Final answer:
Osteoclast activity is inhibited by the presence of calcitonin, which is released by the thyroid gland to lower high blood calcium levels by reducing bone resorption and promoting bone formation. In contrast, osteoporosis involves increased osteoclast activity, leading to weakened bones and a greater risk of fractures.
Step-by-step explanation:
The scenario that describes the impact on osteoclast activity concerning calcitonin is that the presence of calcitonin inhibits osteoclast activity. When calcitonin is released from the thyroid gland in response to elevated calcium levels in the blood, it serves to decrease bone resorption by inhibiting osteoclasts. This hormone also increases the activity of osteoblasts, which leads to a net removal of calcium from the blood to build up bone, thereby lowering blood calcium levels. Therefore, osteoclast activity when calcitonin is present is reduced, not greater.
Osteoporosis, which is characterized by an increase in osteoclast activity relative to osteoblast activity, results in weakened bones and a higher risk of fractures. This is directly the opposite of the desired effect of calcitonin, which aims to strengthen bones by promoting calcium addition to the bone matrix.