Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Digestive System and Body Metabolism  Digestion  Breakdown of ingested food  Absorption of nutrients into the blood  Metabolism  Production of cellular energy (ATP)  anabolic and catabolic cellular activities

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Organs of the Digestive System Figure 14.1

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Layers of Alimentary Canal Organs  Structure: 4 common layers throughout the system  Mucosa: innermost layer, nutrients pass through  Submucosa: connective tissue, lymph and blood vessels, nerves  Muscularis: two or three layers of smooth muscle, responsible for motility in GI tract  Serosa: outermost layer, connective tissue sheath

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Processes of the Digestive System Figure  Mechanical processing and movement: chewing, mixing  Secretion: fluid, digestive enzymes and hormones, bile, acid, alkali, mucus  Digestion: breaking down food to smallest absorbable units  Absorption: through mucosa, into blood or lymph vessels  Elimination: undigested material eliminated

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Digestive Activities of the Mouth  Mechanical breakdown  Food is physically broken down by chewing  Chemical digestion  Food is mixed with saliva  Breaking of starch into maltose by salivary amylase

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Teeth  The role is to masticate (chew) food  Humans have two sets of teeth  Deciduous (baby or milk) teeth  20 teeth are fully formed by age two

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Deglutition (Swallowing) Buccal phase  Food is formed into a bolus  The bolus is forced into the pharynx by the tongue Pharyngeal-esophageal phase  All passageways except to the stomach are blocked  Mucus-secreting cells: assist passage of food  Food motility: gravity and peristalsis

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Stomach Functions  Acts as a storage tank for food  Mechanical breakdown, chemical breakdown of protein begins  Regulates delivery of 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 Food Breakdown in the Stomach  Gastric juice is regulated by neural and hormonal factors  Presence of food or falling pH causes the release of gastrin  Gastrin causes stomach glands to produce protein- digesting enzymes (pepsinogen)  HCl makes the stomach contents very acidic  Intrinsic Factor; for absorption of Vitamin B12  Mucus: protects stomach lining from acid

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Chemical Digestion in the Small Intestine Figure 14.6  Source of enzymes: intestinal cells, pancreas, bile (made by liver) enters from the gall bladder

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Role of the Liver in Metabolism  Bile - bile salts, pigment, cholesterol, phospholipids, electrolytes  Detoxifies drugs and alcohol  Degrades hormones  Produce blood proteins (albumin and clotting proteins) and lipids  Central role in glucose metabolism  Converts NH4+ to urea for excretion  Destroys old RBCs

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Propulsion in the Small Intestine  Suspended from the posterior abdominal wall by the mesentery  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 Small Intestine  Chemical breakdown to small products amino acids, sugars, lipids  95% of food is absorbed here  Water is absorbed along entire length  End products of digestion  Most absorbed by active transport  Lipids are absorbed by diffusion

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Wall of the Small Intestine  Villi - fingerlike structures formed by the mucosa, with capillaries  Microvilli - small projections of the plasma membrane  Found on absorptive cells Figure 14.7a

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Absorption of Nutrients  Proteins and carbohydrates: active transport  Lipids: broken down and reassembled  Water: osmosis  Vitamins and minerals: assorted means Press to play Digestion animation PLAY

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Absorption of Proteins and Carbohydrates Figure 14.13

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Absorption of Fats Figure 14.14

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings 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  Remaining materials are eliminated via feces

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Large Intestine Figure 14.8

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Propulsion in the Large Intestine  Sluggish peristalsis  Mass movements  Slow, powerful movements  Occur three to four times per day  Presence of feces in the rectum causes a defecation reflex  Internal anal sphincter is relaxed  Defecation occurs with relaxation of the voluntary (external) anal sphincter

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Endocrine and Nervous Systems Regulation of Digestion  Regulation dependent on volume and content of food  Nervous system: 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 Dietary Sources of Major Nutrients  Carbohydrates  Mostly from plants  Includes sugars, starch, cellulose, glycogen (animals)  Lipids  Saturated fats from animal products  Unsaturated fats from nuts, seeds, and vegetable oils  Trans fats - hydrogenated plant oils  Cholesterol from egg yolk, meats, and milk products

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Dietary Sources of Major Nutrients  Proteins  Complete proteins – contain all essential amino acids  Most are from animal products  Plant tissues also have proteins, but do not have the needed ratios of amino acids  Vitamins  Needed as cofactors with enzymes  Found in all major food groups

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Dietary Sources of Major Nutrients  Minerals  Play many roles in the body  Most mineral-rich foods are vegetables, legumes, milk, and some meats  Water

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Carbohydrate Metabolism  The body’s preferred source to produce cellular energy (ATP)  Glucose (blood sugar) is the major digestive product and serves as fuel to make ATP Figure 14.17

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure Metabolic Pathways Involved in Cellular Respiration

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Glycolysis harvests chemical energy by oxidizing glucose to pyruvic acid Figure 6.9A GlucosePyruvic acid

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Each pyruvic acid molecule is broken down to form CO 2 and a two-carbon acetyl group, which enters the Kreb cycle Pyruvic acid is chemically groomed for the Kreb cycle Figure 6.10 Pyruvic acid CO 2 Acetyl CoA (acetyl coenzyme A)

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  enzymes convert acetyl to CO 2 and generate many NADH and FADH 2 molecules The Krebs cycle completes the oxidation of organic fuel Figure 6.11A Acetyl CoA KREBS CYCLE 2 CO 2

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Steps in the Electron Transport System Figure Set up H + gradient using energy of e- 2. Downhill flow of H + is used to make ATP

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings cell inner membrane outer membrane mitochondrion

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  An overview of cellular respiration Figure 6.8 High-energy electrons carried by NADH GLYCOLYSIS GlucosePyruvic acid KREBS CYCLE ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS Mitochondrion Cytoplasmic fluid

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Without oxygen, cells can use glycolysis alone to produce small amounts of ATP  But a cell must replenish NAD+ Fermentation is an anaerobic alternative to aerobic respiration GlucosePyruvic acid

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  In lactic acid fermentation, pyruvic acid is converted to lactic acid  NAD + is recycled  Contributes to muscle soreness GLYCOLYSIS 2 Pyruvic acid 2 Lactic acid Glucose Figure 6.15B

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Pathways of molecular breakdown Figure 6.16 Food, such as peanuts PolysaccharidesFatsProteins SugarsGlycerolFatty acidsAmino acids Amino groups GlucoseG3P Pyruvic acid GLYCOLYSIS Acetyl CoA KREBS CYCLE ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Biosynthesis of macromolecules from intermediates in cellular respiration Figure 6.17 ATP needed to drive biosynthesis PolyscaccharidesFatsProteins KREBS CYCLE Acetyl CoA Pyruvic acid G3PGlucose GLUCOSE SYNTHESIS Amino groups Amino acidsFatty acidsGlycerolSugars Cells, tissues, organisms

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Body Energy Balance  Energy intake = total energy output (heat + work + energy storage)  Energy intake from food oxidation  Proteins, carbs have 4 Cal/gm  Fats have 9 Cal/gm  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  Body weight is usually relatively stable  Energy intake and output remain about equal  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 Metabolic Rate and Body Heat Production  Basic metabolic rate (BMR) reflects the amount of energy spent per unit of time by a body at rest  Factors that influence BMR:  Body shape (height and weight), gender, body composition, age, stress, food intake, genetics  TMR = Total Metabolic Rate  Total energy spent, includes activity above BMR

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Disorders of the Digestive System  Disorders of digestive (GI) tract: lactose intolerance, diverticulosis, colon polyps  Disorders of accessory organs: hepatitis, gallstones  Malnutrition: 13% of world’s population undernourished  Obesity: epidemic in US  Eating disorders: anorexia nervosa, bulimia