2. 6.1 Digestion Readings 203-208 IB Pg 209 1-8

3. Overview: The Need to Feed Heterotrophs –dependent on a regular supply of food Animals fall into three categories: –Herbivores eat mainly autotrophs (plants and algae) –Carnivores eat other animals –Omnivores regularly consume animals as well as plants or algal matter An adequate diet must satisfy three needs: –Fuel –Materials for biosynthesis –Essential nutrients the animal cannot make itself

4. Caterpillar Feces

5. 6.1.1 Explain why digestion of large food molecules is essential Most food molecules are large polymers and insoluble They must first be digested to smaller soluble molecules before they can be absorbed into the blood

6. Pieces of food Chemical digestion (enzymatic hydrolysis) Food Nutrient molecules enter body cells Small molecules Undigested material ELIMINATION ABSORPTION DIGESTION INGESTION Mechanical digestion

8. 6.1.2 Explain the need for enzymes in digestion Enzymes –increase the rate of reaction –Lower activation energy Digestive enzymes – are secreted into the lumen of the gut – increase the rate of reaction of the hydrolysis of insoluble food molecules to soluble end products – increase the rate of reaction at body temperature

10. 6.1.3 State the source, substrate, products and optimum pH conditions for one amylase, one protease, and one lipase Pancreatic amylase: –Source the Pancreas –Substrate is starch –Optimal pH 7.5-7.8 –End product is the disaccharide maltose

11. Pepsin is a protease: –Source is the stomach –Substrate is a polypeptide chains of amino acids –Optimal pH is 2 –End product is small polypeptides

12. Pancreatic lipases: –Source is the pancreas –The optimal pH is 7.2 –The substrate is a triglyceride lipid –The product is glycerol and fatty acid chains

13. 6.1.4 Draw & label a diagram of the digestive system Each organ of the mammalian digestive system has specialized food-processing functions The mammalian digestive system consists of an –alimentary canal –accessory glands that secrete digestive juices through ducts (a tube within a tube) Mammalian accessory glands? –salivary glands, the pancreas, the liver, and the gallbladder Peristalsis? –rhythmic contractions of muscles in the wall of the canal to move food along

14. Esophagus Pharynx Oral cavity Stomach Pyloric sphincter Cardiac orifice Liver Tongue Salivary glands Ascending portion of large intestine Gall- bladder Pancreas Ileum of small intestine Rectum Anus Appendix Cecum Large intestine Small intestine Duodenum of small intestine

15. Esophagus Stomach Liver Salivary glands Gall- bladder Pancreas Rectum Anus Large intestines Small intestines Mouth A schematic diagram of the human digestive system

17. 6.1.5 Outline the function of the stomach, small intestine, and large intestine The stomach stores food and secretes gastric juice, which converts a meal to acid chyme Gastric juice is made up of hydrochloric acid and the enzyme pepsin Pepsin is secreted as inactive pepsinogen; pepsin is activated when mixed with hydrochloric acid in the stomach Mucus protects the stomach lining from gastric juice

19. Esophagus Cardiac orifice Pyloric sphincter Small intestine Stomach Epithelium Pepsin (active enzyme) Pepsinogen HCl Pepsinogen and HCl are secreted into the lumen of the stomach. HCl converts pepsinogen to pepsin. Pepsin then activates more pepsinogen, starting a chain reaction. Pepsin begins the chemical digestion of proteins. Parietal cellChief cell Chief cells Mucus cells Parietal cells Interior surface of stomach Gastric gland 5 µm

20. Most common regulation in biological systems The accumulation of an end product of a process slows the process or system Less common End product of a reaction speeds up production of that reaction

21. (a) Lumen (b) Gastric pits (mucus) (c) Mucus secreting cells. (d) Parietal cells that produce HCL which kills microorganism that enter the digestive system. This also converts inactive pepsinogen to active pepsin (e) Chief cells: produces pepsinogen a protease enzyme

22. Bacteria Mucus layer of stomach 1 µm Gastric ulcers, lesions in the lining, are caused mainly by the bacterium Helicobacter pylori

23. The small intestine The first portion  duodenum, –acid chyme from the stomach  –digestive juices from… –pancreas, liver, gallbladder, and the small intestine itself The small intestine is the longest section of the alimentary canal and… –major organ of digestion and absorption Digestion is completed here The products of digestion are absorbed into the blood stream

24. (a) Villus which increase the surface area (b) Microvilli further increases the surface for absorption. (c) Lacteals are connected to the lymphatic system for the transport of lipids. (d) In the wall of the small intestine are the blood vessels to transport absorbed products to the general circulation. There are also the muscle to maintain peristalsis WHAT TYPE OF MUSCLE? SMOOTH MUSCLE

26. The LARGE intestine or colon The large intestine, or colon, is connected to the small intestine Its major function is to recover water that has entered the alimentary canal Wastes of the digestive tract, the feces, become more solid as they move through the colon Feces pass through the rectum and exit via the anus The colon houses strains of the bacterium Escherichia coli, some of which produce vitamins

27. (a) The lumen of the colon (b) The mucus producing goblet cells (b) Muscular walls to maintain peristalsis

28. 6.1.6 Distinguish between ABSORTION and ASSIMILATION

29. 6.1.7 Explain how the structure of the villi is related to its role in absorption and transport of the products of digestion The small intestine has a huge surface area, due to villi and microvilli that are exposed to the intestinal lumen The enormous microvillar surface greatly increases the rate of nutrient absorption