Calcium is physiologically active in which form?

Calcium is physiologically active in its ionized form, which plays a crucial role in numerous biological functions within the body. Ionized calcium, also referred to as free calcium, is the portion of calcium that is not bound to proteins or complexed with other substances. This form of calcium is readily available for physiological processes, such as muscle contraction, neurotransmitter release, and blood coagulation.

In contrast, calcium that is protein bound or complexed does not contribute directly to these active physiological roles, as it is not in a usable form for cellular activities. The body maintains a tightly regulated balance of ionized calcium because even slight fluctuations can have significant effects on various bodily functions. Understanding the role of ionized calcium is fundamental in clinical chemistry, particularly in diagnosing and managing conditions associated with calcium metabolism.