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6.1 Digestion Eating starts the process that leads to your body cells gaining necessary nutrients. In General: Ingestion – eating the food Digestion – Series of chemical evens that break food down into smaller molecular forms Absorption – small molecules pass through digestive cells and into the blood stream/lymphatic vessels Transport – circulatory system delivers molecules to body cells to serve as nutrients 6.1.1 Explain why digestion of large food molecules is essential. Most ingested molecules are polymers and insoluble, must first be broken down so smaller soluble molecules are can be absorbed into the blood. Smallest components can then be used to build larger molecules, useful to organism. 6.1.2 Explain the need for enzymes in digestion. 3 The need for increasing the rate of digestion at body temperature should be emphasized. Enzymes are biological catalysts Digestive enzymes secreted into the lumen of the gut, and increase the rate of hydrolysis of insoluble food molecules, breaking them down into soluble products. Digestive enzymes increase the rate of reaction at body temp (37 C) o o 6.1.3 State the source, substrate, products and optimum pH conditions for one amylase, one protease and one lipase. Any human enzymes can be selected. Details of structure or mechanisms of action are not required. Salivary Amylase Pepsin (a protease) Pancreatic Lipase Source Substrate Products Optimum pH 6.1.4 Draw and label a diagram of the digestive system. (The diagram should show the mouth, esophagus, stomach, small intestine, large intestine, anus, liver, pancreas and gall bladder. The diagram should clearly show the interconnections between these structures.) 6.1.5 Outline the function of the stomach, small intestine and large intestine. Stomach – food brought to stomach by esophagus, using peristalsis, or a sequential series of smooth muscle contractions o Once in stomach, food is held for a period of time to mix it with a variety of secretions known as gastric juice: Pepsin Hydrochloric Acid Mucus o Lumen of stomach stores the food from a meal o Gastric pits secret mucus, enzymes, and acid o Mucus Secreting Cells – secret mucus to protect surface of stomach from auto digestion o Parietal Cells produce HCL – kills microorganisms that enter digestive center and converts inactive pepsinogen into active pepsin o Chief Cells – produces pepsinogen Small Intestine – digestion is completed and the vast majority of absorption occurs o o o o o o In duodenum (first portion of small intestine) three different organs insert digestive juices Bile from liver and gall bladder Trypsin (protease), lipase, amylase, and bicarbonate from pancreas Products of digestion absorbed into blood stream or lymphatic system Villus – increases surface area for absorption of products Microvilli – border epithelial cell (cells lining small intestine) increases surface area for absorption Lacteals – connect to the lymphatic system for transport of lipids Capillary beds – connect to circulatory system for transport of products to body cells Large Intestine – colon is responsible for the reabsorption of water from the gut o o Contains large number of bacteria, including E. coli, that serve a mutualistic relationship – they receive nutrients, water, and a warm environment, we receive vitamin K and a healthier overall environment Undigested food is eliminated as feces 6.1.7 Explain how the structure of the villus is related to its role in absorption and transport of the products of digestion. Villus increases surface area of digestive system Each villus contains: o Capillary bed – small blood vessels of circulatory system that absorbs most nutrients, except fatty acids o Lacteal – small vessel of lymphatic system that absorbs fatty acids. Folds of small intestine increase SA:V ration by 3, Villi increase SA:V ratio by 10, Microvilli increase SA:V ratio by 10 6.1.6 Distinguish between absorption and assimilation. Absorption – digested nutrients are absorbed through digestive cells into the blood stream of lymphatic system Assimilation – movement of nutrients into body cell to be used to produce energy or to build larger molecules.