The body must be regularly fed with nutrients, for several reasons. Nutrients form molecules that are needed for new body tissue during growth. Nutrient supply is also needed to replace older, worn-out tissues. The body needs nutrients, such as glucose and other sugars, as they provide energy for thousands of chemical reactions (so-called metabolic reactions) that are constantly occurring in the body.
The body gets nutrients from the food we eat when it passes through the digestive system. The digestive system consists of digestive tract and digestive glands. The digestive tract is basically a long tube extending from mouth to anus. The digestive glands, liver and pancreas produce the various chemical compounds needed to degrade the pieces of food we eat. The digestive tract and digestive glands act together as a system whose function is to receive food and to degrade it into small parts (molecules) that can be absorbed into the bloodstream.
The first part of the tract is the mouth. The front teeth is tearing or crushing pieces of food, and the back teeth slash and grind them into small pieces, mixing them with saliva. The saliva “lubricates” the food and makes chewing and swallowing easier. The tongue moves the food in the mouth and adheres it during chewing, and then it shapes the food into a ”ball” and pushes into the back of the mouth, prepared for swallowing.
The second part of the digestive tract is the muscular tube, called the esophagus. As the food is ingested, the contraction of the esophagus muscles causes food to go through the esophagus. At the end of the esophagus there is a muscle ring, an esophagus sphincter, which relaxes to pass the food into the third part of the digestive tract, the stomach. As food enters the stomach, strong gastric wall muscles smash food and form a puply mass. In addition, the stomach wall produces strong digestive juices, including hydrochloric acid.
Juices chemically decompose food to even smaller parts. The semi-processed food then passes through another muscular ring, the pyloric sphincter, and with the short tube, the duodenum, enters the fourth part of the digestive tract, a small intestine. This is an area from which the majority of nutrients are absorbed into the bloodstream.
Immediately below the liver is a gallbladder. A bile is stored and concentrated in the gallblader; it is a liquid that is produced by a liver and which mainly contains degradable products of metabolic reactions. After a meal, the bile is discharged into a small intestine and helps to digest fat. Pancreas releases additional digestive juices (enzymes) through a conduit that connects to the bile duct just before entering the small intestine.
Enzymes and other chemical compounds break the food down into molecules, i.e. parts that are small enough to pass through the small intestine wall and enter the bloodstream. Nutrients then go to the liver to store and distribute.
Behind the small intestine is the last portion of the digestive tract, the colon. Water is absorbed here from indigestible food; the result is a feces. Fesec is stored in the back of the colon, mostly in the part called the back of the colon or rectum. Finally, waste materials are released at suitable intervals through the last part of the digestive tract, a muscle ring (sphincter) called an anus.