The Digestive System Digestive System has four main processes: INGESTION DIGESTION ABSORPTION EXCRETION

Mouth 11 cm long Mechanical digestion - teeth, tongue, cheeks - chew and masticate food to form a “bolus” at the back of throat “pharynx” Chemical digestion – saliva (mucus –to lubricate food, the enzyme AMYLASE to break down starch (amylose)  simple sugars (maltose), and water to break food down by hydrolysis) 11 cm long

Esophagus Muscular tube Peristalsis –rhythmic movement of muscle that squeezes food along the alimentary canal. About 25 cm long

Stomach Mechanical Digestion: - Nerves sense the stretching of stomach lining and signal the strong muscles to mix the contents. Folds in the stomach are called rugae Chemical Digestion: - Digestive juices – called gastric juices is secreted by epithelial tissue that lines the stomach. Includes Hydrochloric acid, and the enzyme pepsin. Pepsin breaks down protein. Mucus is secreted by goblet cells which protects the stomach from self digestion. Chyme- is the name of the liquid that now is ready to exit the stomach About 22 cm long Cardiac Sphincter – circular muscle that prevents stomach acid and chyme from back splashing into the esophagus… if it does not work properly you may suffer from heart burn. Pyloric Sphincter – circular muscle that allows food to exit stomach when it has sufficiently been broken down.

Small Intestine –long tube, small lumen Most digestion occurs here Small intestine has 3 main parts: Duodenum Small ducts (tubes) from the pancreas, liver and gall bladder empty enzymes into this area, most of chemical digestion occurs in this 1 meter tube. Jejunum – the next area, where absorption occurs – lining of intestine is covered with villi and microcilli to increase surface area for absorption. (without these villi, the surface area would be 0.5 m2 but these specialized structures of the inner wall increase the area to 250 m2… the size of a volley ball court! 3 meters long Ilium – last segment of the small intestine – 2 meters long

The accessory Organs (don’t copy, just look) Cardiac sphincter Pyloric sphincter LIVER, GALL BLADDER, PANCREAS

Pancreas Accessory organ Food does not go through the pancreas Produces chemical enzymes (pancreatic juice) to help break down macromolecules of protein, carbohydrate and lipids. Also makes insulin which regulates the concentration of glucose (sugar) in the blood. Diabetes is a disease where the pancreas produces too much or too little insulin.

Liver Accessory organ – largest internal organ Has many jobs In digestion, it produces bile to help digest fat

Gall Bladder Accessory organ Stores bile to be released as needed Helps digest fat by emulsifying it from large globules to tiny microdroplets.

Large Intestine (Colon) –shorter length but larger in diameter. Absorbs extra nutrients & water Bacteria make Vitamin K and Vitamin B Forms wastes into solid feces Three segments: ascending, transverse and descending colon. About 152 cm long * note the appendix is located at the junction between the small and large intestine.

Rectum Stores temporarily wastes About 14 cm long

Anus Muscle that controls when wastes leaves the body (a.k.a. anal sphincter muscle)