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The Digestive System and Body Metabolism Digestion Breakdown of ingested food Absorption of nutrients into the blood Metabolism Production of cellular energy (ATP) Constructive and degradative cellular activities Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Processes of the Digestive System Mechanical propulsion Secretion Digestion mechanical and chemical breakdown Absorption Elimination Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Mechanical Processing • Teeth break down food molars (12) premolars (8) canines (4) lower jaw incisors (8) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings upper jaw Stomach Functions Acts as a storage tank for food Mechanical, chemical breakdown of protein begins Delivers chyme to the small intestine Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Propulsion in the Stomach Food must first be well mixed Rippling peristalsis occurs in the lower stomach Figure 14.15 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Chemical Digestion in the Small Intestine Pancreatic enzymes digest starch, proteins, nucleic acids, fats; reset pH. Gall bladder Figure 14.6 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Propulsion in the Small Intestine Peristalsis is the major means of moving food Segmental movements Mix chyme with digestive juices Aid in propelling food Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Absorption in the Small Intestine Site of nutrient absorption into the blood Villi = Fingerlike structures on the mucosa surface Microvilli on cells All increase surface area Figure 14.7a Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Absorption of Proteins and Carbohydrates Amino acids, sugars move by active transport into blood vessels Next stop: liver, where glucose glycogen amino acids protein Excess molecules are converted to fats Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 14.13 Absorption of Fats Lipids are absorbed into lymph system, which drains into heart Emulsified with bile salts Digested into fatty acids, glycerol With bile salts, diffuse into cells Reassembled into fats, exocytosis Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 14.14 Food Breakdown and Absorption in the Large Intestine No digestive enzymes are produced Resident bacteria digest remaining nutrients Produce some vitamin K and B Release gases Water and vitamins K and B are absorbed Undigested fiber keeps materials moving and is eliminated via feces Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Control of Digestive Activity Regulation dependent on volume and content of food Nervous system: sight, smell of food, stretch receptors in stomach Hormones: Gastrin: stimulates release of gastric juice Secretin: stimulates pancreas to secrete water and bicarbonate Cholecystokinin (CCK): signals pancreas to secrete digestive enzymes Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Nutrition Carbohydrates: major energy source, simple or complex Lipids: cell components and energy sources, saturated or unsaturated Proteins: 20 amino acids Vitamins: fat soluble and water soluble Minerals: recommended daily allowance Fiber Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Food Guide Pyramid Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 14.16 Body Energy Balance Energy intake = total energy output (heat + work + energy storage) Energy intake from food oxidation Energy output Heat is usually about 60% Storage energy is in the form of fat or glycogen Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Regulation of Food Intake Mechanisms that may regulate food intake Levels of nutrients in the blood Hormones Body temperature Psychological factors Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Basal Metabolic Rate BMR– amount of heat produced by the body per unit of time at rest Factors that influence BMR Surface area Gender Age – children and adolescents have a higher BMR thyroxine from thyroid gland Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Total Metabolic Rate (TMR) Total amount of kilocalories the body must consume to fuel ongoing activities TMR increases with an increase in body activity Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings