Calcitonin: Encyclopedia II - Calcitonin - Physiology

Calcitonin - Physiology

The hormone participates in calcium and phosphorus metabolism and it was found in fish, reptiles, birds and mammals. Most evidence points to that Calcitonin is not of physiological importance to humans, except for it's pharmacological use (see below).

Specifically, calcitonin reduces blood calcium levels in three ways:

• decreasing calcium absorption by the intestines
• decreasing osteoclast activity in bones
• decreasing calcium and phosphate reabsorption by the kidney tubules

Its actions, broadly, are:

• bone mineral metabolism
  • prevent postprandial hypercalcemia resulting from absorption of Ca++ from foods during a meal
  • promote mineralization of skeletal bone
  • protect against Ca++ loss from skeleton during periods of Ca++ stress such as pregnancy and lactation
• Vitamin D regulation
• A satiety hormone
  • inhibit food intake in rats and monkeys
  • may have CNS action involving the regulation of feeding and appetite

Like the PTH receptor, the receptor of calcitonin is a serpentine G protein-coupled receptor with seven membrane spanning regions which is coupled by Gs to adenylyl cyclase and thereby to the generation of cAMP in target cells. Indeed, the PTH and calcitonin receptors are family members which are related in amino acid sequence, though their ligands are not.

Adapted from the Wikipedia article "Physiology", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki