CCK is a gastrointestinal hormone that acts to decrease gastric emptying when stimulated by the presence of fat and protein. This hormone also has a direct effect on the brain centers responsible for hunger to reduce further eating. The majority of other gastrointestinal hormones are stimulated by the presence of fat.

The mouth is the start of the gastrointestinal tract. It is the site of both mechanical and chemical digestion via chewing, and saliva, respectively. Saliva contains the enzyme amylase that breaks down carbohydrates.

CCK is a gastrointestinal hormone that acts to decrease gastric emptying when stimulated by the presence of fat and protein. This hormone also has a direct effect on the brain centers responsible for hunger to reduce further eating. The majority of other gastrointestinal hormones are stimulated by the presence of fat.

The mouth is the start of the gastrointestinal tract. It is the site of both mechanical and chemical digestion via chewing, and saliva, respectively. Saliva contains the enzyme amylase that breaks down carbohydrates.

The mouth, stomach, and small intestine all contain enzymes that help chemically digest food. The mouth contains salivary amylase to digest carbohydrates. The stomach contains pepsin to digest proteins. The small intestine contains numerous enzymes from pancreatic secretions that digest carbohydrates, fats, and proteins.

The esophagus serves to transport food from the mouth to the stomach via smooth muscle contractions. No chemical digestion takes place in the esophagus, and no digestive enzymes are secreted into this region.

The mouth, stomach, and small intestine all contain enzymes that help chemically digest food. The mouth contains salivary amylase to digest carbohydrates. The stomach contains pepsin to digest proteins. The small intestine contains numerous enzymes from pancreatic secretions that digest carbohydrates, fats, and proteins.

The esophagus serves to transport food from the mouth to the stomach via smooth muscle contractions. No chemical digestion takes place in the esophagus, and no digestive enzymes are secreted into this region.

The pancreas is responsible for secreting digestive enzymes into the small intestine. These enzymes are responsible for digesting lipids (lipase), proteins (trypsin), nucleic acids (nucleases), and starches (amylase). In addition, the pancreas secretes bicarbonate to help neutralize the acids coming from the stomach. Pepsin's zymogen, pepsinogen is released by chief cells in the stomach, and gets activated by the acid that is also produced by the stomach (by parietal cells).

The pancreas is responsible for secreting digestive enzymes into the small intestine. These enzymes are responsible for digesting lipids (lipase), proteins (trypsin), nucleic acids (nucleases), and starches (amylase). In addition, the pancreas secretes bicarbonate to help neutralize the acids coming from the stomach. Pepsin's zymogen, pepsinogen is released by chief cells in the stomach, and gets activated by the acid that is also produced by the stomach (by parietal cells).

Vitamin B12 absorption requires intrinsic factor (IF), which is a protein secreted by the parietal cells of the stomach. When vitamin B12 binds to IF, it is able to be absorbed by the body in the terminal ileum. Therefore, removal of the ileum would likely result in a vitamin B12 deficiency, since the body cannot absorb the B12-IF complex.

Pepsinogen is an inactive enzyme that is released into the stomach lumen by chief cells. Parietal cells are responsible for secreting hydrochloric acid. This acid will cleave the pepsinogen and make it an active enzyme, pepsin, which can then cleave peptide bonds and begin protein digestion.

Goblet cells secrete mucus to protect the epithelium of the stomach from the acid in the lumen. G cells secrete gastrin, which promotes the secretion of hydrochloric acid and pepsinogen.