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Digestion of Protein

Digestion of Protein


As food containing protein enters our mouth, mucus is secreted to bind the particles together.  As the food then travels down the esophagus -the alimentary canal that connects the throat to the stomach– more mucus is secreted by the wall of the esophagus.

The gastric juices secreted in the stomach contain an enzyme precursor called pepsinogen.  As soon as pepsinogen comes in contact with hydrochloric acid in the stomach, it is converted into active pepsin. This begins the chemical digestion process of dietary protein as pepsin breaks down the proteins.

After the food is mixed and churned in the stomach, it is converted into chime – the combination gastric juices mucus, hydrochloric acid and enzymes).

The liver also plays a vital role in protein metabolism by de-aminating amino acids and forming urea nitrogen.  It also is responsible for synthesizing certain blood proteins and converting certain amino acids to other amino acids.

KETO Intestinal villi-and-absorptionThe chyme moves into the duodenum (the first section of the small intestines immediately beyond the stomach) and enzymes begin to work on the protein.  When dietary protein reaches the duodenum, a hormone called intestinal gastrin secreted in the duodenum which stimulates the gastric glands to increase secretion.

During this process, another  hormone called cholecystokinin is released from the intestinal walls, which stimulates the release of pancreatic juice.

The pancreatic juice contains protein splitting enzymes in inactive form:

  • trypsinogen,
  • chymotrypsinogen
  1. Trypsin is activated once trypsinogen comes in contact with the enzyme called enterokinase.
  2. The presence of trypsin then activates the inactive chymotrypsinogen and procarboxypeptidase.
  3. Chymotrypsinogen and procarboxypeptidase are converted into chymotrypsin and carboxypeptidase.
  4. Chymotrypsin and carboxypeptidase enzymes are then able to work on the protein.

The mucosal cells secrete an enzyme called peptidase, which splits peptide bonds into amino acids to allow for digestion.

KETO Inner wall of small intestine - villi and microvilliProtein digestion is completed in the small intestines. The interior wall of the small intestines is covered with tiny projections called the villi (plural: villus). These projections contain even smaller extensions, called microvilliVilli projections increase the surface area of the intestines and play an important part in the process of absorption of the nutrients.

Smaller particles of amino acids are absorbed into the villi, and are carried away by the blood.

Embedded in the microvilli are digestive enzymes –including sucrase, maltase, and lactase- which further break down carbohydrates into monosaccharide.



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