Chapter 2Chapter 2

Epithelium Epithelium

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

ubstance2) Polarisaton: ---free surface: face air or other things ---basal surface: have basement membrane, to face underlying connective tissue (CT) 3)  Avascularity, but innervation: ---no blood vessels ---rich in nerve terminals4) Having functions of protection, secretion, absorptionand sensory reception

2.Classification of Epithelium

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

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

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

3. Classification of covering epithelium: According to the number of layer and shape

of cellsSimple epi.: ---simple squamous epi. ---simple cuboidal epi. ---simple columnar epi. ---pseudostratified ciliated column

ar epi.

Stratified epi.: ---stratified squamous epi. ---stratified columnar epi. ---transitional epi.

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

---structural feature:

one layer flattened cells, cell border are interdigitate

with flattened ellipsoid nucleus

---distribution: • mesothelium: the simple squamous epi. w

hich line the inner surface of body cavities such as thoracic, pericardiac and abdominal cavities.

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

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

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

Vascular endothelium

Mesothelium on Mesothelium on abdominal cavityabdominal cavity

2)      simple cuboidal epi.:

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

agonal outline in surface view.• spherical centrally-located nucleus

---distribution: /the renal tubule

/thyroid

/the some ducts of glands

---function: covering and secretion

thyroidrenal tubule

3)      simple columnar epi.:

---structural features: • one layer of columnar cells, with basally locate

d ovoid nucleus•

---distribution: gastrointestinal tract gall bladder uterus---function: secretion and absorption

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

goblet cellsimple columnar epi

4)      pseudostratified ciliated columnar epi.:

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

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

four types of cells

---distribution: inner surface of large duct of respiratory

trachea

bronchi

nasal

The epithelium of trachea

5)      stratified squamous epi.:

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

of polygonal –shaped cells • to the surface: more and more flattened cells

---distributon: • non-karatinised: mouth, pharynx, oesophag

us, urethra and vagina

• karatinised: the surface of body, make up the skin

non-karatinised karatinised

6)      transitional epi.:

• flexible-including the number of layers and shape of cells

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

• in the contracted bladder : there are six to seven layers of cells.

• The surface cells are very large and cuboidal in shape, covering several deep cells.

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

in the in the contracted bladderbladder

in the distendeddistended bladder

4. Epithelial specializations4. Epithelial specializations

1)1)            Specialisations of free surfacSpecialisations of free surfacee

     ①    microvilli: ---defination: delicate finger-liked projec

tions of cell-membrane and cytoplasm protruding from the free surface

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

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

ment at the apical side of cells

---function: increase the surface areas

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

brush border, e.g. proximal renal tubule

② cell coat: ---defination: a thick layer of extracellular glycoprotein

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

     ③ cilia:---defination: elongated, mobile projections of c

ell membrane and cytoplasm protruding from free surface

---structure: • 5-10um long, 300-500nm in diameter• surface: cell membrane• core: microtubules, 9X2+2• basal body: centrioles-connected with microtubules

---function: swing to produce a forward-moving wave

---distribution: epithelial cells of respiratory tract

respiratory tract

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

---intercellular connection of adjacent cells: • non-special: the minute space and cadheri

n -- cell adherent molecules

• special: junctional structures

① Tight junction (zonula occludens):

---structure: • apical part• point-liked fused between a

djacent cells• arranged in 2-4 thread-liked

structures• form anastomosing network

---function: seal the space between cells

 ② intermediate junction (zonula adherens):

---structure: • below the tight junction• a gap of 15-20nm in width with

medium electron-density filament material

• plaque of electron-dense materials, with attached microfilament-make up of terminal web

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

terminal web

intermediate junction

Tight junction

desmosome

cilia

③ desmosome (macula adherens):

---structure: • plate or spot-shaped• a gap of 20-30 nm, with low

electron-density filaments interdigitate

• attachment plaque: with attached tonofilament-inter

mediate filament (karatin)

---function: firmly connection

④ gap junction (communicating junction):

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

of proteins- connexin -2nm channel: hydrophilic

channel

---function: provide a pathway between cells

connexons

junctional complex: four types of junctional structures (at least two types) get together.

3)3)            specialization of basal surfacespecialization of basal surface

①     basement membrane:---defination: a sheet of membrane-liked amorph

ous material interposed between epi. cells and underlying CT.

---structure: • HE: pink colour, hard to see

• Under EM: --basal lamina: 20-300 nm, electron-dense, t

hread-liked and amorphous ground substance, produced by epi. cell

--reticular lamina: reticular tissue + ground substance, produced by CT

•

---function: • support, connection, fixation• semi-premeable membrane• induce the movement, proliferation and differenti

ation of epi. cell

 ② plasma membrane infolding

(basal longitudinal striation): ---defination: the infolding of cell-membrane with man

y mitochondria at the basal surface of epi. cell

---function: • increase the basal surface areas• facilitate the passage of water and ions

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

③    hemidesmosomes

---is half of desmosome.

5. Glandular epi. and gland• glandular epi.: epi are specialized for secreti

on• gland: organs composed mainly of glandula

r epi.

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

2) structure of exocrine gland:

①acinus (secreting unit):

according the nature

of secretion

a.    serous acinus:

serous secretory cells

---structure: • pyramid-shaped cell• basally-located round nucleus• acidophilic cytoplasm: eosinophilic zymogen

granules: contain enzymes• EM: RER, Golgi complex ---function: produce a serous secretion

b.      mucous acinus: mucous secreting cells

---structure: • pyramid-shaped cell• flattened dark nucleus against the basal cell

membrane• slightly basophilic cytoplasm-large mucigen g

ranules• EM: some RER, Golgi complex

---function: secretes mucus

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

serous demilune

②     ducts:

---from simple squamous epi to simple columnar or stratified epi.

---carry out the secretions

---secrete or absorb water and ions

Multichosen question Multichosen question

• 1.The lining epithelium of the serous body cavities (pericardial, pleural and peritoneal) is

• endothelium

• mesothelium

• simple cuboidal epithelium

• stratified squamous epithelium

• transitional epithelium

√

2. An endocrine gland passes its secretion directly into the

• blood or lymph

• duct

• body surface

• digestive tract

• lumen of acinus

√

3. The nucleus is flattened against the basal plasma memberane of the cells, the cytoplasm is filled with large mucigen droplets, it is the

• serous cell

• mucous cell

• serous demilune

• goblet cell

• myoepithelial cell

√

Fill in the blanks Fill in the blanks

In H.E. stain sections, the cytoplasm is stained pink by ___________, the nucleus is stained purple-blue by___________________________.

Hematoxylin

Eosin

The procedure of preparation of histologic slides includes mainly______________________, ___________,_________________,

_____________, ______________,and sectioning.

Obtaining the specimen

Fixation DehydrationClearing Embedding

The 4 basic types of tissue are ______________,_________________,_________________ and _________________.

epithelium connective tissuemuscular tissuenervous tissue

Epithelia are mainly classified into 2 groups: ______________and_______________.

Simple epi. Stratified epi

The intercellular junctions of epithelial cells are (1) _______________,

(2) ___________________,

(3) _____________, and (4)______________. When 2 or more kinds of them are present together, we called it __________________.

Tight junction

Intermediate junction

DesmosomeGap junction

Junctional complex

7. Specialized structures on basal surface of epithelial cells are ________________________________,_____________________________ and ______________________.

basement membraneplasma membrane infolding

hemidesmosomes

8. Pseudostratified columnar ciliated epithelium consists of 4 kinds of cells with different shape and height, but all set on the basal membrane: ________________________,

________________,_____________and ________________.

columnar cell (ciliated)

goblet cell fusiform cellbasal cell

Questions Questions

• Describe the characteristics of epithelial tissue.

• Describe the structural characteristics and functions of each covering epithelial type.

• Compare the structure of microvilli with cilia.

• Compare the structure of intermediate junction with desmosome.