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Digestion Journey of a cheeseburger http://www.flickr.com/photos/liujoanne/2172007698/in/pool-47991555@N00 What is digestion? • Digestion is the mechanical and chemical breakdown of food into usable molecules • The Alimentary Canal (GI Tract) extends from the mouth to the anus with acessory organs (liver and pancreas) • It is a 9 meter long tube • Your entire body can be thought of as a tube within a tube. • Movement through the tube is by wavelike motion called peristalsis Peristalsis (The British spelling of esophagus is “oesophagus”) Major Parts and Function of the Digestive System: • Mouth – Teeth begin digestion mechanically • Chewing (“mastication”) breaks apart food • 2 sets of teeth – Primary or “baby teeth” (20 in all) – Permanent teeth (32 in all) • Incisors for cutting • Canines “fangs” for tearing • Premolars and molars for grinding – Tooth has a crown and a root • Pulp contains the nerve and blood supply for nutrients and waste removal Tooth Diagram Digestive System – Saliva - begins chemical digestion of carbohydrates & secrete amaylase (digestive enzyme) – Tongue - Pushes food back towards throat – Palate (hard and soft) - roof of oral cavity – Palatine tonsils - lymphatic tissue – Pharyngeal tonsils (adenoids) - lymphatic – Pharynx - connects nasal and oral cavities Digestive system • Esophagus - food passageway (heartburn is caused by the effects of gastric juice on the esophagus) • Stomach - secretes gastric juices (pepsin, hydrochloric acid) which digest proteins and creates a paste of food called chyme. • Pancreas - secretes pancreatic juice which helps digest carbs, fats, and nucleic acids and proteins. Digestive system functions: • Liver has many functions. The major are: – production of bile, which helps carry away waste and break down fats in the small intestine during digestion – production of certain proteins for blood plasma – production of cholesterol and special proteins to help carry fats through the body – conversion of excess glucose into glycogen for storage (This glycogen can later be converted back to glucose for energy.) Digestive system functions: • Liver functions (continued): – regulation of blood levels of amino acids, which form the building blocks of proteins – processing of hemoglobin for use of its iron content (The liver stores iron.) – conversion of poisonous ammonia to urea (Urea is one of the end products of protein metabolism that is excreted in the urine.) – clearing the blood of drugs and other poisonous substances Digestive system functions: • Liver functions (continued): – regulating blood clotting – resisting infections by producing immune factors and removing bacteria from the blood stream – stores vitamin D • Gall Bladder – Stores bile, releases through bile duct – Bile in the gall bladder can precipitate and form solids or “stones” Digestive System functions • Small Intestine – Receives secretions from pancreas and liver,completes digestion of nutrients in chyme, absorbs products of digestion through fingerlike projections called villi; transports residues to large intestine – 3 major sections • Duodenum • Jejunum • Ileum – Connected by mesentery which suspends these portions from abdominal wall Digestive System Components • Large Intestine – Absorbs water and electrolytes from chyme, forms and stores feces – Cecum = beginning of large intestine – Appendix - small closed part, no longer serves a digestive function, but contains lymphatic tissue – Colon - 4 sections • • • • Ascending colon, begins at cecum Transverse colon Descending colon Sigmoid colon Digestive System • Rectum – Last part of large intestine • Anus – Expels waste - two sphincter muscles guard the anus (one under involuntary control ,the other, and final one, is under voluntary control) Nutrients • 4 major nutrients – Carbohydrates - supply energy (1 calorie per gram) – Lipids - supply energy for cellular processes and for building cells, stores energy (9 calories per gram) – Proteins - control metabolic rates, clotting factors, keratin of skin and hair, source of energy (1 calorie per gram) Vitamins • Organic compounds required in small amounts for normal metabolic processes. Must come from foods. • Vitamins A,C,D, and E appear to have anticancer effects. Most vitamins function as coenzymes to help an enzyme accomplish a function • Fat soluble - A,D,E,K • Water-Soluble - Thiamin, Riboflavin, C, Niacin, B6, Folate, B12, Biotin, Pantothenic acid Vitamins • A for healthy eyes, skin, bones and hormone synthesis • C for collagen, detoxification • Folate needed for DNA and RNA metabolism • Niacin, Biotin, Thiamin needed for energy metabolism Minerals • Concentrated in bones and teeth • Major minerals are calcium and phosphorous • The body needs 7 - potassium, sulfur, sodium, chloride and magnesium in addition to trace amounts • Fats and sugars have few minerals. Minerals • Phosphorus needed for bone and tooth formation • Magnesium needed for bone, tooth, and enzyme formation • Sulfur needed for cartilage, tendon, and proteins • Sodium needed for nerve impulse transmission • Potassium - nerve function • Chloride - gastric juices and electrolyte balance More Minerals • • • • • • • • Iron - for hemoglobin Iodine for thyroid function Fluoride - for bones and teeth Zinc for insulin, sperm production Selenium is an antioxidant Copper helps produce hemoglobin Chromium for energy metabolism Manganese and molybdenum are components of enzymes