antrum
Summary
The antrum is the lower part of the stomach, just before the pyloric sphincter, where churning turns food into chyme and G cells secrete gastrin. Testable point: antral gastrin stimulates HCl release by parietal cells, and low luminal pH shuts it off by negative feedback.
Detail
Meaning: The antrum (pyloric antrum) is the lower stomach region, between the body and the pyloric sphincter. Its thick smooth muscle contracts in strong waves that grind and mix food with gastric juice into chyme and release small amounts through the pylorus into the duodenum. The antrum also holds G cells, which release gastrin into the blood in response to peptides, stretch and vagal input. Gastrin stimulates parietal cells to secrete HCl and increases gastric motility. When luminal pH falls, D cells release somatostatin, which inhibits gastrin (negative feedback). A second sense: the antrum of an ovarian follicle is its fluid-filled cavity.
On the MCAT: Expect questions on where a hormone is made (gastrin comes from antral G cells) or on predicting a change. Removing the antrum, or blocking G cells, lowers gastrin and therefore acid output. Raising gastric pH removes the inhibition, so gastrin rises. Know the food path: esophagus → fundus and body → antrum → pyloric sphincter → duodenum.
Common confusion: Gastrin is not made by parietal cells. G cells in the antrum make it, and it acts on parietal cells, which are found mostly in the body and fundus.
Sources
- Campbell Biology
- Human Physiology: An Integrated Approach
- Principles of Anatomy and Physiology
Written for the MCAT and checked before it was published. For study reference only. Spotted an error? Let us know.