? 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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BasementMembrane
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 tissueStructure 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 cellmembrane 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 reticularcollagen (type IV) fibrils
? Lamina Lucida
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? clear layer close to epithelium
Apical surface
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Lateral surfaceEpithelium
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 tissuesFusion 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'scapsule
? 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 lungcapillaries
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Basement MembraneCancer 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 bymorphology of epithelial cells
1. Simple epithelium- composed of single layer
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of cells2. 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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onelayer, but only one); ciliated = with cilia
Terms referring to the cell shapes
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Squamous = flatCuboidal = cube
Columnar = rectangular (column)
Transitional = ability to change shape
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Apical surfaceBasal surface
Simple
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Apical surface
Basal surface
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StratifiedClassification 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 activityFigure 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 simplestof the epithelia.
Air sacs of
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Function: Allows passage of
lung tissue
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materials by diffusion and filtrationin 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; liningof 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 sFunction: Secretion and
absorption.
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Basement
Location: Kidney tubules;
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membraneducts and secretory portions
of smal glands; ovary surface.
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Connective
tissue
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Photomicrograph: Simple cuboidalepithelium 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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cellmucus, 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 regionsBasement
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 atCilia
different levels; may contain mucus-
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Mucus of
secreting cells and bear cilia.
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mucous cellPseudo-
stratified
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Function: Secretion, particularly of
epithelial
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mucus; propulsion of mucus bylayer
ciliary action.
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Location: Nonciliated type in male'ssperm-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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BasementPhotomicrograph:
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--- Content provided by FirstRanker.com ---
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 tissueWhere 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 bladderWhat kind of tissue does this represent?
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Transitional epithelial tissueWhere 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 membranecomposed 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 areful 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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squamousepithelium
Function: Protects underlying
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tissues in areas subjected to abrasion.
Nuclei
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Location: Nonkeratinized type formsBasement
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 dryConnective
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 bothstratified 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 betweenneighboring 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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CelltoCellJunctionsandAdhesion
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. Cadherins2. 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 specializedproteins 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 helphold animal cells together.
Cell junction molecules
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Four main types:
? Selectins,
? Cadherins
? Integrins
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? Immunoglobulin superfamilyTissue composition
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Cel junctionsThree 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 sOccluding junctions
Example: Tight junctions
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of intestinal epithelium
1.Occluding -Tight junction
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Each celpossesses
integral
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membrane
proteins that
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bind tosimilar
proteins in
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the adjacent,
forming a
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continuous"weld"
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2. Anchoring junctionsIntegral 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 matrixAnchoring 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 membrane2a. Cadherins and desmosomes
Cel to cel connections
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are mediated by
cadherins.
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These receptorsextend 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 ofmicrofilaments
connect to cel
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membrane proteins
cal ed cadherins
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They surround thecel , forming a belt
Desmosomes
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Cadherins can also form localized spot connections
Cadherins
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attach tointermediate
filaments via
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anchoring
proteins: a
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desmosomeCel s-to-ECM attachments:
Focal adhesions and hemidesmosomes
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Cytoskeletal fibers
attach to
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transmembranereceptors (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
--- Content provided by FirstRanker.com ---
and/or chemical signalsComposed 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 gapjunction.
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Gap junctionsSummary
Summary
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