Many of us, who have no specialized knowledge about biology or who have forgotten the minute details of how and where food travels, should read this article to find out. Biological research has advanced so far that we can see the tiny cells lining our digestive cavity magnified a 100000 times. If what we see is not fascinating enough, then what these minuscle digestive cells have the ability to do to our steaks and hamburgers is surely awe-inspiring.
The minimum 4 hour journey of food, starting from the mouth, down the oesophagus, churning and mixing in the stomach to breaking down and absorption in the intestines, with waste taken to the rectum, ends with excretion of undigested food. In order to keep the details of each type of specialized cell functioning here, the description starts from the stomach. The stomach wall is lined with strong muscle. Like the rest of the digestive tract, the epithelial (or the first level) cells are mainly for secretion of mucus, in order to help the passage of food. Then there are three types of gland cells (which secrete enzymes and other chemicals needed for food digestion): 1) chief cells- which secrete pepsinogen; the main function of the stomach is to break down proteins in the food we eat, and that is carried out by pepsin. 2) parietal cells- which produce HCL (acid) that is used to neutralize the chemicals inside the stomach and kill bacteria, as well as to create the right pH for enzymes to work in. We often hear of 'acidity' in the stomach. This may be due to imbalance between acid/alkaline quantity in the stomach. 3) neck mucous cells- which are involved in the production of mucus. In addition to that, the stomach contains lymphatic cells and plasma cells to fight any 'foreign' agents inside the stomach.
Moving down to the duodenum or the upper half of the small intestine, there is a main type of cell we should be familiar with. The walls of the ileum are lined with finger-like projections called 'villi'. These projections have an ample supply of blood vessels and connections to the liver in order to transport digested food to its correct location. Microvilli, or smaller versions of these villi are on the surface of each on to increase the surface area and make digestion more efficient. Villi are aided in their apsorption and digestion of food molecules by goblet cells which release mucus to protect against friction and stress within the intestine walls.
Then into the large intestine, the first thing to know is that there are no villi. Food that hasn't been digested is converted into faeces here and unused water and nutrients are absorbed back into the body. After a brief period of storage in the rectum, faeces are removed from the body through the anus.
The main functions and specialized treatment of food is carried out in the stomach and small intestine. These are aided by accessory organs such as the pancreas, gall bladder and the liver which release the required hormones and enzymes needed to break down food and absorb the necessary proteins, glucose and fats and oils into the body.