Weak acids physiological actions

Biochemists and molecular biologists use phosphate buffers to match physiological conditions. A buffer solution that contains H2 PO4 as the weak acid and HP04 as the weak base has a pH value very close to 7.0. A biochemist prepares 0.250 L of a buffer solution that contains 0.225 M HP04 and 0.330 M H2 PO4. What is the pH of this buffer solution Is the buffering action of this solution destroyed by addition of 0.40 g NaOH ... 

Carbonic acid, H2CO3, is a weak acid that dissociates by the above reaction (B). In general, a solution of a weak acid HA that dissociates into H and A will serves as a buffer solution. Thus, respiration in lungs contributes to physiological buffer actions. 

This is a lipophilic weak base (pKa 4), which crosses cell membranes easily at physiological pH. It is a prodrug, which at the acidic intracellular pH in the gastric parietal cell converts to the active sulfenamide form, which is lipophobic and so is trapped and preferentially concentrated in the parietal cells. Omeprazole is highly protein-bound. Hepatic metabolism is rapid, with a plasma half-life of 0.5-1.5 h, but because of covalent binding to the H-1-/K-1- ATPase enzyme, the duration of action exceeds 24 h. 

It was soon recognized that gastric HVK -ATPase is the site of action for omeprazole [27,43] and that enzyme inhibition parallels inhibition of gastric acid secretion in laboratory animals [38]. Physico-chemically, omeprazole represents a lipid-permeable weak base with a pK of 4 [42]. At physiological pH, it is predominantly unionized and this neutral form passes freely across biological membranes. However, in an acidic environment with a pH below 4, it is predominantly protonated. This results in a limited permeability of the drug [28]. Due to the unique structure of the gastric... 

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