Epithelial Transport Flashcards
Na/K channels are located on apical/basolateral membrane.
Basolateral side
give some examples of where tight epithelia are located
- sweat glands
2. distal parts of kidney tubules
apical synonyms
mucosal
lumenal
basolateral
serosal
peritubular
Majority of epithelia are leaky/tight
leaky: massive transport of substances
Functions of epithelia
- absorption of salt
- secretion of fluid
- turning on Cl- channel
- absorption of nurtrients
- regulation
- transport of water
- ridding body of metabolic waste
List Some Different areas in the body that contain epithelial cells
Gi tract, Kidneys, exocrine glands gall bladder choroid plexus ciliary body corneal epithelium mucous membranes
Is the lung lined with epithelium or endothelium?
endothelium
The apical surfaces faces what? What does the apical surface contain that gives the epithelium its special function?
the ‘special fluid’ or lumen side
- contains special transporters
In epithelial cells where tight junctions are leaky, what pathway is provided and what is its function?
peracellular shunt pathway: allows movement of water and solutes
Some examples of leaky tight junctions
proximal part of kidney
gallbladder
small and large intestines
two routes to cross epithelium
- can cross both membranes by entering one and exiting other (apical or basal visa versa)
- not cross membranes but instead pass through pericellular shunt
Na/K pump is the driving force for transport of what? (give some examples)
nearly all transport: water, salts, nutrients, non volatile metabolic wastes
Are protons dependent on Na/K pumps?
No - protons rely on primary active transport
- ie: stomach and kidneys
The apical/basolateral membrane is highly permeable to K and contain low Na permeability?
Basolateral (like most cells)
What is the value of the membrane potential of the basolateral membrane? Apical membrane?
basolateral: Vm = -70mV
apical: Vm = ~+10mV
The apical/basolateral membrane is highly permeable to Na and contain low K permeability?
apical
How is salt and water transported from the apical to basolateral solution?
- sodium leak thru apical membrane (down [ ] gradient]
- sodium pumped back out thru basolateral side via Na/K pump
- Cl passively follows (bc its attracted to positive ch)
- water is 3rd wheel and follows.
If the Na/K pump was blocked,, what would happen to water flow?
decrease
- with pump closed, Na entry reduced, Cl entry reduced, water entry reduced.
The apical solution is positive/negative with respect with basolateral solution
negative
(Na+ leaks thru apical, pumped thru basolateral side,
apical side becomes more negative)
transepithelial potential difference measures what?
Difference between
Vm (basolateral) - Vm (apical)
What is an electroneutral cotransporter?
A transporter that transports equal charges of ions across the membrane.
-ie: 1 K, 2 Cl-, 1 Na
in normal resting cells, the Cl- channel is open/closed
closed
main defect in cholera and cystic fibrosis?
Defect in Cl- channel in apical membrane (In Gi tract and lung)
-causes channel to be overly activated –> secretes electrolyte into lumen –> water follows (DIARRHHEEAA)
These channels/pumps are located on the apical/basolateral membrane
- Na/K pump
- Cl- channel .
- K+ channel
- Na/K/Cl cotransporter (pump)
- basolateral
- apical
- basolateral
- basolateral
compare paracellular and intercellular shunt pathways
Apical Basolateral
_________________________
Na leaks ———————–>
Cl follows via paracellular SP
<———————— Cl- leaks
Na follows via intercellular shunt pathway
Describe how nutrients are absorbed
amino acids/sugars are pumped from the GI lumen into the blood by GI epithelium.
then passively diffuses out of the cell into interstitial fluid
What types of transport are sugar and amino acid pumps?
secondary active transport
this means that if Na is removed, pumps stop working
Describe differences of glucose transport across epithelial and non epithelial membranes
epithelial apical membrane:
- secondary AT
everything else:
- facilitation Diffusion
(plasma membrane of non epithelial cells + basolateral membrane)
absorbed/not absorbed in GI?
- L-amino acids
- L-sugars
- D-amino acids
- D- sugars
- Absorbed
- Not absorbed
- not absorbed
- absorbed
rise/reduction in plasma osmolarity will cause you to be thirsty
rise
- severe dehydration occurs when plasma osmolarity is raised by less than 10%
What is the most important function of the kidney!!??
getting rid of non volatile metabolic waste products. (urea and protons)
(cant be expelled by lungs like volatile CO2)
Uremia
urine in the blood
Instead of a urea transporter (none exists), what does the kidney have?
an ULTRAfiltrate. duh
- requires lots of ATP
- regulates ECF composition
How does the kidney regulate water?
kidney tubule lumen reabsorbs solutes.
epithelium is made water impermeable (cannot follow solutes) and gets pissed out
What makes the epithelium impermeable to water?
the hypothalamus senses too much water/drop in plasma osmolarity
- stops secreting ADH (vasopressin) and causes epithelial cells to remove aquaporins from their apical membrane
4 important substances that are never pumped across the membrane
water
O2
CO2
Urea
Explain CBIGK and functions of each
treatment of hyperkalemia
- Calcium: quiets cells
- Bicarb: start reuptake of K
- Insulin + Glucose: Juices/fires up Na/K pump
- kayexalate: get K out of body
