What do humans require from food? How does the vertebrate gastrointestinal system function?

1. David Sadava H. Craig Heller Gordon H. Orians William K. Purves David M. Hillis Biologia.bluC – Il corpo umanoNutrition, Digestion, and Absorption

2. Nutrition, Digestion, and Absorption • What do humans require from food? • How does the vertebrate gastrointestinal system function? • How is the flow of nutrients controlled and regulated? • What causes ulcers in the stomach?

3. Nutrition, Digestion, and Absorption - What do humans require from food? Humans require organic molecules to supply a carbon skeleton. The acetyl group (CH3CO––) is used to build more complex molecules. Acetyl groups can be derived from almost any food.

4. Nutrition, Digestion, and Absorption - What do humans require from food? The acetyl group is an acquired carbon skeleton

5. Nutrition, Digestion, and Absorption - What do humans require from food? The human digestive system

6. Nutrition, Digestion, and Absorption - How does the vertebrate gastrointestinal system function? The gut has a layered plan: • lumen– the gut cavity; • mucosal epithelium – layer of cells that secrete mucus, digestive enzymes or hormones, some absorb nutrients through microvilli; • submucosal layerhas blood and lymph vessels, and nerves.

7. Nutrition, Digestion, and Absorption - How does the vertebrate gastrointestinal system function? Two layers of smooth muscle are outside the submucosa: • the circular muscle layer - innermost cells oriented around the gut, constrict the gut; • the longitudinal muscle layer - outermost cells oriented along the gut, shorten the gut.

8. Nutrition, Digestion, and Absorption - How does the vertebrate gastrointestinal system function? Between layers of smooth muscle are nerves that coordinate movement of the gut. The peritoneum is a membrane that surrounds the gut and lines the wall of the cavity.

9. Nutrition, Digestion, and Absorption - How does the vertebrate gastrointestinal system function? Tissue layers of the gut

10. Nutrition, Digestion, and Absorption - How does the vertebrate gastrointestinal system function? Greater intestinal surface area means more nutrients absorbed

11. Nutrition, Digestion, and Absorption - How does the vertebrate gastrointestinal system function? Mechanical activity in digestion: • the tongue pushes a bolus to the soft palate, and initiates swallowing, food passes into the esophagus; • food is kept out of the trachea by the closed larynx and the epiglottis; • peristalsis - waves of muscle contractions that move food toward the stomach.

12. Nutrition, Digestion, and Absorption - How does the vertebrate gastrointestinal system function? Swallowing and peristalsis (part 1)

13. Nutrition, Digestion, and Absorption - How does the vertebrate gastrointestinal system function? Swallowing and peristalsis (part 2)

14. Nutrition, Digestion, and Absorption - How does the vertebrate gastrointestinal system function? Part of the esophagus is skeletal muscle and part of the esophagus is smooth muscle. As food reaches the smooth muscle, the esophagus contracts and pushes the food toward the stomach. Nerves coordinate the muscles of the esophagus: • contraction is preceded by an anticipatory wave of relaxation; • as an area contracts, the region below it relaxes so food does not move upwards; • as food moves down, it causes the next region to contract.

15. Nutrition, Digestion, and Absorption - How does the vertebrate gastrointestinal system function? The lower esophageal sphincter, a ring of muscle, prevents food from moving backward into the esophagus. The pyloric sphincter controls the passage of food into the intestine.

16. Nutrition, Digestion, and Absorption - How does the vertebrate gastrointestinal system function? • Teeth structure: • enamel composed of calcium phosphate covers the crown; • dentine in the crown and root; • pulp cavity contains blood vessels, nerves and dentine-producing cells.

17. Nutrition, Digestion, and Absorption - How does the vertebrate gastrointestinal system function? Teeth have shapes adapted to specific functions: • incisors - used for cutting, chopping, or gnawing; • canines - for stabbing, gripping, or ripping; • molars or premolars - shearing, crushing, or grinding.

18. Nutrition, Digestion, and Absorption - How does the vertebrate gastrointestinal system function? Macromolecules are broken down by digestive enzymes, known by the substances they hydrolyze: • protease -breaks bonds of amino acids; • carbohydrase - carbohydrates; • peptidase - peptides; • lipase - fats; • nuclease -nucleic acids.

19. Nutrition, Digestion, and Absorption - How does the vertebrate gastrointestinal system function? Chemicals in the mouth and stomach begin digestion: • salivary glands secrete amylase; • gastric pits in the stomach are lined with three types of secretory cells (chief cells, parietal cells, and mucus-secreting cells) which protect the stomach.

20. Nutrition, Digestion, and Absorption - How does the vertebrate gastrointestinal system function? Action in the stomach (part 1)

21. Nutrition, Digestion, and Absorption - How does the vertebrate gastrointestinal system function? Chief cells secrete pepsinogen, the inactive form of a proteolytic enzyme, pepsin. The low pH of the stomach converts it to the active form. Newly active pepsin activates other pepsinogen molecules—a process called autocatalysis.

22. Nutrition, Digestion, and Absorption - How does the vertebrate gastrointestinal system function? Action in the stomach (part 2)

23. Nutrition, Digestion, and Absorption - How does the vertebrate gastrointestinal system function? Parietal cells secrete HCl and keep the stomach pH below 1. Carbonic anhydrase catalyzes the formation of H2CO3 from CO2, which dissociates into HCO3– and H+. H+ ions are exchanged for K+ in the lumen of the gastric pits. K+ leaks back into the cells and H+ is continually returned to the stomach.

24. Nutrition, Digestion, and Absorption - How does the vertebrate gastrointestinal system function? Action in the stomach (part 3)

25. Nutrition, Digestion, and Absorption - How does the vertebrate gastrointestinal system function? Chyme is a mixture of gastric juice and partly digested food. The stomach walls contract and move the chyme to the bottom of the stomach. The pyloric sphincter allows small amounts to enter the small intestine.

26. Nutrition, Digestion, and Absorption - How does the vertebrate gastrointestinal system function? The small intestine has three sections: duodenum, the initial section and site of most digestion, jejunum and ileum, that carry out most absorption. The liver synthesizes bile, which flows through the hepatic duct to the duodenum, and through a branch to the gallbladder. Fat entering the duodenum signals the gallbladder to contract. Bile is released and flows via the common bile duct to the duodenum.

27. Nutrition, Digestion, and Absorption - How does the vertebrate gastrointestinal system function? Ducts of the gallbladder and pancreas (Gallbladder)

28. Nutrition, Digestion, and Absorption - How does the vertebrate gastrointestinal system function? Bile contains salts that emulsify fats and expose them to lipases; enzymes that digest fats. Micelles are small fat particles that result from the action of bile salts. The pancreas is an endocrine and exocrine gland. Endocrine functions include hormone release. Exocrine functions include secretions through the pancreatic duct to the gut lumen, via the common bile duct.

29. Nutrition, Digestion, and Absorption – How is the flow of nutrients controlled and regulated? Digestive hormones and sites of production: • secretin - in the duodenum, causes pancreas to secrete digestive juices; • cholecystokinin - in the small intestine, causes gallbladder to release bile, stimulates pancreas, slows stomach; • gastrin - released by the stomach into the blood.

30. Nutrition, Digestion, and Absorption – How is the flow of nutrients controlled and regulated? Hormones control digestion (part 1)

31. Nutrition, Digestion, and Absorption – How is the flow of nutrients controlled and regulated? Hormones control digestion (part 2)

32. Nutrition, Digestion, and Absorption – How is the flow of nutrients controlled and regulated? Gluconeogenesis in the liver is the conversion of amino acids and other molecules into glucose. The liver also converts molecules into glycogen and controls fat metabolism through lipoproteins. Lipoproteins produced in the liver: • high-density lipoproteins (HDLs) remove cholesterol from tissue and carry it to the liver; • low-density lipoproteins (LDLs) transport cholesterol in body; • very-low-density lipoproteins (VLDLs) transport triglycerides to fat cells.

33. Nutrition, Digestion, and Absorption – How is the flow of nutrients controlled and regulated? Insulin is released by the pancreas during the absorptive period, when blood glucose levels (glycemia) rise. Insulin promotes uptake and utilization or storage of glucose, and it acts in skeletal muscle, adipose tissue, and in the liver. Blood glucose levels fall in the postabsorptive period. Insulin release is lower and glucose uptake is slowed. If blood glucose level is very low, glucagon is released and causes the liver to break down glycogen and begin gluconeogenesis.

34. Nutrition, Digestion, and Absorption – How is the flow of nutrients controlled and regulated? Regulating glucose levels in blood

35. Nutrition, Digestion, and Absorption - What causes ulcers in the stomach? Ulcers are sites of damage to the stomach lining. Causes include stress and lifestyles that lead to excess stomach secretions, like HCl. Warren and Marshall noted that ulcer patients always had an unknown bacterium present. They discovered Helicobacter pylori also causes ulcers; it survives in the stomach by an enzyme reaction that neutralizes acid. Antibiotics are able to cure this type of ulcer.