Figure 47.10 illustrates the layers of the vertebrate gut. Learn these various layers and the association of the pancreas and its duct with the gut. Digestion begins in the mouth where salivary amylase starts the breakdown of carbohydrates. Some digestion as well as absorption occurs in the stomach. Protein digestion begins in the stomach.
Pepsinogen is converted to the active protein digesting form, pepsin.
This conversion is aided by the low pH of 1-3, which is due to the HCl secreted by specific stomach mucosal cells. Food and liquid are mixed with stomach secretions to form acidic chyme . Chyme is squirted into the duodenum of the small intestine through the pyloric sphincter . The stomach absorbs relatively few substances and these are absorbed in small amounts. Some of the substances absorbed are caffeine, aspirin, and alcohol.