Final answer:
Parathyroid hormone (PTH) regulates blood calcium levels by stimulating osteoclast activity, inhibiting osteoblast activity, promoting calcium reabsorption in the kidneys, converting vitamin D into its active form, and blocking renal phosphate reabsorption. Hyperparathyroidism leads to excess PTH, which can disrupt calcium and phosphate balance and cause various health issues.
Step-by-step explanation:
Parathyroid Hormone (PTH) and Calcium Homeostasis
Parathyroid hormone (PTH), an 84-amino acid peptide, plays a critical role in maintaining calcium homeostasis. Produced by the parathyroid glands in response to low blood calcium levels, PTH has several effects on the body:
It stimulates osteoclasts, which are cells that resorb or break down bone tissue, thereby releasing calcium ions into the bloodstream.
PTH inhibits osteoblast activity, which are the bone-forming cells, sparing blood calcium.
It promotes the reabsorption of calcium by the kidney tubules, preventing its loss in urine.
Additionally, PTH stimulates the conversion of vitamin D into calcitriol, which increases the absorption of dietary calcium in the small intestine and maintains higher circulating calcium levels.
PTH also has an impact on phosphate homeostasis by blocking its reabsorption in the kidneys, which prevents the formation of calcium phosphate that could lower free calcium levels in the blood.
Hyperparathyroidism can result in an excess of PTH, potentially causing an imbalance of calcium and phosphate, leading to a range of health issues including bone resorption and altered acid-base status.