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Infection & Immunity Block > Epithelium > Flashcards

Flashcards in Epithelium Deck (19):

Terminal Bars

Terminal bars represent cell-to-cell attachment sites in apical region


Characteristics of Epithelium

Avascular; dependent on diffusion of nutrients thus, limits its thickness.

Cytokeratin intermediate filaments

Continuouslly renewed by mitosis; in layer closest to the basal lamina (stem cells)

Variable mitotic rate:
Intestinal epithelium half-life = 4-6 days
Skin epidermis half-life = 2-4 weeks

Can form various glands



5-10 mm long; can see individually

motile structures

function to move fluid over cells

found in trachea, bronchi, oviducts, flagella of sperm


Cilia/Flagella Internal Structure

Motile; 7 – 10 mm long

Microtubular core: 9+2

Dynein motor proteins: ATPase

Basal body: attachment of a cilium to the cell’s apex; 9 triplets of microtubules; no central pair



Can’t see a single microvillus
Striated border (gut)
Brush border (kidney)
Function: involved in absorption of excess fluid, nutrients, etc.


Microvilli Internal Structure

Non-motile; 1-2 mm long

Core of actin filaments

Anchored in terminal web (contractile)

Intermediate filaments = cytokeratin

Other cross-linking proteins:
villin: anchors actin to the tip
myosin I anchors actin to cell membrane

Has fuzzy coat of glycoproteins with enzymatic activity = Glycocalyx



Long microvilli; 120 um
No villin in the tip
Ezrin anchors actin to cell membrane (no myosin I)

Limited in distribution: in epididymis, inner hair cells, trachea

Function is absorption and are non-motile


Types of Cell Junctions

Occluding (tight) junctions (seals) join cells together to form an impermeable barrier.

Adhering junctions (cables) provide mechanical stability by linking cytoskeletons of adjacent cells.
a: zonula adherens
b macula adherens or desmosome

Communicating (gap) junctions (channels) permit movement of ions or molecules between cells.


Zonula Occludens

A belt of membrane fusion

Relatively impermeable diffusion barrier between adjacent cells

A physical & chemical separation b/n lumen and intercellular space

Prevents movement of fluid, so must go through cytoplasm, basement membrane, and go into blood vessels underneath
Excess fluid and tight junction destroyed = diarrhea and fluid leaving into lumen of intestines


Zonula Occludens Molecular Structure

3 transmembrane proteins, JAM, occluding, and claudin function like a zipper between cells

3 cytoplasmic proteins: ZO-1, 2, 3, connect to actin microfilaments


Zonula Occludens Pathologies

Can have mutations of proteins or bacterial toxins act on proteins
Cholera toxin work on ZO 1 and 2; causes dehydration and death
Claudin: clostridium bacterium destroys this transmembrane protein to increase permeability and causes diarrhea


Zonula Adherens

Belt Desmosome

Cell membranes not fused but velcro-like
Calcium-dependent cell adhesion molecules link cytoskeletons of adjacent cells
Actin filaments facilitate attachment to adjacent cells

alpha-actinin – an actin-binding protein also found in the Z-line of skeletal muscle and the dense bodies of smooth muscle.
Proteins that are Ca2+ dependent adhesion molecules


Macula Adherens

Desmosome/Spot Weld

Intermediate filaments help dissipate force pulling on attachment site = tonofilaments

Desmocollin and desmoglein are types of calcium-adhesion molecules.
Intracellular space between cells: desmocolin and desmoglein attach to attachment plaques



Cells on basement membrane will be attached via a hemidesmosome
Plaque of different proteins with keratin filaments attached


Gap Junction

Allow diffusion of small (


Basement Membrane

Underlies all epithelia

A barrier for tumor cell invasion b/n the epithelium and the adjacent CT


Basement Membrane Components

Basal Lamina : laminin & type IV collagen (epithelial cells)
fibronectin (fibroblasts)
heparan sulfate proteoglycans (perlecan)
nidogen/entactin (glycoprotein)

Reticular fibers: type III made by fibroblasts from CT


Major Proteins in Basal Lamina

The interwoven network of proteins allows for: structural attachment, filtration, compartmentalization, tissue scaffolding, regulation & signaling

Base of cells to attach to basement membranes: integrins and integrin receptors
Sheet like layer called laminin = cross shape, and self assembles into the sheet and below that sheet is type IV collagen and proteins act as bridges between these two sheets called nitogen and entactin and perlecan (heparin sulfate)
Perlecan is the most common proteoglycan in BL

All made by epithelial cells


Cell-Basal Lamina Interactions

Basal epithelial cells have cell-surface molecules (integrins) that bind to collagen, laminin, and fibronectin in the BL