[k] Gastroenteritis And Blood Volume

THE KIDNEY

Gastroenteritis and Blood Volume

A 35-year-old man develops an acute episode of vomiting and diarrhea and loses 3 kg (7 lbs) in body weight over a 24-hour period. A blood sample shows that the plasma [Na+] is normal at 145 mEq/L. Indicate whether the following parameters would be increased, decreased, or unchanged from what they were before this illness. Plasma osmolality

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Effective circulating volume ______________________ Plasma ADH levels ______________________ Urine osmolality ______________________ Sensation of thirst ______________________

It is assumed that the 3 kg weight loss reflects only the loss of fluid. Because the plasma [Na +] is unchanged, this represents a loss of isotonic fluid (3 L) from the ECF.

Plasma osmolality: because the plasma [Na+] is unchanged, the plasma osmolality is unchanged.

Effective circulating volume (ECV): the loss of fluid from the ECF will decrease the effective circulating volume.

ADH secretion: the decrease in ECV, through the vascular baroreceptors, will stimulate ADH secretion.

Urine osmolality: the increased levels of ADH will lead to water conservation by the kidneys, and a concentrated urine will be excreted.

Sensation of thirst: again, the decrease in ECV, through the vascular baroreceptors, will lead to an enhanced sensation of thirst.