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Also known as "chymus", it is the liquid substance found in the stomach before passing through the pyloric valve and entering the duodenum. It results from the mechanical and chemical breakdown of a bolus and consists of partially digested food, water, hydrochloric acid, and various digestive enzymes. Chyme slowly passes through the pyloric sphincter and into the duodenum, where the extraction of nutrients begins. Depending on the quantity and contents of the meal, the stomach will digest the food into chyme in anywhere between 40 minutes to a few hours.
With a pH of around 2, chyme emerging from the stomach is very acidic. To raise its pH, the duodenum secretes a hormone, cholecystokinin (CCK), which causes the gall bladder to contract, releasing alkaline bile into the duodenum. The duodenum also produces the hormone secretin to stimulate the pancreatic secretion of large amounts of sodium bicarbonate, which raises the chyme's pH to 7 before it reaches the jejunum. As it is protected by a thick layer of mucus and utilizes the neutralizing actions of the sodium bicarbonate and bile, the duodenum is not as sensitive to highly acidic chyme as the rest of the small intestine.
At a pH of 7, the enzymes that were present from the stomach are no longer active. This then leads into the further breakdown of the nutrients still present by anaerobic bacteria which at the same time help to package the remains. These bacteria also help synthesize vitamin B and vitamin K.
Chyme has a low pH that is countered by the production of bile, helping to further digest food. Chyme is also part liquid and part solid: a thick semifluid mass of partially digested food and digestive secretions that is formed in the stomach and intestine during digestion.
After hours of mechanical and chemical digestion, food has been reduced into chyme. As particles of food become small enough, they are passed at regular intervals into the small intestine, which stimulates the pancreas to release fluid containing a high concentration of bicarbonate. This fluid neutralizes the gastric juice, which can damage the lining of the intestine, resulting in duodenal ulcer. Other secretions from the pancreas, gallbladder, liver, and glands in the intestinal wall help in digestion. When food particles are sufficiently reduced in size and composition, they are absorbed by the intestinal wall and transported to the bloodstream. Some food material is passed from the small intestine to the large intestine. In the large intestine, bacteria break down proteins and starches in chyme that were not fully digested. When all of the nutrients have been absorbed from chyme, the remaining waste material changes into semi solids called feces, which then passes to the rectum, to be stored until it is ready to be expelled from the body.