Passage
Gastric acid is one of many acids important to biological function in the human body. Production of the main component of gastric acid, hydrochloric acid (HCl) , is accomplished in the stomach by the parietal cells, as shown in Figure 1.
Figure 1 Formation of gastric acid in the stomachFacilitated by the carbonate dehydratase enzyme (1) , the parietal cells utilize the interaction between aqueous carbon dioxide and water in the blood as a source of bicarbonate ions and acidic H⁺ ions (protons) . The H⁺ ions produced in this process are then exchanged for potassium ions through the cell membrane by a proton pump, the H⁺/K⁺-ATPase (2) . In conjunction with this proton exchange, bicarbonate ions are also exchanged for chloride ions from the interstitial fluid. As a result, H⁺ and Cl⁻ ions are concentrated in the lumen of the stomach to form aqueous hydrochloric acid.Because the production of the acid proceeds with a drop in pH from 7.0 in the cell cytosol to 1.0 in the stomach lumen, the process occurs against a concentration gradient and is endergonic, requiring the input of energy supplied by the hydrolysis of ATP. Ignoring effects from ion charge, the free energy change for ion transport across the cell membrane (ΔG_t) can be estimated by Equation 1:
∆Gt=kRT logCfCiEquation 1where R is the gas constant (8.32 J/mol·K) , k is a logarithm conversion constant, T is the absolute temperature, and C_i and C_f are the initial and final molar concentrations across the gradient, respectively.Although dilute, the gastric (hydrochloric) acid released into the lumen yields a strongly acidic environment crucial to protein digestion and the destruction of harmful micro-organisms. A comparison of its acid dissociation constant (K_a) to those of other biologically relevant organic acids is given in Table 1.Table 1 Comparison of Strengths of Selected 0.10 M Acids at 25°C
Adapted from Koolman J, Roehm KH. Color Atlas of Biochemistry. Thieme; 2011: 268-271; and Lehninger AL, Nelson DL, Cox MM. Lehninger Principles of Biochemistry. Macmillan; 2005: 397-398, 419, 520.
-What happens to the pOH of the gastric acid entering the duodenum (pH 6.0) as a result of the introduction of bicarbonate ions from incoming pancreatic secretions?

Question

Passage
Gastric acid is one of many acids important to biological function in the human body. Production of the main component of gastric acid, hydrochloric acid (HCl) , is accomplished in the stomach by the parietal cells, as shown in Figure 1.

Figure 1 Formation of gastric acid in the stomachFacilitated by the carbonate dehydratase enzyme (1) , the parietal cells utilize the interaction between aqueous carbon dioxide and water in the blood as a source of bicarbonate ions and acidic H⁺ ions (protons) . The H⁺ ions produced in this process are then exchanged for potassium ions through the cell membrane by a proton pump, the H⁺/K⁺-ATPase (2) . In conjunction with this proton exchange, bicarbonate ions are also exchanged for chloride ions from the interstitial fluid. As a result, H⁺ and Cl⁻ ions are concentrated in the lumen of the stomach to form aqueous hydrochloric acid.Because the production of the acid proceeds with a drop in pH from 7.0 in the cell cytosol to 1.0 in the stomach lumen, the process occurs against a concentration gradient and is endergonic, requiring the input of energy supplied by the hydrolysis of ATP. Ignoring effects from ion charge, the free energy change for ion transport across the cell membrane (ΔG_t) can be estimated by Equation 1:

∆Gt=kRT logCfCiEquation 1where R is the gas constant (8.32 J/mol·K) , k is a logarithm conversion constant, T is the absolute temperature, and C_i and C_f are the initial and final molar concentrations across the gradient, respectively.Although dilute, the gastric (hydrochloric) acid released into the lumen yields a strongly acidic environment crucial to protein digestion and the destruction of harmful micro-organisms. A comparison of its acid dissociation constant (K_a) to those of other biologically relevant organic acids is given in Table 1.Table 1 Comparison of Strengths of Selected 0.10 M Acids at 25°C

Adapted from Koolman J, Roehm KH. Color Atlas of Biochemistry. Thieme; 2011: 268-271; and Lehninger AL, Nelson DL, Cox MM. Lehninger Principles of Biochemistry. Macmillan; 2005: 397-398, 419, 520.
-What happens to the pOH of the gastric acid entering the duodenum (pH 6.0) as a result of the introduction of bicarbonate ions from incoming pancreatic secretions?

Quizplus · Accepted Answer

11ecba2d_11d6_8a6f_a3bf_7d5c58720b65_MD0008_00 Just as the pH scale assesses acid-base measurements with respect to the concentration of the hydrogen ion, [H⁺], the pOH scale assesses acid-base measurements with respect to the concentration of the hydroxide ion, [OH⁻]. Therefore, the pOH scale is defined analogously to pH as given by pOH = −log[OH⁻]. Accordingly, lower pOH values indicate more alkaline solutions with higher [OH⁻]. This is opposite to the pH scale, in which lower pH values indicate more acidic solutions. Consequently, pH and pOH are inversely correlated. As pH rises, pOH falls (and vice versa) while maintaining the relationship pH + pOH = 14. The bicarbonate ion (HCO₃⁻) is a base (proton acceptor) capable of neutralizing gastric acid through the formation of carbon dioxide and water: H⁺ + HCO₃⁻ → CO₂ + H₂O The [H⁺] decreases as bicarbonate consumes the available H⁺ from the gastric acid, and the relative [OH⁻] increases. As a result, the duodenum (pH 6.0) is less acidic than the upper stomach (pH = 1.0). Therefore, going from the highly acidic stomach to the less acidic duodenum gives a higher pH and a lowerpOH, meaning [H⁺] decreases and [OH⁻] increases. (Choices A, C, and D) Pancreatic secretions release bicarbonate (a base), which neutralizes gastric acid and causes an increase in [OH⁻]. Increasing values of [OH⁻] yield decreasing values of pOH on the logarithmic pOH scale. Educational objective: Analogous to the pH scale, the pOH scale is defined as pOH = −log[OH⁻]. The pOH scale assesses acid-base measurements with respect to [OH⁻] whereas the pH scale operates with respect to [H⁺]. The pH and pOH scales are inversely correlated (as one decreases, the other increases), such that pH + pOH = 14.

Passage Gastric Acid Is One of Many Acids Important to Biological