During human digestion, the bolus enters the stomach through the esophagus via the lower esophageal sphincter. The stomach relea
ses proteases and hydrochloric acid, which kills or inhibits bacteria and provides the acidic pH of 2 for the proteases to work. Food is churned by the stomach through muscular contractions of the wall called peristalsis and the bolus is converted into chyme. According to the text, the stomach's environment is very acidic. How does this acid stay in the stomach?
The stomach is protected from the hydrochloric acid by
epithelial cells, which secrete a bicarbonate substance that covers the mucosa.
Since the bicarbonate solution is alkaline, it neutralizes the hydrochloric
acid produced by parietal cells and subsequently results in formation of water.
Importantly, the consistent secretion of the bicarbonate solution is what
protects the stomach from the strong acidic environment.
