The hormones of the body are not destroyed by boiling like the ferments but are soon oxi dized in the body, especially in the presence of alkalis.
The Composition and Functions of Pan creatic Juice.—Pancreatic juice may be obtained from animals by introducing a canula into the pancreatic duct and by an operation providing an external opening for this canula to empty itself into vessels tied underneath the abdomen of the animal. As early as 1677 Rene de Graaf employed a method of obtaining pancreatic juice and published an illustration of a dog with a pancreatic and also a salivary fistula. Consult Ernest H. Starling's work on (Recent Advances in the Physiology of Digestion> (page 81).
Pawlow's method of making a permanent fistula is to cut out a patch of the duodenal wall with the opening of the pancreatic duct in its centre and stitch up the gap in the duodenum and then suture this patch containing the open ing of the duct into the abdominal wall. Pan creatic juice obtained in this way is a clear, limpid fluid with a specific gravity of 1006, strongly alkaline in reaction. The degree of alkalinity is such that equal volumes of gastric juice and pancreatic juice neutralize each other.
Pancreatic juice contains four enzymes, a nucleo-protein, inorganic salts, chief of which is sodium carbonate. The enzymes are a pro tase called Trypsin, converting proteins into peptones and polypeptids; a diastase called Amylopsin which converts starch into maltose, but unlike saliva the amylase of pancreatic juice is capable of digesting unboiled starch; thirdly, it contains a lipase called Steapsin, and fourthly contains a milk curdling enzyme.
Pure pancreatic juice obtained directly from the duct without coming in contact with the intestinal membrane possesses no action on pro teins. If, however, the juice has flowed over the duodenal membrane it becomes proteolytic. The inactive juice contains not Trypsin in its active state but it contains Trypsinogen, which is a precursor of Trypsin.
Trypsinogen is converted into active Tryp sin by an activator or coenzyme which is formed in the mucous membrane of the small intestines and the name Enterokinase has been given to this activator. Trypsinogen may also be converted into Trypsin by calcium salts, but not so rapidly as by Enterokinase. Bayliss and Starling have shown that the secretion of pan creatic juice is due to a hormone which they called Secretin, and which is formed in the mucous membrane of the small intestine. The
production of this hormone is brought about by the presence of the acids of the gastric contents when they enter the duodenum.
Pawlow has shown that stimulation of the vagus will start a small flow of the pancreatic juice even when the pylorus of the stomach is ligatured so that the passage of acid contents from the stomach into the duodenum is pre vented. It is possible that the first few cc of juice of the pancreas that are secreted may be of nervous origin.
Secretin is not secreted in its complete or active form, but as a precursory state called pro secretin, and the amount of secretin in former as shown by the amount of pancreatic juice that is secreted varies with the nature of the food. The effect of Tryptic digestion may be repre sented in tabular form in the following manner: Protein Soluble Globulin Alkali Metaprotein Primary Proteoses Secondary Proteoses Peptones Pnlvnentids and Amino-arida The action of the pancreatic juice on starch is effected by an, enzyme called Amylopsin or Amylase forming maltose from starch, but as the maltose is formed it is hydrolyzed by a ferment called Maltase contained in the pan creatic juice and also in the intestinal juice. Under the influence of maltase each molecule of maltose takes up a molecule of water and is split into two molecules of dextrose. Pan creatic juice differs, however, from the intes tinal juice in having no similar action on other disaccharides, such as lactose and cane sugar.
Action of Pancreatic Juice on If neutral olive oil be shaken with pancreatic juice and the mixture kept at a temperature of 37° C., the fatty ester will be hydrolyzed, producing fatty acid and glycerine, and the reaction will become acid. The digestion of fats is greatly aided by the presence of bile and also mechani cally assisted by the formation of soaps. Some of the fatty acid which is set free combines with the alkali of the intestinal contents to form soap. Each fat droplet becomes coated with a fine film of soap, which prevents it from coalescing with adjacent fat droplets and in this way the formation of a still finer emulsion is brought about and the fat made more accessible to the fat-splitting enzyme.