The right of this video solely belongs to the owner (The McGraw-Hill Companies, Inc). Digestive System- The primary functions of the digestive system are the breakdown of food (called digestion) and absorption of nutrients. Digestion begins in the mouth, where the teeth break food into smaller particles during mastication. Salivary glands located near the oral cavity secrete saliva, which begins chemical digestion and keeps the food moist. As food is swallowed, the soft palate blocks the upper pharynx to prevent food from entering the nasal cavity, and multiple voluntary muscles in the face, neck, and tongue contract, pushing food particles through the pharynx. The food passes over the epiglottis, which prevents food entry into the respiratory system, and then into the esophagus, which connects the pharynx to the stomach. The one-way movement of the food mass, now called a bolus, is controlled by wave-like involuntary muscle contractions. This movement is known as peristalsis. The bolus now enters the stomach. Folds in the stomach wall called rugae allow for expansion as the stomach fills. Stomach cells secrete HCl (Hydrochloric acid), pepsinogen, and various regulatory hormones that chemically digest the bolus. Muscular contractions in the stomach churn its contents to further breakdown the bolus and mix it with stomach secretions to form a thick liquid called chyme. Chyme exits the stomach through the pyloric sphincter and enters the small intestine, the major site of nutrient absorption. The small intestine consists of three parts: the duodenum, jejunum, and ileum. Bile from the liver and digestive enzymes from the pancreas empty into the duodenum to aid in digestion. Absorbed nutrients pass from the lumen of the small intestine into blood and lymph. Chyme not absorbed in the small intestine enters the large intestine. As it passes through the cecum and ascending, transverse, descending, and sigmoid colon, water and salts are absorbed and chyme is converted into feces. The rectum stores feces until nervous stimulation initiates the defecation reflex, resulting in elimination through the anal canal.