What are the three main functions of the digestive system

The digestive system includes the digestive tract and its accessory organs, which process food into molecules that can be absorbed and utilized by the cells of the body. Food is broken down, bit by bit, until the molecules are small enough to be absorbed and the waste products are eliminated. The digestive tract, also called the alimentary canal or gastrointestinal (GI) tract, consists of a long continuous tube that extends from the mouth to the anus. It includes the mouth, pharynx, esophagus, stomach, small intestine, and large intestine. The tongue and teeth are accessory structures located in the mouth. The salivary glands, liver, gallbladder, and pancreas are major accessory organs that have a role in digestion. These organs secrete fluids into the digestive tract.

Food undergoes three types of processes in the body:

• Digestion
• Absorption
• Elimination

Digestion and absorption occur in the digestive tract. After the nutrients are absorbed, they are available to all cells in the body and are utilized by the body cells in metabolism.

The digestive system prepares nutrients for utilization by body cells through six activities, or functions.

Ingestion

The first activity of the digestive system is to take in food through the mouth. This process, called ingestion, has to take place before anything else can happen.

Mechanical Digestion

The large pieces of food that are ingested have to be broken into smaller particles that can be acted upon by various enzymes. This is mechanical digestion, which begins in the mouth with chewing or mastication and continues with churning and mixing actions in the stomach.

Chemical Digestion

The complex molecules of carbohydrates, proteins, and fats are transformed by chemical digestion into smaller molecules that can be absorbed and utilized by the cells. Chemical digestion, through a process called hydrolysis, uses water and digestive enzymes to break down the complex molecules. Digestive enzymes speed up the hydrolysis process, which is otherwise very slow.

Movements

After ingestion and mastication, the food particles move from the mouth into the pharynx, then into the esophagus. This movement is deglutition, or swallowing. Mixing movements occur in the stomach as a result of smooth muscle contraction. These repetitive contractions usually occur in small segments of the digestive tract and mix the food particles with enzymes and other fluids. The movements that propel the food particles through the digestive tract are called peristalsis. These are rhythmic waves of contractions that move the food particles through the various regions in which mechanical and chemical digestion takes place.

Absorption

The simple molecules that result from chemical digestion pass through cell membranes of the lining in the small intestine into the blood or lymph capillaries. This process is called absorption.

Elimination

The food molecules that cannot be digested or absorbed need to be eliminated from the body. The removal of indigestible wastes through the anus, in the form of feces, is defecation or elimination.

The human body uses the process of digestion to break down food into a form that can be absorbed and used for fuel. The organs of the digestive system are the mouth, esophagus, stomach, pancreas, liver, gallbladder, small intestine, large intestine and anus. Recognizing how these organs work together to digest food is key to understanding how digestion works.    

The digestive process begins in the mouth. Even before eating begins, the anticipation of eating stimulates glands in the mouth to produce saliva. The digestive system carries out three primary processes: mixing food, moving food through the digestive tract (peristalsis) and using chemicals to break down food into smaller molecules.

Consult a health care provider about specific questions regarding how digestion works and any related digestive health problems.

• Definition
  • What Is the Digestive System?
• Physiology
  • What Are the Four Main Functions of the Digestive System?
• Guide
  • What Are the Four Main Functions of the Digestive System? Topic Guide

What Is the Digestive System?

Motility, digestion, absorption and secretion are the four vital functions of the digestive system.

The digestive system breaks down the foods we eat into energy our bodies can use. 

The organs that make up the digestive tract include: 

• Mouth
• Salivary glands
• Esophagus
• Stomach
• Liver
• Gallbladder
• Pancreas
• Small intestine
  • Duodenum
  • Jejunum
  • Ileum 
• Large Intestine
  • Appendix
  • Cecum
  • Colon
  • Rectum
  • Anus

Bacteria in the gastrointestinal tract (also called gut flora or microbiome) also help with digestion, along with parts of the nervous and circulatory systems.

What Are the Four Main Functions of the Digestive System?

The main functions of the digestive system include: 

• Motility
  • Food moves through the digestive tract due to a process called peristalsis, which is the movement of muscles in the GI tract that move the food through the digestive system 
  • This involves the breakdown and mixing of ingested nutrients all the way through the elimination of undigested waste from the body
• Secretion
  • This is the release of enzymes, hormones, and other substances that help the body digest the food that is eaten
  • Hormones tell the body when to produce digestive juices and signal the brain when you are hungry or full
• Digestion
  • Ingested nutrients including proteins, fats, carbohydrates, vitamins, minerals, and water are reduced into molecules small enough to pass through the lining of the gut and so they can enter the bloodstream 
  • The digestive system breaks down foods we consume so the body can use them for energy, growth, and cell repair
    • Proteins break down to amino acids
    • Fats break down to fatty acids and glycerol
    • Carbohydrates break down to simple sugars
• Absorption
  • The digested nutrients pass from the gut into the blood so the circulatory system or lymph system can pass them on to the rest of the body to use or store 
  • The lymph system absorbs fatty acids and vitamins
  • The blood carries simple sugars, amino acids, glycerol, and some vitamins and salts to the liver
    • The liver stores, processes, and delivers these nutrients to the body when needed

Reviewed on 2/1/2021

References

https://www.niddk.nih.gov/health-information/digestive-diseases/digestive-system-how-it-works

http://www.s-hamilton.us/BiologyHomepage/Term4-98/keittreim-digestivesystem/tothe.htm

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