Final answer:
Diseases of the digestive system usually result from ingesting bacteria or their toxins in food and water. Gastrointestinal illnesses caused by foodborne microbes range in severity and can be caused by viruses, parasites, and other microbial agents.
Step-by-step explanation:
Diseases of the digestive system usually result from ingesting bacteria or their toxins in food and water. Bacterial contamination of food can lead to gastrointestinal illnesses, with symptoms such as abdominal discomfort, nausea, diarrhea, and vomiting. Other microbial agents responsible for digestive diseases include viruses, parasites (such as Giardia), fungi, protozoa, and helminths.