Download MBBS Anatomy PPT 28 Simple Epithelium Notes

Epithelial Tissue -- General Features

? Closely packed cells with little extracellular

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material

? Many cell junctions often provide secure

attachment.

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? Cells sit on basement membrane

? Apical (upper) free surface

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? Basal surface against basement membrane

? Avascular---without blood vessels

? nutrients and waste must move by diffusion

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Epithelial Tissue -- General

Features

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

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digestion, absorption, transportation,

excretion, sensory reception, and

reproduction.

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Types of Epithelium

1. Covering and lining epithelium

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? epidermis of skin

? lining of blood vessels and ducts

? lining respiratory, reproductive, urinary & GI

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tract

2. Glandular epithelium- originate from

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invaginated epithelial cells

? secreting portion of glands

? thyroid, adrenal, and sweat glands

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Epithelium

? Epithelium is derived from all three germ

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layers

? Ectoderm-oral and nasal mucosa,cornea ,

epidermis, glands of skin, mammary glands

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? Endoderm-Lining of respiratory and

gastrointestinal tract, liver , panceas

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? Mesoderm-lining of urogenital system,

circulatory system and body cavities lining-

mesothelium

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Typical

Arrangement

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of Epithelial

Tissue and its

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Basement

Membrane

Basement Membrane

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Basement Membrane

? The basement membrane is a thin sheet of

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fibers that underlies the epithelium

? The basement membrane is the fusion of two

lamina, the basal lamina-elaborated by

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epithelial cells and the reticular lamina (or

lamina reticularis)-manufactured by cells of

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connective tissue


Structure of Basement membrane

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? Basement Membrane

? Basal Lamina

? Lamina Lucida

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? Extracellular glycoprotein-

Laminin,integrins,entactins,dystroglycans

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? Transmembrane laminin receptors-project from epithelial cell

membrane into basal lamina

? Lamina Densa consists of a network of fine filaments.

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

the basement membrane its tensile strength

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Structure of Basement membrane

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

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Reticular Laminae)-all elaborated by fibroblast

of connective tissue

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

lamina lucida &lamina densa

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? Lamina Densa

? dense layer closer to the connective tissue
? 30?70 nm in thickness

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? consists of an underlying network of reticular

collagen (type IV) fibrils

? Lamina Lucida

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? clear layer close to epithelium

Apical surface

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Lateral surface

Epithelium

Basal lamina

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Reticular lamina

Connective tissue

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Epithelial Tissue

Epithelial Tissue

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Functions of basement membrane

? anchor down the epithelium to its loose

connective tissue (the dermis) underneath

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? provide structural support to the tissue

? a mechanical barrier, preventing malignant

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cells from invading the deeper tissues

Fusion of basal laminae

? Glomerular filtration of the kidney

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? by the fusion of the basal lamina from the

endothelium of glomerular capillaries and the

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basal lamina of the epithelium of the Bowman's

capsule

? Gaseous exchange between lung alveoli and

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pulmonary capillaries

? by the fusion of the basal lamina of the lung

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alveoli and of the basal lamina of the lung

capillaries

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Basement Membrane

Cancer cells (Malignant)

? If the epithelial cells become transformed

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(cancerous) and become 'malignant', they are

able to break through the basement

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membrane and invade the tissues beneath.

This characteristic is used in the diagnosis of

malignant epithelial tumors

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A poorly functioning basement membrane

Diseases

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? Genetic defects

? Injuries by the body's own immune system

? Other mechanisms

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? Alport syndrome

? Genetic defects

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? Goodpasture's syndrome

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

in the autoimmune disease

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? Epidermolysis bullosa

? Skin

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? Muscular dystrophy

? Dystrophin . a glycoprotein in the plasma membrane of muscle

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

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Classification Of epithelium

According to number of cell layers between

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basal lamina and free surface and by

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

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of cells

2. Stratified epithelium- composed of more

than one cells

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

Terms referring to the layers

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

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

Terms referring to the cell shapes

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

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Apical surface

Basal surface

Simple

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Apical surface

Basal surface

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Stratified

Classification based on number of cell layers.

Squamous

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Cuboidal

Columnar

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Classification based on cell shape.

The following types of epithelial tissues are covered
in this activity:
1. Simple squamous epithelial tissue (lungs)

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2. Simple cuboidal epithelial tissue (kidneys)
3. Simple columnar epithelial tissue (small intestine)
4. Pseudostratified (ciliated) columnar
epithelial tissue (trachea lining)

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The following types of epithelial tissues are

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covered in this activity

Figure 4.3a Epithelial tissues.

(a) Simple squamous epithelium

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Description: Single layer of flattened

cells with disc-shaped central nuclei

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and sparse cytoplasm; the simplest

of the epithelia.

Air sacs of

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Function: Allows passage of

lung tissue

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materials by diffusion and filtration

in sites where protection is not

Nuclei of

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important; secretes lubricating

squamous

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substances in serosae.

epithelial

cells

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Location: Kidney glomeruli; air sacs

of lungs; lining of heart, blood

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vessels, and lymphatic vessels; lining

of ventral body cavity (serosae).

Photomicrograph: Simple squamous epithelium

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

Simple Squamous Epithelium

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Figure 4.3b Epithelial tissues.

(b) Simple cuboidal epithelium
Description: Single layer of

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cubelike cel s with large,

spherical central nuclei.

Simple

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cuboidal

epithelial

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cel s

Function: Secretion and

absorption.

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Basement

Location: Kidney tubules;

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membrane

ducts and secretory portions

of smal glands; ovary surface.

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Connective

tissue

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Photomicrograph: Simple cuboidal

epithelium in kidney tubules (430x).

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Figure 4.3c Epithelial tissues.

(c) Simple columnar epithelium

Description: Single layer of tall cells

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with round to oval nuclei; some cells

bear cilia; layer may contain mucus-

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secreting unicellular glands (goblet cells).

Simple

columnar

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epithelial

Function: Absorption; secretion of

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cell

mucus, enzymes, and other substances;

ciliated type propels mucus (or

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

the digestive tract (stomach to anal canal),

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gallbladder, and excretory ducts of some

glands; ciliated variety lines small

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bronchi, uterine tubes, and some regions

Basement

of the uterus.

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membrane

Photomicrograph: Simple columnar epithelium

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of the stomach mucosa (860X).

Figure 4.3d Epithelial tissues.

(d) Pseudostratified columnar epithelium

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Description: Single layer of cells of

differing heights, some not reaching

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the free surface; nuclei seen at

Cilia

different levels; may contain mucus-

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Mucus of

secreting cells and bear cilia.

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mucous cell

Pseudo-

stratified

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Function: Secretion, particularly of

epithelial

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mucus; propulsion of mucus by

layer

ciliary action.

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Location: Nonciliated type in male's

sperm-carrying ducts and ducts of

large glands; ciliated variety lines

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the trachea, most of the upper

respiratory tract.

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Basement

Photomicrograph:

membrane

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Pseudostratified ciliated

Trachea

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columnar epithelium lining the human trachea (570x).

Given the previous examples

(consider the morphology only)

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Can you name?

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

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What kind of tissue does this represent?

Simple squamous epithelial tissue

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Where in the body would you find this tissue?

lungs

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What kind of tissue does this represent?

Simple squamous epithelial tissue (superior view)

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What kind of tissue does this represent?

Simple cuboidal epithelial tissue

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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

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What kind of tissue does this represent?

Simple columnar epithelial tissue

Where in the body would you find this tissue?

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small intestine

What kind of tissue does this represent?

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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?

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trachea lining

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What kind of tissue does this represent?

Stratified squamous epithelial tissue

Where in the body would you find this tissue?

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mouth lining

What kind of tissue does this represent?

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Stratified cuboidal epithelial tissue

Where in the body would you find this tissue?

salivary glands, sweat glands

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What kind of tissue does this represent?

Stratified columnar epithelial tissue

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Where in the body would you find this tissue?

male reproductive tract

What kind of tissue does this represent?

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Transitional epithelial tissue

Where in the body would you find this tissue?

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empty bladder


What kind of tissue does this represent?

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Transitional epithelial tissue

Where in the body would you find this tissue?

distended (full) bladder

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Figure 4.3e Epithelial tissues.

(e) Stratified squamous epithelium

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Description: Thick membrane

composed of several cell layers;

basal cells are cuboidal or columnar

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and metabolically active; surface

cells are flattened (squamous); in the

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keratinized type, the surface cells are

ful of keratin and dead; basal cells

are active in mitosis and produce the

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cells of the more superficial layers.

Stratified

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squamous

epithelium

Function: Protects underlying

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tissues in areas subjected to abrasion.

Nuclei

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Location: Nonkeratinized type forms

Basement

the moist linings of the esophagus,

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membrane

mouth, and vagina; keratinized variety

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forms the epidermis of the skin, a dry

Connective

membrane.

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tissue

Photomicrograph: Stratified squamous epithelium

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lining the esophagus (285x).

Figure 4.3f Epithelial tissues.

(f) Transitional epithelium

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Description: Resembles both

stratified squamous and stratified

cuboidal; basal cells cuboidal or

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columnar; surface cells dome

shaped or squamouslike, depending

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on degree of organ stretch.

Transitional

epithelium

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Function: Stretches readily and

permits distension of urinary organ

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by contained urine.
Location: Lines the ureters, urinary

Basement

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bladder, and part of the urethra.

membrane

Connective

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tissue

Photomicrograph: Transitional epithelium lining the urinary

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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.

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Cell junctions

? Cell junctions consist of multiprotein

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complexes that provide contact between

neighboring cells or between a cell and the

extracellular matrix.

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? They also build up the paracellular barrier of

epithelia and control the paracellular

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transport.

? Cell junctions are especially abundant in

epithelial tissues.

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CelltoCellJunctionsand

Adhesion

A.CellAdhesionMolecules

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B.Cell-CellJunctions

1.OccludingJxs-zonulaoccludensortightjunctions
2.AnchoringJxs

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

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3.CommunicatingJxsorgapjunctions

Formationofmulticellorganismsrequiresspecificinteraction
betweencellstoholdthecellstogetherandtocommunicate

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inordertocoordinateactivities.

A.4typesofCellAdhesionMolecules(CAMs)
areusedtoholdanimalcellstogether:

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1. Cadherins

2. Ig-likeCAMs

3. Selectins

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4. Integrins

Allaresingle-passtransmembraneproteinsanchoredtothe
cytoskeletonbytheircytoplasmicdomains.

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Importance of Cell junction

? Cell junctions enable communication

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between neighboring cells via specialized

proteins called communicating junctions.

? Cell junctions are also important in

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reducing stress placed upon cells.

? Combined with CAMs( cell adhesion

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molecule) and ECM, cell junctions help

hold animal cells together.

Cell junction molecules

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Four main types:
? Selectins,
? Cadherins
? Integrins

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? Immunoglobulin superfamily


Tissue composition

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Cel junctions

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

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sheets (forming an impermeable barrier)

2. Anchoring junctions: attach cel s (and their

cytoskeleton) to other cel s or extracel ular matrix

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(providing mechanical support)

3. Communicating junctions: al ow exchange of

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chemical/electrical information between cel s

Occluding junctions

Example: Tight junctions

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of intestinal epithelium

1.Occluding -Tight junction

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Each cel

possesses

integral

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membrane

proteins that

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bind to

similar

proteins in

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the adjacent,

forming a

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continuous

"weld"

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2. Anchoring junctions

Integral membrane proteins connect a cel 's

cytoskeleton to another cel or extracel ular matrix

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Anchoring junctions

Integral membrane proteins connect a cel 's

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cytoskeleton to another cel or extracel ular matrix

Anchoring junctions

Cytoskeletal fibers (MF, intermediate filaments)

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connect to a

Membrane protein receptor

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

or

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-another cel membrane

2a. Cadherins and desmosomes

Cel to cel connections

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are mediated by

cadherins.

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These receptors

extend out from the

cel , binding to other

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cadherens


Cadherins participiate in adherens junctions

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Under the cel

membrane,

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contractile fibers of

microfilaments

connect to cel

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membrane proteins

cal ed cadherins

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They surround the

cel , forming a belt

Desmosomes

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Cadherins can also form localized spot connections

Cadherins

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attach to

intermediate

filaments via

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anchoring

proteins: a

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desmosome

Cel s-to-ECM attachments:

Focal adhesions and hemidesmosomes

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Cytoskeletal fibers

attach to

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transmembrane

receptors (integrins)

that are attached to

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extracel ular matrix

components
?Focal adhesions use

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MF
?Hemidesmosomes use

IF

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Gap junctions

Gap junctions al ow cel s to exchange electrical

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and/or chemical signals

Composed of proteins that form channels that al ow

smal molecules to pass.

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Subunits of these channels are connexins that are

assembled together to make connexons. The

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connexons from 2 cel s join together to make a gap

junction.

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Gap junctions

Summary

Summary

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