The human digestion system is comprised of several organs, which carry on the process of intake of nutritional substances, digesting them, absorbing them into the body and expelling the unneeded parts. In order to better understand the workings of the system, we shall overview the digestion process of a small meal, which includes meat (ham), wheat (bread), fat (mayonnaise), vegetables and milk (about 87% water). The process is described according to its natural order, from the mouth to the anus:
- The substances are brought into the mouth, where they are chewed and added saliva – an enzyme, which is produced by the salivary glands and speeds up the absorption of the food.
- After the initial swallowing process in the mouth, the food or liquid is pushed into the esophagus, a tube that connects the throat with the stomach and has many muscles, which push the food downward.
- Before the esophagus reaches the stomach, it must pass the esophageal sphincter, a ring muscle that allows food to pass when it is not contracted.
- In the stomach, the substances are mixed, being added with more digestive juices and are pushed slowly into the small intestine. The length of stay in the stomach differs between the different materials: carbohydrates (from the bread and the ham) will be transported faster than the proteins, while the fat is expected to remain for the longest time.
- The small intestine is responsible for most of the absorption process. It uses different enzymes for every type of nutrient, which are capable of absorbing the needed molecules and break down the molecules that the body does not need (known as fibers). These enzymes are produced in several organs, including the liver and the pancreas.
- After the digestion process, the nutrients are absorbed through the intestinal walls to the rest of the body. The undigested substances, waste and old cells are pushed into the colon, and from there they are eventually pushed out by a bowel movement and though the anus.
