Lecture 4- Principles of solute and water movement Flashcards
in a 70kg man how much of him is water
60% of 70kg= 42L
men are 60% water- Kg=L
how much of total water volume in humans is intracellular
2/3
how much of total water volume in humans is extracellular
1/3
extracellular spaces are also called
interstitial
therefore in a 60kg man with 42 L of water, how much is intracellular
28L
2/3 of 42
therefore in a 60kg man with 42 L of water, how much is extracellular
14L
1/3 of 42
E.g. if someone’s put on 1.5kg and has oedema they will have increased how much fluid in ECF
- 1.5kg=1500ml
* 1/3 of 1500 = 500 ml
what counts as intracellular fluid
within cvcells
what counts as extracellular fluid
- interstitial
- plasma
- lymph
- trancellular fluid
ionic concnetrations within ECF
- High [sodium]
- Low [potassium]
- High [chloride]
ionic concentrations within the ICF
- Low [ sodium]
- high [potassium]
osmolarity of of the ECF
between 285-310 mOsm
osmolarity of ICF
290mOsm
osmolarity of ICF and ECF should be
equalise- prevent water flooding into he cell- ions in equilibrium
phospholipid membrane permeable to
uncharged and non polar molecules, small hydrophobic molecules e.g. ammonia and water
cell membrane lets what in
CHO, sugars, proteins amino acids lipids, salts, O2 and water into the cell
cell membrane lets what out
lets Water, ammonia. Salts, CO2 out
what maintains cholesterol fluidity
cholesterol
what can slip through the membrane
lipid soluble molecules e.g. fats and lips
large hydrophobic molecules
struggle to pass the membrane
what sort of molecule can pass the membrane
- Small uncharged non-polar
- Small hydrophobic molecules can get through e.g. gases
- Urea can easily diffuse through membrane (accept in kidneys)
what sort of molecule cannot pass the membrane
- Large uncharged molecules e.g. glucose cannot just pass through the membrane
- Large charged molecules cannot pass through (e.g. ATP, amino acids)
cell membrane example of permeability
- permeable to urea and water.
- not permeable to ions
capillary example of permeability
Permeable to urea, water,Na or K (fenestrations). Not permeable to plasma proteins
types of movement between compartments
passive transport
active transport
vesicular transport
passive transport
- No energy needed- diffusion
- Movement down concentration gradient
- E.g. Facilitated diffusion (water through an aquaporins)
- E.g.Osmotic, oncotic and hydrostastic
active transport
- Uses ATP
* Movement against conc gradient
vesicular transport
- Pinocytosis (cell drinking)
- Phagocytosis
- Form of active transport
- Not using channels
diffusion
Solute movement across a lipid bilayer through entry into the lipid phase occurs by simple diffusion- movement occurs downhill and is passive
diffusion is irrespective of
other substances
flux describes
• ‘Flux’ describes how molecules move expressed in moles/cm2/second
when there is no movement
flux is 0
movement of change is proportional to
gradient of conc difference
if membrane is thicker
flux will be slower e..g single cell wall of alveolus
diffusion of 2 solute
Concentration gradient of different substances are independent of each other
facilitated diffusion e.g. aquporins
Move from, high to low concentration through a protein channel
• Protein molecules spans the membrane
• Permeable to the movement of that substance (specific)
• No energy needed
• Facilitated= with help
• E.g. aquaporins
gated channels
Proteins that open only in presence of stimulus (signal)
- Stimulus different from transported molecules
- E.g. ion-gated
- E.g. voltage gated
active transport
Cells need molecules to moleucles against concentration gradients
- Need protein pump
- Requires ATP
e. g. Na/K+ ATPase pump
large molecules are transported bvia
vesicular transport- requires ATP
two main types of vesicular transport
1) exocytosis
2) endocytosis
exocytosis
out of cell
types of endocytosis
1) phagocytosis
2) pinocytosis
3) receptor mediated endocytosis
phagocytosis
cellular eating
pinocytosis
cellular drinking
constitutive secretion
is the default pathway and is used primarily to replenish material at the plasma membrane and certain membrane-bound organelles.
regulated secretion
Regulated secretion terminates in secretory vesicles that store secreted material until a signal triggers fusion with the plasma membrane.
–> triggered by Ca2+!!!!!!!!!
water moves across the membrane relatively
slowly
aquaporins
allow water to move across the plasma membrane very quickly
if the solution becomes hypotonic
then water will move across membrane by osmosis an enter the cell and the cells will swell and burst
if the solution is isotonic
same osmolarity either side of the membrane) water molecules will enter and exit the cell in equilibrium- as many will enter as will leave
in hypetonic solutions the cell will
shrinking because the water would move across the membrane into the ECF
water will move until
osmotic forces on either side of the membrane is equal
Osmole is the measure of
solutions ability to create osmotic pressure and move water
- Proportional to the number of osmotic particles formed in solution
In normal conditions osmolality of plasma is
equal to interstitial fluid = intracellular fluid = 280-210 mOsm/kg
clinically how is osmalility determined
by ECF (Na+ and Cl- =80%) - Serum osmolality can be estimated by doubling serum sodium
hyperotnic
more solute, less water
hypertonicity
hypertonic solution will loose water, shrivel and lyse
hypotonic
less solute, more water
hypotonicity
hypotonic solution will gain water, swirl and cytosolyse
isotonic
equal solute, equal water- no movement of water
aquaporins work through
facilitated diffusion
how much quicker can water diffuse across the membrane using aquaproins
200x quicker
structure of aquaporins
- Made up of 5 subunits - tetrameric
- 6 transmembrane alpha helix protein
- Inner cavity narrow and lined withy hydrophilic AA
- At the centre (+) residues
- Prevents movement of charged ions e.g. protons
- Aquaporins don’t disrupt H+ ion gradient in ATP production
what does aquaporins let through
just water- occasionally urea
how many isoforms of aquaporins
10
how does water move through aquaporins
Water molecules line up one behind the other and pass single file through the hydrophilic channel
1000,000 molecules/ min
why is movement through aquaporins movement still osmosis
Movement still depends on solute concentration gradient
Still osmosis
