Final answer:
Calcitonin regulates blood calcium levels by inhibiting osteoclast activity in bone tissue and decreasing calcium reabsorption in the tubules of the kidneys.
Step-by-step explanation:
To regulate blood calcium levels, calcitonin targets a few specific effectors in the body. When blood calcium levels are too high, the thyroid gland releases calcitonin, which primarily affects:
- B. osteoclasts in bone tissue by inhibiting their activity which reduces bone resorption and the release of calcium into the bloodstream.
- A. tubules of kidneys by decreasing reabsorption of calcium, which leads to an increase in calcium excretion in urine.
These actions collectively lower the blood calcium levels back to normal. Therefore, the correct answers are A: tubules of kidneys and B: osteoclasts in bone tissue.