For each of the descriptions related to body fluids A–E, select the most appropriate option from the following list

A. Option 2 Plasma albumin. Colloid osmotic pressure is due to protein molecules which cannot readily cross the capillary wall; albumin constitutes the larger portion of the plasma protein mass, its molecules are smaller than globulin so it exerts much more osmotic pressure.

B. Option 1 Osmolality. Water passes across the cell wall by osmotic forces due to the sum of the effects of all dissolved particles – the osmolality.

C. Option 4 Sodium. Sodium has a concentration around 135 mmol per litre and provides nearly half of the total osmolality of around 285 mosmol per kg.

D. Option 2 Plasma albumin. Because most particles are in equilibrium across the capillary wall they do not contribute to the osmotic force opposing fluid leak. The proteins provide an opposing force and albumin is the commonest protein particle.

E. Option 1 Osmolality. Osmolality can be measured by noting the freezing point of the solution being tested.