CHAPTER IV
THE STOMACH
Laboratory methods may be applied to the diagnosis of stomach disorders in: I. Examination of the gastric contents removed with the stomach-tube. II. Certain other examinations which give information as to the condition of the stomach.
I. EXAMINATION OF THE GASTRIC CONTENTS
Stomach digestion consists mainly in the action of pepsin upon proteids in the presence of hydrochloric acid and in the curdling of milk by rennin.
Pepsin and rennin are secreted by the gastric glands as zymogens—pepsinogen and renninogen, respectively—which are converted into pepsin and rennin by hydrochloric acid. Hydrochloric acid is secreted by certain cells of the fundus glands. It at once combines loosely with the proteids of the food, forming acid-albumin, the first step in proteid digestion. Hydrochloric acid, which is thus loosely combined with proteids, is called "combined" hydrochloric acid. The acid which is secreted after the proteids present have all been converted into acid-albumin remains as "free" hydrochloric acid, and, together with pepsin, continues the process of digestion.
At the height of digestion the stomach-contents consist essentially of: (1) Water; (2) free hydrochloric acid; (3) combined hydrochloric acid; (4) pepsin; (5) rennin; (6) mineral salts, chiefly acid phosphates, of no clinical importance; (7) particles of undigested and partly digested food; (8) various products of digestion in solution. In pathologic conditions there may be present, in addition, various microscopic structures and certain organic acids, of which lactic acid is most important.
A routine examination is conveniently carried out in the following order:
(1) Give the patient a test-meal upon an empty stomach, washing the stomach previously if necessary.
(2) At the height of digestion, usually in one hour, remove the contents of the stomach with a stomach-tube.