Class 02(Epithelium)

8/11/2019 Class 02(Epithelium)

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Cells which have similar

Morphologic characteristics

and functions

Intercellular substance

—— more or little

Tissue

Four basic types of tissues ——

Epithelial tissue

Connective tissueMuscular tissue

Nervous tissue

These tissues associate one and

another in variable proportions,

forming different organs and systems

of the body.

Epithelial tissue



1. Location:

on the surface of body as sheets

(external or internal )

e.g. skin, digestive tract, bladder, blood vessel,

body cavity (pleural cavity

pericardial cavity

abdominal cavity)

2. Function

Protection :

protect organs and body from physical,

chemical, biological damage

Absorption : nutrients are absorbed in

gastro-intestinal tract

Secretion : e.g. the epi. cells of gland

Sensation : receive the stimulus of chemistry or

physics,

e.g. olfactory epi. cells

Transportation :

the epithelial cells can transportions(electrolytes), e.g. in kidney

Contractility : myoepithelial cells

Reproduction:

e.g. germinal epithelium in the testis



3. General structural features

Sheets : Many cell a little intercellular substance

* cells are closely aggregated together forming a thin membrane

* intercellular substance is homogeneous

* adhesion between cells is strong

Polarisation :

epithelial cells have free surface and basal surface.

In different surface,

the structure and function are different

Avascularity: Generally, there are no blood vessels

in epithelium tissue.

Innervation:

Epithelium is rich in nerve ending

between epithelial cells.



II. The Classification of Epithelial tissue

According to their functions, epi. can be classified into :covering epi.

glandular epi.

sensory epi.

myoepitheliumgerminal epi.

III . Covering epithelium

I）

classification of covering epi.

1

The principles of classification in covering epi.

1） Cell shape :

polygonal in superficial view, three main types of cell in vertical section

columnar 柱状 height > width

cuboidal 立方 height = width

squamous 扁平 height < width



(2) number of the cell layer

simple layer —— simple epi.

stratified layer —— stratified epi.

(more than one layer 复层 )

squamous

Cuboidal

columnar

Simple

Stratified

2 How to name:

(superficial layer)



（ II） Common type of covering epi.1 simple squamous epithelium

(单层扁平上皮)

Facilitates movement of viscera.

Active transport by pinocytosis.

in circulatory system —— endothelium (内皮

)

in body cavity —— mesothlium (间皮)

2 simple cuboidal epithelium

(单层立方上皮)

covering ovary, thyroid, kidney… Covering

Secretion

absorption



3 simple columnar epithelium

lining gastrointestinal tract, gallbladder...

Absorption;

Protection;

Secretion ---goblet cell

lubrication

4 pseudostratified ciliated columnar epithelium

Pseudo —— false

columnar, fusiform, pyramid, goblet

Some cells are higher, some are shorter,

their nuclei are at different levels and not all cells reach to

surface

but all cells attach to

basement membrane



Lining of respiratory tract

Protection， Secretion，

Transport of particles out of air passages



5、 Stratified squamous epithelium

(复层扁平上皮)stratif ied squamous

Keratinized (角化的) epi. —— skin

stratif ied squamous

Nonkeratinized (未角化的) epi.

—— mouth, esophagus

vagina, anal canal

Protection

Withstand wearing and tearing



6、 transitional epithelium

(变移上皮)

lining of urinary tract

(urinary bladder, ureter)

cell layer & cell shape can change

according to the degree of

distention of organs

Protection



LM: * brush border (刷状缘) —— kidney

* striated border (纹状缘) —— intestine

EM: fingerlike projection surface —— cell membrane, cell coat

core —— cytoplasm

(contain microfilaments)

Function: enlarge the surface of cells

（2） cilium (纤毛)

—— larger, longer and motile;

5-10μlong, 0.2μin diameterEM:

a central pair of microtubules

9 pairs of microtubules

9+2” arranged in a circle

Function:

make the fluid flow in one direction

by their rapid back-forth movement



cell cohesion:Cell cohesion between epithelium cells related to

*glycoproteins, proteoglycans, calcium…

However, the most important factors in cell

cohesion are special

—— intercellular junctions

which are specialization of lateral cell membrane.

• tight junction

• intermediate junction

• desmosome

• gap junction

2

lateral surface



near the lumen,

the outer lamina of

two adjacent cell membrane are fused into one

（1）Tight junction紧密连接

(zonula occludens闭锁小带)

zonula: this J form a band completely

encircling the cell

occludens: membrane fusion close off

the intercellular space

Function: to form a tight seal —— barrier

preventing the free passage of

materials across epi.



belt-like

But the outer lamina of cell membrane are

not fused , just adhered.

Function: adhere the cells together

（2）intermediate junction 中间连接 (zonula adherens粘着

小带)

（3） desmosome 桥粒 (macula adherens粘着斑)

elliptic patch(disk-like) —— attachment plaques

intermediate filaments (loop-like structure)

intermediate line

Function: make the cells bind together very tightly



（4） gap junction 缝隙连接



like a patch:

some tubules connect cells

Tubule－

consists of six subunits;

center is a 0.5 nm hydrophilic canal

which permit interchange of ions

Function: interchange information



junctional complex

(连接复合体)

two or more junctions get together



3、Basal surface



（1） basement membrane(基膜)

LM: homogeneous,acidophilic thin membrane



EM: basement lamina 基板

reticular lamina网板

(somewhere,the reticular lamina is absent,

and could not be seen in LM)



Function:

① support,connect,anchor the epi.

② orient epithelial cells location

③ selective barrier



2） plasma membrane infolding

(质膜内褶

)



LM: longitudinal striation in basal partof epi cells

EM: The cell membrane of basal surface

invaginate into cell body.

Mitochondria distribute between

these infolings.



Function:

• enlarge the surface of cell membrane

• Present in the cells which transport ions

and water.



（3） Hemidesmosome半桥粒

• Between some epithelial cells and basal lamina

• half a desmosome on the epitheliul cell membrane

•

bind the epithelial cells to basal lamina.



IV . Glandular epithelium (腺上皮)



Glandular epithelia —— tissues formed by cells specialized

to produce a fluid secretion

Gland ——

organ mainly formed by

Glandular epithelia



Exocrine gland

Endocrine gland

Unicellular gland

multicellular gland



Secretory portion:contains the cells responsible

for the secretory process.

Ducts: transport secretion to the

exterior of the gland.

Class 02(Epithelium)

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