How does the Digestive System Work?

The digestive system is the main functional system in the human body. It helps to provide essential energy and nutrients in our body by performing ADME (Absorption, Distribution, Metabolism and Excretion) of the foods, drinks or anything we ingest. In other words, the digestive system is a series of responsible organs that help to produce energy and digest foods in a human body.

Picture of human digestive system

Organs of the Human Digestive System

Several functional and auxiliary organs are involved in the digestion of foods. Organs of the upper and lower gastrointestinal tract are directly involved in the digestion process.
  • Upper Gastrointestinal Tract: Mouth, teeth, tongue, pharynx, esophagus, and stomach.
  • Lower Gastrointestinal Tract: Small intestine, large intestine, and anus.
  • Liver, pancreas and gall bladder are also part of the digestive system, but as they indirectly involve in digestion, they're considered as auxiliary organs.

How the Digestive System Works?

When food enters into the mouth, it mixes with saliva. As the teeth break down the food into small particles, the saliva starts to dissolve the particles to form a watery mixture. The tongue then forces back these particles into the throat (pharynx). Particles in the pharynx stimulate the swallowing reflex. As a result, larynx is called upward to connect with the epiglottis and block off the trachea.

After that, the crushed food drives from the larynx to the esophagus, and travels down the esophagus by the peristalsis. As the peristaltic wave touches the esophageal sphincter, these particles enter into the stomach. The hydrochloric acid and other digestive enzymes break down the food into smaller pieces and releases nutrient. These smaller pieces are called chyme. From the stomach, they (chyme) pass through the pyloric sphincter, and enter into the small intestine (duodenum). In a digestive system, most of the tasks of absorption, distribution and metabolism are done in the small intestine.

The small intestine consists of three parts:
  1. Duodenum
  2. Jejunum
  3. Ileum
Bile from liver and digested enzymes from the pancreas enters into the duodenum to aid in digestion. Absorbed nutrients pass from the lumen of the small intestine into the blood and lymph. Finally, the undigested particle from the small intestine goes to the ileo-cecal valve and moves into the colon or large intestine. The undigested residue passes through Cecum, Ascending colon, transverse colon, descending colon and sigmoid colon. The colon of our digestive system absorbs water, produces vitamins and mucous, forms stool and defecates feces. The rectum stores feces until nervous stimulation initiates defecation reflex resulting in elimination through anal canal.

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