Final answer:
The increase in HCO₃- concentration in blood from the stomach during digestion is referred to as the alkaline tide, occurring due to the secretion of gastric acids and the associated production of bicarbonate ions.
Step-by-step explanation:
The increased concentration of HCO₃- in blood draining from the stomach is known as the alkaline tide. This phenomenon occurs during the gastric phase of digestion when hydrogen ions are actively pumped into the stomach, increasing the acidity to aid in digestion. Concurrently, the excess HCO₃- ions are transported back into the bloodstream, leading to a temporary increase in blood pH.
Once the food enters the stomach, it causes distension, leading to the production of gastric juices including hydrochloric acid (HCl). This HCl is produced from CO2 and H2O with the help of an enzyme called carbonic anhydrase, which leads to a byproduct of bicarbonate ions. The bicarbonate ions are then absorbed into the blood, resulting in the alkaline tide.