Final answer:
Parathyroid hormone and calcitriol synergistically increase blood calcium levels by enhancing renal calcium reabsorption, osteoclast activity, and intestinal calcium absorption. These hormones play crucial roles in maintaining calcium homeostasis.
Step-by-step explanation:
Parathyroid hormone (PTH) and calcitriol work together to increase blood calcium concentrations when calcium ion levels are low. This is accomplished through several mechanisms: PTH enhances reabsorption of Ca2+ by the kidneys, stimulates osteoclast activity (bone resorption) and inhibits osteoblast activity (bone formation), and stimulates the synthesis and secretion of calcitriol by the kidneys.
Calcitriol, the active form of vitamin D, further supports this function by enhancing Ca2+ absorption in the digestive system. It is essential for maintaining calcium homeostasis, which is crucial for bone health, muscle function, and overall cellular processes. While PTH and calcitonin generally have opposing effects, PTH and calcitriol cooperate to manage and maintain adequate calcium levels in the blood.