The Digestive System Ingestion Digestion Secretion Absorption Excretion

1. The Digestive System Ingestion Digestion Secretion Absorption Excretion

3. What happens in digestion? • Ingestion • Mechanical (chewing) • Chemical (enzymes)

6. Esophagus ca. 10 inches long peristalsis independent of gravity “False sphincter” at junction of esophagus and stomach

9. Empty stomach capacity is 50 ml Can expand to hold several liters stretch receptors signal HYPOTHALAMUS when stomach is full Hypothalamus- a major control center in the brain hunger (and satiety) thirst body temperature emotions memory

11. Dr. William Beaumont, 1820s had a unique opportunity to study the stomach Contains acid Acid breaks down protein Acid is produced when you eat Chewing affects rate of digestion

12. Protein digestion starts in stomach (acid and enzymes) Rennin and lipase help digest milk Mucus protects stomach; also epithelial cells divide very rapidly Very little absorption- aspirin and alcohol Taks 3-5 hours to move to intestine

13. “Heartburn”- gastric juice (acid) backs up into esophagus Bicarbonate- neutralize acid Tagamet, Prilosec, Zantac- inhibit acid formation Propulsid- acts on sphincter Peptic ulcers- erosion of stomach lining bacterial infection- H. pylori Product of stomach digestion is called chyme- moves into small intestine

15. Small intestine Digestion completed Absorption Digestive enzymes come mostly from pancreas and liver (‘recruited” by small intestine) Proteases, lipases, nucleases Bile

17. Gastrin promotes digestion of protein Cells in small intestine secrete hormones CCK and secretin These hormones cause pancreas to secrete various digestive enzymes gallbladder to secrete bile

19. Pancreatic juice contains several enzymes that digest several kinds of molecules (see p. 414) also contains sodium bicarbonate to neutralize acid Bile- helps with fat digestion produced in liver, stored in gallbladder

20. Large intestine Cecum, colon, anus Absorption of water and a few other molecules What’s left? undigested (indigestible) food bacteria Bacteria actually produce vitamins (B and K)

21. Gas production by bacteria (from undigested food) Lactose intolerance- lack of LACTASE (enzyme that breaks down lactose, a milk sugar) Some bacteria make this enzyme

22. Diarrhea- too little water absorbed bacterial toxins nervous stimulation can lead to dehydration, electrolyte imbalance Constipation not enough water intake behavioral dietary

23. After absorption into bloodstream- then what? Goes to liver

25. Liver cleans up blood Stores iron, vitamins, glycogen Makes important blood proteins Controls blood cholesterol levels

26. Nutrition What do we need from food? calories carbohydrates fats proteins vitamins minerals Food pyramid- out of date? (USDA, 1992)

28. Carbohydrates Simple Complex other nutrients fiber aids in digestion may help reduce blood cholesterol

29. Carbohydrates and lipids can be stored in the body. Proteins are not. Some amino acids can be synthesized in the body; eight cannot.

30. Sources of complete protein Animal proteins Combinations of: grains legumes nuts and seeds vegetables

31. Lipids (fat and cholesterol) Saturated fats raise blood cholesterol (LDL) some unsaturated fats lower it Vitamins- coenzymes fat-soluble (A, D, E, K) water-soluble (B vitamins, C)

32. Minerals many different types Too much or too little can be harmful

33. Why do we need calories? How many do we need?