Organ systems 2 NCERT BIOLOGY PDF

The food after ingestion through oral cavity passes along the various parts of digestive tract, uents. The digestive tract, thus in addition to uents.

Digestion: is the process of breaking down of the complex food stuff with the help of digestive juices into simple constituents, which can be normally absorbed and assimilated in the body. The food after ingestion through oral cavity passes along the various parts of the digestive tract, where it is converted into simple absorbable constituents. The digestive tract, thus in addition to digestion is also concerned with the process of absorption. The undigested and the unabsorbed food along with the other waste products from the body and bacterial flora constitutes the faeces which is excreted out from the terminal part of the tract (anus) by act of defecation. In the human digestive system, food enters the mouth and mechanical digestion of the food starts by the action of mastication, a form of mechanical digestion, and the wetting contact of saliva. Saliva, a liquid secreted by the salivary glands, contains salivary amylase, an enzyme which starts the digestion of starch in the food. After undergoing mastication (chewing) and starch digestion, the food will be in the form of a small, round slurry mass called a bolus. It will then travel down the esophagus and into the stomach by the action of peristalsis. Gastric juice in the stomach starts protein digestion. Gastric juice mainly contains hydrochloric acid and pepsin. As these two chemicals may damage the stomach wall, mucus is secreted by the stomach, providing a slimy layer that acts as a shield against the damaging effects of the chemicals. At the same time protein digestion is occurring, mechanical mixing occurs by peristalsis, which is waves of muscular contractions that move along the stomach wall. This allows the mass of food to further mix with the digestive enzymes. After some time (typically 1-2 hours

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