Main Difference – Digestion vs Absorption
Digestion and absorption are two processes of the heterotrophic nutrition mode. Animals, as well as fungi, are heterotrophs that take organic carbon from outside as food. The main difference between digestion and absorption is that digestion is the mechanical and chemical breakdown of food whereas absorption is the process by which the nutrients are taken into the body of the organism. Animals ingest food using their mouths and digestion occurs inside the elementary tract. The absorption occurs in the small intestine of animals.
Key Areas Covered
1. What is Digestion
– Definition, Characteristics, Function
2. What is Absorption
– Definition, Characteristics, Function
3. What are the Similarities Between Digestion and Absorption
– Outline of Common Features
4. What is the Difference Between Digestion and Absorption
– Comparison of Key Differences
Key Terms: Absorption, Chemical Digestion, External Digestion, Internal Digestion, Mechanical Digestion, Mouth, Mucosal Epithelium, Small Intestine, Stomach
What is Digestion
Digestion is the process by which food is broken down into small nutrients, facilitating the absorption. The large insoluble molecules are broken down into small water-soluble molecules by the digestive enzymes. In animals, digestion occurs inside the body. Therefore, animal digestion is called internal digestion. Animals have a specialized organ system called the digestive system to carry out the digestion of food. They ingest food into the digestive system through the mouth. Inside the mouth, both mechanical and chemical digestion of food occurs. The mechanical digestion is achieved by the chewing. The food is chemically digested by the enzyme amylase present in the saliva. Both the mechanical and chemical digestion continue inside the stomach. A variety of digestive enzymes are secreted into the stomach to dissolve and break down carbohydrates, proteins, and lipids in food. The small intestine also secretes digestive enzymes for the further break down of the materials. Ultimately, carbohydrates, proteins, lipids, and nucleic acids in the food are broken down into monosaccharides, disaccharides, oligosaccharides, amino acids, triglycerides, and nucleotides in the small intestine. These small nutrients are absorbed by the stomach, small intestine, and the large intestine. The components of the human digestive system and their functions are shown in figure 1.
Figure 1: Human Digestive System
However, fungi do not ingest food. Instead, they secrete digestive enzymes on the external food materials. Therefore, their digestion is called the external digestion.
What is Absorption
Absorption refers to the assimilation of substances into the blood stream from the digestive tract. The small intestine is the major component of the animal digestive system where absorption takes place. The components of the digested food such as simple sugars, amino acids, fatty acids, triglycerides, and nucleotides move across the wall of the small intestine into the blood stream. In order to increase the efficiency of absorption in the small intestine, the epithelium of it contains small projections called villi. The epithelium of the villi consists of microvilli. Two types of blood vessels are involved in absorbing nutrients from the small intestine. They are the capillaries and lacteals. The nutrients absorbed by the capillaries are transported to the liver by the hepatic portal vein. Most of the products of the fat digestion are absorbed by lacteals and are released into the blood stream. The anatomy of the small intestine wall is shown in figure 2.
Figure 2: Small Intestine Wall
In fungi, the absorption of the nutrients from the externally digested food occurs through their cell wall.
Similarities Between Digestion and Absorption
- Digestion and absorption are two sequential events of the obtaining nutrients by the heterotrophs.
- Both digestion and absorption occur in animals and fungi.
- Both digestion and absorption require energy.
Difference Between Digestion and Absorption
Definition
Digestion: Digestion is the mechanical and chemical breakdown of food by the action of digestive enzymes.
Absorption: Absorption is the assimilation of substances into the bloodstream from the digestive tract.
In Animals
Digestion: The digestion occurs inside the gastrointestinal tract.
Absorption: The absorption occurs through the mucosal epithelium of the small intestine.
In Fungi
Digestion: In fungi, digestive enzymes are secreted to the external food source.
Absorption: The absorption of nutrients occurs through the cell wall.
Start
Digestion: The digestion starts in the mouth in animals.
Absorption: The absorption starts from the stomach in animals.
Occur by
Digestion: The digestion occurs by the action of digestive enzymes.
Absorption: The absorption occurs by active transport or passive transport.
Energy Requirement
Digestion: Digestion requires energy to break down food.
Absorption: Passive absorption does not require energy.
Role
Digestion: Digestion mechanically and chemically breaks down food, facilitating the absorption.
Absorption: Absorption takes nutrients from the food and releases them into the blood stream.
Conclusion
Digestion and absorption are two steps of the intake of nutrients in animals and fungi. Digestion is the mechanical and chemical breakdown of food. It facilitates absorption. In animals, digestion occurs inside the digestive system. Absorption is the assimilation of nutrients from the digestive tract to the blood stream. The small intestine is involved in the absorption of nutrients. In fungi, external digestion occurs, and nutrients are absorbed through the cell wall. The main difference between digestion and absorption is the mechanism and function of each step during the intake of nutrients into the body.
Reference:
1. “Digestive System.” InnerBody, Available here. Accessed 1 Sept. 2017.
Image Courtesy:
1. “2405 Digestive Process” By OpenStax College – Anatomy & Physiology, Connexions Web site. Available here, Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia
2. “2418 Histology Small IntestinesN” By OpenStax College – Anatomy & Physiology, Connexions Web site. Available here, Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia
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