The document summarizes key aspects of gut structure and function. It describes the layers of the gut wall and pH ranges throughout the gastrointestinal tract. The buccal cavity, esophagus and stomach have a small surface area, while the duodenum and small intestine have a very large surface area of 10-14 feet. Transit times are shortest in the buccal cavity, esophagus and stomach at 30-40 minutes, while the large intestine has the longest transit time of up to 24 hours.