Human Digestive System

Human Digestive System diagram showing mouth, oesophagus, stomach, liver, pancreas, small intestine, large intestine and more (source : Wikimedia)

Video of Human Digestion Process

Human Digestive System – see the video of human digestion process. This video is based on the science model of human digestive system. Learn how the food passes through different parts of the digestive system and gets digested.

Components of the Human Digestive System

See and learn from the science model about the human digestion process and the components of the human digestive system . These include mouth, salivary glands, oesophagus, stomach, gastric juice, liver, pancreas, gall bladder, small intestine and large intestine.

Mouth and Salivary Glands

The food is first chewed in the mouth. Enzymes are secreted by the salivary glands. This is the beginning of the process of digestion of the food. Salivary glands are present in the cheeks, under the tongue and around the jaw. Salivary enzymes include Amylase and Lysozyme. Amylase breaks down starches or complex carbohydrates. Lysozyme helps to keep the mouth free from germs. Saliva also contains mucus, which coats the food. This ensures smooth passage of the chewed food through the digestive tract.


The food, which is processed by the enzymes, travels through the oesophagus, which is the food pipe. The food then reaches stomach. Churning of the food takes place inside the stomach. The gastric glands that line up the stomach wall, produce gastric juice which is acidic. The gastric juice is made up by a combination of hydrochloric acid, water and enzymes. Hydrochloric acid in tandem with the pepsin which is the main gastric enzyme, ensures digestion of protein-rich foods like soya, eggs, meat. The acid production is facilitated by gastrin, which is a hormone, produced by certain cells lining the stomach. The stomach also produces gastric lipase, which helps in digesting fats.


The pancreas is a leaf-shaped organ, which is below the stomach. Pancreatic juices are rich in enzymes. They also contain significant amount of sodium bicarbonate, which neutralizes the acid from the stomach. Pancreatic enzymes do most of the fat digestion, secreting pancreatic lipase, esterase and phospholipase.Similarly, trypsin and carboxypolypeptidase break down proteins, and pancreatic amylase breaks down carbohydrates.


The liver produces bile, which is greenish in colour. It is stored and concentrated by the gall bladder. Bile acts like soap, breaking the bonds that hold these spheres together and turning them into tiny globules that are easily taken up by the body. Bile is not an enzyme but is is essential for the fat-digesting enzymes to work.

Small Intestine

The process of digestion gets accelerated when food enters the small intestines. It is here that secretions from the pancreas, liver and small intestines do their work. The lining of the small intestine is covered with villi, which are tiny finger-like extensions. It is here that nutrients get absorbed into the blood. Enzymes at the tips of villi have enzymes that digest protein, carbohydrates and fat. Enzymes that digest simple sugars such as lactase and sucrase, are secreted here. There are deep spaces between the villi, which are called crypts. The crypts secrete mucus, bicarbonate and water. In addition to these secretions, the cells of the small intestine also produce hormones, such as secretin and cholecystokinin. These hormones stimulate other organs to release their digestive juices.

Large Intestine

In the large intestine, the passage of the digesting food in the colon is a lot slower, taking from 12 to 50 hours until it is removed by defecation. The colon mainly serves as a site for the fermentation of digestible matter by the gut flora. The time taken varies considerably between individuals. The remaining semi-solid waste is termed feces and is removed by the coordinated contractions of the intestinal walls, termed peristalsis, which propels the excreta forward to reach the rectum and exit via defecation from the anus.


(1) This video of Human Digestive System has been created by Khula Aasmaan using the science model at Science Park, Savitribai Phule Pune University.

(2) Wikipedia

(3) Wikimedia

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