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Digestive System Overview Oral Cavity • Composed of teeth, tongue, and salivary glands. • Oral cavity receives food. • Teeth: chewing breaks down toughconnective tissues in meat and plant fibers. • Tongue: mechanically manipulates food to assist in chewing and swallowing; also has touch, taste, and temperature receptors. • Salivary glands: produces saliva that that lubricates mouth and food; also controls the amount of oral bacteria in mouth. Oral Cavity Pharynx • “Back of throat” • Passageway for food, liquid and air. • Leads to the esophagus and trachea. Esophagus • Muscular tube that transports food to the stomach. • Posterior (behind) to the trachea. Stomach • Temporary storage of food • mechanical breakdown of food • produces acids and enzymes that break chemical bonds in food Small Intestine • 90% of nutrient absorption. • About 20ft long. • Consist of villi and microvilli that help with absorption by increasing surface area. • Has three segments: Duodenum, jejunum, and ileum. Small Intestine Small Intestine Large Intestine • Reabsorbs water and compacts waste into feces. • Stores fecal matter prior to defecation • Consists of three segments: the cecum, the colon, and the rectum. Liver • All blood leaving the absorptive areas of the digestive tract flow through the liver before circulating to the rest of the body. • Extracts toxins from blood. • Regulates blood sugar levels. • Remove damaged and old blood cells from circulation as well as pathogens • Produces bile, which helps neutralize chyme from the stomach before it enters the small intestine. Liver Gallbladder • Stores and concentrates bile that was made in the liver. • Releases bile into the duodenum (small intestine) Pancreas • Produces the hormone insulin, which regulates blood sugar levels. • Secretes pancreatic juice into duodenum (small intestine), which contains digestive enzymes to help chemically break down food. Pancreas How does food move through digestive tract? • Peristalsis: a series of wave-like muscle contractions that moves food to different processing stations in the digestive tract Peristalsis Sphincters • Ring-like muscles that contract to close bodily passageways and openings. • There are six found in the digestive tract. – Upper esophageal sphincter: separtes pharynx and esophagus. – Lower esophageal sphincter: (cardiac sphincter) separates esophagus and stomach – Pyloric sphincter: separates stomach and small intestine – Ileocecal valve: separates small and large intestine – Internal anal sphincter: smooth muscle that controls outflow of stool – External anal sphincter: skeletal muscle that controls outflow of stool. Sphincters