Intro to Epithelium Flashcards
Tight junctions (zonula occlundes)
- Block movement of extracellular molecules between adjacent cells
- Maintain cell membrane polarity
- Made of claudins and occludins
Apical domain membrane specializations
- Microvilli
- Stereocilia
- Cilia
Apical junction complex
Tight junctions + Adherens junctions + Desmosomes = segmented membrane
Stereocilia
- Long, thin, non-motile microvilli
- Found in male reproductive tract (epididymis and ductus deferens)
Keratinized/cornified
with protective layers of dead cells and keratin
Lateral membrane
Faces side (another epithelial cell)
Gap junctions
- Pore between two membranes allowing passage of small molecules and nutrients
- Made of connexin proteins that form connexons => multiple connexons from two cells align to form gap junction
Pseudostratified epithelium
Structure: 1 layer (all cells touch basement membrane) but looks like multiple as nuclei aren’t aligned
Examples:
- large airways (trachea)
- epididymis
Simple columnar epithelium
Structure: 1 layer, rectangular cells
Examples:
- small intestine
- terminal/small airways of respiratory system (bronchioles)
Microvilli
- small processes that project from surface to increase SA (great for absorption)
- found at intestinal brush border and PCT of kidney
Adherens junctions (zonula adherens)
- link actin cytoskeletons of adjacent cells => epithelial strength
- form continuous contractile band around cells
- made of transmembrane cadherins; cytoplasmic tails bind anchor proteins in an intracellular plaque
Desmosomes (macula adherens)
- beneath adherens junctions
- in stratified epithelia exposed to stress
- made of transmembrane cadherins; cytoplasmic portion binds IFs not actin
Where is epithelium found?
- covers/lines free surfaces of the body
- interface between different biological compartments
Stratified squamous epithelium (keratinized)
Structure:
- multiple layers: more cuboid => flat => dry, protective layer of dead cells and keratin
Example: skin
Stratified
more than one layer of cells
Transitional epithelium
- Changes structure depending on stretch/relaxation
- Found in the bladder
- Relaxed: 5-6 layers, top layer very cuboid
- Stretched: 2-4 layers, top layer very flat
Apical membrane
Faces lumen (inside of tube like structure)
Cubiodal
square cells
Squamous
flat cells
Basal membrane
Faces underlying connective tissue
3 characteristics that describe different kinds of epithelium
- Number of cell layers - simple - stratified - pseudostratified 2. Cell shape - squamous - cubiodal - columnar 3. Keratinization - keratinized/cornified - non-keratinized/non-cornified
Pseudostratified
one layer of cells (all cells touch basement membrane) but looks like more than one because nuclei are not aligned
Simple cuboidal epithelium
Structure: 1 layer, square cells
Examples:
- renal tubules
- thyroid follicles
- glandular tissue
Simple squamous epithelium
Structure: single layer, flat cells
Examples:
- parietal layer of Bowman’s capsule
- lining of blood vessels (endothelium)
- lining of body cavities (mesothelium)
- lung alveolar walls
Hemidesmosome
- Anchor cell to basement membrane
- Attachemnt site for keratin IFs
- Transmembrane integrins bind extracellular lamins (type IV collagen) in basement membrane
Defining characteristics of all epithelium
- anchored to basement membrane (which rests on underlying connective tissue)
- avascular: relies on diffusion of nutrients and gases from vasculature in adjacent connective tissue
- tightly connected at lateral surface via specialized junctional complexes
Columnar
rectangular cells
Stratified squamous epithelium (non-keratinized)
Structure:
- multiple layers: more square towards basement membrane => more flat
- all cells have nuclei
Examples:
- esophagus
- oral cavity
- vagina
- anal cavity
Cilia
- Actively motile with complex inner structure
- Found in lining of respiratory tract and female reproductive tract
Basal domain
- 30-60nm non-cellular membrane between epithelium and connective tissues
- Made of collagenous and non-collagenous glycoproteins and proteoglycans
- Gives structural support and is a selective barrier to/from supporting tissue
Junctional complexes of the lateral domain
- tight junctions (zona occludens)
- adherens junctions (zonula adherenes)
- desmosomes (macula adherens)
- gap junctions
