Outline the distribution of total body water.
In order to pass this viva, candidates were expected to know the distribution of water in
different body compartments, the difference in electrolytes composition in different
compartments (E1), definition of osmosis and diffusion, and where osmosis and diffusion
occurs in the body (B1f and D1), measurement and calculation of osmolality (E1), and how
different intravenous fluids will be distributed in different body compartments (E2a).
The common deficiency in the candidates’ answers included the difference in electrolytes
composition between interstitial fluid and plasma and the reason behind it (F2a), how
osmolality can be measured, the presence of an osmotic process in the medulla of the kidney
where re-absorption of water occurs through the collecting tubules in the presence of antidiuretic
hormone (D1), and how the fluids will be distributed in the body when different
intravenous fluids are administered.
Syllabus : E1 2
References : Chapter 1 of Review of Medical Physiology by Ganong
Vander’s Renal Physiology for details on this topic.