Lecture 2- Epithelial tissues Flashcards
What are the two main criteria of epithelial classification?
1) SHAPE
squamous
cuboidal
columnar
2) LAYERING
single layer= simple
multi-layered= stratifiedWhere can you find simple squamous epithelia and why?
lung alveolar epithelium, mesothelium (lies body cavities) and endothelial lining of blood vessels
- thin = allows exchange to occur
Where can you find simple cuboidal epithelia?
kidney collecting duct, other ducts
Where can you find simple columnar epithelia?
enterocytes, other absorptive and secretory epithelia
What are the two main types of stratified squamous epithelia and where an you find them?
1) Keratining: epidermis (skin) (nuclei are not visible)
2) Non-Keratinising: lining of mouth, oesophagus, anus, cervix, vagina (nuclei are visible)
What is pseudo stratified epithelium and where can it be found?
= falsely stratified, looked multi-layered but surface cells have contact with basal lamina
- tracheal/ bronchial epithelium, ducts in the urinary and reproductive tracts
What is the importance of epithelial polarity?
- To give directionality to epithelial function
- need plasma membrane polarity for this
- apical vs basolateral domains
How is this polarity established?
- Have belt junctions which seal off the paracellular pathway and helps maintain conc gradients
- tight junctions form focal connections between membranes of adjacent cells
- TJ strands interact with proteins (Claudine & occludin)
What are the gate and fence functions of tight junctions?
Gate- sealing off the paracellular pathway
Fence- segregating the apical and basolateral polarity
How can membrane polarity polarity be maintained?
- Have pumps on only one side= uni-directional flow of ions and molecules
- Have secretory vesicles only on one side
- lots of mitochondria near secretory domain for AT of molecules across membranes
What are the major epithelial functions?
- Absorptive epithelium (PCT)
- Fluid transporting (DCT)
- Selectively permeable (Thin limb of LoH)
- Secretory (pancreas)
- Protective
What are the features of Transpoting epithelium?
- high conc of ion transporters
- Mitochondria associated with basal membrane to provide energy for AT
- Basal membrane infoldings, increase SA for pumping ions & water
Ions transported from APICAL -(DCT lumen) -> BASAL (capillary)
What are the features of absorptive epithelium?
e. g. Enterocytes
- villi and microvilli to increase SA for absorption
e. g. PCT lumen
- brush border made of microvilli
What are the features of secretory epithelium? Give example of where they can be found
Pancreas:
1) Exocrine: secreted into duct
Secretion: BASAL (capillary)–> APICAL (lumen)
- secretory granules found in apical cytoplasm
- RER found in basal
2) Endocrine: secreted into bloodstream
Secretion: APICAL –> BASAL (capillary)
-secretory granules found in basal cytoplasm
- RER found in apical
What are the different classes of secretion?
Endocrine vs Exocrine
Constitutive vs Stimulated
What are the two different types of protective epithelia?
Keratinising: no nuclei (dry surfaces)
Non-keratinising: nuclei visible in surface cell layers (surface vulnerable to chemical damage)
What happens when there are defects in cytokeratins or cell junctions?
Blistering diseases–> damage to fragile epidermal cells
What links ECM to cells
Hemidesmosomes
Describe how villus cells are regenerated
- New cells produced in Crypt of Leiberkhun by stem cells
- Cells move up along villus
- Cells then die and are lost at the tip of the villus
What happens when cell- turnover is unbalanced in the intestines?
Cell loss> proliferation = villi shorten (cancer drugs do this)
Cell proliferation > cell loss = too much tissue (benign tumour, polyp)
Describe how epidermal cells are regenerated
- Surface cells are continuously lost
- new cells formed on basal layer which migrate up
- Flatten out and differentiate on the way (e.g. keratinise)
What causes a callus?
- constant abrasion stimulates cells to divide
- proliferation > loss
- -> increase in tissue mass
Give an example of an infectious agent affecting epidermal turnover
HPV- hijacks cell proliferation machinery
- increased cell proliferation
- –> warts
When might changes to steady state be physiologically normal?
1) Mentrual cycle- changes to endometrial epithelial lining
2) Pregnancy- increase in epithelial glands of breast
