What is the Difference Between Digestion in Stomach and Digestion in Intestine

The main difference between digestion in stomach and digestion in intestine is that the stomach is responsible for protein digestion whereas the intestine is responsible for carbohydrate and fat digestion. Furthermore, stomach performs a considerable part of mechanical digestion of food while intestine performs only a small part of mechanical digestion.

Digestion in mouth, digestion in stomach, and digestion in intestine are three major phases of the food digestion process in vertebrates.

Key Areas Covered

1. What is the Digestion in Stomach
     – Definition, Mechanical Digestion, Chemical Digestion
2. What is the Digestion in Intestine
     – Definition, Mechanical Digestion, Chemical Digestion
3. What are the Similarities Between Digestion in Stomach and Digestion in Intestine
     – Outline of Common features
4. What is the Difference Between Digestion in Stomach and Digestion in Intestine
     – Comparison of Key Differences

Key Terms

Churning, Digestive Enzymes, Digestion in Intestine, Digestion in Stomach, Digestive System, Gastric Juice, Segmentation

What is Digestion in Stomach

The digestion of stomach is the mechanical and chemical digestion of food in the stomach. The form of mechanical digestion that occurs in the stomach is churning. The contraction of muscles in the lining of the stomach is responsible for churning. It mixes food with gastric juice while breaking the food particles mechanically. Several hours of this process produces chyme, a creamy paste, which eventually enters into the intestine.

Figure 1: Protein Digestion

Gastric juice is the secretion of the stomach, which is responsible for the chemical digestion of food in the stomach. It includes pepsin, hydrochloric acid, intrinsic factor, mucus, and water. Hydrochloric acid destroys the pathogens in food by increasing the pH inside the stomach. Also, this acidic pH denatures proteins in the food while providing the optimal pH for the functioning of pepsin. Pepsin is a type of protease that breaks down proteins into small peptides. Moreover, the intrinsic factor protects vitamin B12 and facilitates its later absorption while mucus is important for the lubrication of the chyme and the protection of the stomach lining from the acidic pH. Meanwhile, water dilutes food, facilitating the mixing. Generally, the stomach keeps food inside it for about four hours and eventually, the chyme enters the small intestine.

What is the Digestion in Intestine

The digestion of intestine is the mechanical and the chemical digestion of food that occurs in the intestine. Here, the two main parts of the intestine are small intestine and large intestine. The form of mechanical digestion that occurs inside the intestine is segmentation. The contraction and the relaxation of the circular, smooth muscles in the adjacent segments of the small intestine are responsible for this movement. Segmentation pulls the content in the intestine in both directions, allowing the mixing. Also, it facilitates the physical breakdown of food particles.

Figure 2: Carbohydrate Digestion in Small Intestine

Different secretions in the intestine are responsible for the chemical digestion of food. The secretions from the liver and the pancreas mix with the chyme at the former part of the small intestine called the duodenum. Furthermore, the liver produces bile, which helps in the emulsification of fat. The secretions of the pancreas include bicarbonate, lipase, amylase, and proteases. Bicarbonate neutralizes the acidic pH of the chyme while lipase is responsible for the digestion of fat, and amylase breaks down carbohydrates. Pancreatic proteases are responsible for the further digestion of small peptides into amino acids. Also, pancreatic juice contains deoxyribonucleases and ribonucleases, which break down DNA and RNA into mononucleotides respectively.

Similarities Between Digestion in Stomach and Digestion in Intestine

• Digestion in the stomach and the digestion in the intestine are the two latter phases of the food digestion process in vertebrates.
• The mechanical digestion in both stomach and intestine are less intense than the digestion that occurs in the mouth.
• Also, both stomach and the intestine undergo chemical digestion of food more intensely than the mouth.
• Furthermore, both secrete digestive enzymes for the chemical digestion of food.
• In addition, stomach and intestine undergo peristalsis in which the propulsion of food occurs through the digestive system.
• Apart from digestion, both stomach and intestine are responsible for the absorption of nutrients.

Difference Between Digestion in Stomach and Digestion in Intestine

Definition

The digestion in stomach refers to the part of digestion, chiefly of proteins, carried on in the stomach by the enzymes of the gastric juices while the digestion in intestine refers to the digestion by the action of intestinal juices. Hence, this is the fundamental difference between digestion in stomach and digestion in intestine.

Consequence

Moreover, the stomach digests the food coming from the mouth while the intestine digests the food coming from the stomach.

Anatomy

Stomach is a muscular sac while intestine is a long, narrow, folded tube.

Storage

The stomach stores food for about four hours while intestine does not store food. Thus, this is another difference between digestion in stomach and digestion in intestine.

Mechanical digestion

Another difference between digestion in stomach and digestion in intestine is that the stomach undergoes mechanical digestion by churning while the intestine undergoes mechanical digestion by segmentation.

Secretions

Secretions is a major difference between digestion in stomach and digestion in intestine. The secretions of the stomach include pepsin, hydrochloric acid, intrinsic factor, mucus, and water while the secretions of the intestine include bile, bicarbonate ions, lipase, amylase, maltase, trypsin, peptidase, lipase, nuclease, and nucleosidase.

Type of Chemical Digestion

Proteins are digested in the stomach whereas carbohydrates and fats are digested in the intestine. Furthermore,  intestine also carries out the digestion of the rest of the proteins.

pH

Moreover, the stomach is highly acidic while the small intestine is neutral and large intestine is slightly acidic.

Absorption

Stomach absorbs water and lipid-soluble substances like alcohol and aspirin while the small intestine absorbs most of the nutrients and large intestine absorbs water, minerals, vitamins, and organic molecules. Hence, this is also difference between digestion in stomach and digestion in intestine.

Conclusion

The digestion of the stomach is responsible for the breakdown of proteins in the food while the digestion of intestine is responsible for the breakdown of carbohydrates and fat. Furthermore, the stomach performs a considerable part of the mechanical digestion by peristalsis while the intestine performs a small part of the mechanical digestion by segmentation. The main difference between digestion in stomach and digestion in intestine is the type of food digested and the type of mechanical digestion.

Reference:

1. Cornell, Brent. “Mechanical Digestion.” Available Here
2. Cornell, Brent. “Digestive Juices.” Available Here

Image Courtesy:

1. “2429 Digestion of Proteins (Physiology)” By OpenStax College – Anatomy & Physiology, Connexions Web site, Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia  
2. “Small intestine sugar enzymes” By Boumphreyfr – Own work (CC BY-SA 3.0) via Commons Wikimedia