Describe the physiological consequences of the oral ingestion of 1 litre of water in a young adult.
It was expected candidates would provide details the consequences of water ingestion from its rapid absorption in the small intestine to the resultant impact on plasma osmolarity and the minimal impact of plasma volume of this volume. Some detail on the mechanisms of absorption (transcellular vs osmosis) was expected and the distribution of water across body fluid spaces. Many candidates accurately described the small drop in plasma osmolarity that is sufficient to trigger osmoreceptors with better answers providing details of the locations and mechanisms involved. The physiological consequences of inhibition of ADH, including the renal effects of decreased water permeability in distal renal tubules and collecting ducts. The volume load after distribution would be lower than the plasma volume triggers for the circulatory reflex responses.
Absorption of water is near-complete, rapid, and mainly occurs in the proximal small bowel
Distribution is equal into all body fluid compartments and proportional to their relative sizes:
Elimination is by renal excretion, where the filtered fraction is reabsorbed by a highly regulated mechanism.
Physiological consequences of oral water ingestion:
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