The digestive tract is one long tube from the mouth to the anus, several meters long in an adult. Along the way food is broken down, nutrients are absorbed and waste is formed.
The tube
Food passes through the mouth, pharynx, esophagus, stomach, small intestine (duodenum, jejunum and ileum), large intestine, rectum and anus. Each part has its own job, from grinding food to absorbing water.
Accessory organs
The salivary glands, liver, gallbladder and pancreas add saliva, bile and enzymes, but food never passes through them. Bile helps break up fat, and pancreatic juice digests protein, fat and carbohydrate.
Moving food along
Waves of smooth muscle contraction called peristalsis push food forward. Sphincters, such as the lower esophageal sphincter and the pyloric sphincter, control passage from one section to the next.
Wall and nerves
The wall has four layers: mucosa, submucosa, muscle layers and an outer serosa. Its own enteric nervous system coordinates movement and secretion, and the vagus nerve increases digestive activity at rest.
| Quadrant | Main organs | Pain may suggest |
|---|---|---|
| Right upper | Liver, gallbladder, duodenum | Gallstones, hepatitis |
| Left upper | Stomach, spleen, pancreas | Gastritis, splenic injury |
| Right lower | Cecum, appendix | Appendicitis |
| Left lower | Sigmoid colon | Diverticulitis |
At the bedside
Picture the organs under each quadrant when you examine the abdomen, so you can link the site of pain to a likely source. Listen to bowel sounds before you palpate, because pressing can change them.
Related guides
Written by Making Synapses. Topic reference: OpenStax, Anatomy and Physiology 2e (no text adapted).