The alimentary canal is the digestive system which starts from the mouth, where food is ingested, and ends at the anus, where the waste is eliminated. There canal consists of six major components, namely the mouth, pharynx, esophagus, stomach, intestines and the anus. The system is also known as gastrointestinal tract, and is divided broadly into two regions, the upper gastrointestinal tract and the lower gastrointestinal tract. The tract can measure about six meters in an adult human being.
The upper tract consists of mouth, pharynx, esophagus, stomach and the uppermost part of the small intestine. The process of digestion starts at the mouth itself, where the saliva, teeth and tongue help start the process. The food then moves down into the pharynx and the esophagus. A series of muscular contraction in the esophagus, called peristalsis, forces the food into the stomach through the cardiac orifice, where the second stage of digestion starts.
Gastric juices secreted by the stomach, which contains two ferments, namely, rennet & pepsin ferment and hydrochloric acid & salt speed up the digestive process. The gastric juice, which is an antiseptic too, neutralizes the effect of saliva swallowed along with the food. The juices mix with the food and a continuous churning process involving contraction and relaxation of the stomach muscles brings the consistency of the food to a thick liquid form. The process usually takes up to four hours depending on the food swallowed.
Once the food is made into this liquid form, it is passed into the duodenum. At this stage, the food would be in an assorted mixture of undigested, partly digested and digested forms where some of the starch has been turned into sugar, some peptides turned into peptones and fats set free from the food particles. At this stage, pancreatic secretions and juices from the liver mix up with the food and further digestion would take place in the intestines.
The lower alimentary canal consists of the intestines and the anus. The small intestine is divided into three parts, the duodenum, the jejunum and the Ilium. The jejunum works as tract to transport food from duodenum to the Ilium and also aids in absorption of nutrients from the food. Once the food is in the Ilium, all soluble molecules are broken down and absorbed by blood vessels. The large intestine also is divided into three. The cecum is the connecting point where the two intestines meet. The second portion, the colon absorbs all water and salt from the digested food and the rectum is where the feces is kept for excretion through the anus.