1. If the plasma pH is 7.4 and the plasma concentration of HCO3- is 15 mM, what

Question

1. If the plasma pH is 7.4 and the plasma concentration of HCO3- is 15 mM, what is the plasma concentration of H2CO3? What is the plasma concentration of CO2 (dissolved)? If metabolic activity changes the concentration of CO2 (dissolved) to 3 mM, and [HCO3-] remains at 15 mM, what is the pH of plasma? Show all your calculations. (Useful information can be found on pages 66 and 67 of your book. At 37 °C, the pKa of carbonic acid (H2CO3) is 3.57. The equilibrium constant for the hydration of CO2 is 3 x10-3)

Explanation / Answer

Part a

From the Henderson-Hasselbalch equation

pH = pKa + log[HCO3-]/[H2CO3]

7.4 = 3.57 + log[HCO3-]/[H2CO3]

log[HCO3-]/[H2CO3] = 3.83

[HCO3-]/[H2CO3] = 6760.829

15mM/[H2CO3] = 6760.829

[H2CO3] = 0.002218 mM

Part b

[H2CO3]/[CO2] Kh (hydration equilibrium constant)

[H2CO3]/[CO2] 3×10^3

[CO2] = 0.002218/3*10^-3 = 0.739 mM

Part C

[H2CO3]/[CO2] 3×10^3

[H2CO3]/3 3×10^3

[H2CO3] = 9*10^-3 mM

pH = pKa + log[HCO3-]/[H2CO3]

pH = 3.57 + log(15/9*10^-3)

pH = 6.79

Related Questions

Navigate

• Browse (All)
• Browse 1
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.