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Chapter 2 Epithelium. 1.General feature: 1) contain more cells and less extracellular ground substance 2) Polarisaton : --- free surface: face air or other things --- basal surface: have basement membrane, to face underlying connective tissue (CT)

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Chapter 2 epithelium

Chapter 2Epithelium


1.General feature:

1) contain more cells and less extracellular ground substance

2) 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 terminals

4) Having functions of

protection, secretion,

absorption

and 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 cells

Simple epi.: ---simple squamous epi.

---simple cuboidal epi.

---simple columnar epi.

---pseudostratified ciliated columnar epi.

Stratified epi.:---stratified squamous epi.

---stratified columnar epi.

---transitional epi.


1 simple squamous epi
1)simple squamous epi:

---structural feature:

one layer flattened cells, cell border are interdigitate

with flattened ellipsoid nucleus


---distribution:

  • mesothelium: the simple squamous epi. which 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
Vascular endothelium


Mesothelium on abdominal cavity
Mesothelium on abdominal cavity


2)simple cuboidal epi.:

---structural feature:

  • one layer of cells, with same height and width , hexagonal outline in surface view.

  • spherical centrally-located nucleus


---distribution: /the renal tubule

/thyroid

/the some ducts of glands

---function: covering and secretion

renal tubule

thyroid


3)simple columnar epi.:

---structural features:

  • one layer of columnar cells, with basally located ovoid nucleus


---distribution: gastrointestinal tract

gall bladder

uterus

---function: secretion and absorption

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

goblet cell

simple columnar epi


four types of cells

4)pseudostratified ciliated columnar epi.:

---Structural feature:

1, Four types of cells

columnar cell (ciliated); goblet cell

fusiform cell; basal cell: pyramid-shaped

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


---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, oesophagus, urethra and vagina

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

karatinised

non-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.



In the contracted bladder
in the contractedbladder

in the distendedbladder



1 specialisations of free surface
1)Specialisations of free surface


microvilli:

---defination: delicate finger-liked projections 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 fixed on terminal web

terminal web: made up of transverse-arranged filament at the apical side of cells


---function: increase the surface areas

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

brush border, e.g. proximal renal tubule


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 cell 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 specializations of the lateral surface
2)specializations of the lateral surface


---intercellular connection of adjacent cells:

  • non-special: the minute space and cadherin -- cell adherent molecules

  • special: junctional structures


Tight junction (zonula occludens):

---structure:

  • apical part

  • point-liked fused between adjacent 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


cilia

Tight junction

desmosome

intermediate junction


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-intermediate filament (karatin)

    ---function: firmly connection


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



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


3 specialization of basal surface
3)specialization of basal surface


basement membrane:

---defination: a sheet of membrane-liked amorphous material interposed between epi. cells and underlying CT.

---structure:

  • HE: pink colour, hard to see


  • Under EM:

    --basal lamina: 20-300 nm, electron-dense, thread-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 differentiation of epi. cell


② plasma membrane infolding

(basal longitudinal striation):

---defination: the infolding of cell-membrane with many 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.


hemidesmosomes

---is half of desmosome.


5. Glandular epi. and gland

  • glandular epi.: epi are specialized for secretion

  • gland: organs composed mainly of glandular epi.


1)classification:

exocrine gland: discharge the secretion through a duct system

endocrine 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 basophiliccytoplasm-large mucigen granules

  • 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


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 memberane of the cells, the cytoplasm is filled with large mucigen droplets, it is the

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

Dehydration

Clearing

Embedding


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

epithelium

connective tissue

muscular tissue

nervous 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

Desmosome

Gap junction

Junctional complex


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

basement membrane

plasma 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 cell

basal cell


Questions
Questions 4 kinds of cells with different shape and height, but all set on the basal membrane: ________________________,

  • 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.


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