Chapter 2
Epithelial tissue
Zhong jie Li （李仲杰）
School of medicine, Zhejiang University
lizhongjie@zju.edu.cn
1.General feature:
1) contain more cells and less extracellular ground substance
2) Polarity:
---free outer surface: face the surface of the body or the
lumen of an organ or gland
---basal surface: attached underlying connective tissue
3) Avascularity, but innervation:
Free (apical) Surface
---no blood vessels
---rich in nerve terminals
4) High regeneration capacity
5) Functions: protection
secretion
absorption
sensory reception
Basement Membrane
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.
* germinal epithelia
3. Classification of covering epithelium:
According to the number of layer and the shape of
surface 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.
Cell Layers
Simple
Stratified
Cell shape
• Free surface
• basal surface
• lateral surface
1)
simple squamous epi:
---structural feature:
/one layer flattened cells, cell border are interdigitate
closely
/with flattened ellipsoid nucleus
---Distribution:
• mesothelium: the simple squamous epi. which
line the inner surface of body cavities such as
thoracic, abdominal cavities and pericardiac .
• endothelium: the simple squamous epi. which
line the inner surface of cardiovascular and
lymph vessels.
• other place: alveoli, parietal layers of renal
capsule.
---function: a) transport of materials
b) facilitates movement of viscera
1.
2.
Nuclei (flat and parallel to the
surface of the epithelium)
Face to lumen
1
* The entire circulatory system is
lined by a S. S. Epi. that is called
endothelium.
The major body cavities ( peritoneal, pleural, pericardial) are
lined by S. S. epi that is called mesothelium.
Mesotheliu
m
Mesothelium on abdominal cavity
2)
simple cuboidal epi.:
---structural feature:
• one layer of cells, with same height and width , hexagonal
in shape.
• 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-mucus
striated border ：free surface of cells often bear microvilli-thin
finger-like cellular protjections which form striated border.
simple columnar epi
goblet cell
4)
pseudostratified ciliated columnar epi.:
four types of cells
---Structural feature:
1, Four types of cells
columnar cell (ciliated); goblet cell
fusiform cell;
basal cell: pyramid-shaped
2, Every cell locate on basement membrane: Simple epi.
---distribution:
inner surface of large duct of respiratory passages
nasal
trachea
cilia
bronchi
The epithelium of trachea
Basement membrane
1. Nuclei
2. Epithelium
3. Cilia
4. Lumen
Pseudostratified ciliated
columnar epithelium
5)
stratified squamous epi.:
---structural features:
• Multi-layer cells
• 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-keratinised: mouth, pharynx, oesophagus,
urethra and vagina
• keratinised: the surface of body, make up the
skin
non-karatinised
Keratinization:
a process by which the superficial cells die and become tough, hard squama.
6) transitional epithelium:
• Multi-layer cells
• Flexible qualities
--- change the number of layers and shape of cells
(empty state — distended state）
in the contracted bladder
in the distended bladder
---distribution: renal pelvis, ureters, urinary
bladder, part of the urethra.
Dome-shaped cells.
4. Epithelial
specializations
Sides of cells:
--- Apical (free)
--- Basal
--- Lateral
1)Specializations of the apical surface
• Cell coat: Glycocalyx--- glycoprotein containing coat
• Microvilli
• Stereocilia: very long microvilli (immotile)
• Cilia
①
microvilli:
---definition: delicate finger-liked projections of cellmembrane 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, thus aid in the
processes of secretion and absorption.
---distribution: /striated border: intestinal epi. cell
/brush border: proximal renal tubule
Striated border
② cell coat:
---definition:
a thick layer of extracellular glycoprotein
---function:
adherence, supporting, protection, exchange of material and
recognize
③
cilia:
---definition: 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 of cilia
---function: beat in a rhythmical manner and produce a
forward-moving wave
---distribution: epithelial cells of respiratory tract
respiratory tract
Difference between microvilli & cilia
appearance
Microvilli
Small and short
Cilia
Big & long
observation
EM
Surface
Cell-membrane
Axes
Cytoplasm
Microfilament
Terminal web
Increase surface
area
LM
Cellmembrane
Cytoplasm
Microtubule
Basal body
Movement
Basal portion
Function
2) specializations
of the lateral surface
---intercellular connection of adjacent cells:
• non-special manner: the minute space and adherent
molecules (glycoproteins, proteoglycans, cadherin)
• Special manner: junctional structures
① 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
③ desmosome (macula adherens):
---structure:
• plate or spot-shaped
• a gap of 20-30 nm, with
•
•
•
low electron-density filaments
interdigitate
attachment plaque
Many tonofilaments are inserted into
attachment plaque, each filament
make a hairpin loop and then passes
back into the cytoplasm
---function:
firmly connection
Pemphigus
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: electron-lucid
central channel
---function:
provide a ions and small molecules
pathway between cells
connexons
junctional complex:
at least two types of junctional structures get
together.
3)
specialization of basal surface
① basement membrane:
---definition: a sheet of membrane-liked amorphous
material interposed between epithelium cells and
underlying CT.
---structure:
• HE: pink colour, hard to see
• PAS +
• EM: two layers
--basal lamina: 20-300 nm, electron-dense,
thread-liked and amorphous ground substance,
produced by epithelium Cell
--reticular lamina: RT+ground substance,
produced by CT
---function:
• support, connection, fixation
• semi-permeable membrane
• induce the movement, proliferation and
differentiation of epithelium cell
② plasma membrane infolding
(basal longitudinal striation):
---definition: the infolding of cell-membrane with many
mitochondria at the basal surface of epithelium cell
---function:
• increase the basal surface areas
• facilitate the passage of water and ions
---distribution: mainly in proximal and distal renal
tubule.
③ hemidesmosomes
---is half of desmosome.
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.
5. Glandular epithelium and gland (study yourself )
•
•
glandular epithelium: are specialized for secretion
gland: organs composed mainly of glandular
epiithelium
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:
Simple gland
compound alveolar gland
compound tubulo-alveolar gland
① acinus (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 granules
• EM: some RER, Golgi complex
---function: secretes mucus
Mucous acinus
c. mixed acinus: two types of cells
---structure:
• mucous acinus
• with several serous cells attach on one sideserous demilune
② ducts:
---from simple squamous epithelium to simple
columnar or stratified epithelium
---carry out the secretions
---secrete or absorb water and ions
Thank you !