Human digestive system chewing pieces of food into smaller and smaller pieces. This results in a much larger surface area for the action of digestive enzymes. The teeth are named after their particular roles in the process of mastication—incisors are used for cutting or biting off pieces of food; canines, are used for tearing, premolars and molars are used for chewing and grinding. Mastication of the food with the help of saliva and mucus results in the formation of a soft bolus which can then be swallowed to make its way down the upper gastrointestinal tract to the stomach. The digestive enzymes in
Development of the digestive system from four components: the septum transversum (central tendon), the pleuroperitoneal membranes, the dorsal mesentery of the esophagus, and muscular components from somites at cervical levels three to five (C3–5) of the body wall. Since the septum transversum is located initially opposite cervical segments of three to five, and since muscle cells for the diaphragm originate from somites at these segments, the phrenic nerve, which innervates the diaphragm, also arises from these segments of the spinal cord (C3, 4, and 5). The thoracic cavity is divided into the pericardial cavity and two pleural cavities for the lungs by the pleuropericardial membranes.