The digestive system describes organs and glands within the body that work together to bring about the digestion of food. With the help of these glands, the body is able to break down foods so that the nutrients within them can be absorbed into the bloodstream. After the body has taken all that it can use from the food, the digestive tract converts the remainder into waste that is eliminated from the body. Some of the more prominent organs within the digestive system include the mouth, stomach, intestines, and rectum.
Eating is the first step in digestion, and it is typically prompted by appetite. In most cases, appetite is stimulated by the reaction of salivary glands to the aroma of nearby food. Foods are first broken down within the mouth, by chewing. The swallowed food then moves through the esophagus, where it is finally deposited into the stomach. Once in the stomach, enzymes and acids work to break the food down into a liquid called chyme, so that it can easily move on to the intestines.
The intestinal portion of the digestive system includes the small and large intestines. Inside the small intestine, the pancreas, liver, and gallbladder act on food to help ease digestion and maximize nutrient absorption. A series of ducts allow these organs to interact with the contents of the small intestine. The small intestine also has millions of tiny outgrowths called villi, which help nutrients pass from the intestines into the bloodstream. Parts of foods that cannot be completely digested by the body leave the small intestine and are deposited into the large intestine.
Converting undigested food into waste is the primary function of the large intestine. This intestinal tract includes the rectum, colon, and cecum. The cecum is the part of the large intestine where the undigested food first arrives, before it moves on to the colon. Inside the colon, bacteria help transform undigested food into waste. Once foods are converted to waste, they move on to the rectum.
The body uses the rectum and anus to remove waste. Inside the rectum, waste stools are housed until they are expelled through the anus. This is brought about by both voluntary and involuntary muscle contractions that cause the stools to be pushed from the rectum out through the anal opening.
If the processes of the digestive system have gone properly, digestion typically takes about 24 hours. This tends to vary with each individual, and for some, the digestive process can take as many as 72 hours. When digestion takes longer than this, constipation usually occurs, and laxatives may be necessary to bring about evacuation.