Osmoregulation Flashcards
What is the apical membrane of a cell?
side that faces the environment
What is the basolateral membrane of a cell?
side that faces the lumen/blood
What is interstitial fluid?
fluid trapped between cells that does not exchange easily
- composition similar to plasma in most organisms (few exceptions)
- composition differs dramatically in freshwater vs. seawater environments
What is the endothelium?
separates skin layer from blood layer
What are the 3 homeostatic processes?
- osmotic regulation: osmotic pressure of body fluids
- ionic regulation: concentrations of specific ions
- nitrogen excretion: excretion of end-products of protein metabolism
What is the Fick equation?
calculates rate of diffusion (flux rate)
dQs/dt = Ds x A x dC/dX
- Ds: diffusion coefficient (Ds): includes size of molecule and hydration shell
- A: diffusion area
- dC/dX: size of concentration gradient, where x = distance
- direction of diffusion depends on concentration gradient
What is osmotic pressure?
pressure that draws water largely due to driving force of solute concentration
What counteracts osmotic pressure?
- hydrostatic pressure
- gravity
What are the 3 ways to classify/compare two solutions?
- solution with higher osmolarity is hyperosmotic
- solution with lower osmolarity is hyposmotic
- osmolarities that are the same are isosmotic
What is a semipermeable membrane permeable to? How does this affect responses in regulation?
- permeable to water
- impermeable to salt
- water moves quicker than ions (charged molecules)
- first response is water movement, second response is potential salt movement (depending on membrane permeability)
What is tonicity?
effect of a solution on cell volume
What are the 3 classes of tonicity?
- hypertonic solution: cells shrink – water leaves cell by osmosis
- hypotonic solution: cells swell – water enters cell by osmosis
- isotonic solution: cell neither shrinks nor swells – no net osmosis (but water is still always moving)
Why is water and solute regulation of the intracellular and extracellular space important? (2)
- increased intracellular osmolarity can directly interfere with cellular processes (ie. protein-protein interactions, cellular fluidity for diffusion)
- changes in osmolarity can result in movement of water across membrane, which changes cell volume
How does increased intracellular osmolarity affect proteins such as hemoglobin?
- crystallizes – cannot hold O2 anymore, therefore non-functional
- Hb is packed in RBC, on the verge of solubility and turning into crystals – dehydrated RBC can cause Hb to crystallize inside RBC
How does increased intracellular osmolarity affect cellular and membrane fluidity?
cellular fluidity and membrane fluidity is largely affected by volume
- stretches membranes
- changes barrier of membrane between inside and outside
Changes in osmolarity can result in movement of water across membrane, which changes cell volume. Why is this important?
cells are very susceptible to volume changes, but also well-designed to deal with changes
- moderate cell swelling → disruption of membrane
- excessive cell swelling → cell lysis
- excessive cell shrinkage → macromolecular crowding
How is cell volume regulated?
- cells transport solutes in and out of ECF (regulates composition) to control cell volume
- water follows solutes by osmosis
What is sodium regulated by?
- Na+/K+ ATPase: pumps 3 Na+ out for 2 K+ in
- Na+/H+ exchanger: driven by potential difference across cell membrane (does not require ATP) that is usually generated by NKA
What is potassium regulated by?
- Na+/K+ ATPase: pumps 3 Na+ out for 2 K+ in
What is chloride regulated by?
- generally distributed passively (Goldman equation)
What is calcium regulated by?
- Na+/Ca+ antiporter
- Ca2+ ATPase
What is regulatory volume increase (RVI)?
cells increase volume (swell) by actively importing ions, then water follows ions passively causing swelling and expansion
- different cells use different transporters
- usually achieved by activating NKCC
- alternatively by opening Na+ channels, Cl- channels, Na+/H+ exchangers
How do Na+/H+ exchangers work?
H+ comes from metabolism or CO2 and is pumped out while bicarbonate stays inside
What is regulatory volume decrease (RVD)?
cells actively decrease volume by exporting ions into lumen, then water follows passively
- different cells use different transporters
- usually achieved by opening K+ channels – K+ leaves cell (down electrochemical gradient) because RMP for K+ is -90 mV
- Cl- channels also open – Cl- leaves cell in response to hyperpolarizing effects of K+ movement
- Na+/K+ ATPase also pumps 3 Na+ out for 2 K+ in