polar head

two hydrophobic fatty acid chains

• round polar heads contact water on inside and outside
• long hydrophobic tails form the inner portion of the membrane
  • sets up a barrier to polar compounds and ions
    • allow for different concentrations of ions across the membrane
  • small uncharged water solubule molecules can pass (ex: urea)

• phopholipids bilayer
• cholesterol
• imbedded membrane proteins
  • move fluidly within membrane
  • often anchored at specific sites by other proteins

• transmitter receptor (ex: ligand gated, metabotropic)
• ion channels (ex: Na, K, Ca channels)
• transporters/pumps (ex: Na/K ATPase)
• aquaporins

• ECF (33%)
  • blood plasma (8% of TBW)
  • interstitial fluid (25% of TBW)
• ICF (67%)

Tracer used to measure TBW

• Used to measure the size of a fluid compartment via tracer
• Volume = amount of tracer/concentration of tracer

51Cr labeled RBC's

Tracer for plasma volume

Why is mannitol a good tracer for ECF volume?

• small, so it can cross blood capillary barrier but cant cross cell membranes
• nontoxic
• non metabolized
• excreted unchanged in the urine

cells (mostly RBC's)

plasma

Define hematocrit

• J = PA (Ca-Cb)
  • P= permeability (cm/sec)
  • J= net rate of diffusion (mmol/sec)
• This will tell net flux of a particular compound across a membrane

glucose transporters

aquaporins

• get energy via ATP hydrolysis
• against gradient

• Ca/ATPase of SR (two Ca in SR for each ATP hydrolyzed)
• Na/K ATPase

• Process 
  • for every ATP hydrolyzed, 3 Na out and two K in
  • electrogenic pump with coupling ratio of 3:2
• function- maintain electrochemical gradient across the membrane
  • results in reducing osmotic particles inside cell so cell does not swell, burst
  • THUS, NORMAL CELL VOLUME AND PRESSURE DEPEND ON PROPER FUNCTION OF THIS ACTIVE TRANSPORTER

receives energy using an electrochemical gradient set up by another transporter as a source of energy

co-transport

antiport/countertransport

examples of cotransport

Na-AA transporter

Na-glucos transporter

Ca/Na exchanger in muscle cells (Ca out and Na in)

• differences in osmotic pressure in two compartments which is caused by concentration of impermeant solutes
  • compartment with more impermeant solutes will have increase in water volume within its compartment

∏ = g C σ RT

g= number of particles per mole of solution

σ = reflection coefficient

lipid solubility

molecular weight of solute

• albumin = 1 (impermeabile)
• electrolytes = 0.85-0.95
• urea = 0 (small permeable)

normal osmolarity of RBC

swell, then burst (hypotonic solution)

*in plasma, RBC would burst when in soln of less than 200 mOsm/L

• osmolarity- all solute particles in solution determine it (permeable and impermeable)
• tonicity- depends only on impermeable particles (permeable particles like urea will equalize across membrane)

Explain why 300 mM of urea is hypotonic to RBC

Urea is freely permeant in solution, so it enters the RBC until its intracellular concentration is 300 mM.

treatment of hypernatremia

Describe what happens to 300 mM of D glucose      

(5% dextrose solution) once it enters the body

• normal = 136-145 mmol/L
• hyponatremia = below 135
• life threatening = below 120

• headaches
• seizures
• coma
• arrhythmia due to electrolyte imbalance