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The Digestive System By Dr Tajdar Husain Khan Digestive Process 1. Ingestion 2. Propulsion 3. Mechanical Digestion • Mastication • Churning food in stomach 4. Chemical digestion 5. Absorption 6. Defecation Digestion: The process of breaking food down to be used by the body. Why is digestion important? Food must be broken down in order for our body to be able to absorb all of the substances important for daily functions. Food must small enough to be absorbed into the blood and carried to the cells. Two types of digestion: Mechanical Digestion: occurs in the mouth (chewing), and in the stomach (churning of stomach muscles) Chemical Digestion: occurs through the use of enzymes (substances which chemically act on food to break it down) in saliva, the stomach, in the small intestine Organs of the Digestive System Mouth: The first step in digestion is actually getting the food into your body. Teeth: mechanically break food down into smaller pieces Saliva: softens food and chemically breaks food down further (mucin + amylase + water) Tongue: moves food around the mouth, forms a bolus (ball of food) Salivary Glands Teeth premolars GI Tract- 4 basic tunics: GI Tract (alimentary canal) 1. Mucosa- wet epithelial membrane Major function: • secretion • absorption • protection • reduce friction • protect cells from being digested 2. Submucosa- moderately dense connective tissue Contains: • blood • lymphatic vessels • scattered lymph nodules and nerve fibers Major function: • nutrition • protection 3. Muscularis externa- bilayer of smooth muscle and superficial longitudinal muscle Major function: • regulate GI motility (churning) 4. Serosa- serous membrane Major function: • reduce friction • anchor and protect the surrounding GI tract organ Organs of the Digestive System Esophagus: a hollow tube at the back of the throat that connects to the stomach. To prevent food from “going down the wrong pipe” a flap of skin called the epiglottis closes over the opening of the trachea (windpipe) when we swallow Peristalsis: muscular contractions that move food down the esophagus into the stomach. Imagine squeezing a tube of toothpaste… Stomach: a hollow, Jshaped organ located below the esophagus and above the small intestine. The stomach uses both mechanical and chemical digestion to break food particles down. Mechanical digestion: 3 layers of muscles Chemical digestion: digestive or gastric enzymes Small Intestine: responsible for absorbing nutrients from food. First 1/3 of the S.I. :Bile from the gall bladder and digestive enzymes from the pancreas and walls of the small intestine further break food down. Second 1/3 of the S.I.: contains finger-like projections called villi Villi: increase the surface area of the S.I. so that more nutrients can be absorbed into the blood stream Large intestine: “large” because it is wider in diameter than the small intestine (about 3” vs. 1”). Responsible for absorbing water from undigested food. Material found in the large intestine is mostly food that cannot be digested any further and water. Large Intestine: 3 parts Colon: Absorbs water and nutrients from food, as the material moves through the colon it gets harder and harder-turning into feces. Rectum: Stores feces. Feces move to the anus by peristalsis. Anus: Eliminates solid waste from the body Other Organs Liver: produces bile, is located to the right of the stomach. Bile: responsible for breaking down fats Pancreas: located behind the stomach, and above the small intestine. Secretes digestive enzymes Gall Bladder: stores and excretes bile