Epithelia Flashcards
Why is it important that epithelial cells divide rapidly?
- To have a quick turnover –> due to damage, infection
Primary cilia
Non-motile, present in non-dividing cells
Mucous glands
- structure x2
- Flat, dense nuclei
- Foamy cytoplasm
Serous glands
- structure x2
- Round vesicular nuclei
- Eosinophilic cytoplasm
Simple epithelium occurs where….
There’s diffusion, absorption, secretion etc.
Stratified epithelium occurs where…
Protection is needed (as there are more layers)
Qualities of simple squamous x4
- Single layer
- Thin flattened cells w central nucleus
- Close proximity (no gaps)
- Some secretion
Mesothelium
- type of endothelium
- where
- function
- example
- simple squamous
- lines body cavities
- secretes fluid –> less friction
- e.g. pleura, peritoneum
Endothelium
- type of endothelium
- where
- function
- variations in structure…
- simple squamous
- lines blood vessels
- secretes fluid –> less friction
- can be almost impermeable vs having fenestrae (allows different molecules through)
Blood brain barrier
- function x2
- Protects brain from infection
- Restricts passage of potentially harmful molecules
BUT - Allows essential ones through (O2, nutrients, ALSO drugs, alcohol etc)
Qualities of simple cuboidal x2
- Round, central nucleus
- Approx. equal height & width
Qualities of simple columnar x1
- Basal nucleus
Small Intestine
- type of epithelium
- where specifically
- why this one
- surface modifications x2
- Simple columnar
- Villi
- More cytoplasm = more organelles for secretion/active transport
- Microvillus brush border on apical surface
- Goblet cells = release mucus, stopping pathogens binding
Modified columnar epithelium
- examples & their modification x2
- Villi (GI tract) –> + goblet cells & microvillus brush border
- Kidney –> microvillus brush border
Qualities of pseudo-stratified columnar epithelium
Appears to have multiple layers, but just nuclei at different levels, as not all cells reach the apex
Respiratory epithelium
- type of epithelium
- types of cells
- adaptation
- Pseudo-stratified ciliated columnar
- Columnar, goblet, basal
- Cilia –> protection –> as pathogens transported upwards towards larynx
Stratified squamous:
- Apical layer (+ the 2 variations)
- Basal layer
- Function
- Squamous epithelial cell –> of the keratinising or non-keratinising type
- Columnar/cuboidal
- Protection –> abrasion & pathogens
Stratified squamous keratinised
- example
- function
- basal layer structure
- apical layer structure
- Lips, skin
- Resists dehydration, abrasion
- Mainly keratinocytes
- Mainly dead cells, consisting of keratin
Keratinocytes
what happens as they move basal –> apical
- As become more apical, fill w keratin
- Junctions fill w waxy substance, restricting nutrients –> cells die
- At apical surface, mostly hard, dead, keratin-filled cells
Stratified squamous non-keratinised
- example
- function
- Tongue, oesophagus
- Resists abrasion BUT not dehydration
Desquamation
When epithelial cells = worn off and shed
Oesophagus
- type of epithelium
- why this structure
- wet epithelium so subject to….
- Stratified squamous non-keratinised
- lots of layers to protect from abrasion
- abrasion BUT not dehydration
Transitional epithelium
- example
- structure
- ‘transitional’ as
- adaptation that goes w this
- Bladder
- Crowded basal layers, which extend towards lumen
- Can change shape –> e.g. become more distended
- Lots of tight junctions –> prevent leakage
Simple squamous
- function x2
- example x2
- Rapid diffusion, smooth surface
- Endothelium, mesothelium
Simple cuboidal
- function x2
- example x2
- Secretion, absorption
- Liver, kidneys
Simple columnar
- function x2
- example
- Secretion, absorption
- GI tract
Pseudostratified
- example
- Respiratory epithelium
Stratified squamous (keratinised)
- function
- example x2
- Protects from abrasion & dehydration
- Lips, skin
Stratified squamous (non-keratinised)
- function
- example
- Protects from abrasion
- Oesophagus
Stratified cuboidal
- example
- Sweat glands
Stratified columnar
- function
- example
- High protection
- Male urethra
Transitional
- function
- example
- Changes shape as stretched
- Bladder
Tight junctions
- function x2
- Join cells together
- Helps control passage of molecules BETWEEN cells
Membrane proteins: connexin
Communication between cells
Membrane proteins: occluding, claudin
Binding of cells
Adherens junctions
- function x2
- Encircles cell –> stability
- Binds cells, linking cytosolic bundles, creating 1 functional unit
Gap junctions
- function x1
- Allows small molecules to pass between cells
Desmosomes
- function x2
- subject to…
- Strength
- Strong cell attachment (as link filament networks)
- Subject to abrasion
Sealing strands
- Where
- Contain
- More =
- Within tight junctions
- Actin, claudins, occludins –> amounts vary in diff. body parts
- More sealing strands = more difficult to get through
Routes for molecular movement x3
- Between cells
- Trans-cellular (through cells)
- Paracellular (movement occurring in and out)
Different roles of tight junctions x3
- BARRIERS –> no movement
- FENCES –> maintains distribution between membranes
- GATES –> selective, regulated movement
