PSC2002/L04 Structure & Function of Epithelia Flashcards
Describe the structure of epithelia. (3)
Sheet-like structure
Line external and internal surfaces
Internal called endothelium
What percentage of human cancers originate from epithelial origin?
85%
Give 3 functions of epithelia.
Protection
Filtration (kidney tubule lining)
Exchange (alveoli)
Absorption (intestine)
Sensation (taste)
Secretion (gland lining)
What is the function of simple squamous epithelia? (3)
Absorption
Filtration
Minimal barrier to diffusion
Where is simple squamous epithelium found? (2)
Capillaries
Abdominal and pleural cavities (mesothelium)
What is the function of simple cuboidal epithelia? (2)
Secretion
Transportation
Where is simple cuboidal epithelium found? (3)
Glands & ducts
Kidney tubules
Ovaries
Which kind of epithelium can be ciliated or non-ciliated?
Simple columnar
What is the function of simple columnar epithelia? (3)
Absorption
Protection
Secretion
Where is simple columnar epithelium found?
Digestive tract
What is the function of stratified squamous epithelia?
Protection
Where is stratified epithelium found? (4)
Skin
Mouth
Upper throat
Oesophagus
Which kind of epithelia can be keratinised or non-keratinised?
Stratified squamous
What is the function of pseudostratified columnar epithelia? (2)
Absorption
Protection
Where is pseudostratified columnar epithelium found? (2)
Upper respiratory tract
Trachea
Where is transitional epithelia found? What is its function?
Bladder
Stretchable layer
How do epithelia form a functional unit?
Attached to extracellular matrix of basal lamina
Give 3 specialised structures that link epithelial cells to one another.
Tight junctions
Anchoring junctions
Channel forming junctions
Describe tight or occluding junctions. (3)
Membrane proteins seal adjacent cells together
Ensure molecules cannot leak freely between cells
Prevent lateral migration of membrane proteins (creating membrane domains/polarity)
What is the difference between claudins and occludins?
Claudins have multiple isoforms
Claudins create physical barrier that regulate permeability
Occludins are single type of protein
Role of occludins less clear
What does the resistance of epithelia correlate to?
Leakiness of epithelia
High resistance = tight junction
What defines whether an epithelial junction is tight or leaky?
Presence of Cld3 or Cld2 with Cld1
Cld1 + Cld3 = tight
Cld1 + Cld2 = leaky
How is Claudin-2 introduced into Madin-Darby Canine Kidney I cells?
Using mRNA
What is the function of anchoring junctions? (3)
Provide mechanical stability
Anchor cells to basal lamina and other cells
Allows functioning as a cohesive unit
What are anchoring junctions categorised by?
Type of cytoskeletal filament they interact with
What are:
a) cell-cell
b) cell-basal lamina
actin junctions called?
a) Adherens junction
b) Focal adhesion
What are
a) cell-cell
b) cell-basal lamina
intermediate junctions called?
a) Desmosomes
b) Hemidesmosomes
Describe the basal lamina. (2)
40-120nm thick
Strong, flexible foundation underlying all epithelia
What 4 materials make up the basal lamina?
Laminin
Type IV collagen
Entactin
Perlecan
What is the basement membrane?
Combination of basal lamina and reticular lamina
What is the reticular lamina mainly composed of?
Type II collagen
What is the function of gap/channel-forming junctions? (2)
Allow diffusion between cells
Enable cell-cell communication
What is an Ussing chamber used for? (2)
Measure resistance of ion transport
Determine what ion channels are present (and concentration/expression)
Why is frog skin a good model system?
Frogs are able to absorb Na+ from salty water across skin
What happens when frog skin is dissected and mounted as a flat sheet containing solution of identical composition?
Transepithelial potential difference due to active transepithelial movement
What happens when an epithelial cell is polarised?
Transepithelial voltage generated
What is the equation for transepithelial voltage?
V(te) = V(bl) - V(ap)
What is the voltage outside and inside of the epithelia?
Apical -158mV
Basolateral 0mV
What is the voltage inside of the epithelia?
-92mV
What is amiloride used for?
Chemical probe for apical Na+ channel?
What is ouabain used for?
Na+/K+ ATPase inhibitor
What is barium used for?
Blocking K+ channels
