The stomach is a J-shaped muscular bag in the left upper abdomen, just under the diaphragm. It stores a meal, churns it into a liquid called chyme and starts protein digestion.
Regions
The stomach has the cardia, fundus, body and antrum, and ends at the pyloric sphincter. Inner folds called rugae let it stretch to hold more than a liter.
Gastric juice
Parietal cells secrete hydrochloric acid and intrinsic factor, which is needed to absorb vitamin B12. Chief cells release pepsinogen, which acid turns into pepsin to break down protein.
Protecting the wall
A thick layer of mucus and bicarbonate shields the wall from its own acid. NSAIDs, alcohol and Helicobacter pylori weaken this barrier and can cause ulcers.
Emptying
The pylorus lets small amounts of chyme into the duodenum at a time. Fatty meals leave the stomach more slowly than liquids or carbohydrates.
| Cell | Makes | Role |
|---|---|---|
| Parietal cell | Hydrochloric acid and intrinsic factor | Kills microbes, activates pepsin, allows B12 absorption |
| Chief cell | Pepsinogen | Protein digestion |
| G cell | Gastrin | Stimulates acid secretion |
| Mucous cell | Mucus and bicarbonate | Protects the lining |
At the bedside
Epigastric pain, vomiting blood or black stools can point to a bleeding ulcer. Ask about NSAIDs and alcohol, and check vital signs for signs of blood loss.
Related guides
Written by Making Synapses. Topic reference: OpenStax, Anatomy and Physiology 2e (no text adapted).