Introduction
The human body is capable of making some of the vitamins and other nutrients it needs to survive on its own (such as biotin and pantothenic acid). However, most nutrients come from the food you consume on a daily basis. For these nutrients to be absorbed, the food must first be broken down through a process called digestion. Digestion allows the body to reap the necessary nutrients it needs while effectively getting rid of any left over waste product.
Chewing
Digestions starts with chewing and swallowing. Chewing breaks up the food that you eat into more manageable pieces that the body can further break down once it enters the digestive tract. Chewing also gives time for the body to produce saliva to lubricate the food and make it easier to swallow. Your saliva also contains the enzyme amylase, which starts the breakdown process of the food before it enters the stomach.
Stomach
Once the food has been chewed, it is sent down the esophagus to the stomach. The esophagus (as well as most structures associated with digestion) has layers of muscles within its walls. These muscles move the food through the different parts of the digestive system and help mix the digestive contents with other additives needed to perform digestion. As the food travels down the esophagus it hits the lower esophageal sphincter. This sphincter blocks stomach acid from traveling into the esophagus, while at the same time controls the food's ability to enter the stomach. Once the stomach is ready, the esophageal sphincter relaxes and lets the food drop into the stomach. Once in the stomach, the food will be combined with digestive juices (hydrochloric acid and enzymes) which further break down the food into smaller molecules. The muscles of the stomach also act as a mixer, helping the food break down faster. The final product of all these actions is a thick liquid called chyme.
Pancreas and Gall Bladder
Once the stomach has completed its work, the mixture is combined with liquids from the gall bladder and pancreas. The gall bladder liquid, called bile, is used to break down the fats of the food you consume. The pancreas adds liquid that breaks down the carbohydrates and proteins. This converts the fats, carbohydrates and proteins into particles that can be later used by the body to produce energy.
Intestines
Once all the digestive fluids have completed their work, the final mixture is dumped into the small intestine. The small intestine consists of a tube as long as 22 feet full of small structures called villi. Inside the villi are blood vessels with the ability to absorb needed nutrients from the chyme and put them into the bloodstream. The food that the body did not need is placed into the large intestine as waste. The tissues of the large intestines absorb any remaining water in the waste product creating a firm product called feces. After approximately 12 hours in the large intestines, the feces is sent out of the colon and out of the body through the anus.
