The pH in the small intestine increases from pH 6 in the duodenum to pH 7.4 at the distal end of the small intestine in the terminal ileum. The pH decreases to pH 5.7 in the cecum but increases to pH 6.7 in the rectum.
The most acidic part of the human gastrointestinal tract is the stomach, which is generally around pH 1 to pH 3. The high acidity in the stomach fights bacteria that are ingested with food. As the distance increases from the stomach, the pH level gradually increases. The large intestine is pH 5.5 to pH 7.