Epithelium Flashcards
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
Cilia
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
Microvilli
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
Stereocilia/Stereovilli
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
Hemidesmosome
Cells on basement membrane will be attached via a hemidesmosome
Plaque of different proteins with keratin filaments attached
Gap Junction
Allow diffusion of small (
