The digestive system includes the alimentary canal and accessory organs. Protection against infections of the digestive system can come from mucus, saliva, and other secretions (including immunoglobin A antibodies) from these organs. Illnesses that affect the digestive system may be acquired via ingestion. The digestive system has many means of protecting the body from these infections, including a mucus layer and low pH. Bacteria, viruses, fungi, protozoa, and helminths can all cause diseases of the digestive system, with symptoms often including diarrhea. Transmission of digestive system disease is most commonly fecal-oral in contaminated food or water. Bacteria such as Salmonella and Campylobacter jejuni are spread in this way, as is norovirus.
At A Glance
- The alimentary canal consists of the mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus.
Natural defenses include mucus, secretory immunoglobulin A (IgA), fluids with antimicrobial properties, saliva, and the low pH of stomach fluid.
- Millions of microorganisms are residents of the alimentary canal, where they provide digestive and immune services including training their host's immune system.
- Digestive system diseases are caused by bacteria, viruses, fungi, helminths, and protozoa. The infection may target organs of the alimentary canal or the accessory organs, and the symptoms may appear in the mouth, stomach, or other organs.
Bacteria cause a wide array of alimentary canal diseases, with severity ranging from inconsequential to life-threatening.
- The five hepatitis viruses are characterized by liver inflammation and may cause chronic debilitating disease. Common viral infections of the alimentary tract are generally not life-threatening and resolve without treatment.
- Alimentary canal diseases are rarely caused by fungi in healthy individuals; however, Aspergillus and Candida mycoses are increasingly recognized as complications in immunocompromised patients.
- Several single-celled eukaryotes, protozoa, are pathogenic and result in digestive system disease.
Helminths that parasitize humans include nematodes, trematodes, and cestodes.
Foodborne illness is common in the United States and is most often caused by norovirus.