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Digestive system

Grade 8
Aug 19, 2022

Key Concepts

  • What is the digestive system?
  • Levels of organization
  • Parts of the digestive system
  • Functions of various parts of the digestive system


Food is essential for the body. We know that food gives us energy. The food we eat goes through our bodies. It moves from the mouth to the  stomach and is finally expelled via the anus. The whole process is done by the digestive system. The beneficial parts of food get absorbed. This helps to give our body the necessary energy and essential nutrients. 

Digestive System

Level of organization 

Levels of organization

Humans—and other complex multicellular organisms—have systems of organs that work together, carrying out processes that keep us alive. 

The body has levels of organization that build on each other. Cells make up tissues, tissues make up organs, and organs make up organ systems. 

The function of an organ system depends on the integrated activity of its organs. For example, digestive system organs cooperate to process food. 

The survival of the organism depends on the integrated activity of all the organ systems. 


At each level of organization—cells, tissues, organs, and organ systems—structure is closely related to function. For example, the cells in the small intestine that absorb nutrients look very different from the muscle cells needed for body movement. The structure of the heart reflects its job of pumping blood throughout the body, while the structure of the lungs maximizes the efficiency with which it can take up oxygen and release carbon dioxide. 

Fig 1
Fig 1

We know that the body is a system of interacting sub-systems composed of 

groups of cells. Let us discuss the digestive system and its sub-systems. 

Digestive system 

The Digestive system is a system that helps in the process of breaking down complex food into a simpler form in order to absorb nutrients. Most of the food we eat is  in insoluble form. The food has to undergo five stages of processing in order to absorb nutrients in the process of digestion. 

Organs of digestive system 

The human digestive system consists of following organs: 

Digestive System


It is the opening in the lower part of the human face, surrounded by the lips, through which food is taken. The digestive system begins with the mouth. The following processes take place in the mouth. 


Cuts the food into small bits, saliva softens the food to the pulp. Tongue helps in pushing the bits of food into the throat (food pipe). 

Esophagus (food pipe) 

The part of the alimentary canal that connects the throat to the stomach. The wall of the esophagus expands and relaxes, which makes a wave-like action to push the food to the stomach. 


A sac-like enlargement of the alimentary canal forming an organ for storing, diluting, and digesting food. Most of the food gets digested in the stomach and intestines. It secretes digestive juice like gastric juice, which breaks proteins into amino acids. Hydrochloric acid kills germs by the action of enzymes into a semi-solid state called chyme. 

Small intestine 

The narrow, winding, upper part of the intestine where digestion is completed and nutrients are absorbed by the blood. Food mixes with bile juice and pancreatic juice then enter the intestine. It gets mixed with intestinal juices that contain enzymes that help in digestion. The various enzymes it gets mixed with include proteins, amino acids by bile juice, fat and fatty acids, glycerol by intestinal juice, simple sugars by the pancreatic juice. Finger-like projections called villi absorb nutrients.  

  • Enzymes are proteins that help speed up metabolism or the chemical reactions in our bodies. 

Large intestine 

The portion of the intestine that transports waste out of the body and absorbs water from the waste before it leaves. The leftover liquid mixture of undigested food and water in the small intestine passes into the large intestine. The walls of the large intestine allow water and useful leftover substances to pass back into the blood. The moist undigested solids remain inside. 


The rectum muscles create pressure that helps in removing solid waste out of the body. 

They are joined together in a long tube called the alimentary canal.  Accessory organs, such as the liver and pancreas, also help in the process of digestion 

All these parts (sub-systems) work in coordination and digest the food. 


  • Food is essential for the body, and it gives us energy.
  • Life processes of the human body are maintained at several levels of structural organization.
  • The major levels of organization in the body, from the simplest to the most complex, are atoms, molecules, organelles, cells, tissues, organs, organ systems, and the human organism.
  • The digestive system is the group of organs that break down food in order to absorb its nutrients.
  • The digestive system includes the mouth, pharynx (throat), esophagus, stomach, small intestine, large intestine, rectum, and anus.
Digestive system


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