The respiratory system regulates acid-base balance by:
A. Increasing mucus production.
B. Changing the rate and depth of respiration.
C. Forming bicarbonate.
D. Reabsorbing bicarbonate.
Correct Answer: B. Changing the rate and depth of respiration
Through changes in the rate and depth of respiration, the acid-base balance is achieved via CO2 elimination and retention. The pulmonary system adjusts pH using carbon dioxide; upon expiration, carbon dioxide is projected into the environment. C and D are responses that refer to ways in which kidneys balance acids and bases.
Option A: Mucus production is not part of the pulmonary regulatory system. Due to carbon dioxide forming carbonic acid in the body when combining with water, the amount of carbon dioxide expired can cause pH to increase or decrease. When the respiratory system is utilized to compensate for metabolic pH disturbances, the effect occurs in minutes to hours.
Option C: If bicarbonate is reabsorbed and/or acid is secreted into the urine, the pH becomes more alkaline (increases). When bicarbonate is not reabsorbed or acid is not excreted into the urine, pH becomes more acidic (decreases). The metabolic compensation from the renal system takes longer to occur: days rather than minutes or hours.
Option D: The renal system affects pH by reabsorbing bicarbonate and excreting fixed acids. Whether due to pathology or necessary compensation, the kidney excretes or reabsorbs these substances which affect pH. The nephron is the functional unit of the kidney.
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