A healthy male with a body weight of 70 kg has a normal extracellular osmolarity

Question

A healthy male with a body weight of 70 kg has a normal extracellular osmolarity of 300 mOsm and a normal ICF volume and ECF volume. One day he is a victim of severe burns and he suffers a water loss of 2.5 L of water (the salt loss is covered). a) Will the ECF osmolarity change in light of his water loss? If yes, how? What would the body have to do to correct for this change? Following total restitution of the water compartments the patient undergoes surgery with skin grafts. During the long procedure he receives sufficient water by glucose infusion, but he loses 900 mOsmol of Na^+. b) Which fluid compartment would be affected (ECF/ICF)? Why? What would the effect on the cell be? c) Is it dangerous for a healthy individual to lose 6 kg of water without solutes?

Explanation / Answer

Ans:

6 (a): All cell membrane are water permeable therefore, the body water is evenly distributed across the cell membrane. And there is no loss of solute, thus the toal amount is maintained i.e., 300 mOsmol/kg * 42 kg = x * 39.5 kg.

300 * 42 / 39.5 = 319 mosmol / kg.

And the hypothalamic osmoreceptors are stimulated and they release ADH from the neurohypophysis. Increased serum ADH will increase the water reabsorption and mimimise the hyperosmolality.

(b): Almost all Nacl of the body is located in the ECV

Thus, the normal content 300 * 14 = 4200 mOsmol is reduced to 4200 – 900 = 3300.

And the new osmolality = 300 * 300 / 4200

                                        = 236 mOsmol / kg

And if the cell membrane were permeable but the cell swell and a higher osmolality is maintained by reduced ECV and vascular phase.

(c): With the water loss the person has increased osmolality in the ECV. This is stimulates ADH release. And the person is in antidiuresis in order to recover the water loss, and the water is drawn from the cells into ECV. the condition is rapidely compensated for and not really dangerous.

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