Beachey: Respiratory Care Anatomy and Physiology, 2nd Edition

Answers to Concept Questions

Chapter 23: Electrolyte and Acid-Base Regulation

23-1	A low-sodium diet decreases the amount of Na+ ions in the filtrate and thus the amount of Na+ the kidney can transport from the filtrate into the tubule cell. This in turn decreases the amount of Na+ the Na+-K+-ATPase pump can transport out of the tubule cell (on the nonluminal side) in exchange for K+. This inhibits K+ secretion into the tubular filtrate, and extracellular K+ concentration tends to rise, leading to hyperkalemia.

23-2	The acidemic patient with coexisting hypokalemia has the most severe depletion of potassium stores. Acidemia is normally associated with hyperkalemia because K+ tends to move out of the cell in exchange for H+ (see Figure 23-8). A low blood K+ concentration in the presence of acidemia means intracellular stores of K+ are profoundly depleted. Conversely, low blood K+ in alkalemia is expected because alkalemia causes K+ to move into the cell (Figure 23-8). Thus hypokalemia in alkalemia does not necessarily mean overall body stores of K+ are low.

23-3	The metabolic acidosis that accompanies uremia stimulates compensatory hyperventilation; thus people in uremic kidney failure may be tachypneic and hyperpneic (rapid, deep breathing).

23-4	The compensatory hyperventilation stimulated by uremic kidney failure may precipitate ventilatory failure in individuals with an already reduced ventilatory reserve capacity, such as people with severe chronic obstructive pulmonary disease.