week 2 forces acting across membranes Flashcards
what are aquaporin channels
channels that are permanately open to water
what is the [K+] like in ICF and ECF
[K+] is high in intracellular fluid, low in extracellular fluid
what is the [Na+] like in ICF and ECF
[Na+] is low in ICF and high in ECF
what can pass freely through the capillary wall
ions
so they can exchange between plasma and ISF
they do NOT penetrate the cell membrane!!!!!!
where can gases pass through
gases can pass freely through all three compartments (plasma, ICF, ISF)
nutrients and waste also pass easily but sometimes need help crossing the cell membrane
what are 7 important things to remeber about membranes
- cell membrane is a selective barrier
- permeability can vary
(may increase or decrease at certain times) - membranes are dynamic
(continually being formed and maintained/dismantled and metabolised) - membrane is double layer of lipid
- membranes are flexible
(because of the fatty acids they can act like an oil) - membranes are insulators, so no ions can pass
- membranes are embedded with proteins
what are the 5 common functions of membrane proteins
- receptors
- transport
- enzymes
- structural (anchorage)
- communication
what are the two types of transport proteins
- channel proteins: can be open (water) or gated (ions)
- carrier mediated transport proteins (transporters)
what do structural proteins do
they anchor the cell membrane to the intracellular skeleton, to the extracellular matrix (collagen) and/or to other cells
what do glycoproteins do
- membrane protein with carbohydrate attached to the external surface
- act as markers that tell the immune system whether a cell is one of our own of a foreign cell
do membranes differ in their protein content
yes
myelin = 18%
plasma membranes of cells = typically 50%
membranes involved in energy transduction = 75%
is there a physical barrier to water movement
no
what is an electrochemical gradient
- large concentration gradient exist between ICF and ECF for ions
- because it is ions creating the concentration gradient there is also a difference in charge. this creates an electrical gradient
- these two forces make the electrochemical gradient which ultimately drives the direction of passive movement
what are the mechanisms of movement across membranes
- diffusion (passive or facilitated - channels or transporters)
- active transport
- osmosis
- filtration (movement between plasma and ISF)
what is endocytosis
invagination of membrane to form vesicle which then disintegrates inside cell
what is exocytosis
invagination of cell membrane to form vesicle and substances are released outside of cell
what happens in passive diffusion
substances move directly through the lipid bilayer
what are the characteristics of molecules which can pass through the lipid bilayer
- small
- uncharged
- lipophilic (hydrophobic)
what is a molecule that is moved across the membrane via transporter
glucose
how does sodium potassium pump work
- 3 Na+ bind from inside cell
- ATPase is phosphorylated and changes conformation
- 3 Na+ released to outside into ECF
- 2 K+ bind from outside cell
- ATPase is dephosphorylated and changes conformation
- 2 K+ released inside cell
what is osmotic pressure
the pressure applied to oppose osmosis
what are the protein concentrations like in the cell compartments
plasma = [plasma protein] is high ISF = [protein] is low ICF = [protein] high
what is the osmolarity of normal human plasma
285 mOsmol/l
it is the same in cell
often rounded to 300
what is osmolarity
the total number of particles in solution
what is tonicity
the number of non-penetrating particles in solution
e.g. ions
what is an isometric solution
has the same total number of solute particles as normal ECF (plasma)
what is a hypo-osmotic solution
solutions with fewer total solute particles
what is hyper-osmotic
solutions with greater number of total solute particles
what is an isotonic solution
solution with the same number of non-penetrating solute particles as normal ECF (plasma)
what is a hypotonic solution
solution with fewer non-penetrating solute particles
what is a hypertonic solution
solutions with greater number of non-penetrating solute particles
is urea penetrating or non-penetrating
penetrating
if we have an isosmotic solution and all those particles are non-penetrating what is the tonicity
isotonic
if we have an isosmotic solution and half the concentration is penetrating and the other half is non-penetrating what is the tonicity
hypotonic
if all the particles in a hyper osmotic solution are non-penetrating what is the tonicity
hypertonic
if a hyper osmotic solution has the same number of non-penetrating particles as ECF what is the tonicity
isotonic
if a hyper osmotic solution has less penetrating particles than normal what is the tonicity
hypotonic
what tonicities can isosmotic solutions be
isotonic or hypotonic
what tonicities can hyperosmotic solutions be
isotonic, hypotonic or hypertonic
what tonicities can hypo osmotic solutions be
hypotonic
what is normal tonicity of ECF
close to 285 mosmol/L
what happens to cells in hypotonic solutions
they swell
what happens to cells in hypertonic solutions
they shrink
when should you transfuse a patient with pure water
never!!
what is the tonicity of saline solution
0.9% saline is isotonic
what is the osmolarity of 1M solution of NaCl
2 osmoles/l
what is the osmolarity of 1mM solution of glucose
1 mosmole/l
what is the most sensitive organ to changes in tonicity
the brain
