Final answer:
Calcitonin and parathyroid hormone (PTH) work in opposition to each other to maintain calcium homeostasis in the human body; calcitonin lowers blood calcium levels when they are high, and PTH raises them when they are low.
Step-by-step explanation:
Role of Calcitonin and Parathyroid Hormone in Maintaining Homeostasis
The human body maintains calcium homeostasis through the actions of two primary hormones: calcitonin and parathyroid hormone (PTH). Calcitonin, produced by the thyroid gland, helps to regulate calcium levels by inhibiting osteoclast activity and stimulating calcium excretion in the kidneys when blood calcium levels are high. This effectively lowers the calcium levels in the body fluids. On the other hand, PTH, secreted by the parathyroid glands, works to increase blood calcium concentrations when they fall below normal. PTH enhances calcium reabsorption in the kidneys, stimulates osteoclast activity, and promotes calcitriol secretion, which in turn enhances calcium absorption in the digestive system. These actions collectively raise the calcium levels in the body fluids. Together, calcitonin and PTH maintain calcium balance within a narrow, healthy range, ensuring proper function of various physiological processes such as nerve conduction, muscle contractions, and blood clotting.