Final answer:
Parathyroid hormone (PTH) and vitamin D3 work together to maintain calcium levels in the body through bone metabolism, renal function, and gastrointestinal absorption. PTH regulates bone resorption, phosphate excretion, and transformation of vitamin D into its active form to increase calcium uptake in the intestines. Calcitonin acts to counterbalance the effects of PTH, keeping the calcium in the blood at an optimal level.
Step-by-step explanation:
Role of PTH and Vitamin D3 in Calcium Homeostasis
The regulation of calcium levels in the body is crucial for maintaining various physiological functions, and it is primarily mediated by parathyroid hormone (PTH) and vitamin D3. PTH, an 84-amino acid peptide, is produced by the parathyroid glands in response to decreased circulating calcium levels. It stimulates osteoclasts, which leads to bone resorption and the release of calcium into the bloodstream. Additionally, PTH promotes the synthesis of active vitamin D (calcitriol) in the kidneys, which is essential for the absorption of dietary calcium in the small intestine.
PTH affects calcium homeostasis by inhibiting the reabsorption of phosphate in the kidneys, leading to its excretion. This action prevents the formation of calcium phosphate in the plasma, which would lower blood calcium levels. Moreover, PTH influences the reabsorption of calcium from the urine, contributing to an increase in circulating calcium levels. The opposing hormone, calcitonin, produced by the thyroid gland, helps reduce blood calcium levels by inhibiting osteoclast activity and promoting calcium uptake in bones.
Overall, the interplay between PTH and vitamin D3 is vital for calcium balance. It involves bone metabolism, renal function, and gastrointestinal absorption, all of which are crucial for maintaining calcium homeostasis.