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Chapter 14 The Digestive System and Body Metabolism The Digestive system takes food, breaks it down into nutrient molecules and absorbs them into the blood stream and then rids the body of indigestible remains Figure 14.1 Organs of the Digestive System (DS) 1. Alimentary Canal or Gastrointestinal tract (GI tract) • Digests and absorbs • Continuous muscular hollow tube A. Mouth or Oral Cavity • Food enters – masticated (chewed) • Tonsils – located at the base of the tongue • Tongue – mixes food with saliva and initiates swallowing – taste receptors Figure 14.2a Figure 14.2b B.Pharynx (air goes through too) Peristalsis – contraction of muscles that moves food involuntary C. Esophagus (10 in) The walls of the esophagus to the intestines – four basic tissue layers Figure 14.3 D.Stomach C shaped 10 inches long Full – 4 L or 1 gallon Storage tank and site of food breakdown Gastric pits – release gastric juice Chyme – digested food – like heavy cream Figure 14.4a Figure 14.4c E. Small Intestine Major digestive organ 2 meters or 6 feet Mesentery holds in place 3 subdivisions a.Duodenum b.Jejenum c.Ileum Chemical digestion occurs in the stomach Bile (fats) from liver Pancreatin from pancreas (contains 4 enzymes) Almost all food absorption occurs in the small intestine Villi – finger-like projections that increase the surface area for absoprtion F. Large Intestine Larger diameter than Small Intestine 1.5 m or 5 ft Major Functions 1. absorbing water from undigested food 2. eliminate residues as feces 2. Accessory Digestive Organs Assist the process of digestive breakdown A. Pancreas Produces enzymes for food breakdown Located under the stomach B. Liver and Gallbladder Liver Largest organ Four Lobes Very Important Organ Produces Bile Bile Yellow to green watery solution Not an enzyme Bile salts emulsify (break down) fats Gallbladder Small thin walled green sac – attached to liver Stores bile Gallstones – bile stored too long – cholesterol crystallizes C. Salivary Glands Three pairs empty into the mouth Product – saliva Bolus – mass of food binded by mucous Salivary amylase – breaks down starch D. Teeth Masticate or chew Permanent full set – 32 teeth Impacted – tooth remains embedded in the jaw Figure 14.9 (1 of 2) Figure 14.9 (2 of 2) Tooth Two regions – crown and root Enamel – hardest substance in the body Pulp – supplies nutrients to the tooth tissues Figure 14.10 Functions of the Digestive System Major Functions Digestion and Absorption Six Processes of the GI Tract 1. Ingestion – into the mouth 2. Propulsion – movement from organ to organ (peristalsis) 3. Food Breakdown – Mechanical Digestion Mixing in the mouth Churning in the stomach 4. Food Breakdown – Chemical Digestion (breaking bonds) Sequence of steps where large food molecules are broken into small ones 5. Absorption Movement of digested end products from the GI tract to the blood Occurs in the Small intestines 6. Defecation - elimination Activities in the Mouth, Pharynx, and Esophagus Food Ingestion and Breakdown Chewing – physical breakdown Mix with saliva – chemical breakdown Pharynx and esophagus passageways Food Propulsion – Swallowing and Peristalsis Two Phases Buccal Phase – tongue forces food into the pharynx 2. Pharyngeal-Esophageal Phase 1. involuntary Coughing – forcing food out of the lungs Gravity is not involved Activities of the Stomach Food Breakdown Gastric juice released HCl makes stomach acid – pH of 2 Ulcers – stomach digests itself Heartburn – stomach acid goes into the esophagus Pepsin – digestive enzyme – activated by acid – digests protein Only protein digestion begins in the stomach Exception – Alcohol and Aspirin absorb through stomach walls Stomach fill – mechanical digestion continues – smashing the food Food Propulsion 3 mL of chyme squirted into small intestine – stops when the small intestine in is full 4-6 hours for stomach to empty after a meal Activities of the Small Intestine Food breakdown and absorption Food only partially digested Carbohydrate and protein started – no fats 3-6 hours in small intestines Pancreas secretes enzymes to the small intestines. 1. Pancreatic amylase – starch 2. Trypsin – proteins 3. Lipases – fats 4. Nucleases – nucleic acids Pancreatic Juice – Bicarbonate – pH of 8 – made of 4 enzymes Liver secretes Bile Breakdown fats and helps them be absorbed Fat soluble vitamins (K, A, D) Food absorbed a long the way End: Water, undigested food, bacteria Activities of the Large Intestine Food breakdown and absorption 12-24 hours in Large Intestine Bacteria use some of the remaining nutrients and release gas - methane (CH4) and H2SO4 500mL of gas produced a day Bacteria also make vitamins (K & B) Absorption – water, ions and vitamins Propulsion of the Residue and Defecation Peristalsis and mass movements cause defecation Typically occur after eating Diarrhea – not enough water absorbed Constipation – too much water absorbed Figure 14.11 Nutrition and Metabolism Energy value of food is measure in kilocalories (kcal) Nutrition Nutrient – substance in food that is used by the body to promote normal growth, maintenance and repair The Six Nutrients 1.Carbohydrates – sugars and starch mostly from plants – cellulose – fiber 2.Lipids – Fats, oil and waxes Saturated fats – animals, meat and dairy Unsaturated – plants, seeds, nuts, veggie oils 3. Proteins – (made of amino acids – AA’s) – animal products – Eggs, milk and meat Vitamins – organic nutrients needed in small amounts – coenzymes 5. Minerals – Ca, P, K, S, Na, Cl, Mg also needs trace amounts of others mineral rich food – veggies, legumes, milk and some meat 6. Water 4. Organic Compounds Monomers – one unit in a macromolecule Polymer – many monmers Nucleic Acids DNA and RNA Monomers – nucleic acids Lipids Three fatty acids and a glycerol Fats, oils, and waxes Carbohydrates Sugars Three Types 1. Monosaccharides 2. Disaccharides 3. Polysaccharides Examples – Glycogen – animals Starch – plants Glucose Proteins Monomers – amino acids – 20 AA held together by peptide bonds Dipeptide – 2 amino acids Organic Compound Test Positive Reagent Test Examples Carbohydrate Benedicts Orange Sugars, milk, Apple juice, glucose Carb. – Starch Iodine Black Potato, Bread Protein Biuret Purple Meat, enzymes Lipids Brown paper Grease spot Fats, oils, Waxes Metabolism All the chemical reactions that are necessary to maintain life 1. Catabolism – breaking down 2. Anabolism – building larger molecules How Food Stuffs are treated: Carbohydrates – Make ATP Fats – Cell membrane, Insulation, Fuel when no carbohydrates Proteins – hoarded – building cells Body Energy Balance When energy intake and energy outflow are balanced, body weight remains stable. Metabolic Rate and Heat Production Kilocalorie (kcal) – unit used to measure energy value of foods Carbohydrates and proteins = 4 kcal/g Fats = 9 kcal/g Basal Metabolic Rate (BMR) Amount of heat produced by the body when at rest Just what is needed for essential life activities 154 lb adult = 60-72 kcal/hr BMR – influenced by surface area and gender Thyroxine produced by the thyroid determines BMR Hyperthyroidism – lose weight Hypothyroidism – gain weight Total Metabolic Rate Total amount of kcal the body must consume to fuel ongoing activities Muscle work – causes biggest increase Body Temperature Regulation 60% of energy from food breakdown is lost as heat The blood moves the heat to all the tissues Heat Promoting Mechanisms Vasoconstriciting – blood is not sent to the skin Shivering – muscle movement – heat Frostbite – when oxygen does not go to the skin and cells begin to die Hypothermia – low body temperature, vital signs, decrease drowsy, comfortable, death The End