The human body takes in nutrients from the outside world as raw materials for growth, development, and maintenance of life, but food that cannot be used directly must be digested to make it into small molecules before it can be absorbed by the body. The digestive system consists of two parts: the digestive tract and the digestive glands.
The digestive tract is a long muscular duct that extends from the oral cavity to the pharynx, esophagus, stomach, small intestine, large intestine, and to the anus. The organs that pass through include the oral cavity, pharynx, esophagus, stomach, and small intestine (duodenum, jejunum, Ileum) and large intestine (cecum, colon, rectum) and other parts.
There are two types of digestive glands: small digestive glands and large digestive glands. The small digestive glands are scattered in the walls of the digestive tract. The large digestive glands have three pairs of salivary glands (parotid gland, submandibular gland, and sublingual gland), liver and pancreas. They all use ducts to discharge secretions into the digestive tract.