The composition of gastric juice

INTERACTIONS BETWEEN RESPONSES TO DISTURBANCES OF ACID-BASE PHYSIOLOGY AND OF FLUID VOLUME SUCH AS VOMITING 

The effect of vomiting on add-base status depends on whether there is a net loss of add or of alkali in the vomitus. In cases where the movement of chyme from the stomach to the duodenum is obstructed, the resulting vomiting will be of gastric contents which are add. In other cases of vomiting due, for instance, to irritation of the small bowel, the vomitus is a mixture of gastric contents, which are add, and of duodenal contents, which are alkaline. In this situation the vomitus is add if gastric juice predominates and alkaline if duodenal contents predominate. 

With hypovolaemia, there is a reflex constriction of the afferent arterioles 

From the point of view of potassium balance, there is increased renal excretion of potassium, loss of potassium in the vomitus and no potassium being delivered for absorption in the alimentary tract. All these factors contribute to a severe depletion of the body s total potassium content. Yet another factor contributes to potassium loss. A drop in volume of the circulating blood leads to aldosterone secretion via the renin-angiotensin mechanism which, in turn, promotes sodium reabsorption in the renal tubule this contributes further to excessive renal loss of potassium and hydrogen ions. The acidity of the urine is inappropriate as a response to metabolic alkalosis, but the preservation of electrolyte and fluid volume takes precedence over the acid-base disturbance. These various efiects all combine to yield a positive feedback system driving the metabolic alkalosis which, if not treated, reaches lethal levels in a few days. 

The potassium leaving cells and entering the extracellular fluid partially replaces the potassium lost into the renal tubular fluid and is of itself just a redistribution of potassium within difleient fluid compartments in the body. It is not lost from the body. However, the potassium moving from the intra- to the extracellular compartment bolsters the extracellular concentration of potassium, and, by the electroneutrality effect described earlier, becomes available for excretion in the urine, thereby being lost to the body entirely. The overall effect is a dramatic lowering of total potassium content of the body. 

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About 1895 Benjamin Moore, then an assistant professor of physiological chemistry at University College London, began to assemble data for his chapter on Chemistry of the Digestive Processes, to be published in 1898 in the first volume of E. A. Schafer s Text-book of Physiology To establish the composition of gastric juice, Moore quoted the data that Carl Schmidt had collected in Dorpat and had published in Bidder and Schmidt s Die Verdauungssaefte und der Stoffwechsel in 1852 (Table 1-1). ... 

Source Compiled from data in Gray JS, Bucher, GR, The composition of gastric juice as a function of the rate of secretion. Am J Physiol 133 542-550, 1941. 

Teorell demonstrated that his model could describe the composition of gastric juice at increasing rates of secretion (Fig. 1-11). In this example, primary acidity and the concentration of NaCl in plasma are assumed to be equal at 162 mN. As the secretion rate rises, the chloride concentration at first falls and then rises to approach its concentration in the primary secretion. The sodium concentration falls and the hydrogen ion concentration rises to meet the chloride concentration. ... 

Figure 3.7. Bar diagram to show the composition of gastric juice. The anion composition is always of chloride at a concentration typically of 150 mM. The cation composition reflects the pH of the gastric juice, as the diagram illustrates. The potassium concentration is fairly constant at around 10 mM. The sodium and hydrogen ion concentration together provide the remaining 140 mM. The hydrogen ion concentration, shown as the shaded area, is 120 mM at pH = 0.9,100 mM at pH =1.0 and 10 mM at pH = 2.0. The respective concentrations of sodium ions are therefore 20, 40 and 130mM.

Other workers determined the entire carbohydrate spectrum of human gastric juice in an attempt to evaluate the composition of gastric mucosubstances. Richmond et al. (R4) and Hoskins and Zamcheck (H50) studied a large number of individual gastric juices in our laboratory (G55) a large pool of normal gastric juices was studied for hexoses, hexosamine, fucose, sialic acid, uronic acid, and total carbohydrate content. Results obtained in normals and patients with various gastric diseases are summarized in Tables 8 and 9. 

Influence of Feeding on the Quantity and the Composition of the Gastric Juice Secreted. — First of all, it has been established that there exists a very definite relation between the secretorial functions and the food absorbed. Thus Chigin, by measuring the quantity of gastric juice which flows after the ingestion of various foods, has found ... 

The existence of more than one mucoprotein in the dissolved mucin fraction of the gastric juice was further substantiated in our laboratory (G26, G27, G36). We found (G27) that the composition of dissolved mucin varied markedly, depending upon the stimulus applied to gastric secretion. These variations included degree of hydration, extractability with 60% alcohol, and content of tyrosine, nitrogen, and reducing substances. We therefore postulated that, in man, at least two but probably three different mucous substances were present within the mixture of mucosubstances called dissolved gastric mucin (Gll, G27) (Fig. 16). 

When 1.5 volumes acetone is added to the trichloroacetic acid filtrate of the gastric juice, an abundant flocculent precipitate forms, which contains all the components of dissolved mucin with the exception of soluble mucus. If this precipitate is taken up in dilute alkali and then acidified with dilute HCl down to pH 3.5, a fine flocculent precipitate forms, which we named dissolved mucoprotein (G27, G36). It was later renamed glandular mucoprotein (G9, G38) because of its close relationship to the fundic glands of the stomach. This material contained much protein its nitrogen content was 12.61 0.44% and its tyrosine content 7.50 0.65% by the Folin-Giocalteu reaction. The reducing substance content was 6.38 1.48% before and 12.5% after hydrolysis (G9, G27, G36) (see Table 4). Werner (W9) determined the composition of this mucoprotein fraction and found that it contained 11.2% N by Kjeldahl, 8.8% hexosamine, 4.8% uronic acid, and 2.0% sialic acid. 

The composition of various blood group substances from human gastric juice, as reported by Masamune et al. (M22), Tiba (T29) and Yosizawa (Y3), varies only little. The N content is in the range 4.7-4.9%, hexos-amine 29.0-30.8%, galactose 26.6-27.8%, fucose 12.9-14.1%, and sialic acid 3.0-5.2%. Presence of considerable amounts of sialic acid in these materials perhaps indicates their contamination with sialomucin. 

In work from our laboratory, Ibanez determined the composition of the first fractions eluted from the Amberlite IRC-50 column of gastric juice pools from indh iduals with various blood groups. The first fraction eluted with citrate of pH 3.2-S.5 is known (R4, R4a) to contain blood group substances. 

Figure 1 -5. Franklin Hollander s plot of neutral chloride concentration (total chloride minus total acidity) as ordinates against total acidity in 121 samples of dogs gastric juice. (From Hollander F. The composition of pure gastric juice. Am I Dig Dis 1 319-329, 1934.)...

Figure 1-7. A "Gamblegram" showing the relationship between the electrolyte composition of cats gastric juice and blood plasma. (From Gamble JA, Mclver MA. The acid-base composition of gastric secretions. I Exp Med 48 837-857, 1928, by copyright permission of the Rockefeller University Press.)...

For the chamber, see Rehm WS, Dennis WH, Schlesinger H. Electrical resistance of the mammalian stomach. Am J Physiol 181 451-470, 1955. For attempts to modify the blood, see Thull NB, Rehm WS. Composition and osmolarity of gastric juice as a function of plasma osmolarity. Am J Physiol 185 317-324,1956. For early isolated mucosa work, see Rehn WS. Acid secretion, resistance, short-circuit current and voltage clamping in frog s stomach. Am J Physiol 203 63-72, 1962. 

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