How does the stomach protect us from infection?

• A. The stomach warms pathogens
• B. The acidic environment kills most pathogens
• C. It blocks pathogens with a sphincter
• D. It has enzymes that digest pathogens

Answer: (B)

The stomach protects us from infection mainly through its acidic environment. The stomach secretes strong hydrochloric acid, creating a very low pH that denatures microbial proteins and disrupts cell membranes, so many ingested pathogens are killed or inactivated before they can cause trouble. This chemical barrier is a first line of defense that reduces the number of microbes reaching the intestines. Enzymes like pepsin also help by digesting proteins, including some microbial proteins, but the key protective effect comes from the extreme acidity. Keep in mind that a few hardy organisms can resist acid, so acidity isn’t perfect, but it’s the primary way the stomach lowers infection risk.