Beachey: Respiratory Care Anatomy and Physiology, 2nd Edition

Answers to Concept Questions

Chapter 10: Acid-Base Regulation

10-1	The pH equals 6.00, meaning [H+] is 106, or 0.000001 M/L. This represents a greater H+ concentration than a pH of 7.00: [H+] = 107, or 0.0000001 M/L.

10-2	A solution of HCl and its conjugate base, Cl, is not an effective buffer because HCl is almost 100% dissociated in solution (i.e., it has an extremely large ionization constant [K]). Thus the dissociation of HCl molecules is irreversible, eliminating it as an effective buffer.

10-3	The pH of a solution with an HCO3/(PCO2  0.03) ratio of 25:1 is calculated as follows: 	pH = 6.1 + log (25)
  pH = 6.1 + 1.398
  pH = 7.498

10-4	If the lungs fail to ventilate adequately, carbon dioxide elimination slows, decreasing the ability of plasma HCO3 to buffer H+ because the hydrolysis reaction’s leftward movement is impeded. Complete cessation of ventilation would create a closed system in which plasma [HCO3] reaches equilibrium with the fixed acid it attempts to buffer, making HCO3 unavailable for further buffering (see Figure 10-6).

10-5	Use the following formula:
  [HCO3] = antilog (pH  6.1)  (PCO2  0.03)
  [HCO3] = antilog (7.40  6.10)  (60  0.03)
  [HCO3] = antilog (1.3)  1.8
  [HCO3] = 19.95  1.8
  [HCO3] = 35.9 mEq/L
If we know that [HCO3] is 24 mEq/L when the pH = 7.40 and the PCO2 = 40 mm    Hg, we can now calculate how much the plasma [HCO3] must increase to maintain a pH of 7.40 when PCO2 rises to 60 mm Hg: (35.9  24) = 11.9 mEq/L.

10-6	To compensate for metabolic acidosis (i.e., low plasma HCO3), the lungs must hyperventilate, lowering arterial PCO2 and thus the amount of volatile acid in the blood; the effect is to bring pH back up toward normal.