Download MBBS Anatomy PPT 28 Simple Epithelium Notes

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Epithelial Tissue -- General Features

? Closely packed cells with little extracellular

material

? Many cell junctions often provide secure

attachment.

? Cells sit on basement membrane

? Apical (upper) free surface

? Basal surface against basement membrane

? Avascular---without blood vessels

? nutrients and waste must move by diffusion

Epithelial Tissue -- General

Features

? Good nerve supply
? Rapid cell division (high mitotic rate)
? Functions
? protection, filtration, lubrication, secretion,

digestion, absorption, transportation,

excretion, sensory reception, and

reproduction.

Types of Epithelium

1. Covering and lining epithelium

? epidermis of skin

? lining of blood vessels and ducts

? lining respiratory, reproductive, urinary & GI

tract

2. Glandular epithelium- originate from

invaginated epithelial cells

? secreting portion of glands

? thyroid, adrenal, and sweat glands

Epithelium

? Epithelium is derived from all three germ

layers

? Ectoderm-oral and nasal mucosa,cornea ,

epidermis, glands of skin, mammary glands

? Endoderm-Lining of respiratory and

gastrointestinal tract, liver , panceas

? Mesoderm-lining of urogenital system,

circulatory system and body cavities lining-

mesothelium


Typical

Arrangement

of Epithelial

Tissue and its

Basement

Membrane

Basement Membrane

Basement Membrane

? The basement membrane is a thin sheet of

fibers that underlies the epithelium

? The basement membrane is the fusion of two

lamina, the basal lamina-elaborated by

epithelial cells and the reticular lamina (or

lamina reticularis)-manufactured by cells of

connective tissue


Structure of Basement membrane

? Basement Membrane

? Basal Lamina

? Lamina Lucida

? Extracellular glycoprotein-

Laminin,integrins,entactins,dystroglycans

? Transmembrane laminin receptors-project from epithelial cell

membrane into basal lamina

? Lamina Densa consists of a network of fine filaments.

? Type IV collagen. forms felt-like network of fibers that gives

the basement membrane its tensile strength

Structure of Basement membrane

? Lamina Reticularis
? Type II collagen (as reticular fibers)
? Attaching proteins (between Basal and

Reticular Laminae)-all elaborated by fibroblast

of connective tissue

? Type VI collagen (anchoring fibrils)
? fibrillin (microfibrils)
? Fibronectin

lamina lucida &lamina densa

? Lamina Densa

? dense layer closer to the connective tissue
? 30?70 nm in thickness
? consists of an underlying network of reticular

collagen (type IV) fibrils

? Lamina Lucida

? clear layer close to epithelium

Apical surface

Lateral surface

Epithelium

Basal lamina

Reticular lamina

Connective tissue


Epithelial Tissue

Epithelial Tissue

Functions of basement membrane

? anchor down the epithelium to its loose

connective tissue (the dermis) underneath

? provide structural support to the tissue

? a mechanical barrier, preventing malignant

cells from invading the deeper tissues

Fusion of basal laminae

? Glomerular filtration of the kidney

? by the fusion of the basal lamina from the

endothelium of glomerular capillaries and the

basal lamina of the epithelium of the Bowman's

capsule

? Gaseous exchange between lung alveoli and

pulmonary capillaries

? by the fusion of the basal lamina of the lung

alveoli and of the basal lamina of the lung

capillaries


Basement Membrane

Cancer cells (Malignant)

? If the epithelial cells become transformed

(cancerous) and become 'malignant', they are

able to break through the basement

membrane and invade the tissues beneath.

This characteristic is used in the diagnosis of

malignant epithelial tumors

A poorly functioning basement membrane

Diseases

? Genetic defects

? Injuries by the body's own immune system

? Other mechanisms

? Alport syndrome

? Genetic defects

? Goodpasture's syndrome

? Collagen type IV is autoantigen (target antigen) of autoantibodies

in the autoimmune disease

? Epidermolysis bullosa

? Skin

? Muscular dystrophy

? Dystrophin . a glycoprotein in the plasma membrane of muscle

cells re In muscular dystrophy, this protein is defective or missing

Classification Of epithelium

According to number of cell layers between

basal lamina and free surface and by

morphology of epithelial cells
1. Simple epithelium- composed of single layer

of cells

2. Stratified epithelium- composed of more

than one cells


Terms that help us understand what kinds of tissues we are identifying:

Terms referring to the layers

Simple = one layer
Stratified = more than one layer
Pseudostratified = false layered (appears to be more than

one
layer, but only one); ciliated = with cilia

Terms referring to the cell shapes

Squamous = flat
Cuboidal = cube
Columnar = rectangular (column)
Transitional = ability to change shape

Apical surface

Basal surface

Simple

Apical surface

Basal surface

Stratified

Classification based on number of cell layers.

Squamous

Cuboidal

Columnar

Classification based on cell shape.

The following types of epithelial tissues are covered
in this activity:
1. Simple squamous epithelial tissue (lungs)
2. Simple cuboidal epithelial tissue (kidneys)
3. Simple columnar epithelial tissue (small intestine)
4. Pseudostratified (ciliated) columnar
epithelial tissue (trachea lining)




The following types of epithelial tissues are

covered in this activity

Figure 4.3a Epithelial tissues.

(a) Simple squamous epithelium

Description: Single layer of flattened

cells with disc-shaped central nuclei

and sparse cytoplasm; the simplest

of the epithelia.

Air sacs of

Function: Allows passage of

lung tissue

materials by diffusion and filtration

in sites where protection is not

Nuclei of

important; secretes lubricating

squamous

substances in serosae.

epithelial

cells

Location: Kidney glomeruli; air sacs

of lungs; lining of heart, blood

vessels, and lymphatic vessels; lining

of ventral body cavity (serosae).

Photomicrograph: Simple squamous epithelium

forming part of the alveolar (air sac) walls (125x).

Simple Squamous Epithelium

Figure 4.3b Epithelial tissues.

(b) Simple cuboidal epithelium
Description: Single layer of

cubelike cel s with large,

spherical central nuclei.

Simple

cuboidal

epithelial

cel s

Function: Secretion and

absorption.

Basement

Location: Kidney tubules;

membrane

ducts and secretory portions

of smal glands; ovary surface.

Connective

tissue

Photomicrograph: Simple cuboidal

epithelium in kidney tubules (430x).


Figure 4.3c Epithelial tissues.

(c) Simple columnar epithelium

Description: Single layer of tall cells

with round to oval nuclei; some cells

bear cilia; layer may contain mucus-

secreting unicellular glands (goblet cells).

Simple

columnar

epithelial

Function: Absorption; secretion of

cell

mucus, enzymes, and other substances;

ciliated type propels mucus (or

reproductive cells) by ciliary action.
Location: Nonciliated type lines most of

the digestive tract (stomach to anal canal),

gallbladder, and excretory ducts of some

glands; ciliated variety lines small

bronchi, uterine tubes, and some regions

Basement

of the uterus.

membrane

Photomicrograph: Simple columnar epithelium

of the stomach mucosa (860X).

Figure 4.3d Epithelial tissues.

(d) Pseudostratified columnar epithelium

Description: Single layer of cells of

differing heights, some not reaching

the free surface; nuclei seen at

Cilia

different levels; may contain mucus-

Mucus of

secreting cells and bear cilia.

mucous cell

Pseudo-

stratified

Function: Secretion, particularly of

epithelial

mucus; propulsion of mucus by

layer

ciliary action.
Location: Nonciliated type in male's

sperm-carrying ducts and ducts of

large glands; ciliated variety lines

the trachea, most of the upper

respiratory tract.

Basement

Photomicrograph:

membrane

Pseudostratified ciliated

Trachea

columnar epithelium lining the human trachea (570x).

Given the previous examples

(consider the morphology only)

Can you name?

First, the tissue type
Second, where in the body the tissue is found

What kind of tissue does this represent?

Simple squamous epithelial tissue

Where in the body would you find this tissue?

lungs




What kind of tissue does this represent?

Simple squamous epithelial tissue (superior view)

What kind of tissue does this represent?

Simple cuboidal epithelial tissue

Where in the body would you find this tissue?

Kidneys (tubules)
The lining of the kidney glomerulus (sing.)/glomeruli (pl.) is simple squamous epithelial tissue

What kind of tissue does this represent?

Simple columnar epithelial tissue

Where in the body would you find this tissue?

small intestine

What kind of tissue does this represent?

Pseudostratified (ciliated) columnar epithelial tissue
"false layered"; it looks like more than one layer, but it is not

Where in the body would you find this tissue?

trachea lining




What kind of tissue does this represent?

Stratified squamous epithelial tissue

Where in the body would you find this tissue?

mouth lining

What kind of tissue does this represent?

Stratified cuboidal epithelial tissue

Where in the body would you find this tissue?

salivary glands, sweat glands

What kind of tissue does this represent?

Stratified columnar epithelial tissue

Where in the body would you find this tissue?

male reproductive tract

What kind of tissue does this represent?

Transitional epithelial tissue

Where in the body would you find this tissue?

empty bladder


What kind of tissue does this represent?

Transitional epithelial tissue

Where in the body would you find this tissue?

distended (full) bladder

Figure 4.3e Epithelial tissues.

(e) Stratified squamous epithelium

Description: Thick membrane

composed of several cell layers;

basal cells are cuboidal or columnar

and metabolically active; surface

cells are flattened (squamous); in the

keratinized type, the surface cells are

ful of keratin and dead; basal cells

are active in mitosis and produce the

cells of the more superficial layers.

Stratified

squamous

epithelium

Function: Protects underlying

tissues in areas subjected to abrasion.

Nuclei

Location: Nonkeratinized type forms

Basement

the moist linings of the esophagus,

membrane

mouth, and vagina; keratinized variety

forms the epidermis of the skin, a dry

Connective

membrane.

tissue

Photomicrograph: Stratified squamous epithelium

lining the esophagus (285x).

Figure 4.3f Epithelial tissues.

(f) Transitional epithelium
Description: Resembles both

stratified squamous and stratified

cuboidal; basal cells cuboidal or

columnar; surface cells dome

shaped or squamouslike, depending

on degree of organ stretch.

Transitional

epithelium

Function: Stretches readily and

permits distension of urinary organ

by contained urine.
Location: Lines the ureters, urinary

Basement

bladder, and part of the urethra.

membrane

Connective

tissue

Photomicrograph: Transitional epithelium lining the urinary

bladder, relaxed state (360X); note the bulbous, or rounded,

appearance of the cells at the surface; these cells flatten and

become elongated when the bladder is fil ed with urine.

Cell junctions

? Cell junctions consist of multiprotein

complexes that provide contact between

neighboring cells or between a cell and the

extracellular matrix.

? They also build up the paracellular barrier of

epithelia and control the paracellular

transport.

? Cell junctions are especially abundant in

epithelial tissues.
CelltoCellJunctionsand

Adhesion

A.CellAdhesionMolecules

B.Cell-CellJunctions

1.OccludingJxs-zonulaoccludensortightjunctions
2.AnchoringJxs

a.Desmosomesormaculaadherens(adhesivespots)
b.Zonulaadherensoradhesivebelt
c.Fasciaadherensoradhesivestrips
d.Hemidesmosomes

3.CommunicatingJxsorgapjunctions

Formationofmulticellorganismsrequiresspecificinteraction
betweencellstoholdthecellstogetherandtocommunicate
inordertocoordinateactivities.

A.4typesofCellAdhesionMolecules(CAMs)
areusedtoholdanimalcellstogether:

1. Cadherins

2. Ig-likeCAMs

3. Selectins

4. Integrins

Allaresingle-passtransmembraneproteinsanchoredtothe
cytoskeletonbytheircytoplasmicdomains.

Importance of Cell junction

? Cell junctions enable communication

between neighboring cells via specialized

proteins called communicating junctions.

? Cell junctions are also important in

reducing stress placed upon cells.

? Combined with CAMs( cell adhesion

molecule) and ECM, cell junctions help

hold animal cells together.

Cell junction molecules

Four main types:
? Selectins,
? Cadherins
? Integrins
? Immunoglobulin superfamily


Tissue composition

Cel junctions

Three types of cel junctions:
1. Occluding junctions: seal cel s together into

sheets (forming an impermeable barrier)

2. Anchoring junctions: attach cel s (and their

cytoskeleton) to other cel s or extracel ular matrix

(providing mechanical support)

3. Communicating junctions: al ow exchange of

chemical/electrical information between cel s

Occluding junctions

Example: Tight junctions

of intestinal epithelium

1.Occluding -Tight junction

Each cel

possesses

integral

membrane

proteins that

bind to

similar

proteins in

the adjacent,

forming a

continuous

"weld"


2. Anchoring junctions

Integral membrane proteins connect a cel 's

cytoskeleton to another cel or extracel ular matrix

Anchoring junctions

Integral membrane proteins connect a cel 's

cytoskeleton to another cel or extracel ular matrix

Anchoring junctions

Cytoskeletal fibers (MF, intermediate filaments)

connect to a

Membrane protein receptor

which attaches to another protein in either:
-the extracel ular matrix

or

-another cel membrane

2a. Cadherins and desmosomes

Cel to cel connections

are mediated by

cadherins.

These receptors

extend out from the

cel , binding to other

cadherens


Cadherins participiate in adherens junctions

Under the cel

membrane,

contractile fibers of

microfilaments

connect to cel

membrane proteins

cal ed cadherins

They surround the

cel , forming a belt

Desmosomes

Cadherins can also form localized spot connections

Cadherins

attach to

intermediate

filaments via

anchoring

proteins: a

desmosome

Cel s-to-ECM attachments:

Focal adhesions and hemidesmosomes

Cytoskeletal fibers

attach to

transmembrane

receptors (integrins)

that are attached to

extracel ular matrix

components
?Focal adhesions use

MF
?Hemidesmosomes use

IF

Gap junctions

Gap junctions al ow cel s to exchange electrical

and/or chemical signals

Composed of proteins that form channels that al ow

smal molecules to pass.

Subunits of these channels are connexins that are

assembled together to make connexons. The

connexons from 2 cel s join together to make a gap

junction.


Gap junctions

Summary

Summary

This post was last modified on 05 April 2022