The Digestive System and Body Metabolism Digestion Breakdown

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 p. H. 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. 7 a 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