Epithelial Cells Flashcards
(33 cards)
How do adhesion junctions form?
Cadherins binds to similar molecules on adjacent cell and cluster to form these junctions; closely associated with actin cytoskeleton
How do desmosomes form?
- Have cadherin like molecules involved in transmembrane cell adhesion
- Desmosomal cadherins link to intermediate filament cytoskeleton
How do cell to cell junctions occur?
zonulae (belts) or maculae (spots)
What is the structure of the apical junction complex?
tight, adhesion, desmosomes
What are tumour types originating from main cell types?
- Epithelial - carcinoma
- Mesenchymal: sarcoma
- Hematopoietic: leukaemia and lymphoma
- Neural: neuroblastoma and glioma
Define cytoskeleton
three type filament system formed by polymerisation
What is the function of a Tight junction?
- Paracellular pathway: contact points form networks (more elaborate = tighter seal)
- Segregate membranes and stop proteins which diffuse through membranes therefore allowing adjacent cells to be different and establishing polarity
What is the structure of a gap junction?
- Clusters of pores formed by 6 membrane subunits (continuous with pores on adjacent membrane)
- Allow ions and small molecules to pass through cells
- Open and close pores - intracellular communication
What is the direction of flow in absorptive endothelium?
- apical to basal
Which direction does exocrine secretion occur?
-apical to lumen
What direction does endocrine secretion occur?
- basal to circulation
What is the rate of cell turnover in different tissue types?
- Small intestine: 3-5 days
- Colon: 5-7 days
- Epidermis of skin: 48 days
How does cell division occur in the epidermis?
- Cells at top lost
- Replaced by new (stem) cells in basal layer (can be stimulated by mechanical irritation)
- Undergo differentiation as move up layers - replacing ones lost
- Eventually leads to them flattening out and keratinizing
How does cell division occur in villus?
- Intestinal stem cells (ISC) present in crypt
- Constant cell turnover
- Cells lost at tip and new one produced in crypt (acts as escalator - as cells mature and move up towards villus tip)
How are the cells made tough?
production of keratin proteins and lipids so have dry protective quality
What is the structure of transporting epithelia?
- In transporting epithelium mitochondria run parallel between apical and basal membrane
○ Lots of plasma membrane very close to mitochondria
○ Infoldings in basal plasma membrane increases surface area
○ Basolateral membrane full of pumping ion transporters (ATP from mitochondria)
○ Sodium pumped out from basal side
○ Apical membrane has passive channels so sodium and water drawn in
What happens in transporting epithelia when ATP production is inhibited
If inhibit ATP products would cause swelling in apical part because passive transport not matched by active
Where are layers of epithelial cells found?
- basal lamina
- under lamina
- interstitial connective tissue
- ECM
Why do epithelial cells form layers?
form stable cell to cell junctions
What is the function of epithelial cells?
- transport
- absorption
- secretion
- protection
What is the size of intermediate filaments?
10-15nm
What is the size of microtubules?
20nm or more
What is the structure of microfilaments?
actin polymers
- helical globular actin
- filamentous actin near periphery
What is the structure of intermediate filaments?
rope like polymers of filamentous protein
