Calcium is needed for strong bones, blood clotting and normal nervous system and muscle function. Calcium is found in large amounts in dairy products and dark green vegetables, with lesser amounts in nuts and seeds. It's absorbed in your small intestine and either stored in your bones or sent to your blood or cells. This process is regulated by your endocrine system.
Calcium in Your Body
Most of the calcium in your body is stored in your bones, but a small amount is found in your blood and the cells of your body. Your body regulates the amount of calcium in your blood. Too much calcium in the blood is called hypercalcemia and results in organ dysfunction and damage. Too little calcium is called hypocalcemia and can cause muscle spasms and heart problems.
Parathyroid Hormone
Parathyroid hormone is secreted by the parathyroid glands located near the thyroid gland. It's stimulated when the amount of calcium in your blood decreases to a certain level. Parathyroid hormone increases the amount of calcium in your blood by releasing some of the calcium from your bones, increasing the amount of calcium reabsorbed by the kidneys and stimulating the production of active vitamin D.
Vitamin D
Vitamin D is made by your body when your skin is exposed to ultraviolet light. The storage form of vitamin D is called cholecalciferol. The parathyroid gland stimulates your body to convert the stored form of vitamin D to the active form that increases your body's ability to absorb calcium in your small intestine. It also affects the release of calcium from your bones.
Calcitonin
Calcitonin is a hormone produced and secreted by the thyroid gland, lungs and intestinal tract. It's stimulated when your blood levels of calcium start to get too high. Calcitonin reduces blood levels of calcium by suppressing the release of stored calcium from the bones by inhibiting the cells that normally break down the calcium. It also increases the amount of calcium released by the kidneys into the urine, so less is returned to the blood.
