Calcitonin and calcium have a clear connection in the metabolism of many different animals. Calcium is needed to maintain many different systems in an animal's body, including cell metabolism and the contraction of various muscles, including the heart muscle that allows the blood to flow through the body. As calcium is important to the proper functioning of many different body systems, the levels of this mineral in the bloodstream must be carefully regulated. Calcitonin is one of the hormones that help maintain the proper balance of calcium in the bloodstream of many different animals, including humans. The connection between calcitonin and calcium levels, however, is less important in humans than in other mammals.
In many animals, calcitonin and calcium levels are very closely linked. A specialized gland, often the thyroid gland, releases calcitonin when the level of calcium in the bloodstream exceeds what the animal can safely use and metabolize. The calcitonin prevents additional calcium from being broken down from where it is stored in the skeletal system and allows excess calcium to pass through the urinary system without being reabsorbed by the animal's kidneys. In this way, excess calcium in the blood is flushed out of the body, decreasing the level of calcium in the animal's bloodstream.
In humans, the connection between calcitonin and calcium is not as integral to the calcium cycle as it is with many other animals. The thyroid gland in humans still secretes calcitonin when levels of calcium in the blood are too high, instigating the same response as it does in other animals. Humans that have had extensive damage to the thyroid gland, however, as well as those who are lacking the gland altogether are able to successfully regulate the calcium cycle without the presence of calcitonin. Many animals that are unable to produce calcitonin, on the other hand, can easily suffer from hypercalcemia, a condition that can become life-threatening.
The connection between calcitonin and calcium has also led to the use of this hormone as a medical treatment. Patients with osteoporosis may be administered calcitonin in order to stop the body from breaking down the calcium in the bones. Though treatment with calcitonin is not as common as other treatments, the ability of this hormone to prevent bone loss makes it effective for many patients.