USMLE (United States Medical Licensing Examination) Step 1 Practice Exam

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What is the correct association between Respiratory alkalosis and Ca2+ homeostasis?

Decreases PTH levels
Causes metabolic acidosis
Increases ionized calcium levels
Leads to tetany due to decreased ionized calcium levels

The correct answer is: Leads to tetany due to decreased ionized calcium levels

Respiratory alkalosis is characterized by a decrease in carbon dioxide levels in the blood, often due to hyperventilation. This drop in carbon dioxide leads to a reduction in hydrogen ion concentration, which can enhance the binding of calcium to proteins, particularly albumin. As a result, there is a decrease in the ionized form of calcium (the biologically active form) in the serum. As ionized calcium levels drop, this can lead to neuromuscular excitability and ultimately cause symptoms such as tetany, which is characterized by muscle spasms and increased nerve excitability. The association between respiratory alkalosis and tetany due to decreased ionized calcium levels is thus well-documented and is a critical concept in understanding acid-base imbalances and their effects on electrolyte homeostasis. In summary, the physiological response to respiratory alkalosis includes decreased ionized calcium levels, leading to the clinical manifestation of tetany. This makes the association between respiratory alkalosis and tetany due to decreased ionized calcium levels accurate and clinically relevant.