Normally the volume of the stomach residue is 20 to 100 mL and the pH is acidic (1.5 to 3.5).

• Ulcers may be caused by delayed emptying or increased secretion of acid.
• The presence of bile in the stomach indicates regurgitation from the duodenum. This may occur after a partial gastrectomy. (See also gastroesophageal reflux disease.)
• Decreased levels of stomach acid or gastrin can cause malabsorption (inadequate absorption of nutrients from the intestinal tract).
• Increased levels of gastrin may cause increased secretion of acid and may lead to ulcers (Zollinger-Ellison syndrome).