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CHAPTER 21 DIGESTION & NUTRITION OBTAINING AND PROCESSING FOOD Copyright © 2009 Pearson Education, Inc. Animals ingest their food in a variety of ways • Most animals have one of three kinds of diets – Herbivores, plant-eaters—cattle, snails, sea urchins – Carnivores, meat-eaters—lions, hawks, spiders – Omnivores, eating both plants and other animals—humans, roaches, raccoons, crows Copyright © 2009 Pearson Education, Inc. Overview: Food processing occurs in four stages • Food is processed in four stages – Ingestion – Digestion – Absorption – Elimination Copyright © 2009 Pearson Education, Inc. Small molecules Pieces of food Mechanical digestion Chemical digestion (hydrolysis) Nutrient molecules enter body cells Undigested material Food 1 Ingestion 2 Digestion 3 Absorption 4 Elimination Overview: Food processing occurs in four stages • Mechanical digestion breaks food down into smaller pieces – Smaller pieces are easier to swallow – Smaller pieces have more surface area exposed to digestive fluids Copyright © 2009 Pearson Education, Inc. Overview: Food processing occurs in four stages – Chemical digestion (HYDROLYSIS) breaks down large organic molecules into their components – Proteins split into amino acids – Carbohydrates into monosaccharides (including GLUCOSE) – Nucleic acids into nucleotides – Lipids into glycerol & fatty acids Why does your body need these monomers??? Copyright © 2009 Pearson Education, Inc. WHAT DOES YOUR BODY NEED FOR DIGESTION??? • Lots of WATER • And ??? Macromolecule Components Proteindigesting enzymes Protein Polysaccharide Amino acids Carbohydratedigesting enzymes Disaccharide Monosaccharides Nucleic aciddigesting enzymes Nucleic acid Nucleotides Fat-digesting enzymes Fat Glycerol Fatty acids What conditions are necessary for Digestion??? HUMAN DIGESTIVE SYSTEM Copyright © 2009 Pearson Education, Inc. Oral cavity Tongue Mouth Salivary glands Pharynx Salivary glands Mouth Esophagus Esophagus Liver Gallbladder Liver Pancreas Esophagus Stomach Sphincter Stomach Small intestine Large intestine Rectum Anus A schematic diagram of the human digestive system Sphincter Gallbladder Pancreas Small intestine Large intestine Rectum Anus Small intestine Digestion begins in the ORAL CAVITY • Teeth break up food, saliva moistens it – Salivary enzymes (CARBOHYDRASES) begin the hydrolysis of CARBOHYDRATES – Buffers neutralize acids (Need pH???) – Antibacterial agents kills some bacteria ingested with food • The tongue tastes, shapes the bolus of food, and moves it toward the pharynx Copyright © 2009 Pearson Education, Inc. Teeth Incisors Canine Premolars Molars Tongue Salivary glands Opening of a salivary gland duct “Wisdom” tooth After swallowing, peristalsis moves food through the esophagus to the stomach • The trachea conducts air to the lungs • The esophagus conducts food from the pharynx to the stomach Copyright © 2009 Pearson Education, Inc. Bolus of food Tongue Pharynx Epiglottis up Larynx up Larynx Trachea Epiglottis down Epiglottis up Larynx down Esophageal sphincter Esophagus Sphincter contracted Esophagus Sphincter relaxed Sphincter contracted Esophageal sphincter (contracted) Bolus of food Bolus of food Muscles contract, constricting passageway and pushing bolus down Muscles relax, allowing passageway to open Stomach The STOMACH stores food and breaks it down with acid and enzymes • Acid – pH 1-2 – Parietal cells secrete hydrogen and chloride ions, which combine to make HCl – Acid kills bacteria and breaks apart cells in food • Pepsinogen and HCl produce pepsin – Pepsin begins the chemical DIGESTION of PROTEIN What happens to the carbohydrate digestion that started in the oral cavity??? Copyright © 2009 Pearson Education, Inc. Esophagus Sphincter Lumen (cavity) of stomach Sphincter Small intestine Interior surface of stomach Stomach Gastrin CONNECTION: Digestive ailments include acid reflux and gastric ulcers • Acid reflux into esophagus—heartburn • Bacterial infections (Helicobacter pylori) in the stomach and duodenum can produce ulcers Copyright © 2009 Pearson Education, Inc. Bacteria Mucous layer of stomach The SMALL INTESTINE is the major organ of chemical digestion and nutrient absorption • Small intestine is named for its smaller diameter—it is about 6 meters long • Alkaline pancreatic juice neutralizes the stomach acid (pH back to 7) • Bile, made in the liver and stored in the gall bladder, emulsifies fat so it can be digested by pancreatic enzymes • Digestion of ALL molecules occurs (carbohydrates, proteins, nucleic acids, fats) Copyright © 2009 Pearson Education, Inc. Liver Bile Gallbladder Stomach Acid chyme Intestinal enzymes Pancreatic juice Duodenum of small intestine Pancreas The small intestine is the major organ of chemical digestion and nutrient absorption – Enzymes from cells of the intestine continue digestion Copyright © 2009 Pearson Education, Inc. The small intestine is the major organ of chemical digestion and nutrient absorption – Surface area forABSORPTION is increased by – Folds of the intestinal lining – Fingerlike villi Copyright © 2009 Pearson Education, Inc. Vein with blood en route to the liver Lumen of intestine Nutrient absorption Epithelial cells Muscle layers Amino Fatty acids acids and and sugars glycerol Lumen Fats Blood capillaries Large circular folds Lymph vessel Villi Blood Lymph Nutrient absorption Villi Intestinal wall Lumen of intestine Nutrient absorption into epithelial cells Microvilli Epithelial cells lining villus The LARGE INTESTINE (COLON) reclaims water and compacts the feces • Diarrhea occurs when too little water is reclaimed • Constipation occurs when too much water is reclaimed • Feces are stored in the rectum • Colon bacteria produce vitamins—biotin, vitamin K, B vitamins Copyright © 2009 Pearson Education, Inc. Large intestine (colon) Small intestine Sphincter End of small intestine Appendix Cecum Rectum Anus Unabsorbed food material NUTRITION Copyright © 2009 Pearson Education, Inc. Overview: A healthy diet satisfies THREE NEEDS • FUEL (ENERGY) to power the body • Organic Molecules to build molecules • Essential Nutrients—raw materials that animals cannot make for themselves Copyright © 2009 Pearson Education, Inc. Chemical energy (ATP) powers the body • Nutrients are oxidized inside cells to make ATP • ATP is the main energy “currency” in a cell • Proteins, carbohydrates, and fats are the main sources of dietary calories WHAT CHEMICAL REACTION USES GLUCOSE FROM CARBOHYDRATES TO PRODUCE ATP MOLECULES? Copyright © 2009 Pearson Education, Inc. Chemical energy powers the body – Basal metabolic rate (BMR) is the energy a resting animal requires each day – Metabolic rate is the BMR plus the energy needed for physical activity – Excess energy is stored as GLYCOGEN or FAT – Metabolic rates usually decrease through adulthood • So what should you do to maintain a healthy weight??? Copyright © 2009 Pearson Education, Inc. An animal’s diet must supply Essential Nutrients – Animals cannot produce eight of the 20 amino acids – These eight amino acids are essential amino acids – These eight amino acids must come from the diet Copyright © 2009 Pearson Education, Inc. CONNECTION: Vegetarians must be sure to obtain all eight essential amino acids • The eight essential amino acids can be obtained from – Animal protein – The proper combination of plant foods Copyright © 2009 Pearson Education, Inc. Essential amino acids Methionine Valine (Histidine) Threonine Phenylalanine Leucine Corn Isoleucine Tryptophan Lysine Beans and other legumes A healthy diet includes 13 vitamins and many essential minerals • Essential vitamins and minerals – Required in very small amounts – Extreme excesses can be dangerous – Excess water-soluble vitamins can be eliminated in urine – Excess fat-soluble vitamins can accumulate to dangerous levels in body fat Copyright © 2009 Pearson Education, Inc. A healthy diet includes 13 vitamins and many essential minerals • Minerals are simple inorganic nutrients usually required in small amounts – Calcium and phosphorus are required in larger amounts – Most people ingest more salt than they need, but some needed Copyright © 2009 Pearson Education, Inc. CONNECTION: Do you need to take vitamin and mineral supplements? • Recommended Dietary Allowances (RDAs) are debated • Excessive doses of vitamin A and iron can be dangerous Copyright © 2009 Pearson Education, Inc. CONNECTION: Do you need to take vitamin and mineral supplements? • Extra doses of some vitamins are recommended by the USDA – Extra B12 for people over 50 – Extra vitamin D for people with dark skin or who get little sun Copyright © 2009 Pearson Education, Inc. CONNECTION: What do food labels tell us? • Food labels indicate – Serving size – Calories per serving – Amounts of selected nutrients per serving and as a percentage of daily value – Recommendations for daily limits of selected nutrients Copyright © 2009 Pearson Education, Inc. Ingredients: whole wheat flour, water, high fructose corn syrup, wheat gluten, soybean or canola oil, molasses, yeast, salt, cultured whey, vinegar, soy flour, calcium sulfate (source of calcium). EVOLUTION CONNECTION: The human health problem of obesity may reflect our evolutionary past • Overnourishment: consuming more food energy than is needed • World Health Organization recognizes obesity as a major global health problem • Of people in the United States – 30% are obese – 35% are overweight – 15% of children and adolescents are overweight Copyright © 2009 Pearson Education, Inc. EVOLUTION CONNECTION: The human health problem of obesity may reflect our evolutionary past – Obesity leads to – – – – Diabetes Cancer Cardiovascular disease 300,000 deaths per year in the United States How might this affect the debate on HEALTH CARE REFORM in the U.S.??? Copyright © 2009 Pearson Education, Inc. CONNECTION: Diet can influence cardiovascular disease and cancer • A healthy diet may reduce the risk of – Cardiovascular disease – Cancer • Two main types of cholesterol – LDL—contributes to blocked blood vessels and higher blood pressure – HDL—tends to reduce blocked blood vessels – Exercise increases HDL levels – Smoking decreases HDL levels Copyright © 2009 Pearson Education, Inc. CONNECTION: Diet can influence cardiovascular disease and cancer • The relationship between food and health is complex • The American Cancer Society recommends – Regular exercise – A diverse diet of healthy foods with an emphasis on plant sources Copyright © 2009 Pearson Education, Inc.