Which of the following statements regarding calcium homeostasis is true?Multiple ChoiceWhen blood calcium levels are too low, osteoclast activity increases.Parathyroid hormone inhibits osteoclast activity.Parathyroid hormone increases calcium loss from the kidney.Calcitonin elevates blood calcium levels.Increased osteoblast activity increases blood calcium levels.

The statement "When blood calcium levels are too low, osteoclast activity increases" is true.

Here's why:

1. Calcium homeostasis refers to the regulation of calcium levels in the bloodstream. This is crucial for many bodily functions, including bone health, nerve transmission, muscle contraction, and blood clotting.

2. Osteoclasts are cells that break down bone, releasing calcium into the bloodstream. This process is known as bone resorption.

3. When blood calcium levels are too low, the parathyroid glands release parathyroid hormone (PTH).

4. PTH stimulates osteoclast activity, leading to increased bone resorption and thus raising blood calcium levels.

5. Therefore, when blood calcium levels are too low, osteoclast activity does indeed increase.

The other statements are incorrect because:

• Parathyroid hormone stimulates, not inhibits, osteoclast activity.
• Parathyroid hormone decreases, not increases, calcium loss from the kidney.
• Calcitonin lowers, not elevates, blood calcium levels by inhibiting osteoclast activity and stimulating calcium uptake by the bones.
• Increased osteoblast activity decreases, not increases, blood calcium levels because osteoblasts build bone, which removes calcium from the bloodstream.