PH of gastric juice

The pH of gastric juice is 1 to 3. The pKa of benzoic acid, a weak acid, is 4. Taking the pH in the stomach as 2, and using the Henderson-Hasselbach equation as described above, it can be calculated that benzoic acid is almost completely nonionized at this pH (Fig. 3.13) ... 

For in vivo electrochemical measurement, the placement of the electrodes is important. In the potentiometric measurement (e.g., measurement of the pH of gastric juices) both the working electrode and the reference electrode are placed in the stomach. On the other hand, when amperometric measurement is done, the working electrode is in the place where you are getting the information from, but the auxiliary (reference) electrode can be anywhere, even on the skin. 

For example, phenytoin is absorbed primarily from the upper intestinal tract. Phenytoin is an acid with a pKa of 8.3 to 9.2 and is insoluble at the pH of gastric juice (pH, 2.0). Therefore, it cannot be absorbed significantly from the stomach. On passage into the small intestine, where the pH is less acidic (7 to 7.5), phenytoin is absorbed in a nonionized form. 

In experiments with rabbits, Kuriyama found that raffinose is not digested.47 Raffinose, injected parenterally, was recovered to the extent of 88% in the urine. Although, at the pH of gastric juice, there is slow inversion of raffinose, there is no raffinase present in saliva, bile, pancreatic juice, liver, lor intestine. Kuriyama concluded that raffinose has no food value. 

Answer Pepsin proteins have a relatively low pi (near the pH of gastric juice) in order to remain soluble and thus functional in the stomach. (Pepsin—the mixture of enzymes—has a pi of 1.) As pH increases, pepsins acquire a net charge and undergo ionic interactions with oppositely charged molecules (such as dissolved salts), causing the pepsin proteins to precipitate. Pepsin is active only in the stomach. In the relatively high pH of the intestine, pepsin proteins precipitate and become inactive. 

The pH of gastric juice is 1. The cells that produce gastric juice have an internal pH of 7. Calculate the AG for transport of protons from these cells into the stomach at 37°C. (R, the gas constant, is 8.3 J mol-1 K 1.)... 

The pH of gastric juice is about 1.5. Assuming that the pH inside the cells of the gastric mucosa is 6.8, calculate the amount of energy required to secrete a mole of H ions. Assume T = 37 C. 

The pH of gastric juice in the human stomach is 1.5. This strongly acidic environment activates digestive enzymes, such as pepsin, that work in the stomach. 

The activity of most enzymes depends on pH. The pH-enzyme activity profile of most enzymes delineates a bellshaped curve (Figure 6-3), exhibiting an optimal pH at which activity is maximal. This pH is usually the same as the pH of the fluid in which the enzyme functions. Thus, most enzymes have their highest activity between pH 6 and pH 8 (the pH of human blood is about 7.4). However, pepsin, which must function at the low pH of gastric juice, has maximal activity at about pH 2. 

J. F. McClendon used it for determining the pH of gastric juice. The properties of the substance were studied later on in greater detail by I. M. Kolthoff. Commercial preparations are available in the form of a dark red-black powder. The indicator is insoluble in water but dissolves in alcohol producing a dark red solution. A stock solution, containing 0.1 % of indicator in 95% alcohol, should be stored in dark containers. Aside from having a rather large salt error, the indicator is satisfactory. 

Let us apply these concepts and attempt to make some predictions. The very useful, widely used drug aspirin is a weak acid with a pKa of 3.5. It is usually taken orally. The pH of gastric juice in the stomach is about 1 in the small intestine it is about 6. From which area would the majority of this drug be absorbed into the bloodstream By applying Equation 1.6 we find that the drug is almost completely un-ionized in the gastric juice. 

Reflect and Apply Aspirin is an acid with a pJ of 3.5 its structure includes a carboxyl group. To be absorbed into the bloodstream, it must pass through the membrane lining the stomach and the small intestine. Electrically neutral molecules can pass through a membrane more easily than can charged molecules. Would you expect more aspirin to be absorbed in the stomach, where the pH of gastric juice is about 1, or in the small intestine, where the pH is about 6 Explain your answer. 

An average adult produces between 2 and 3 L of gastric juice daily. Gastric juice is an acidic digestive fluid secreted by glands in the mucous membrane that lines the stomach. It contains hydrochloric acid (HCI), among otho" substances. The pH of gastric juice is about 1.5, which... 

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