vomiting causes ECF volume contraction. However, we have not considered the possibility that this ECF volume contraction might cause its own acid–base disturbance. Maria had metabolic alkalosis because she lost H+ by vomiting. To compound the problem, ECF volume contraction caused its own metabolic alkalosis (called contraction alkalosis system (as discussed earlier). Activation of the renin–angiotensin II–aldosterone system causes an increase in blood HCO3− concentration (metabolic alkalosis) in two ways: (i) Angiotensin II stimulates Na+ – H+ exchange in the proximal tubule and leads to an increase in the reabsorption of filtered HCO3