The digestive system, also known as the gastrointestinal tract, alimentary canal or gut, is a series of hollow organs that form a long tube from the mouth to the anus. The organs of the digestive system include the mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum and anus. The liver, gall bladder and pancreas also perform important digestive functions. The digestive system works to break down large molecules of food into smaller molecules that the body utilizes for energy.
Ingestion
The process of digestion begins with ingestion, when food is taken into the mouth.
Mechanical Digestion
The physical breakdown of food particles occurs in the mouth. The teeth masticate or chew the food into smaller bits. The tongue also aids in mechanical digestion by rolling the food to propel it toward the esophagus.
Chemical Digestion
Mechanical digestion alone cannot get the food particles small enough to be absorbed by the cells of the body. Chemical digestion utilizes enzymes secreted in the digestive juices. Several different organs along the digestive system secrete digestive juices. The mouth contains salivary glands which secrete saliva. Saliva contains water, electrolytes, mucus and enzymes. It functions to lubricate food particles as they begin their travel through the digestive system and to initiate the breakdown of starches.
Cells in the lining of the stomach secrete digestive juices, known as stomach acid because it contains hydrochloric acid. Stomach acid contains an enzyme effective in breaking down proteins.
Once in the small intestines, the contents from the stomach mix with digestive juices secreted by the small intestine and the pancreas. These contain enzymes that chemically break down carbohydrates, fats and proteins even further. The liver aids in chemical digestion by secreting bile, which binds to and dissolves the fats.
Movement
The digestive system moves food through the system of organs. Once the tongue moves food toward the esophagus, swallowing begins. Swallowing triggers involuntary movements of the muscles that line the digestive tract, known as peristalsis. The muscles, controlled by nerves, contract, creating a narrowed section that propels the food along the organ. The muscles that line the stomach aid in emptying the contents into the small intestine.
Absorption
The ultimate goal of the process of digestion is to supply cells with usable energy. Specialized cells in the small intestines absorb the molecules, including water and minerals, into the bloodstream, where they are carried to the cells throughout the body. The presence of tiny finger-like projections, called villi, along the membrane of the small intestine, increase the surface area to maximize absorption.
Elimination
The final digestive function is elimination. The large intestine, rectum and anus work together to eliminate those food molecules the body was unable to digest or absorb.
