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Digestion & Absorption

Digestion & Absorption. The body’s breakdown and uptake of nutrients. We are what we eat!. Biochemically, this is true However, most of us don’t look like this guy To build the body out of the materials in food, we must first break foods down. From Atoms to Organisms.

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Digestion & Absorption

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  1. Digestion & Absorption The body’s breakdown and uptake of nutrients

  2. We are what we eat! • Biochemically, this is true • However, most of us don’t look like this guy • To build the body out of the materials in food, we must first break foods down

  3. From Atoms to Organisms

  4. Digestive System Terminology • Digestion: process of breaking food into components small enough to be absorbed by the body • Absorption: process of taking substances into the interior of the body • Gastrointestinal tract: hollow tube consisting of the mouth, pharynx, esophagus, stomach, small intestine, large intestine and anus • Transit time: amount of time it takes food to pass the length of the GI tract • Feces: body waste, including unabsorbed food residue, bacteria and dead cells

  5. The Digestive System

  6. Anatomy of the Digestive Tract • Gastrointestinal (GI) tract • Flexible and muscular • Path • Mouth → esophagus → stomach → small intestine → large intestine → rectum → anus • Lumen • Continuous • Considered outside the body

  7. Digestive Secretions • Digestion inside the GI tract is assisted by digestive secretions • Mucus: viscous material produced by goblet cells • Moistens, lubricates and protects the GI tract • Enzymes: protein molecules that speed up chemical reactions • Enzymes are catalysts • In digestion, speed up breakdown of nutrients

  8. Turning Digestion On • Cephalic phase • Sensory stimuli • Thoughts of food • Tasting and chewing • Gastric and intestinal phases • Presence of food in digestive organs sends signals to brain and the organs themselves • Both phases are mediated by nerves and hormones

  9. Control of Digestion

  10. The Mouth • Process of digestion begins here • Mastication • Saliva • Enzymes • 4 taste sensations • #5: savory or umami • Aroma, texture, and temperature • Movement to pharynx: swallowing reflex • Bolus

  11. Pharynx and Epiglottis

  12. Heimlich Maneuver

  13. Passage Through the Esophagus

  14. The Esophagus and Stomach • Esophagus • Muscular tube; passes through diaphragm • Two sphincters • Upper esophageal sphincter • Lower esophageal sphincter • Stomach • Storage, mixing, and digestion • Chyme • Pyloric sphincter

  15. Small intestine • Three segments • Duodenum, jejunum, ileum • Common bile duct • Pancreas and gall bladder • Absorption! • Large intestine (colon) • Ileocecal valve • Absorption of water, some vitamins, & minerals • Rectum and anus

  16. Structure of the Gut Wall

  17. Absorption in the Small Intestine

  18. Muscular Action of Digestion • Peristalsis • Circular and longitudinal muscles working together • Stomach action • Circular, longitudinal, and diagonal muscles • Pyloric sphincter: times the release of chyme • Sphincter contractions • Periodically open and close • Control pace of GI tract contents

  19. Secretions of Digestion • Five organs • Salivary glands, stomach, pancreas, liver, small intestine • Secretions • Water • Enzymes • Protein facilitator of chemical reactions • Ex: Lipase, protease, carbohydrase (amylase) • Bile: emulsifies fat

  20. Enzymes and Digestion

  21. Secretions of Digestion • Saliva • Moistens food - what does this accomplish? • Protective role • Carbohydrate digestion • Gastric juice • Protein digestion • Mucus • Low pH (very acidic)

  22. The pH Scale

  23. Secretions of Digestion • Pancreatic juice • Released via ducts into duodenum • Enzymes act on all three energy-yielding nutrients • Contains sodium bicarbonate: neutralizes acidic chyme • Bile • Produced in liver • Stored in gallbladder

  24. Signals and Secretions

  25. Large Intestine • No further digestion occurs here, except bacterial breakdown of digestive residues • Slow transit • Water absorption • Some vitamin and mineral absorption • Undigested residues • Exercise intestinal muscles • Fibers: retention of water • Feces stored in rectum prior to defecation • 2 sphincters: internal and external • Intestinal bacteria • Synthesize some B-vitamins and vitamin K • From fiber: short-chain fatty acids

  26. Nutrient Breakdown in Digestion

  27. Nutrient Absorption • Most absorption happens in the small intestine

  28. Nutrient Transport Pathways • Bloodstream • Water-soluble nutrients, smaller products of fat digestion • Sugars, amino acids, small lipid molecules, water-soluble vitamins • Liver: the gatekeeper • Stores some nutrients; allows others to flow to rest of body • Lymphatic system • Larger fats and fat-soluble vitamins • Form large particles called chylomicrons • Lymphatic capillaries in small intestine are called lacteals

  29. Absorption in Villi of Small Intestine

  30. Absorptive Routes

  31. The Vascular Route • Vascular system • Closed system of vessels • Heart is the pump • Blood • Delivers oxygen and nutrients • Removes carbon dioxide and wastes • Blood flow • Special routing for digestive system • Hepatic portal vein

  32. The Lymphatic Route • Lymphatic system: one-way route • No pump • Returns fluid in tissues to bloodstream • Houses immune cells • Chylomicrons: too large to enter capillaries • Taken up by lacteals • Bypass liver at first and enter bloodstream directly via thoracic duct

  33. Health of the GI Tract: Gut Flora • Gastrointestinal bacteria – flora • 300-500 species – about 10x the number of cells in the body! – totaling about 3 pounds • Most are beneficial • Probiotic bacteria: microorganisms that confer a benefit on host when consumed in adequate amount • Prebiotics: indigestible carbohydrates in some foods (fruits, vegetables, and whole grains) that support growth of healthy bacteria • Dysbiosis: imbalance of gut bacteria • What are some probiotic-containing foods?

  34. Direct Immune Function of Probiotic Bacteria

  35. Benefits of Healthy Gut Flora • Break down indigestible substances (fibers, complex proteins) • Improve digestion and absorption • Support health of intestinal tissues – growth, development, and nourishment of cells • Produce vitamin K and some B-vitamins • Improve lactose digestion in lactose-intolerant people • Prevent diarrhea related to antibiotic use; shorten duration of diarrhea from illness • Promote mucin production • Enhance immune function • Positively associated with healthy body weight • Evidence indicates that they may also alleviate constipation, reduce allergy symptoms, and reduce risk of colon cancer

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