Question

If a person drinks a large amount of water very quickly, it is possible to exceed the rate of water removal by the kidney (~1 L/hour), essentially diluting the blood. The resulting osmotic pressure causes cells to swell. Fat and muscle cells have a capacity to adjust to this change in volume, but neurons in the brain do not have room to accommodate this size increase. (The skull is so densely packed, there is no room for swelling!) Consequently, as water enters neuronal cells, pressure is exerted on the brain, causing headache, fatigue, mental disorientation, and in severe cases, loss of consciousness and death.

A healthy adult has 140. mM sodium in 5.0 L of blood. Severe symptoms of water intoxication manifest when sodium concentrations are 135. mM and lower. Assume that the density of water is 1.0 kg/L.

1. a) The freezing point of normal human blood serum is -0.52^o C. Based on this value, what is the concentration of solutes in the blood? (Assume that blood serum behaves like an aqueous solution, with K_f= 1.86 K kg mol-1.)

2. b) Marathon runners are at an increased risk of water intoxication – at the 2002 Boston marathon, a number of runners had sodium levels that were less than 120 mM and suffered from severe water intoxication symptoms. Assuming that the blood of a normally hydrated person is isotonic with cells (i.e. same osmotic pressure inside and outside), what is the difference in osmotic pressure between the blood and cells in one of these marathon runners? Use the answer calculated in part (a), along with the information on the dilution factor given by the change in the sodium concentration. Assume that body temperature is 37^oC.

Answer 1

NOTES Record the list of things you might want to do Healthy Adult - Water Intoxication Na density I = level 140mm in 5L blood. 1 kg/L Na level <135 mm (a) freezing point I with of blood serum = solutes) -0.52°C. truzing Point of pure blood = 0°C kg = 1.866 k kg mot" AT = 4 m 0.52K = 1.86 kkq molt x m m= 0.2796 mol kgl. (6) Marathon runners T: 37 c = Na level 3104 <RomM Osmotic Pressure TT - CRT ( since d= 1kg1 & m = M = 0.2796 mol t) T: 0.2796 mol 1 %0.0821 Latin k'mol' x 310 L T assumine lootonid 7 that with .115 blood cells, atm of normally hydrated given) ! person is