Bone resorption is primarily increased by which hormones?

The correct answer is based on the roles of parathyroid hormone (PTH) and calcitriol (the active form of vitamin D) in regulating calcium levels and bone metabolism.

Parathyroid hormone is secreted by the parathyroid glands in response to low blood calcium levels. It primarily acts to increase blood calcium by stimulating osteoclasts, cells that break down bone and release calcium into the bloodstream, leading to increased bone resorption. Additionally, PTH enhances renal reabsorption of calcium and stimulates the conversion of vitamin D to calcitriol in the kidneys.

Calcitriol, in conjunction with PTH, further promotes bone resorption by increasing the maturation of osteoclasts and enhancing their activity. It also increases intestinal absorption of calcium, contributing to the elevation of calcium levels in the blood.

Therefore, the combination of PTH and calcitriol effectively increases bone resorption, making this the correct answer.

In contrast, other options include hormones that do not primarily function to increase bone resorption. For instance, estrogen and testosterone generally promote bone formation and help maintain bone density. Cortisol can increase bone resorption, but its effects are more complex and can induce osteoporosis when levels are chronically high. Ins