function of epithelia Flashcards
why is water movement across the epithelia important
body temp regulation
mucus movement - pathogen clearance from the lung
renal fluid balance
digestion and nutrient absorption
reproduction
diarrhoea - pathogen clearance from the gut
the transepithelial potential arises from ion movements which are determined by:
ionic valency
concentration gradience
ionic permeability
what is the flux of an ion described as
ficks law of diffusion
what drives water movement across a “tight” epithelial monolayer
ion movement
what determines direction and magnitude of water movement
polarised organisation of channels, pumps, exchangers and junction proteins
what are the 2 routes of transepithelial water movement
intracellular and paracellular
what is required for water to move across membranes
an osmotic graduient (Na+ drives inwardly to move H2O)
how does intracellular movement of water work
occurs within cells and is regulated by water channels known as aquaporins
how does paracellular movement of water work
occurs between cells and is regulated by tight junction permeability
what does adrenaline do to water uptake
increased adrenaline = increased water uptake
what is H2O secretion dependant on
Chloride ions
what keeps the epithelium at a basal moisture level
H2O outtake from Cl-
what drives Na+ uptake
antihistamines
what is fluid uptake dependant on
Na+ (ENaC)
Cl- channels =
fluid secretion (basolateral to apical transport)
Na+ channels =
fluid absorption (apical to basolateral transport)
what do swelling-activated Cl- channels do
activated transiently by osmotic shock - sustained opening does not occur
what do calcium-activated Cl- channels do
activated by release of intracellular Ca2+ stores - activity is transient and therefore unlikely to be sustained in development
what do outwardly rectifiying Cl- channels do
regulated by release of intracellular ATP - maintains cell membrane potential by regulated depolarisation to physiological set point
what do CFTRs do
best characterised channels due to role in CF disease - long presumed to be the channel regulating fluid secretion in adult lungs
what do voltage-dependant Cl- channels do
recently characterised in lung - expression pattern follows the process of lung development
what does CFTR stand for
the cystic fibrosis transmembrane conductance regulator
what is the CFTR a member of
the ATP binding cassette (ABC) glycoprotein superfamily
what is the CFTR
a 170kDa glycoprotein Cl- channel composed of:
2, 6-span transmembrane domains
2 nucleotide binding domains (NBD! and 2)
a single R domain of highly charged amino acids
