There are four ways that parathyroid hormone (PTH) increases the level of calcium in the blood.

1. PTH stimulates osteoclasts to break down bone tissue and release calcium ions from the bone.

2. PTH inhibits osteoblasts to reduce the rate of calcium deposition in bone.

3. PTH enhances the absorption of calcium and phosphate from the small intestine in conjunction with the secretion of calcitriol by the kidneys.

4. PTH promotes the reabsorption of calcium at the kidneys, reducing the amount of calcium excreted in urine.