Final answer:
The parathyroid hormone (PTH) from the parathyroid glands raises blood calcium levels by stimulating osteoclasts, enhancing calcium absorption in the gut via active vitamin D, and increasing calcium reabsorption in the kidneys.
Step-by-step explanation:
Functions of Parathyroid Hormone (PTH)
The parathyroid hormone (PTH) is crucial in maintaining calcium homeostasis in the body. It is produced and secreted by the parathyroid glands when blood calcium levels are low. PTH has several actions that help to raise blood calcium levels:
- It stimulates osteoclasts, which resorb bone and release inorganic calcium-phosphate salts into the bloodstream.
- PTH enhances the gastrointestinal absorption of calcium by stimulating the conversion of vitamin D to its active form, calcitriol. This in turn increases calcium uptake by the intestinal epithelial cells.
- It also increases renal reabsorption of calcium, thus decreasing the amount of calcium excreted in urine.
Together, these mechanisms work to ensure the appropriate release of calcium and phosphate to maintain physiological blood levels. Osteoclast activation and the role of vitamin D are key components in this process.