Gastric chyme

The presence of chyme in the duodenum stimulates neuronal and endocrine responses that stimulate and later inhibit secretion of acid into the stomach. The stimulatory influences dominate when the pH of gastric chyme is above 3. However, when the buffer capacity is exhausted and the pH falls below 2, inhibitory influences dominate. 

The design of a proper delivery system requires a knowledge of the G.I.tract (i). The nature of the gastric acidic and enzymatic medium has been elucidated. More recently Davis (2) and Harris (3) have studied the rate of emptying of the stomach. Dressman (4) has clinically followed pH variations in both the empty stomach and after a meal finding that sinusoidal pH reductions occur during mastication of solid food, whereas the duodenum maintains a relatively constant pH during introduction of the chyme. 

The major gastric factor that affects motility and the rate of emptying is the volume of chyme in the stomach. As the volume of chyme increases, the wall of the stomach becomes distended and mechanoreceptors are stimulated. This elicits reflexes that enhance gastric motility by way of the intrinsic and vagus nerves. The release of the hormone gastrin from the antral region of the stomach further contributes to enhanced motility. 

The most important factors that regulate gastric motility and the rate of emptying of the stomach involve the volume and chemical composition of chyme in the duodenum. Receptors in the duodenum are sensitive to ... 

As the volume of the chyme in the duodenum increases, it causes distension of the duodenal wall and stimulation of mechanoreceptors. This receptor stimulation elicits reflex inhibition of gastric motility mediated through the intrinsic and vagus nerves. Distension also causes release of gastric inhibitory peptide from the duodenum, which contributes to inhibition of gastric contractions. 

Duodenal receptors are also sensitive to the chemical composition of chyme and are able to detect the presence of lipids, excess hydrogen ion, and hyperosmotic chyme. These conditions also elicit the enterogastric reflex and release of the enterogastrones in order to decrease the rate of gastric emptying. 

Hydrodynamics of the upper GI tract are characterized by 1) the kinetics of gastric emptying, and 2) the small intestinal transit and the flow rate of intestinal fluid (chyme). Gastric... 

The stomach receives food from the buccal cavity, it partially digests protein, fat and carbohydrate and it then delivers the resulting mixture (chyme) into the small intestine. The inner surface of the stomach is folded into ridges, to allow for distension after a meal, they contain gastric pits into which several gastric glands discharge their secretions (Table 4.1). 

Pancreatic enemies (B) from slaughtered animals are used to relieve excretory insufficiency of the pancreas ( disrupted digestion of fats steatorrhea, inter alia). Normally, secretion of pancreatic enzymes is activated by cholecystokinin ancreozymin, the en-terohormone that is released into blood from the duodenal mucosa upon contact with chyme. With oral administration of pancreatic enzymes, allowance must be made for their partial inactivation by gastric acid (the lipases, particularly). Therefore, they are administered in acid-resistant dosage forms. 

Pancreatic bicarbonate secretion is also diminished in exocrine pancreatic insufficiency. There may thus be insufficient intraduodenal buffer protection for enzymes against denaturation by gastric acid emptied with postprandial chyme. Indeed, intraluminal pH may decrease below 4.0, which results in irreversible destruction of lipase. 

Q1 The stomach acts as a temporary reservoir for food and as a mixing chamber, allowing small amounts of gastric contents (chyme) to enter the duodenum at intervals. The acid environment and mechanical activity in the stomach starts the breakdown of food items and the acidity of the stomach eliminates many infectious organisms present in ingested material. Finally, an important function is the production and secretion of intrinsic factor, a compound that is necessary for effective absorption of vitamin Bi2 from the diet. 

The intestinal phase, which occurs as chyme enters the duodenum. This involves many inhibitory controls neural and endocrine mechanisms limit the rate of stomach emptying so that the secretory and absorptive mechanisms of the small intestine can cope effectively with the entry of gastric contents. 

Gastric secretion and motility are controlled by both nervous and hormonal mechanisms. The vagus initiates the cephalic phase of secretion in response to the sight or smell of food, before food is eaten. The gastric phase occurs when food enters the stomach and is controlled both by intrinsic nerve reflexes in the stomach wall and released gastrin. The third, or intestinal, phase of secretion is coordinated by nervous and hormonal mechanisms to limit the release of the chyme from the stomach into the duodenum and reduces further acid secretion. 

Pawlow first established the correlation which exists between the gastric and pancreatic secretions. According to him, this second secretion was due to a nervous reflex, resulting from innervation produced by various substances of the chyme, notably its acidity. This opinion is no longer accepted by physiologists. Bayliss and Starling have, in fact, shown experimentally that the nervous system does not intervene at all in the pancreatic secretion, but that this is caused solely by a humoral route, under the action of a special substance, secretin, which is contained in the intestine and which normally, in the course of digestion, is distributed in the blood and directly excites the cells of the pancreas. 

Cannon s work had apparently failed to cross the mile or so separating Harvard s medical school from Tuft s. Eusebio Oehl did mention Cannon in a paper in an Italian journal reporting work probably done before Cannon s paper reached Italy. Oehl had found reducing sugar in the internal part of the gastric contents of dogs and rats fed starchy food, but he found that digestion of starch was more advanced in chyme in the antrum. 

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