Jack T. answered • 04/03/19
Medical Student with over 2 years of physiology tutoring experience
The most important factor that affects parathyroid release is blood calcium levels. When blood calcium drops too low, the parathyroid gland senses this disturbance and releases PTH (Parathyroid hormone). PTH functions to increase blood calcium levels by indirectly stimulating bone breakdown cells or osteoclasts to break down bone and liberate some calcium. PTH activates Vitamin D which can promote reabsorption of calcium in the GI system and Urinary system.
On the opposite side of things, calcitonin is the hormone that is released when calcium levels are too high. Calcitonin is released from C- cells in the thyroid. Calcitonin's job is to lower calcium levels and does this by signaling to bone synthesis cells or osteoblasts to deposit that excess calcium into bones.
You can think of these two hormones acting in a homeostatic loop, like insulin and glucagon do.
