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In this article, we would discuss the human digestive system.
The Digestive System
1. The human digestive system is complex comprising various organs and glands that breakdown food into smaller molecules that can be absorbed and assimilated into the body.
2. It comprises the mouth, esophagus, stomach, small intestine, large intestine and rectum collectively known as alimentary canal. Along with these are accessory digestive organs that include pancreas, liver and gall bladder.
3. Mouth/ Oral cavity: It is the starting point of the digestive system. The salivary glands behind the mandible (jawbone) secrete saliva (that contains amylase enzyme that helps to breakdown food) as soon as the food enters the mouth.
4. Pharynx: Also known as throat, food comes down to the pharynx from the mouth. It further branches into esophagus and trachea. It serves both the digestive and respiratory systems.
5. Esophagus: Esophagus is a muscular tube lined with mucous membrane that can contract and expand to allow passage of food into stomach. This passage is possible due to peristalsis, which is a series of wave – like muscle contractions that help in movement of the food.
6. Stomach: Muscular and hollow, it is a sac-shaped organ that resembles letter ‘J’. The food is churned into a semi-liquid mixture called chyme with the peristaltic movement. The stomach secretes hydrochloric acid (produced by parietal cells) and pepsin (main gastric enzyme) that result in breakdown of food.
7. Small Intestine: It is made up of three segments namely duodenum. jejunum and ileum and is 7 meters long. The small intestine also helps to breakdown food using enzymes released by pancreas (e.g. pancreatic amylase) and liver (e.g. bile). The food mixes with enzymes due to peristaltic movement. Small intestine is the ‘workhorse’ of digestion since the absorption of nutrients takes place here and the nutrients are directed to the bloodstream. The remnants move to the large intestine.
8. Large Intestine: Also known as colon, the large intestine is around 1.5 meters in length. It is largely responsible for processing the waste, which can be eliminated from the system. As the waste passes through the colon, any remaining water is absorbed from the system. The waste is mostly food debris and bacteria. When the colon is full of waste/faeces, it empties its contents into the rectum.
9. Rectum: It is the last segment of the large intestine that ends into anus. 6-8 inches in length, it temporarily stores faeces. When the rectum is full, its walls expand and the sensors within the wall produce the urge to defecate. The base of the rectum is controlled by a sphincter muscle. In the process of defecation, the walls of rectum contract and the sphincter muscle expands thus releasing wastes outside the body through anus.
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