

---function:---function:

• support, connection, fixationsupport, connection, fixation

• semi-permeable membranesemi-permeable membrane

• induce the movement, proliferation and induce the movement, proliferation and differentiation of epithelium celldifferentiation of epithelium cell

 ② ② plasma membrane infoldingplasma membrane infolding

(basal longitudinal striation):(basal longitudinal striation): ---definition:---definition: the infolding of cell-membrane with many mito the infolding of cell-membrane with many mito

chondria at the basal surface of epithelium cellchondria at the basal surface of epithelium cell

---function:---function:

• increase the basal surface areasincrease the basal surface areas

• facilitate the passage of water and ionsfacilitate the passage of water and ions

---distribution:---distribution: mainly in proximal and distal renal mainly in proximal and distal renal tubule.tubule.

③③    hemidesmosomeshemidesmosomes

---is half of desmosome.---is half of desmosome.

5. Glandular epithelium and gland5. Glandular epithelium and gland

• glandular epithelium: are specialized for secretionglandular epithelium: are specialized for secretion• gland: organs composed mainly of glandular epiithgland: organs composed mainly of glandular epiith

eliumelium

1)classification:1)classification: exocrine gland: exocrine gland: discharge the secretion through a duct systemdischarge the secretion through a duct systemendocrine gland: endocrine gland: release the secretion directly into blood steamrelease the secretion directly into blood steam

2) structure of exocrine gland: 2) structure of exocrine gland:

①①acinus (secreting unit): acinus (secreting unit):

according the natureaccording the nature

of secretionof secretion

a.a.        serous acinus:serous acinus:

serous secretory cellsserous secretory cells

Simple gland compound alveolar gland compound tubulo-alveolar glandSimple gland compound alveolar gland compound tubulo-alveolar gland

---structure:---structure: • pyramid-shaped cellpyramid-shaped cell• basally-located round nucleusbasally-located round nucleus• acidophilic cytoplasm-eosinophilic zymogen graacidophilic cytoplasm-eosinophilic zymogen gra

nules-contain enzymesnules-contain enzymes• EM: RER, Golgi complexEM: RER, Golgi complex---function:---function: produce a serous secretion produce a serous secretion

b.mucous acinus:b.mucous acinus: mucous secreting cells mucous secreting cells

---structure:---structure:

• pyramid-shaped cellpyramid-shaped cell

• flattened dark nucleus against the basal cell flattened dark nucleus against the basal cell membranemembrane

• slightly basophilic cytoplasm-large mucigeslightly basophilic cytoplasm-large mucigen granulesn granules

• EM: some RER, Golgi complexEM: some RER, Golgi complex

---function:---function: secretes mucus secretes mucus

c.c.    mixed acinus:mixed acinus: two types of cells two types of cells ---structure:---structure: • mucous acinusmucous acinus• with several serous cells attach on one side- serous demilunewith several serous cells attach on one side- serous demilune

②②    ducts: ducts:

---from simple squamous epithelium to simple colum---from simple squamous epithelium to simple columnar or stratified epitheliumnar or stratified epithelium

---carry out the secretions---carry out the secretions

---secrete or absorb water and ions---secrete or absorb water and ions