Digestive System

The process of digestion involves six key stages that work sequentially to break down food and extract nutrients for the body. First, **ingestion** occurs when food enters the alimentary canal through the mouth. In this stage, food is chewed and mixed with saliva, which contains enzymes that initiate the breakdown of complex molecules. From here, food leaves the mouth when the tongue and pharyngeal muscles propel it into the esophagus. This act of swallowing, the last voluntary act, is an example of **propulsion**, which refers to the movement of food through the digestive tract. **Mechanical digestion** is a purely physical process that does not change the chemical nature of the food. It includes chewing and tongue movements that help break food into smaller bpieces and mix food with saliva. In **chemical digestion**, starting in the mouth, digestive secretions break down complex food molecules into their chemical building blocks (e.g., proteins into separate amino acids). Food that has been broken down is of no value to the body unless it enters the bloodstream and its nutrients are put to work. This occurs through the process of **absorption**, which occurs primarily in the small intestine. In the small intestine, most nutrients are absorbed from the lumen of the alimentary canal into the bloodstream. During **defecation**, the final step in digestion, undigested materials are removed from the body as feces. *LICENSES AND ATTRIBUTIONS CC licensed content, Shared previously, Digestive System Processes and Regulation, Authored by: OpenStax College. License: CC BY: Attribution. License Terms: Download for free at:http://cnx.org/contents/r-g7Ewwc@4/Digestive-System-Processes-and* ## Keywords digestive system oral cavity teeth tongue sublingual salivary gland parotid submandibular pharynx esophagus diaphragm gallbladder liver stomach pancreas colon small intestine rectum appendicitis structure of the digestive system digestion of food intake absorption of nutrients removal of undigested substances