Anatomy and Physiology: Pancreatic Panacea?
The pancreas is my favorite organ, if only because mine doesn't work so well (see Figure 14.8). Beyond the endocrine role as a result of the release of insulin and glucagon (which, ironically, control the products of digestion), the pancreas is also an accessory digestive organ. Many of the enzymes used in digestion are produced here. A listing of them can be found in the following section.
In order to prevent wasteful production of enzymes, the pancreas needs to know what to produce, and when. This is due to the hormonal control of pancreatic secretions. These secretions are exocrine in nature, traveling to the small intestine through the pancreatic duct, which joins up with the common bile duct to form the hepatopancreatic ampulla.
Given that these pancreatic juices go to the duodenum, it only makes sense that the duodenum should be sending the message to make the enzymes. This chemical message is the duodenal hormone cholecystokinin, which causes the release of pancreatic enzymes. In a similar fashion, the duodenum's release of the hormone secretin causes the pancreas to release a buffer solution (pH 7.5 to 8.8) to counteract the acidity of the chyme from the stomach.
Tear 'Em Up!
Remember monomers and polymers? Well, what follows is a table of the basic enzymes produced by each of the major organs of the body, the location where that enzyme is used, the polymers they break down, and the monomers that are produced.
|Digestive Enzymes—Their Production, Use, and Effects|
|Organ||Enzyme Produced||Enzyme Used||Substrate||Products||Organic Molecule|
|Mouth||Salivary amylase||Mouth and stomach||Starch||Maltose||Carbohydrates|
|Mouth||Lingual lipase||Mouth and stomach||Fats||Monoglyceride 2 fatty acids||Lipids|
|Stomach||Gastric lipase||Stomach||Fats||Monoglyceride 2 fatty acids||Lipids|
|Liver||Bile||Gallbladder||Fat globs||Globules (More SA/V)||Lipids|
|Pancreas||Pancreatic amylase||Small int.||Starch||Maltose||Carbohydrates|
|Pancreas||Carboxypeptidase||Small int.||Peptides||Terminal amino acids||Proteins|
|Pancreas||Cholest. esterase||Small int.||Cholest. esters||Cholesterol and fatty acid||Lipids|
|Pancreas||Pancreatic lipase||Small int.||Fats||Monoglyceride 2 fatty acids||Lipids|
|Pancreas||Deoxyribonuclease||Small int.||DNA||DNA nucleotides||Nucleic acids|
|Pancreas||Ribonuclease||Small int.||RNA||RNA nucleotides||Nucleic acids|
|Small int.||Maltase||Small int.||Maltose||2 Glucoses||Carbohydrates|
|Small int.||Sucrase||Small int.||Sucrose||Glucose, fructose||Carbohydrates|
|Small int.||Lactase||Small int.||Lactose||Glucose, galactose||Carbohydrates|
|Small int.||Aminopeptidase||Small int.||Peptides||Amino acids||Proteins|
|Small int.||Dipeptidase||Small int.||Dipeptides||Amino acids||Proteins|
|Small int.||Nucleotidase||Small int.||Nucleotides (Phosphate, Sugar, and Base)||Separates Nitrogenous Base and Sugar||Nucleic acids|
|Small int.||Phosphatase||Small int.||Nucleotides||Removes Phosphate||Nucleic acids|
You might remember that enzymes are basically large proteins with an active site where the substrate, or molecule to be digested, fits. The way an enzyme functions is by changing its shape, and, in the case of digestive enzymes, separating polymers into either monomers or smaller polymers. In the first case, sucrase breaks down sucrose, or table sugar, into glucose and fructose, which are both monomers. Larger polymers, such as starch, are digested in a multistep process; they need to first be broken down by either salivary or pancreatic amylase into small polymers (disaccharides) of maltose, and then the maltose is broken down by what else, maltase, into two molecules of glucose. This is yet another example of the division of labor.
Excerpted from The Complete Idiot's Guide to Anatomy and Physiology © 2004 by Michael J. Vieira Lazaroff. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books, a member of Penguin Group (USA) Inc.