When the blood becomes more basic (alkaline), how does the carbonic acid-bicarbonate buffer system act to restore normal pH?

A. Respiratory rate decreases to retain CO2: To compensate for an alkaline pH, the respiratory center reduces minute ventilation to allow metabolic carbon dioxide to accumulate. This increases the partial pressure of CO2 and the subsequent production of carbonic acid. This respiratory compensation helps shift the pH back toward 7.4.

B. Respiratory rate remains unchanged: Failure to adjust the respiratory rate during a pH disturbance would allow the alkalosis to persist or worsen. The chemoreceptors in the carotid bodies and medulla are highly sensitive to pH shifts. They provide immediate feedback to modulate breathing and restore chemical equilibrium.

C. Respiratory muscles contract more frequently: More frequent contractions would increase the respiratory rate and deepen the alkalotic state by removing more carbon dioxide. This would be a maladaptive response to an already high pH. The body seeks to conserve CO2 rather than accelerate its removal during alkalemia.

D. Respiratory rate increases to eliminate excess CO2: This is the compensatory response for metabolic acidosis, not alkalosis. Increasing CO2 elimination raises the pH further, which would be dangerous in a patient who is already alkalotic. Respiratory alkalosis is characterized by this specific type of excessive CO2 loss.

A. They dissociate completely in water: Complete dissociation is the defining characteristic of strong acids like hydrochloric acid. Weak acids, such as carbonic acid, exist in an equilibrium state where most molecules remain undissociated. This allows them to function effectively within biological buffer systems.

B. They are more acidic than strong acids: Strength in acids is measured by the degree of ionization rather than the concentration of the solution. Strong acids produce a much higher concentration of free protons and therefore a lower pH. Weak acids are less efficient at donating protons.

C. They increase the pH of the solution significantly: All acids donate hydrogen ions, which serves to lower the pH of a solution by increasing its acidity. Only basic or alkaline substances increase the pH. A weak acid will lower the pH less drastically than a strong acid.

D. They release only a small amount of hydrogen ions in solution: In an aqueous environment, weak acids only partially ionize, maintaining a balance between the acid and its conjugate base. This limited release of protons makes them ideal for physiological buffering. They provide a reservoir of potential hydrogen ions.