Difference Between Mechanical Digestion and Chemical Digestion

The key difference between mechanical digestion and chemical digestion is that the mechanical digestion refers to the process of physical breakdown of foods into smaller particles while the chemical digestion refers to the process of chemical breakdown of foods especially by the enzymes into smaller substances that can be absorbed by the cells.

Humans are heterotrophs; hence, we depend on other sources of organic materials for food. Ingestion is the main mode of food intake of humans. Ingestion is simply the process of chewing foods in the mouth. Once we ingest foods, they go into our digestive system and subject to digestion. Digestion is the breaking down process that takes place inside the mouth, stomach and duodenum of the alimentary tract. First, the food has to be digested mechanically and then, chemically. As the food goes into the oral cavity, it is mechanically digested by the teeth and chemically digested by saliva. Moreover, the major chemical digestion occurs with enzyme secretions from different glands associated with the digestive tract in the pharynx and oesophagus. Afterwards, our blood absorbs necessary nutrients when the digested food travels through the intestine. Finally, we get rid of the undigested foods and wastes through defecation.

CONTENTS

1. Overview and Key Difference
2. What is Mechanical Digestion
3. What is Chemical Digestion
4. Similarities Between Mechanical Digestion and Chemical Digestion
5. Side by Side Comparison – Mechanical Digestion vs Chemical Digestion in Tabular Form
6. Summary

What is Mechanical Digestion?

Mechanical digestion is the breakdown of foods into small pieces physically without the involvement of any chemicals. Generally, this starts through the process called mastication as soon as we take foods into our mouth. Mastication, in simple terms, is the chewing of food using our teeth. Teeth are calcified structures inside the oral cavity, designed especially for mastication of food.

The gastroliths perform the function of mechanical digestion of food in crocodiles, ratite birds, and seals. Those are the rock-hard structures inside a crocodile’s stomach. However, other than teeth and gastroliths, peristaltic movements are also helpful for mechanical digestion of food as it passes through oesophagus, stomach, and duodenum. In the other parts of the alimentary tract also the peristalsis occurs, but not the mechanical digestion. Mechanical digestion completes at the duodenum as one of the most important aspects of feeding.

What is Chemical Digestion?

Mechanically broken down food particles consist of finely ground organic materials, which are more often composed of long and complex molecules. These molecules have to be simplified using chemical digestion in order for them to be able to absorb into the body. Digestive enzymes mainly carry out the chemical breakdown of foods. Amylase, trypsin, nuclease, protease, lipase, and collagenase are some of the major digestive enzymes. The concentrations and presence of enzymes determine the speed of chemical digestion. Different enzymes are responsible for digestion of their specific molecules (e.g. proteases for proteins; amylase for carbohydrates; lipase for lipids, etc.).

Accessory organs of the alimentary tract are vital in producing digestive enzymes. Salivary glands, gallbladder, liver, and pancreas, are the major accessory glands that produce digestive enzymes other than the stomach. Additionally, the secretion of Hydrochloric acid inside the stomach creates a very low pH acidic environment, which helps immensely for the enzymatic digestion. Chemically digested food is then ready for the absorption at the small intestine.

What are the Similarities Between Mechanical Digestion and Chemical Digestion?

• Mechanical and chemical digestion are two types of digestion processes occurring in the digestive system.
• Both these digestion processes begin in the mouth.
• These processes break foods into smaller units.

What is the Difference Between Mechanical Digestion and Chemical Digestion?

Mechanical digestion is the process of breaking foods into small pieces by chewing, grinding, swallowing and muscular movements. On the other hand, chemical digestion is the process of breaking foods in the mouth, stomach, and intestines through the use of acids and enzymes. Thus, mechanical digestion is a physical process while the chemical digestion is a chemical process. Hence, this is the key difference between mechanical digestion and chemical digestion.

Mechanical digestion begins with the chewing while chemical digestion initiates when food mixes with saliva. Therefore, this is another difference between mechanical digestion and chemical digestion. Since mechanical digestion breaks food into smaller pieces, it facilitates the chemical digestion. In contrast to mechanical process, the enzymatic digestion changes the chemical formula and more often the complex chains of the molecules are simplified in such a way that they are ready to be absorbed.

Additionally, enzymes are responsible for breaking down of specific food molecules. Hence, different places of the alimentary tract secrete different enzymes to digest food. Furthermore, mechanical digestion takes place mostly inside the mouth while the chemical digestion mostly takes place in the duodenum and stomach. This is another difference between mechanical digestion and chemical digestion. The equilibrium of both these aspects of feeding is necessary for efficient digestion, and hence for a healthy lifestyle.

The below infographic provides additional information on the difference between mechanical digestion and chemical digestion.

Summary – Mechanical Digestion vs Chemical Digestion

There are two types of digestion namely mechanical digestion and chemical digestion. Both digestion processes begin in the mouth. Mechanical digestion refers to the breakdown of food into smaller pieces by the physical means such as chewing, grinding, churning, etc. On the other hand, chemical digestion refers to the breakdown of foods chemically by enzymes into small molecules that can be absorbed into the blood. Therefore, this is the key difference between mechanical digestion and chemical digestion. Mechanical digestion is essential to facilitate chemical digestion. When mechanical digestion breaks food into small pieces, enzymes are able to hydrolyze foods into small molecules. Hence, both digestion processes are important to complete the digestion and absorption of the necessary nutrients to the body.

Reference:

1. “Digestion.” Wikipedia, Wikimedia Foundation, 18 Dec. 2018. Available here  

Image Courtesy:

1.”2426 Mechanical and Chemical DigestionN”By OpenStax College – Anatomy & Physiology, Connexions Web site.  Jun 19, 2013., (CC BY 3.0) via Commons Wikimedia  
2.”Figure 34 03 02″By CNX OpenStax  (CC BY 4.0) via Commons Wikimedia