Part 1 Food Nutrients: Structure, Function, Digestion, Absorption, and Assimilation - PowerPoint Presentation

1. Part 1 Food Nutrients: Structure, Function, Digestion, Absorption, and Assimilation1

2. Chapter 3Nutrient Digestion and Absorption2

3. Food Nutrient Digestion and AbsorptionThe Digestive ProcessDigestion = mechanical and chemical food breakdown of food for absorption into blood for use, storage, or chemical changeRequires 24 to 72 hoursUnder involuntary controlANS controls GI: PNS increases gut activity: SNS inhibits activityProteins and CHO degrade and enter intestinal villi for absorptionBile emulsifies lipids, hydrolyze or degrade them for absorption3

4. Food Nutrient Digestion and AbsorptionBeginning of DigestionDigestion begins with smell and tasteIn mouth, texture and temperature combine with odors to produce perception of flavorFlavor, sensed through smell, signifies what we eatFour Hormones Regulate DigestionGastrin, secretin, cholecystokinin (CCK), and gastric inhibitory peptide (GIP)4

5. Food Nutrient Digestion and AbsorptionFour Hormones Regulate DigestionGastrinSecretinCholecystokinin (CCK)Gastric inhibitory peptide (GIP)Digestive SecretionsOrganTarget OrganSecretionActionSalivary glandsMouthSalivaCHO breakdownGastric glandsStomachGastric juiceMixes with foodPancreasSmall intestinePancreatic juiceDegrades CHO, fats, proteinLiverGallbladderBileStored until neededGallbladderSmall intestineBileEmulsifies fatIntestinal glandsSmall intestineIntestinal juiceDegrade CHO, fats, protein5

6. Food Nutrient Digestion and Absorption Transporting Nutrients Across Cell MembranesTwo process maintain nutrient transportPassive transport through plasma membranes without requiring energyActive transport through plasma membrane, which requires metabolic energy to “power” nutrient exchange6

7. Food Nutrient Digestion and AbsorptionPassive TransportFour TypesSimple diffusionFacilitated diffusionOsmosisFiltration7 FIGURE 3.1 A. Simple diffusion. B. Facilitated diffusion. C. Osmosis. D. Filtration

8. Food Nutrient Digestion and AbsorptionActive TransportSodium-potassium pumpMoves food through semipermeablemembranesRequires energy8FIGURE 3.2 The dynamics of the sodium–potassium pump

9. Food Nutrient Digestion and AbsorptionActive TransportCoupled transportMovement in one directionRequires a cotransporter (symport)9FIGURE 3.3 Coupled transport. A molecule of glucose and a sodium ion move together in the same direction through the plasma membrane in a symport protein

10. Food Nutrient Digestion and AbsorptionBulk TransportEnergy-requiring processesExocytosis: transfers substances through cell membranesEndocytosis: cell’s plasma membrane surrounds substance, pinches away and moves into cytoplasmTwo formsPinocytosis Phagocytosis10

11. Gastrointestinal Tract Anatomy FIGURE 3.4 Structures of the gastrointestinal tract and each structure’s digestive function11

12. Gastrointestinal Tract Anatomy Sphincters Control Food Passage12FIGURE 3.5 Propulsion of nutrients through the GI tract. A. Peristalsis involves the reflex-controlled alternate contraction and relaxation of adjacent segments of the GI tract, which causes one-directional flow of food with some mixing. B. Segmentation contractions involve the alternate contraction and relaxation of nonadjacent segments of the intestine. This localized intestinal rhythmicity propels food forward and then backward, causing food to mix with digestive juices

13. Gastrointestinal Tract AnatomyStomach and Gastric Gland Structures13FIGURE 3.6 Stomach and gastric gland structure. The parietal cells primarily secrete hydrochloric acid, neck cells secrete mucus, and chief cells produce pepsinogen

14. Gastrointestinal Tract AnatomyStomachVolume averages about 1.5 litersExpands to 50 milliliters (1.5 oz) when empty to ~6 liters when distended following a large mealContents mix with chemical substances to produce chymeFollowing meal, stomach usually takes 1 to 4 hours to empty depending on nutrient concentration and volumeCan retain a high-fat meal for up to 6 hours before small intestine absorbs it14

15. Gastrointestinal Tract AnatomySmall IntestineThree sectionsDuodenumJejunumIleumNinety percentage of all digestion occurs in the duodenum and jejunumAbsorption takes place in villi of intestinal mucosa15

16. Gastrointestinal Tract AnatomySmall IntestineMicroscopic structure of small intestine showing villi and microvilli projections16FIGURE 3.7 During digestion, bile produced in the liver and stored and secreted by gallbladder increases lipids’ solubility and digestibility through emulsification

17. Gastrointestinal Tract AnatomyLarge Intestine (Colon or Bowl)Includes cecum, colon, rectum, anusIncludes cecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, anusServes as a storage area for undigested food residue (feces)Absorbs water and electrolytes FIGURE 3.8 The large intestine, a 5-foot-long tube, includes the cecum, colon, rectum, and anal canal. As chyme fills the cecum, a local reflex signals the ileocecal valve to close, preventing material from re-entering the ileum and small intestine17

18. Digestion of Food Nutrients Carbohydrate, Protein, and Lipid Digestion18FIGURE 3.9 Overview of human digestion showing the major enzymes and hormones that act on proteins, lipids, and carbohydrates during their convoluted journey from the mouth through the GI tract

19. Carbohydrate Digestion and AbsorptionIn the mouth, salivary amylase degrades starch to simpler disaccharidesPancreatic amylase continues CHO hydrolysisThree enzymes on the brush border complete final stage of CHO digestion to monosaccharidesMaltaseSucraseLactase19

20. Lipid Digestion and AbsorptionIn the mouth, lingual lipase begins lipid digestion of short-chain and medium-chain SFAGastric lipase continues TG breakdown in the stomachLipid breakdown occurs in small intestineLipid breakdown occurs by emulsifying action of bile and hydrolytic action of pancreatic lipaseCholecystokinin (CCK) releases from duodenumGastric inhibitory peptide and secretin released in response to high lipid content20

21. Lipid Digestion and Absorption Fatty Acid Carbon Chain Length Affects Digestive and Metabolic ProcessesMedium-chain triacylglycerols (MCT)MCT rapidly absorb into the portal veinBound to glycerol and medium-chain free fatty acidsBypasses lymphatic system and enters bloodstreamSupplements have clinical application for patients with tissue-wasting disease or with intestinal malabsorption difficulties21

22. Lipid Digestion and Absorption Fatty Acid Carbon Chain Length Affects Digestive and Metabolic ProcessesLong-chain fatty acids (LCFA)LCFA absorbed by intestinal mucosa reform into TGs to form chylomicronsChylomicrons move through lymphatic system and empty into venous bloodLipoprotein lipase allows chylomicrons to hydrolyze to FFA and glycerol22

23. Lipid Digestion and AbsorptionFIGURE 3.10 Digestion of dietary lipids23

24. Protein Digestion and AbsorptionPepsin initiates protein digestion in stomachGastrin stimulates secretion of gastric hydrochloric acidAcidification of ingested food achieves five objectivesActivates pepsinKills pathogenic organismsImproves absorption of iron and Ca++Inactivates hormones of plant and animal originDenatures food proteins, making them more vulnerable to enzyme action24

25. Protein Digestion and AbsorptionAmino Acids in LiverOne of three events occurs when AA reach liverConverts to glucose (glucogenic AA)Converts to fat (ketogenic AA)Releases directly into the bloodstream as plasma proteins or as free AA25

26. Vitamin AbsorptionOccurs mainly by the passive process of diffusion in the jejunum and ileum26

27. Vitamin AbsorptionLipids absorb fat-soluble vitaminsOnce absorbed, chylomicrons and lipoproteins transport vitamins to the liver and fatty tissuesWater-soluble vitamins diffuse into the blood except for vitamin B12B12 combines with intrinsic factor from stomach and absorbs it via endocytosisWater-soluble vitamins pass into urine when their concentration exceeds renal capacity for reabsorption27

28. Mineral AbsorptionFat-soluble vitamins absorbed with lipidsOnce absorbed, chylomicrons and lipoproteins transport vitamins to liver and fatty tissuesWater-soluble vitamins diffuse into blood, except for vitamin B12B12 combines with intrinsic factor from stomach and absorbs via endocytosisWater-soluble vitamins pass into urine when concentration exceeds renal capacity for reabsorption28

29. Mineral AbsorptionExtrinsic (dietary) and intrinsic (cellular) factors control mineral absorptionMineral availability in the body depends on chemical formExcessive dietary fiber negatively impacts mineral absorptionConsuming recommended daily 30 to 40 grams of fiber eliminates this concern29

30. Mineral AbsorptionFIGURE 3.11 Absorption of minerals and their common excretion pathways30

31. Water AbsorptionMajor absorption of ingested H2O and that contained in foods occurs by the passive process of osmosis in the small intestineIntestinal tract absorbs about ~9 liters of H2O daily72% absorbed in proximal small intestine 20% absorbed from distal segment of small intestine 8% absorbed from large intestine31

32. Water Absorption FIGURE 3.12 Estimated daily volumes of water that enter the small and large intestines of a sedentary adult and the volumes absorbed by each component of the intestinal tract32

33. PA Effects on Gastrointestinal FunctionsAlters blood flow dynamicsDifferent modes, intensities, and durations of PA acutely affect GI functionsModeLight-to-moderate intensity running results in faster fluid GER than cyclingIntensityWide variability in GER at less than max intensities impacted by PA type, training status, timing of ingestionDurationNo duration effects33

34. Health Status, Emotional State, and GI Tract DisordersGI DisordersConstipation: delay in stool movementDiarrhea: loose, watery stoolsDiverticulosis: small pouches that bulge through tissue FIGURE 3.13 Diverticulosis and diverticulitis. Diverticula are pockets that develop in the colon wall. These small pouches bulge outward through weak spots in the colon wall34

35. Health Status, Emotional State, and GI Tract DisordersGI DisordersHeartburn/reflux: sphincter between esophagus and stomach involuntarily relaxes so stomach’s contents flow back into esophagusChronic heartburn develops into Gastroesophageal Reflux Disease (GERD)35

36. Health Status, Emotional State, and GI Tract DisordersGI DisordersIrritable Bowel Syndrome (IBS)Functional GI tract disorder devoid of structural, biomechanical, radiologic, or laboratory abnormalitiesAfflicts up to 20% of adultsTwo IBS forms:Diarrhea predominantConstipation predominant36

37. Health Status, Emotional State, and GI Tract DisordersIrritable Bowel Syndrome (IBS)Eight factors cause IBSIncreased GI motor reactivity to stressFoods high in fat, insoluble fiber, caffeine, coffee, carbonation, alcoholDysfunction of the CCK release systemImpaired bowel gas transitVisceral hypersensitivityImpaired reflex controlAutonomic dysfunctionAltered immune activation37

38. Health Status, Emotional State, and GI Tract DisordersIrritable Bowel Syndrome (IBS)Four common IBS symptomsCramping abdominal pain relieved by defecationAltered stool frequencyAltered stool form (mucous, watery, hard, or loose) and passage (strain, urgency, or sense of incomplete evacuation)Abdominal distension following meals38

39. Health Status, Emotional State, and GI Tract DisordersIrritable Bowel Syndrome (IBS)Four lifestyle and dietary modifications to counter IBSStress reductionDaily small mealsHigh-fiber dietAvoiding foods with lactose and candy with sorbitol39

40. Health Status, Emotional State, and GI Tract DisordersGI DisordersGas: Flatus (lower tract intestinal gas) composition depends on nutrient intake and the colon’s bacterial populationCHO produce most gas; fats and proteins leastIn large intestine, bacteria degrades undigested CHO to produce H+, CO2, and methane gas, which exit through the rectum40

41. Health Status, Emotional State, and GI Tract DisordersGI DisordersFunctional Dyspepsia—chronic pain in upper abdomen without physical causeVague GI symptoms: stomach gnawing or burning, epigastric pain, nausea, vomiting, belching, bloating, indigestion, abdominal discomfortThree most common causes for dyspepsiaPeptic ulcer diseaseGERDGastritis (stomach inflammation)41

42. Physical Activity Effects on Gastrointestinal FunctionsPA alters blood flow dynamicsDepends on modes, intensities, and durations that acutely impact GI functionsFive factors affect gastric emptying rate (GER)Volume: larger food volume increases GERKilocalorie: content—higher kilocalorie solutions decrease GEROsmolality: higher food osmolality decreases GERTemperature: cooler foods increase GERpH: higher acidic foods decrease GERGER also impacted by emotional state, caffeine, environmental conditions, menstrual cycle stage, and fitness status42