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BY 124 SI Test III Session II Food Type Carbohydrates Proteins Fats Enzyme 1. Salivary Amylase 2. Pancreatic Amylase 3. Maltase 1. Pepsin 2. Trypsin 3. Peptidases 1. Lipase Source 1. Salivary Glands 2. Pancreas 3. Small Intestine 1. Stomach mucosa 2. Pancreas 3. Intestinal Mucosa 1. Pancreas Products 1. Maltose 2. Maltose 3. Glucose 1. Peptides 2. Peptides 3. Amino Acids 1. FA and monoglycerides Digestion in the Stomach Gastric juice is a mixture of HCl and pepsinogen What is the purpose of HCl in digestion? Where is HCl secreted? HCl is secreted from parietal cells. The acidic nature of HCl denatures proteins to expose their peptide bonds. How does hydrochloric acid function to aid the other digestive enzyme in the stomach? HCl converts pepsinogen to pepsin. Pepsin is the active form so now it can function. Once pepsin has been generated it can work on itself (pepsinogen) to create even more pepsin. This chain reaction allows a large amount of pepsin to be activated in a short amount of time. Where is pepsin secreted? What is its role in digestion? Chief cells secrete pepsin. Pepsin is a protease that works by attacking peptide bonds. Pepsin breaks down the proteins into smaller polypeptides. Protein digestion starts in stomach and ends in the small intestine! Explain how the HCl/pepsin system is turned on? Do you constantly have HCl and pepsin residing in your stomach? Gastrin is a hormone produced by the lower portion of the stomach. Gastrin travels through the blood stream, to the upper portion of the stomach, and causes the release of HCl and pepsin from parietal and chief cells. If the concentration of HCl is too high it will inhibit gastrin (negative feedback) No you don’t always have HCL and pepsin in your stomach. HCl is so acidic that if left in your stomach all the time, it would deteriorate the lining of your stomach. This is controlled by a negative/positive feedback mechanism using gastrin. Digestion in the Small Intestine The first portion of the small intestine is called the: duodenum When chyme enters the small intestine, what method of negative feedback occurs? When chyme enters the duodenum, it stimulates the release of secretin and CCK which inhibits peristalsis, slowing the rate at which chyme enters. What stimulates the release of secretin? What does secretin cause to be released through positive feedback? HCl in the chyme (so the acidic nature) stimulates the release of secretin. Secretin stimulates the pancreas to release sodium bicarbonate. This functions to neutralize the chyme. You need to neutralize the chyme because the enzymes in the duodenum do not function at an acidic pH! BY 124 SI Test III Session II What stimulates the gall bladder to release bile? How does bile function in digestion? When chyme enters the duodenum, it stimulates the release of CCK. CCK stimulates the release of the pancreatic zymogens AND bile. Bile contains bile salts that help to emulsify fats in the chyme (there are no enzymes in bile) Small intestine: Pancreatic zymogens What causes the release of zymogens from the pancreas? The presence of food in the duodenum stimulates the release of CCK. CCK causes the release of zymogens from the pancreas Small intestine: Pancreatic zymogens -‐ Trypsinogen is converted to trypsin by a membrane bound enteropeptidase -‐ Trypsin can o Convert trypsinogen à trypsin o Convert chymotrypsinogen à chymotrypsin o Convert Procarboxypeptidase à carboxypeptidase Endopeptidase vs. Exopeptidase - Endopeptidases cut polypeptide chains internally Examples: pepsin, trypsin, chymotrypsin - Exopeptidases cut polypeptide chains externally Examples: aminopeptidase and carboxypeptidase CCK Causes the release of: bile from gall bladder, zymogens and bicarbonate from the pancreas, and inhibits peristalsis Secretin Causes the release of sodium bicarbonate from the pancreas, inhibits peristalsis Absorption in Small Intestine Occurs in the: ileum and jejunum The surface area of the small intestine is increased by the presence of __ __microvilli________________. Collectively, these are called the ______brush_______ ____ ___border_________ Which types of nutrients are pumped directly to the blood stream by active transport? Fructose, amino acids, small peptides, vitamins, and most glucose molecules How are fats absorbed? Where are the fats sent to after they enter the epithelial cell? Triglycerides are broken down into fatty acids and monoglycerides in the lumen of the intestine. These molecules are absorbed by the epithelial cells and are re-formed into fats. This fat is then coated with protein, cholesterol and phospholipids to create a chylomicron. The chylomicron exits the cell and enters the lacteal. The lacteal dumps into the lymphatic system which then dumps into the blood system BY 124 SI Test III Session II What is the function of the hepatic portal vein? The hepatic portal vein functions to control the release of nutrients from the liver. Think about it.. what would happen if your body absorbed all of the sugar you ate during one meal? You’d go into a coma! The blood vessels that carry the absorbed nutrients from the small intestine converge at the hepatic portal vein. Here the nutrients can be released in a controlled manner depending upon the body’s needs. Absorption in Large Intestine The colon functions to: absorb water and get rid of salt The last sphincter the feces pass through is the: anal sphincter and it is voluntary! A student conducts an experiment to observe the efficiency of protein digestion by altering digestive enzymes. The student runs a control experiment with all digestive enzymes present and then runs an experiment using an altered enzyme. In his variable test he notices that the time of digestion slows substantially. What could be a possible reason for his results? a. diluted gastrin b. elimination of endopeptidase c. elimination of Exopeptidase d. elimination of lipase e. diluted HCl