Module 16 Introduction

The digestive system, or gastrointestinal (GI) tract, extends from the mouth through the esophagus, stomach, small intestine, and large intestine to the anus, and includes accessory organs such as the salivary glands, liver, and pancreas. This system normally hosts a diverse microbiota that aids digestion and protects against pathogens, but disturbances or the introduction of harmful microbes can lead to infections. Digestive system infections are caused by a variety of agents — including bacteria like Helicobacter pylori and Clostridioides difficile, viruses such as rotaviruses, and parasitic protozoa — and can produce a wide range of symptoms from mild diarrhea to life-threatening conditions. Understanding how these pathogens colonize, invade, and damage the GI tract, as well as how the body responds, is essential for diagnosing, treating, and preventing gastrointestinal diseases.