Final answer:
The hormone secreted in response to low blood calcium levels is parathyroid hormone (PTH), which acts on bones, kidneys, and intestines to increase calcium concentration in the blood.
Step-by-step explanation:
Response to Low Blood Calcium Levels
When blood calcium levels are low, the parathyroid hormone (PTH) is secreted as a regulatory response. The parathyroid glands produce PTH, a peptide hormone consisting of 84 amino acids, which plays a crucial role in maintaining calcium homeostasis. PTH secretion is triggered by a decrease in blood calcium levels and has several targets to increase those levels:
The skeleton: PTH stimulates osteoclasts, which degrade bone and release calcium into the bloodstream. Concurrently, it inhibits osteoblasts to conserve blood calcium.
The kidneys: PTH promotes reabsorption of calcium (and magnesium) from the urine, reducing the amount lost during excretion.
The intestines: Via the production of calcitriol, the active form of vitamin D3, PTH enhances dietary calcium absorption.
A negative feedback loop involving rising blood calcium levels inhibits further release of PTH, ensuring that calcium levels stay within the necessary range for bodily functions.