Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones.

When food enters the mouth, its digestion starts by the action of mastication, a form of mechanical digestion, and the contact of saliva. Saliva, which is secreted by the salivary glands, contains salivary amylase, an enzyme which starts the digestion of starch in the food. After undergoing mastication 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 are 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 an hour or two in humans, 4–6 hours in dogs, somewhat shorter duration in house cats), the resulting thick liquid is called chyme. When the pyloric sphincter valve opens, chyme enters the duodenum where it mixes with digestive enzymes from the pancreas, and then passes through the small intestine, in which digestion continues. When the chyme is fully digested, it is absorbed into the blood. 95% of absorption of nutrients occurs in the small intestine. Water and minerals are reabsorbed back into the blood in the colon (large intestine) where the pH is slightly acidic about 5.6 ~ 6.9. Some vitamins, such as biotin and vitamin K (K2MK7) produced by bacteria in the colon are also absorbed into the blood in the colon. Waste material is eliminated from the rectum during defecation.

Read more about Digestion:  Digestive Systems, Overview of Vertebrate Digestion, Human Digestion Process, Digestive Hormones, Significance of PH in Digestion, Uses of Animal's Internal Organs By Humans

Other articles related to "digestion":

Holozoic Nutrition
... involves the ingestion of liquid or solid organic material, digestion, absorption and assimilation of it to utilize it ... into a simple and soluble form by various enzymes (digestion) simplified products thus formed are then absorbed (absorption) conversion of nutrient into the fluid or solid substance of the ... occurs in Humans as well, as in humans, the digestion is done through Alimentary Canal, which includes all the five processes of Holozoic Nutrition ...
Sewage Sludge Treatment - Digestion - Composting
... Both anaerobic and aerobic digestion processes can result in the destruction of disease-causing microorganisms and parasites to a sufficient level to allow the resulting digested solids to be safely applied to land ...
Sewage Treatment Plants - Sludge Treatment and Disposal - Aerobic Digestion
... Aerobic digestion is a bacterial process occurring in the presence of oxygen ... The operating costs used to be characteristically much greater for aerobic digestion because of the energy used by the blowers, pumps and motors needed to add oxygen to the process ... Aerobic digestion can also be achieved by using diffuser systems or jet aerators to oxidize the sludge ...
Mollusca - A "generalized Mollusc" - Eating, Digestion, and Excretion
... Molluscs' mouths also contain glands that secrete slimy mucus, to which the food sticks ... Beating cilia (tiny "hairs") drive the mucus towards the stomach, so the mucus forms a long string called a "food string" ...
Leech - Anatomy and Physiology - Digestion
... Bacteria in the gut were long thought to carry on digestion for the leech, instead of endogenous enzymes that are very low or absent in the intestine ... endopeptidases, the mechanism of protein digestion cannot follow the same sequence as it would in all other animals in which exopeptidases act sequentially on ... This evolutionary choice of exopeptic digestion in Hirudinea distinguishes these carnivorous clitellates from Oligochaeta ...

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