Final answer:
PTH and calcitonin are hormones that regulate blood calcium levels in opposite ways. PTH increases calcium concentration by releasing it from bones and promoting its reabsorption and absorption, while calcitonin decreases levels by inhibiting osteoclasts and promoting calcium update in bones.
Step-by-step explanation:
Regulation of Calcium Ion Concentrations by PTH and Calcitonin
The homeostatic regulation of calcium ions is crucial for various body functions. The parathyroid hormone (PTH) and calcitonin play opposing roles in maintaining calcium ion concentrations within the blood. When calcium levels drop below the normal threshold, PTH is secreted by the parathyroid glands, which leads to the activation of osteoclasts that release calcium from bones. Furthermore, PTH stimulates the reabsorption of calcium in the kidneys and increases the absorption of calcium in the small intestines by promoting the synthesis of vitamin D.
Conversely, when the calcium ions in the blood are too high, the thyroid gland releases calcitonin. This hormone works to inhibit osteoclast activity, which reduces the breakdown of bone and the release of calcium into the bloodstream. In addition, calcitonin promotes the uptake of calcium into bones and decreases its reabsorption in the kidneys, effectively reducing calcium levels in the blood. These mechanisms are harmonized through negative feedback loops to maintain calcium homeostasis.