Anatomy Practice Exam

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What substance is primarily stored in bones and released into the bloodstream by osteoclasts?

Calcium
Phosphate
Collagen
Magnesium

The correct answer is: Calcium

The primary substance stored in bones that is released into the bloodstream by osteoclasts is calcium. Osteoclasts are specialized cells responsible for the resorption of bone tissue. When bone is resorbed, osteoclasts break down the mineral matrix of bone, which releases calcium ions into the bloodstream. This process is crucial for maintaining calcium homeostasis in the body, as calcium plays a vital role in various physiological functions, including muscle contraction, nerve transmission, and blood clotting. Although phosphate is also stored in bones and has important roles in the body, the primary focus of osteoclast activity is on calcium release. Collagen is a structural protein that provides tensile strength to bones, but it is not a mineral released into the bloodstream. Magnesium, while important in bone health, is stored in much smaller quantities and is not primarily stored in bones to the extent that calcium is. Thus, calcium is definitely the most significant substance regarding release into the bloodstream by osteoclasts.