The digestive juices are the secretions of the digestive tract that break down food. They include saliva, gastric juice, pancreatic juice, bile, and intestinal juice. The digestive juices are secreted by different organs, vary widely in chemical composition, and play different roles in the digestive process. Each is constantly produced by the body in small amounts, but the presence of food as it passes through the digestive tract causes increased production and secretion.
Saliva
Digestion begins in the mouth, where the mechanical action of the teeth and tongue and the chemical action of saliva begin to break down food. Saliva is produced by the salivary glands in the mouth. It is composed primarily of water, mucus, various mineral electrolytes, and digestive enzymes including amylase, which begins the breakdown of food starches. Saliva also serves to moisten and lubricate the mouth, provide minerals to maintain tooth enamel, and reduce the level of bacteria in the mouth.
Gastric juice
Gastric juice is a nearly colorless, strongly acidic liquid secreted by the gastric glands. Its active food-dissolving ingredients are the digestive enzymes pepsin and rennin, which break down proteins, and hydrochloric acid. Gastric juice also contains mucus to protect the stomach lining from being dissolved by the acid.
Pancreatic juice
The next stop for partly-dissolved food is the duodenum, the first section of the small intestine, where it is acted upon by two digestive juices. The first is pancreatic juice, a clear fluid secreted by the pancreas, which contains a plethora of digestive enzymes including tripsin, lypase, and amylase. Tripsin breaks down protein; lypase breaks down fats. Amylase, in the duodenum as in the mouth, works by turning starch into sugar.
Bile Juice
The second digestive juice released in the duodenum is bile, also known as gall, a yellow-green fluid produced by the liver and stored in the gall bladder. Bile contains salts which emulsify the fats in the food and allow them to be absorbed through the lining of the small intestine. Bile also serves to carry waste products from the liver into the intestinal tract, where they will eventually pass from the body.
