Answer;
A.
Calcitonin stimulates the kidneys to excrete calcium when calcium levels are too high, while parathyroid hormone stimulates the kidneys to absorb calcium when calcium levels are too low.
Explanation;
Parathyroid hormone regulates calcium levels in the blood, largely by increasing the levels when they are too low. It does this through its actions on the kidneys, bones and intestine. That is;
- Parathyroid hormone stimulates the release of calcium from large calcium stores in the bones into the bloodstream.
- Parathyroid hormone reduces loss of calcium in urine
- It indirectly increases calcium absorption from food in the intestine
Calcitonin is involved in helping to regulate levels of calcium and phosphate in the blood, opposing the action of parathyroid hormone, it acts to reduce calcium levels in the blood, by;
- Inhibiting the activity of osteoclasts, which are the cells responsible for breaking down bone.
- Decreasing the resorption of calcium in the kidneys, again leading to lower blood calcium levels.
