Epithelial Surfaces Flashcards
2 surfaces of epithelia
Apical membrane- top (lining) in contact with lumen
Basolateral membrane - sides and bottom in contact with interstital fluid and then blood
What are these membranes separated by?
By band at the top - TIGHT JUNCTION.
This has claudins which connect 2 cells at random places
Aquaporins
A tetromer (4 channels) which are always open. Highly selevtive to water Driven by osmosis
K+ ion channels
Usually 4 subunits around central pore
eg. BK1 and IK1
Na+ channels
Single polypeptide chain grouped together forming 24 transmembrane domains
Carrier protein classifications
- Facilitator (uniport - 1 straight through)
- Co-transported (symport - 2 straight through)
- Exchanger (antiport - 1 in, 1 out)
How are receptors and channels formed?
Hydrophobic regions of membrane bunch together to form helical trans-membrane domains (TMDs)
Glucose transporter
Uniport SLC2 Only accepts D glucose 12 TMDs Splits into 2 halves, glucose binds inbetween the 2
Na+/K+/Cl- cotransporter
SLC12
Movement of Na+ in drives
Na+/ H+ exchanger
SLC9
Movement of Na+ in dries H+ out
Na+/K+/ATPase pump
P-type pump
3 Na+ out, 2 K+ in
Active transport as against their chemical gradients
10 TMDs
Alpah and beta subunits
Mechanical - nucleotide binding domain moves towards phosphorylation domain, rotating actuator domain
House keeping intracellular transorters
- Na+/K+/ATPase pump for gradient
- Na+/K+/Cl- cotransporter for increasing volume
- Cl-/K+ both out to reduce volume
- HCO3 out/ Cl- in for base extrusion
- H+ out/ Na+ in for acid extrusion
What is endothelium
Lining of cells between blood plasma and interstitial fluid
What is epithelium
Lining of cells between transcellular fluid and interstitial fluid
What is transcellular fluid
Fluid that is inside the GI tract, kidneys etc LUMENS
