What is the role of calcium in human physiology?

Calcium plays a crucial role in human physiology, primarily due to its significance in maintaining the structure of bones and supporting muscle function. Approximately 99% of the body's calcium is stored in the bones and teeth, providing them with strength and rigidity. This mineral is essential during the growth phases of life, contributing to bone density and health, which is particularly important during childhood and adolescence when bone development is critical.

In addition to its structural role, calcium is vital for muscle contraction. When a muscle is stimulated to contract, calcium ions are released within the muscle cells, interacting with proteins that enable the contraction process to occur. This interaction is fundamental to all types of muscle tissues, including skeletal, cardiac, and smooth muscles.

While the other options do mention important physiological functions, they do not encompass the primary functions of calcium. For example, while calcium may have some involvement in blood pressure regulation and immune function, these roles are not as direct or significant as its involvement in bone structure and muscle contraction. Hence, option C accurately identifies the primary and well-established roles of calcium in human physiology.