Human Digestive System & Nutrition

Human Digestive System and Nutrition is the process of intake of food by an organism and its utilization for energy. This is a vital process which helps living beings to obtain their energy from various sources. The food which we eat undergoes a lot of processing before the nutrients present in them are utilized to generate energy. Humans and other animals have specialized organs and system for this. Let’s go through nutrition in humans and the human digestive system in detail.

What makes up the digestive system?

The digestive system comprises of a  group of organs that work together in converting food into energy and other basic nutrients to power the body. The food we take in is digested and utilized by our body and the unused parts of the food are defecated. The human digestive system is the sum of the gastrointestinal tract (GIT; also called alimentary canal) and accessory organs (tongue, liver, pancreas, etc). These two parts together help in digestion.

The alimentary canal is the long tube through which the food that we eat is passed. It begins at the mouth (buccal or oral cavity), passes through the pharynx, esophagus or food pipe, stomach, small intestines, large intestines, rectum and finally ends at the anus. The food particles get digested gradually as they travel through various compartments of the alimentary canal. Accessory organs are organs which participate in the digestion process but are not actually a part of GIT. They stimulate the digestion by releasing certain enzymes that help in breaking down the food.

Human digestive system

Human digestive system

Mouth and the Buccal Cavity

The process of digestion begins in the mouth where food is mixed with saliva and chewed. It is broken down into small chunks before being swallowed. The mouth is also known as the buccal cavity or the oral cavity. The mouth has many accessory organs such as the tongue, teeth, and salivary glands, which help in the digestion of food. Teeth grind the food into small pieces. Salivary glands secrete saliva which contains an enzyme called the salivary amylase. This enzyme breaks down starch content and moistens the food, before the tongue and other muscles push the food into the pharynx.


The pharynx passes the chewed food into the esophagus from the mouth. The epiglottis is a flap of tissue present in pharynx and it prevents food from entering into the windpipe.

Esophagus or Food Pipe

The esophagus is a muscular tube connecting the pharynx to the stomach. It carries swallowed masses of chewed food along its length and pushes it down to the stomach.


The stomach is a thick-walled muscular bag that is located on the left side of the abdominal cavity. It is the largest part of the human digestive system. Food takes time to digest, hence the stomach acts as a storage tank. It receives food from the food pipe at one end and opens into the small intestine at the other end. The inner walls of the stomach consist of the gastric glands which secrete mucus, hydrochloric acid, and digestive enzymes that help to digest the food.

Mucus protects the lining of the stomach while acid kills bacteria that enter the body along with the food. Hydrochloric acid also makes the medium in the stomach, acidic which helps the digestive enzymes like pepsin to act. The digestive enzymes break down proteins into simpler substances.

Small Intestine

The small intestine is the longest part of the human digestive system. It is a highly coiled long, thin tube which is about 7.5 meters in length. The length of the small intestine depends on the diet of the organism. A major proportion of digestion takes place in the small intestines. All types of nutrients are digested here with the help of secretions which it receives from the liver and the pancreas. The walls of the small intestine also secrete juices for digesting food.

The liver releases bile juice which alkalizes the acidic food received from the stomach and also emulsifies the fat content. The pancreatic juice digests the proteins and lipids. Finally, the intestinal secretions convert the carbohydrates into glucose, proteins to amino acids and fats into fatty acids and glycerol.

Once the food is broken down into the simple particles, it is ready to be absorbed by the body. The villi, finger-like projections present on the walls of the small intestine, absorb the digested food by increasing the surface area. The absorbed food is then transported to different parts of the body through the blood vessels for cell activities.

Large Intestine

The large intestine is a long, thick tube which is about 1.5 meters long. The primary role of the large intestine is to absorb water and residual nutrients from the nearly-digested food. This is done with the help of many symbiotic bacteria residing in the gut. The remaining waste passes into the rectum, where it remains as semi-solid feces. Feces exit the body through the anus via time-to-time excretion. This process of expelling toxic, undigested food from the body is called egestion .

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Practise This Question

The bicuspid valve is the inflow valve for the right ventricle.