Stomach chyme

It has been suggested by Podesta et al. (650) that ambient C02 levels determine the amount of succinate and lactate excreted by intestinal helminths. A summary of the events which they propose lead to succinate accumulation in H. diminuta is provided in Fig. 5.7. There is considerable release of C02 in the post-prandial intestine of the rat host as the acidic chyme is passed into the duodenum and there is an acidification of worm tissues as the C02 diffuses in. The acidification is countered by worm secretion of H+ and by mobilisation of Ca2 + from the calcareous corpuscles (Chapter 4), thus releasing carbonate. The increased osmolality and greater HC03 concentration activate PEPCK, which favours succinate production over lactate. Succinate, being a dicarboxylic acid, is twice as effective as lactate in metabolic disposal of H+. With a decrease in passage of stomach chyme into the intestine, there would be a decrease in acid stress on the worms, accompanied by a concomitant decrease in tissue HC03 concentrations and osmolality, which would favour lactate production. 

The food, now in a liquid form known as chyme, passes through the pyloric sphincter into the duodenum, where stomach acid is neutralized. There is wide variation in lengths of the components of the small intestine (i.e., duodenum, jejunum, and ileum) between individuals (Table 98-1). Most absorption of digested carbohydrate and protein occurs within the jejunum. Most fat absorption occurs within the jejunum and ileum. In the small bowel, breakdown of macronutrients (i.e., carbohydrate, protein, and fat) occurs both within the lumen of the gut and at the intestinal mucosal membrane surface. The absorptive units on the intestinal mucosal membrane are infoldings known as... 

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. 

Food is stored in the body of the stomach, which may expand to hold as much as 11 of chyme. As food enters the stomach, it undergoes a reflex relaxation referred to as receptive relaxation. It enhances the ability of the stomach to accommodate an increase in volume with only a small increase in stomach pressure. The fundus does not typically store food because it is located above the esophageal opening into the stomach. Instead, it usually contains a pocket of gas. 

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 ... 

An important gastric secretion is the hydrochloric acid that performs a number of functions in the stomach. This stomach acid is neutralized by pancreatic bicarbonate ion in the duodenum. Excess acid in the chyme stimulates chemoreceptors in the duodenum. This receptor stimulation elicits reflex inhibition of gastric motility. Excess acid also causes the release of secretin and gastric inhibitory peptide from the duodenum. These hormones contribute to inhibition of gastric contractions so that the neutralization process may be completed before additional acid arrives in chyme from the stomach. 

Pancreatic juice neutralizes the acidic chyme entering the duodenum from the stomach. Neutralization not only prevents damage to the duodenal mucosa, but also creates a neutral or slightly alkaline environment optimal for the function of pancreatic enzymes. The pancreas also secretes several enzymes involved in the digestion of carbohydrates, proteins, and lipids. 

Water and electrolytes. Each day in an average adult, about 5.51 of food and fluids move from the stomach to the small intestine as chyme. An additional 3.5 1 of pancreatic and intestinal secretions produce a total of 9 1 of material in the lumen. Most of this (>7.5 1) is absorbed from the small intestine. The absorption of nutrient molecules, which takes place primarily in the duodenum and jejunum, creates an osmotic gradient for the passive absorption of water. Sodium may be absorbed passively or actively. Passive absorption occurs when the electrochemical gradient favors the movement of Na+ between the absorptive cells through "leaky" tight junctions. Sodium is actively absorbed by way of transporters in the absorptive cell membrane. One type of transporter carries a Na+ ion and a Cl ion into the cell. Another carries a Na+ ion, a K+ ion, and two Cl ions into the cell. 

For the most part, the resting pH of the stomach is nearer to 2 than 1 however, during feeding the meal causes a transient rise in pH to 4—5 depending on the volume and nature of the meal consumed. The fundus undergoes receptive relaxation to allow the proximal stomach to accommodate the food mass in the distal stomach, the food is triturated to form chyme, which is ejected into the duodenum in spurts of 2-5 mL. The division of function causes significant inhomogeneity in... 

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). 

Approximately 1 to 1.5 L of fluid is ingested per day, and coupled with secretions from the stomach, pancreas, and proximal duodenum, approximately 8 L of chyme enters the jejunum per day. Reabsorption of 6 to 7 L occurs within the small bowel, leaving a residual of 1.5 L fluid, 90% of which is reabsorbed in the colon. This pattern of liquid reabsorption permits the elimination of fecal waste containing an average of 0.1 to 0.2 L fluid per day. Diarrhea occurs if there is an altered rate of intestinal motility, if mucosal function or permeability is altered, or if the fluid load entering the colon overwhelms colonic reabsorption. Constipation may occur if intestinal movement is inhibited or if there is a fixed obstruction. 

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. 

The chyme that passes into the intestine from the stomach typically is not hyperosmotic, but as its macromolecular components are digested, the osmolarity of that solution increases (e.g. glucose is osmotically more active than sucrose). 

The digestion of triacylglycerols in adult nonruminant mammals has been described as initiated in the mouth by hngual lipase released in the sahva at the base of the tongue (52). Up to 6% of the fatty acids are hydrolyzed and initiate emulsion formation in the stomach. The digesta (called chyme at this location) is released from the stomach slowly into the duodenum to ensure complete mixing with the bile salts and emulsification. Lipolysis occurs by association of pancreatic lipase and co-lipase at the surface of the bile salt-stabihzed emulsion. Amphipathic molecules (fatty acids, sn-2 monoacylglycerols, and lysolecithins) are produced and associate with the bile salts to form water-soluble micelles from which absorption occurs. 

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 intestinal phase that begins when chyme passes from the stomach to intestine, contributes about 10%of the total response to a test meal. Protein and its digestion products, milk, dilute alcohol, and acid itself are effective stimulants. Although there may be a ner-... 

In the stomach, food is converted into a semi-fluid, homogeneous, gruel-like material (chyme) that passes through the pyloric sphincter into the small intestine. The small intestine consists of three parts the duodenum, jejunum, and ileum. In the adult human, the small intestine is approximately 2 to 3 m long and decreases in cross-section as it proceeds dis-... 

A common duct from the pancreas and gall bladder enters the duodenum. Duodenal pH is 6 to 6.5 due to the presence of bicarbonate that neutralizes the acidic chyme emptied from the stomach. The pH is optimum for enzymatic digestion of protein and peptide food. Pancreatic juice containing enzymes is secreted into the duodenum from the bile duct. Trypsin, chymotrypsin, and carboxypeptidase are involved in the hydrolysis of proteins into amino acids. Amylase is involved in the digestion of carbohydrates. Pancreatic lipase secretion hydrolyzes fats into fatty acids. 

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