Digestive system pancreas

The pancreas is an exocrine gland and an endocrine gland. The exocrine tissue produces a bicarbonate solution and digestive enzymes. These substances are transported to the small intestine where they play a role in the chemical digestion of food. These functions are fully discussed in Chapter 18 on the digestive system. 

The problem to be solved with respect to the chemical reactions that constitute metabolism and sustain life is that, without the action of catalysts, they are far too slow. Let s consider the digestion of the proteins themselves, an important constituent of our diet. In an enviromnent similar to that of our digestive system, several tens of thousand years would be required to digest half of the protein content of a typical meal in the absence of a catalyst. Clearly, this will not do. In reality, the stomach secretes one protein catalyst, the enzyme pepsin, and the pancreas secretes several enzymes that catalyze the digestion of proteins. In the presence of these enzymes, dietary proteins are fully digested and reduced to their basic constituents, the amino acids, in a matter of hours. Obviously, these enzymes are enormously potent catalysts." ... 

PANCREATITIS Inflammation of the pancreas, an essential part of both the endocrine and the digestive systems. The pancreas secretes juices that aid in digestion, and a number of hormones (including insulin). 

The digestive system consists of the mouth, oesophagus, stomach, small intestine, large intestine, rectum and anus together with the liver and pancreas. 

Cystic fibrosis Inadequate lipase produced by pancreas overproduction of mucus in lungs and digestive systems breathing difficulties. 

Fig. 4.14. Scheme of the anatomy and relationship of the pancreatic in pancreas divisum. Note the reversal of the relative size of the ducts. (Drawing adapted from F.N. Netter 1964] The Netter Collection of Medical Illustrations-Digestive System-part III)... 

Hunger and Appetite Anatomy of the Digestive System Physiology of Digestion Mouth Esophagus Stomach Small Intestine Pancreas Liver... 

Because of its role in the digestive system, animal pancreas is rich source of secreted proteases and lipases. Pancreatin from porcine pancreas is a mixture of different enzymes capable of hydrolyzing carbohydrates, lipids, esters, amides and proteins. It can be used directly when the presence of competing catalysts are not a problem. Several individual pancreatic enzymes are also readily available. Porcine pancreatic lipase has been widely used in synthesis. Several proteases from this source are sold commercially and used extensively. Porcine pancreatic trypsin is an inexpensive serine protease that hydrolyzes peptide bonds predominantly on the carboxyl side of lysines or arginines in proteins and peptides. Chymotrypsin is another serine protease from the same source that cleaves amide bonds on the carboxyl side of large hydrophobic amino adds such as tyrosine tryptophan, phenylalanine, and, to a lesser extent, leudne. Several different subtypes of chymotrypsin are known, for example, a-, 3-, y-, with... 

Serum lipase is synthesized and stored in the granules of pancreatic acinar cells and is excreted from the apical poles of the acinar cells into the duct system of the gland. Lipases are produced not only in the pancreas but also at various sites in the human digestive tract [126][127]. Lipases are also found in leucocytes, adipose tissue, lung, and milk. 

FIGURE 23-24 The endocrine system of the pancreas. In addition to the exocrine cells (see Fig. 18—3b), which secrete digestive enzymes in the form of zymogens, the pancreas contains endocrine tissue, the islets of Langerhans. The islets contain a, /3, and S cells (also known as A, B, and D cells, respectively), each cell type secreting a specific polypeptide hormone. 

The human intestine has evolved as a highly efficient organ to digest (i.e. hydrolyse) practically all the macromolecules in the human diet (albeit with the help of a few trillion bacteria ) with the exception of some plant fibres. To do this it possesses a formidable array of enzymes. This is particularly true for the digestion of proteins and peptides where peptidases are found in the stomach, are secreted by the pancreas in considerable quantities and are found on the surface of and inside intestinal epithelial cells. These enzymes work in a co-ordinated fashion to rapidly hydrolyse proteins. They present the major difficulty for designing oral delivery systems for therapeutic peptides, which may explain why 86 years after the first attempt to orally administer insulin (Bliss 1982), there is still not an oral insulin product available for diabetics. 

The acinar cells of pancreas synthesize, not only structural proteins and enzymes for their own metabolism, but also exocrine or exportable enzymes which are carried into the duodenum for digestive purposes. To this dual function corresponds a rather complicated system involving, besides biosynthesis itself, segregation, transport, storage, and final excretion. 

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