Difference Between Ingestion and Digestion

Main Difference – Ingestion vs Digestion 

Ingestion and digestion are two actions that occur in the alimentary canal of animals. The main difference between ingestion and digestion is that ingestion is the taking of food into the body whereas digestion is the breakdown of food into small molecules that can be absorbed by the body. Ingestion can be taking food either into the mouth in animals or into the cytoplasm in protozoans. Mechanical digestion and chemical digestion are the two types of digestions. In mechanical digestion, large food particles are broken down into small food particles. This increases the surface area of food, facilitating their chemical digestion by enzymes. Chemical digestion facilitates the absorption of nutrients from the alimentary canal.

Key Areas Covered

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

Key Terms: Alimentary Canal, Chemical Digestion, Digestion, Exocrine Glands, Ingestion, Mechanical Digestion, Mouth, Phagocytosis, Pinocytosis

What is Ingestion

Ingestion is the process of taking food or another substance into the body by swallowing or absorbing it. In animals, ingestion occurs through the mouth. The ingesting substances can be either food particles, water, fluids or medicine. After the ingestion, these substances enter the alimentary canal. The chewing and the swallowing allow the ingested particles to enter the stomach through the esophagus. The mouth is also an entry point of harmful materials. Microorganisms like bacteria, viruses, and parasites as well as toxic substances may enter the alimentary canal via the mouth. The ingestion of humans is shown in figure 1.

Figure 1: Ingestion

Single-celled protozoa such as amoeba ingest food particles by endocytosis. They may use two endocytic pathways, either phagocytosis or pinocytosis. In phagocytosis, the extending pseudopodia encircle a prey or particles and engulf them into the cell. Phagocytosis is shown in figure 2.

Figure 2: Phagocytosis

In pinocytosis, food particles that are dissolved in fluids are encircled by the forming vesicles.

What is Digestion

Digestion is a process of the alimentary canal in which the food is broken down physically by teeth and chemically by enzymes into small substances that are suitable for the absorption and assimilation by the body. Digestion occurs in two ways; mechanical digestion and chemical digestion. During mechanical digestion, large food particles are broken down into small particles. Chewing in the mouth, churning in the stomach, and segmentation in the small intestine are the three events of the mechanical digestion. Ingested food is chewed inside the mouth by the action of teeth. This food is passed into the stomach through the throat and esophagus in the form of bolus. Peristalsis is the mechanism, which passes bolus through the esophagus. The churning is the squeezing and mixing up of food with the gastric juice. A major part of mechanical digestion occurs in the stomach by its muscular actions. Then, the food enters the small intestine. Mechanical digestion and propulsion of food inside the small intestine occur by the segmentation. The digestive process is shown in figure 3.

Figure 3: Digestive Process

Mechanical digestion facilitates chemical digestion by increasing the surface area of the food particles. Chemical digestion is the breaking down of high molecular weight substances into low molecular weight substances. It is driven by various enzymes secreted by the exocrine glands in the alimentary canal. Acids and bile facilitate chemical digestion. Carbohydrates, proteins, lipids, and nucleic acids are broken down into their monomeric forms during chemical digestion. Therefore, chemical digestion facilitates both absorption and assimilation of nutrients. Major enzymes which are involved in the chemical digestion is shown in figure 4.

Figure 4: Digestive Enzymes

In amoeba-like protozoa, the vesicles that surround the food particles are then fused with the lysosomes, containing digestive enzymes. The digestion occurs inside the large vesicles called phagosomes.

Similarities Between Ingestion and Digestion

• Both ingestion and digestion are the initial events that occur in the digestive tract of animals.
• Both ingestion and digestion take place in the mouth in animals.
• Both ingestion and digestion occur in single-celled organisms such as protozoa.

Difference Between Ingestion and Digestion

Definition

Ingestion: Ingestion refers to the process of taking food or another substance into the body by swallowing or absorbing it.

Digestion: Digestion refers to a process by which food is broken down into simple chemical compounds that can be absorbed and used as nutrients or eliminated by the body.

Occurrence

Ingestion: Ingestion takes place in mouth.

Digestion: Digestion takes place in mouth, stomach, and intestine.

Correspondence

Ingestion: Ingestion occurs first.

Digestion: Digestion follows ingestion.

In Protozoa

Ingestion: Ingestion in protozoa occurs by the endocytosis.

Digestion: Digestion in protozoa occurs inside vesicles in the cytoplasm.

Conclusion

Ingestion is the taking in of food particles into the body. In animals, ingestion occurs in the mouth whereas in protozoans it occurs by endocytosis. Digestion is the mechanical and chemical breakdown of food into small substances, facilitating the absorption and assimilation of nutrients by the body. This is the main difference between ingestion and digestion.

Reference:

1. Madison, N., and Jenn Walker. “What is Ingestion?” WiseGEEK, Conjecture Corporation, 8 Sept. 2017, Available here.
2. Mandal, Ananya Ananya. “What is Digestion?” News-Medical.net, 1 Apr. 2014, Available here.

Image Courtesy:

1. “207410” (Public Domain) via Pixabay
2. “Phagocytosis — amoeba” By Kate Taylor (CC0) via Commons Wikimedia
3. “2405 Digestive Process” By OpenStax College – Anatomy & Physiology, Connexions Web site. Available here, Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia
4. “Major digestive enzymes” By Stephaniegreenwood assumed, Own work assumed (based on copyright claims) (Public Domain) via Commons Wikimedia