What happens in response to blood calcium deficiency?

• A. Increased calcitonin secretion
• B. Decreased parathyroid hormone secretion
• C. Increased osteoclast activity
• D. Decreased absorption of calcium

Answer: (C)

In response to blood calcium deficiency, the body compensates to restore normal calcium levels, which includes increasing osteoclast activity. Osteoclasts are specialized cells responsible for the resorption of bone, which releases calcium into the bloodstream. When calcium levels are low, parathyroid hormone (PTH) is secreted by the parathyroid glands, which stimulates osteoclasts to break down bone tissue, leading to an increase in the release of calcium from the bones into the bloodstream. This action is crucial for maintaining calcium homeostasis, as calcium plays vital roles in various physiological processes, including muscle contraction, nerve transmission, and blood clotting.

In addition to stimulating osteoclasts, PTH enhances the kidney's reabsorption of calcium and promotes the activation of vitamin D, which increases intestinal absorption of calcium. Overall, the increased activity of osteoclasts directly addresses the deficiency by increasing the availability of calcium in the blood.