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The human digestive system consists of the gastrointestinal tract plus the accessory organs of digestion (the tongue, salivary glands, pancreas, liver, and gallbladder). Digestion involves the breakdown of food into smaller and smaller components, until they can be absorbed and assimilated into the body.
In chemical digestion, enzymes break down food into the small compounds that the body can use. In the human digestive system, food enters the mouth and mechanical digestion of the food starts by the action of mastication (chewing), a form of mechanical digestion, and the wetting contact of saliva.
Control of the digestive system is also maintained by ENS, which can be thought of as a digestive brain that can help to regulate motility, secretion and growth. Sensory information from the digestive system can be received, integrated and acted upon by the enteric system alone. When this occurs, the reflex is called a short reflex. [4]
Intracellular digestion is divided into heterophagic digestion and autophagic digestion. [3] These two types take place in the lysosome and they both have very specific functions. [3] Heterophagic intracellular digestion has an important job which is to break down all molecules that are brought into a cell by endocytosis. [3]
The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus.The GI tract contains all the major organs of the digestive system, in humans and other animals, including the esophagus, stomach, and intestines.
It takes place either in the lumen of the digestive system, in a gastric cavity or other digestive organ, or completely outside the body. During extracellular digestion, food is broken down outside the cell either mechanically or with acid by special molecules called enzymes. Then the newly broken down nutrients can be absorbed by the cells nearby.
In the human digestive system, a bolus (a small rounded mass of chewed up food) enters the stomach through the esophagus via the lower esophageal sphincter. The stomach releases proteases (protein-digesting enzymes such as pepsin), and hydrochloric acid, which kills or inhibits bacteria and provides the acidic pH of 2 for the proteases to work.
A fourth phase of acid secretion is known as the basal state which occurs in the times between meals (interdigestive phase). The level of acid secretion during these times is regulated by body weight, individual, number of parietal cells, and time of day. Acid secretion is lowest in the morning before awakening and highest at night. [2]