Final answer:
Parathyroid hormone (PTH) is the primary hormone released from the parathyroid gland. It functions to increase blood calcium concentrations.
Step-by-step explanation:
The primary hormone released from the parathyroid gland is parathyroid hormone (PTH). PTH functions to increase blood calcium concentrations when calcium ion levels fall below normal. It does this by enhancing reabsorption of Ca²+ by the kidneys, stimulating osteoclast activity, inhibiting osteoblast activity, and stimulating the synthesis and secretion of calcitriol by the kidneys, which enhances Ca²+ absorption by the digestive system.