Digestive system is one of the most important constellations of organs in the human body. This system supports the digestion, as a process of mechanical and chemical breakdown of food into smaller components. This makes it possible to absorb small particles of nutrients into the bloodstream. Basically, digestion is a form of catabolism in which the large food molecules are broken down to smaller ones.
Upper Gastrointestinal Tract
The process of digestion starts when the food enters the mouth, where it is mechanically and chemically processed by chewing and softening. The chemicals in the saliva, from the salivary glands, initiate the process of food digestion, as the enzymes in saliva break down some of the starch and fat in the food at the molecular level. Saliva is produced in and secreted from the three pairs of major salivary glands, and hundreds of minor salivary glands. It also makes the chewing easier and transforms the food into the form in which it can be easily swallowed. The food further travels down the esophagus, a narrow muscular tube about 20-30 centimeters long, and then into the stomach where it is mixed with gastric acid, pepsin and other digestive enzymes to break down.
Stomach is a hollow organ made of thick and elastic muscles. The stomach stores food and aids in the process of breaking it down. Various chemicals such as gastric acid, pepsin and other digestive enzymes reduce food content into the small particles making it much easier to absorb into the small intestine. The acids in the stomach are not capable of breaking down molecules, but they provide an optimum pH environment for the digestive enzymes, and destroy any remaining microorganisms from the food. Chyme is the product of digestion that takes place in the stomach. This is the semi-fluid mass of partially digested food. The major part of digestion takes part in the small intestines.
The food enters the small intestine trough the pyloric sphincter and into the duodenum, where it mixes with different liquids: bilin and bile acid, pancreatic juice and intestinal enzymes made by the mucosal membranes. The chyme is broken down into smaller molecules and absorbed into the circulatory and lymphatic system. The blood carries away the nutrients first to the liver, for filtering and removal of toxins, and further to every living cell in the body.
From the small intestine, food enters the large intestine. The large intestine is approximately 1.5 meters long, and it consists of the cecum, at the junction with the small intestine, the colon, and the rectum. The large intestine absorbs the water from the mass of food that has been chewed and stores the feces until they can be expelled. The feces are eliminated from the body due to the contraction and relaxation through the anus.