Complete the following sentences relating to structures of the digestive system. The is connected to the GI tract and has no digestive function, but it may have a role in the defense of the body against disease. It occasionally becomes inflamed and requires removal. The frontal teeth, known as , are used when biting into an apple. The is a muscular stucture covered with many sensory receptors. It is involved with the ingestion stage of digestion. The organ that secretes digestive enzymes into the duodenum of the small intestine is called the . is a type of mechanical digestion that occurs only in the small intestine.