The properties and contents of sweat

The daily loss is about 800ml of "insensible water loss"; half is lost from the skin and half from the respiratory tract. Every gram of water evaporating loses 0.58 kcal of heat. Thus, with 800ml of water per day evaporating away, 464 kcal of heat are lost. That's 25% of basal heat production. The total osmolality of sweat is on average about 120mosm; sodium comprises 65mmol/L of this initially. With acclimatisation to heat stress, the sodium content of sweat decreases (down to a sodium concentration around 5mmol/L) and the volume of sweat increases. The maximum sweat volume is 1500-2000 ml/hr, or a maximum of 12 litres per day.

Distribution of non-ionic solutes such as glucose and urea

Total body glucose content

  • Given the below concentrations in mmol/L, and knowing the total body fluid volume of a random 70kg guy, you can estimate that he will have a total of about 95mmol of glucose in the extracellular fluid.  That comes to about 17 grams, rounded up to 20 according to G.F. Cahill.
  • Glucose is neither acidic nor alkaline.