Download Tissue Types

Chapter 2.
Epithelial tissue
Wang yang
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Cells
Tissue
Extracellular matrix（non-cell component）
(fibers, ground substance, tissue fluid)
◆ Epithelial tissue are composed of closely apposed
polyhedral cells with very little extracellular matrix.
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Key points in this chapter
•
•
•
•
1. Features of epithelium
2. Types of epithelia
3. Classification of covering epithelium
4. Specific structures in epithelium
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General features of epithelium
1、Contain more cells which tightly aggregate
together and very little extracellular matrix.
Apical surface
Vertical surface
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2、Polarity: significantly structural and functional
differences in cell’s opposite surface.
Free surface
Lateral surface
Basal surface
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3、Avascularity: no blood vessels
4、Innervation :rich in sensory nerve ending
5、Basement membrane: a layer of intercellular
substance at the base of epithelium
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Types of epithelia
Two basic types
– Covering epithelia form a continuous layer over all
the free surfaces of the body:
the outer layer of the skin
the inner surface of cavities and vessels;
the ducts of the exocrine glands
– Glandular epithelia:
* with main function for secretion
* make up most of the glands
Other types: sensory/germinal epithelium/myoepithelium
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Classification of covering Epithelia
Principle: based on the following features
 Layers of cells
one layer: simple epi.
several layers: stratified epi.
 Shape of cells on the vertical section
squamous epi.--flat/platelike
cuboidal epi. --having the shape of a cube
columnar epi.--column
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Classification depends on layer
Simple layer
Stratify layers
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12
.
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1、Simple squamous epithelium
surface shape
BM————
CT—————
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Apical surface
Irregular or polygon
border: interdigitate
nucleus: round
Vertical surface
flat
cytoplasm: very thin
nucleus: oblate/oval
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Simple squamous epithelium
•one layer of flat cells (having one flat nucleus).
•found in:
- alveoli of the lung
- kidney glomerulus
- heart, blood and lymphatic vessels
- body cavities
•thinnest of all
- gas diffusion, nutrient absorption
- exchange of waste & metabolite
- keep organ surface smooth/antifriction
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1. nuclei (one row of flat nuclei,
long axis of the nucleus
always parallel to the main
axis of the cell)
2. lumen
1
1
1
2
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The entire circulatory system (blood and lymph
vessles) is lined by simple squamous epithelium
that is called endothelium.
Longitudinal section
of the capillary
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The major body cavities (peritoneum, pleura, pericardium)
are lined by a mesodermally derived simple squamous
epithelium that is called mesothelium.
Function
To keep surface
of vessels or
organ smooth,
reduce friction,
facilitate the
blood/lymph flow
and movement of
viscera.
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2、Simple cuboidal epithelium
--structural features:
•one layer of cuboidal cells, with same height and
width (in side view) and hexagonal outline in
surface view.
• round centrally-located nucleus
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--Distribution:
renal tubule, thyroid gland, ovary surface...
--Main function:
absorption, secretion and covering.
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3、Simple columnar epithelium
--structural features:
• one layer of columnar cells,
with basally located ovoid
nucleus and hexagonal outline
in surface view.
• goblet cell: scattered,
secreting granules-mucinogen
+H2O=mucus: lubricate and
protect epi.
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Vertical section of duodenum
Simple columnar epi. Blue nuclei are almost at the same level, near to
basal surface, goblet cells scattered among the epi.
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4、Pseudostratified ciliated columnar epithelium
Different types of cells
All cells rest on the BM
Not all can reach to the
free surface
Columnar cell---------------------Goblet cell --------------------------------------------cilia on the columnar cell
Fusiform cell-----------------------Basal cell-------------------------------24
PSEUDOSTRATIFIED
• Appears layered but all cells touch the
basement membrane
Stratified
Pseudostratified
B.M.
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1.Nuclei
2.Epithelium
3.Cilia
4.Lumen
Pseudostratified ciliated
columnar epi.
larger respiratory passages
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5、Stratified Squamous Epithelium
* Multi-layer cells
* squamous cells in outermost layers
* Large/polygonal cells in
intermediate regions
* deepest (basal) cells:
cuboidal / low columnar
resting on the BM
strong proliferation ability
* Basal surface is sinuate
not linear:
increase the contact area
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6、Transitional Epithelium
Main Feature:
• The shape and layers of the epithelium are
changeable, and are depend on the
contraction or distention of organ.
Distribution:
Lining of bladder and ureters
surface epithelium
Basal epithelium
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Structural feature of Transitional Epithelium
 flexible-including the number of layers and shape of cells
In the nondistended bladder : there are six to seven layers of
cells.
In the distended bladder: there are two to three layers of
cells. The cells become flattened.
 The surface cells are very large, dome-like or cuboidal in
shape, covering several deep cells.
 Basal surface almostly parallel to the free surface of the
whole transitional epi.
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Specialized Structures
of Epithelial Cell
1) specializations of free surface
2) specializations of lateral surface
3) specializations of basal surface
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EM diagram of
columnar cells
Free surface—
Lateral
surface
—cilia
—
microvillus
Cell
junction
—plasma membrane
Basal
surface
infolding
——BM
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Microvilli
—cell membrane
—cytoplasm
—microfilament
—terminal web
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Definition of microvilli:
Delicate finger-liked projections of cell membrane
and cytoplasm protruding from the free surface.
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Function: increase the cell surface area,
better absorption
Distribution: absorptive cells
i.e.small intestine, proximal renal tubule
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Striated border
EM
LM
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Cilia
—cell membrane
—cytoplasm
—microtubule
——basal body
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Definition of cilia:
Elongated, motile projections of cell membrane
and cytoplasm protruding from free surface.
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Function:
Produce a forward-moving wave (rippling wheat field)
:cilia are motile, move back and forth, cilia movement is
coordinated to push the fluid or particulate matter in one
direction over the ciliated epithelium.
i.e. 1. Remove the inhale granules.
2. Propell the ovum/ germ cells toward the uterus
in oviduct.
Distribution:
Respiratory system and
oviduct.
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Cilia
SEM
LM
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Difference between microvilli & cilia
appearance
observation
Surface
Axes
Composition
Basal portion
Function
Microvilli
Small and short
EM
Cell-membrane
Cytoplasm
Microfilament
Terminal web
Increase surface
area
Cilia
Big and long
LM/EM
Cell-membrane
Cytoplasm
Microtubule
Basal body
Movement
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Specializations of the lateral surface
Cell junction：
Membrane-associated structures contribute to
cohesion and communication between cells.
Distribution:
Present in most tissues:
i.e. muscle tissue and nerve tissue
Prominent in epithelial tissue
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• Tight junction or
zonula occludens
（紧密连接\闭锁小带）
• Intermediate junction or
zonula adherens
（中间连接\粘着小带）
• Desmosome or
macula adherens
（桥粒\粘着斑）
• Gap junction or
communication junction
（缝隙连接\通讯连接）
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Tight junction (zonula occluden)
* Located at the most apical of lateral surface
* Point-liked membrane fusions between adjacent cells
* Arranged in 2-4 thread-liked structures
* Non-fusion space:10-15nm gap
* Serves as a barrier,
form a seal that prevents
flow of materials between cells
= impermeable junction
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Intermediate Junction (Zonula Adherens)
* located just below the tight j as a 'belt'
* a gap of 15-20nm in width with medium electrondensity filament
* on cytoplasmic surface of junction membrane
electron-dense plaques of material
inserted with actin filament
to form terminal web
* Function
/adherent
/keep the cell shape
/transfer cell contract force
=adhering junction
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Desmosome (Macula Adherens)
* plate or disk-shaped
* a gap of 20-30 nm, with low electron-density
filaments interdigitate to form intermediate line
* attachment plaque (made up of 12 proteins):
with attached tonofilament(10nm)
intermediate keratin filament
* Function
firmly adhesion/connection
=adhering junction
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Gap/ Communication Junction
* At deep part of the lateral cell surface
* the smallest gap of 2-4nm
* narrow intercellular space spanned by connexon
Connexon-------------
Cell membrane
Gap junction
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connexon:
-protein unit/individual unit of gap junction
-composed of 6-subunits of proteins--connexin
-hydrophilic pore---1.5nm width in the center
Function:
small molecular exchanges,
ions exchanges,
transmit electrical impulse,
provide a connective pathway
between adjacent cells
= communicating junction
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Review of chapter 2
1. Features of epithelium
2. Types of epithelium
3. Classification of covering epithelium
4. Cell junction
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1. Which of the following specializations of the
apical surface of epithelial cells contain microtubules?
A. Microvilli
B. Cilia
C. Stereocilia
D. Both B and C are correct
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2.The portion of the junctional complex primarily
responsible for restricting the passage of molecules
between adjacent epithelial cells:
A. Zonula occludens
B. Zonula adherens
C. Macula adherens
D. Hemidesmosomes
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E 3. Epithelial type that plays a protective function and is found
________
lining the esophagus.
H
________
4. Epithelial type that is associated with distensible organs
such as the urinary bladder.
A
_______
5. Epithelial type found lining small capillaries where it
modulates diffusion.
________
6. Epithelial type consisting of a single layer of squareB
shaped cells when viewed in tissue sections.
A. Simple squamous
B. Simple cuboidal
C. Simple columnar
D. Stratified cuboidal
E. Stratified squamous
F. Stratified columnar
G. Pseudostratified columnar
H. Transitional
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7. Cilia are commonly seen on cells in tissues that
A. line the blood vessels.
B. line the respiratory tract.
C. form the skin.
D. move from one place to another.
E. All of these are correct.
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8.The type of cell junction that prevents the contents
of the stomach or urinary bladder from leaking into
surrounding tissues is the
A.
B.
C.
D.
E.
adherens junction.
gap junction.
hemidesmosome.
desmosome.
tight junction.
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9. One might expect to see microvilli on epithelial
tissues whose principal function is
A. protection.
B. movement.
C. absorption.
D. mineral storage.
E. transmission of electrical impulses.
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10. Which of the following statements is NOT true
for the epithelium?
A. Epithelium is avascular.
B. Epithelium contains very little intercellular material
C. Epithelial cells lack mitotic activity
D. All epithelial cells of a pseudostratified
epitheliumlie on a basal lamina.
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11. Stratified squamous epithelia are characterized
by always having:
A. A keratinized layer
B. Squamous cells in proximity to the basement
membrane
C. Majority of cells that are squamous in shape
D. Squamous cells at the free surface
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12. Pseudostratified epithelium differs from stratified
epithelia because in the pseudostratified epithelium:
A. Two or more than two layers of cells are present
B. All cells reach the luminal surface but all cells do not
lie on the basal lamina
C. All cells lie on the basal lamina but all cells do not
reach the luminal surface
D. Blood vessels are numerous
E. None of the above is correct
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13. Mesothelium can be defined as:
A. A simple squamous epithelium lining the blood vessels
B. A simple squamous epithelium lining the body cavities
C. A transitional epithelium
D. A pseudostratified epithelium
E. None of the above is correct
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14. Cilia can be distinguished from microvili
because cilia:
A. Are non-motile
B. Are located at the basal lamina
C. Always occur singly
D. Lack 9+2 tubular arrangement
E. Are associated with basal bodies
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15. Which of the following intercellular junctions would
you expect to be most prevalent in an epithelium that
is subject to much wear and tear?
A. Zonula occludens
B. Desmosome
C. Gap junction
D. Tight junction
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