Difference Between Mechanical and Chemical Digestion

Main Difference – Mechanical vs Chemical Digestion

Mechanical and chemical digestion are two processes that occur in the digestive system, enabling digestion, absorption, and excretion of the food. The main difference between mechanical and chemical digestion is that the mechanical breakdown of large food particles into small food particles occur in the mechanical digestion whereas the chemical breakdown of compounds with a high molecular weight into compounds with a low molecular weight occurs in the chemical digestion. Mechanical digestion occurs from mouth to the stomach while chemical digestion occurs from mouth to the intestine. A major part of both mechanical and chemical digestion occurs in the stomach.

Key Areas Covered

1. What is Mechanical Digestion
      – Definition, Mechanism, Role
2. What is Chemical Digestion
      – Definition, Mechanism, Role
3. What are the Similarities Between Mechanical and Chemical Digestion
      – Outline of Common Features
4. What is the Difference Between Mechanical and Chemical Digestion
      – Comparison of Key Differences 

Key Terms: Carbohydrates, Chemical Digestion, Intestine, Lipids, Mechanical Digestion, Mouth, Nucleic Acids, Peristalsis, Proteins, Segmentation, Stomach

What is Mechanical Digestion

Mechanical digestion is the breaking down of food into digestible particles, mainly by the teeth. This means the ingested food particles are broken down into smaller particles by the acts of chewing in the mouth, churning in the stomach, and segmentation in the small intestine. By the grinding action of teeth, the initial breakdown of food occurs in the mouth. It is also called chewing or mastication. Then the tongue pushes the mechanically digested food into the throat as bolus. The movement of these boli into the trachea is prevented by the epiglottis. The uvula prevents the entering of the bolus into the nasal cavity. These boli then travel through the esophagus to the stomach. Peristalsis is the mechanism by which the food moves through the esophagus. The rhythmic contractions and relaxation of the segments of the longitudinal smooth muscles in the wall of the esophagus are involved in the peristalsis, allowing the unidirectional movement of the food through the alimentary canal. The mechanical and chemical digestion in the alimentary canal is shown in figure 1.

Figure 1: Mechanical and Chemical Digestion

The food is gently squeezed and mixed up with digestive juice by the muscular actions of the stomach. This process is called churning. The digestive juice contains different enzymes to chemically break down the food. Both mechanical and chemical digestion of food takes place during several hours inside the stomach, producing a creamy paste called chime. The chime enters the small intestine. Segmentation is the mechanism that moves food through the small intestine. The contractions and relaxation of the circular muscles in non-adjacent segments of the intestine wall are involved in segmentation. Segmentation allows the mixing of food with the digestive juice.

What is Chemical Digestion

Chemical digestion is the process by which the compounds with high molecular weight in the food are broken down into small substances that can be absorbed by the body. It is governed by chemical substances such as enzymes, bile, and acids, which are secreted by the alimentary canal. These chemical substances are secreted into the lumen of the alimentary canal by the salivary glands, stomach, and pancreas. Carbohydrates, proteins, lipids, and nucleic acids in the food are digested by these chemical substances. The digestion of carbohydrates in the food occurs by amylase, which is secreted by the salivary glands and the pancreas. Amylase breaks down starch and glycogen into disaccharides. These disaccharides are further broken down into corresponding monosaccharides in the small intestine. The carbohydrate digestion is shown in figure 2.

Figure 2: Carbohydrate Digestion

The digestion of proteins occurs in the stomach by the action of protease enzyme, producing smaller polypeptide chains. This occurs in acidic pH. These polypeptides are broken down into amino acids by endopeptidases secreted by the pancreas. Lipid digestion occurs in the small intestine. The fat globules are emulsified by bile acids and then digested by the lipases secreted by the pancreas. The nucleic acid digestion also occurs in the small intestine by the nucleases secreted by the pancreas.

Similarities Between Mechanical and Chemical Digestion

• Both mechanical and chemical digestion promote the digestion, absorption, and excretion of the ingested food by animals.
• A major part of both mechanical and chemical digestion occurs in the stomach.

Difference Between Mechanical and Chemical Digestion

Definition

Mechanical Digestion: Mechanical digestion refers to the break down of food into digestible particles, mainly by the teeth.

Chemical Digestion: Chemical digestion refers to the process by which compounds with a high molecular weight in the food are broken down into small substances that can be absorbed by the body.

Occurrence

Mechanical Digestion: Mechanical digestion occurs from the mouth to the stomach.

Chemical Digestion: Chemical digestion occurs from the mouth to the intestine.

Major Part

Mechanical Digestion: A major part of mechanical digestion occurs in the mouth.

Chemical Digestion: A major part of chemical digestion occurs in the stomach.

Driven by

Mechanical Digestion: Mechanical digestion is driven by teeth.

Chemical Digestion: Chemical digestion is driven by enzymes.

Mechanism

Mechanical Digestion: The mechanical breakdown of large food particles into small food particles occur in the mechanical digestion.

Chemical Digestion: The chemical breakdown of compounds with high molecular weights into low molecular weight compounds occurs in the chemical digestion.

Role

Mechanical Digestion: Mechanical digestion increases the surface area for the enzymatic reactions in the chemical digestion.

Chemical Digestion: Chemical digestion enhances the absorption of the nutrients by breaking down them into small molecules.

Conclusion

Mechanical and chemical digestion are two digestive mechanisms that facilitate the absorption and excretion of food ingested by animals. Mechanical digestion is the mechanical breakdown of food into small particles. It occurs from mouth to stomach. Chemical digestion is the chemical breakdown of food into small chemical substances. It occurs from mouth to the intestine. Mechanical digestion facilitates the chemical digestion while chemical digestion facilitates the absorption of nutrients. This is the difference between mechanical and chemical digestion.

Reference:

1.“ Mechanical Digestion.” BioNinja, Available here.
2.Chandler, Stephanie. “What Is the Difference Between Bile Salts & Digestive Enzymes?” LIVESTRONG.COM, Leaf Group, 14 Aug. 2017, Available here.

Image Courtesy:

1. “2426 Mechanical and Chemical DigestionN” By OpenStax College – Anatomy & Physiology, Connexions Web site. Available here, Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia
2. “2427 Carbon Digestion” By OpenStax College – Anatomy & Physiology, Connexions Web site. Available here, Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia