Digestion of Protein

There is a process by which the body converts the ingested foods into its simpler constituents that can be easily absorbed and assimilated. This above mentioned process gives us an idea of what is digestion. Proteins are defined as the group of complex organic macromolecules containing carbon, oxygen, hydrogen, nitrogen and sulfur and are composed of one or more amino acid chains. Proteins are components of enzymes, hormones and antibodies, and therefore are very important for an organism's survival. The present article focuses its discussion on how protein is digested inside a human's body. The digestion of proteins takes place in two organs, stomach and small intestine. Let's learn what happens in each of them during protein digestion.

Digestion of Protein in Stomach

Protein digestion does not start with chewing of food in the mouth. It begins in the stomach. The stomach is especially designed for the purpose of digestion of foods. Its walls are composed of strong muscles. These muscles mix and churn the ingested food. They do it with the help of rhythmic contractions, occurring at the average rate of 3 per min. The lining of the stomach contains glands. Their function is to secrete gastric juice. It is a colorless and strong acidic liquid at a pH of 1-3. The main components of gastric juice are digestive enzymes, hydrochloric acid and mucus.

Hydrochloric acid produced in the stomach is a very strong acid. It is produced by the type of epithelial cells called parietal cells present in the lining of the stomach. HCl is so strong that it can easily digest the stomach itself. But such a destructive process is prevented from occurring by another secretion of the stomach called mucus. It protects the delicate cell lining of the stomach as well as moistens the food present there. However, the cells in the stomach lining keep getting destroyed by hydrochloric acid. It gets replaced by newer cells. According to studies, the lining of the stomach gets completely replaced every third day.

Protein digestion in the stomach occurs mainly by the action of hydrochloric acid (HCl) and enzyme called pepsin. The enzyme pepsin forms in the stomach when its precursor pepsinogen reacts with HCl. Pepsin and HCl breaks the protein bonds. The foods containing proteins are separated from each other. The proteins get separated out, which is necessary for the action of enzymes. The enzymes needed for digesting proteins are proteinases and proteases. These enzymes break down the molecules of proteins into its constituents, amino acids by a depolymerisation process called hydrolysis. It is described as a chemical reaction wherein a water molecule breaks down into hydrogen cations and hydroxide anions.

The rate of action of these protein digestive enzymes is influenced by a number of factors. Some of them are concentration and amount of the enzyme, amount of protein food needed to be digested, temperature of the food, acidity of the food, acidity of the stomach and presence of antacids or other inhibitors of digestion. The task of enzymes is to breakdown of protein molecules into simpler structures called peptones and proteose. They leave the stomach and enter the small intestine with the help of peristalsis movement of the body. It is called chyme. The entire process of protein digestion in the stomach takes about 4 hours.

Digestion of Protein in Small Intestine

The chyme first enters duodenum, which is a part of small intestine. It is a C-shaped structure about 25 centimeters long. The chyme is very acidic but here it mixes with an alkaline secretion and becomes neutral. Pancreas secrete digestive enzyme, trypsin and chymotrypsin, which reach the duodenum through bloodstream and aid in the breakdown of proteins. They break the complex protein molecules into its constituents, amino acids. They accomplish this task of breaking down by hydrolysis, described above.

The walls of the small intestine are covered with numerous finger like projections, known as villi. They increase the surface area of the small intestine by about 600 times. Each villus contains a network of blood capillaries and lymph vessels. The amino acids pass through the capillary walls, and get carried away by the blood flowing through the network. In this manner, the amino acids thus produced get absorbed, reach different body parts and finally get converted to human proteins. The human body uses proteins for building and maintaining its structures, sometimes for energy generation as well.

The above description on digestion of proteins tells you how proteins are made or converted into a form that can be used by your body. Hope, the article proved to be useful in giving you a brief idea of protein digestion.