Final answer:
Parathyroid hormone (PTH) is released due to low blood calcium levels and stimulates the conversion of calcidiol to calcitriol in the kidneys, aiding in increasing blood calcium levels. The correct answer is c. parathyroid hormone.
Step-by-step explanation:
The release of parathyroid hormone is stimulated by low blood calcium, which in turn stimulates the conversion of calcidiol to calcitriol in the kidneys. The correct answer to the student's question is option c. parathyroid hormone.
Parathyroid hormone (PTH) is an important regulator of calcium balance in the blood. It is produced by the parathyroid glands when blood calcium levels are low. PTH acts by increasing calcium levels in the blood through several mechanisms: stimulating calcium release from bones, reducing calcium loss in urine, and increasing the intestinal absorption of calcium with the help of activated vitamin D (calcitriol).
Calcitriol is formed in the kidneys through a PTH-stimulated conversion process. This active form of vitamin D then facilitates calcium absorption from the diet. In contrast, the hormone calcitonin is released in response to high blood calcium levels and works to lower them, primarily by inhibiting bone resorption and promoting calcium excretion in the urine.