Table of Contents
- What Is Calcitonin?
- Discovery of Calcitonin
- Synthesis of Calcitonin
- Function of Calcitonin
- Activity of Calcitonin
- Clinical Significance
What is Calcitonin?
Calcitonin is a peptide hormone made up of 32 amino acid residues that is secreted from the parafollicular cells, also known as C cells. It is found in the thyroid of chordates and humans and the endostyle of invertebrates. It acts opposite to the parathyroid hormone by reducing the blood calcium levels.
It is a member of the calcitonin-like protein family. Previously, calcitonin was also called thyrocalcitonin.
Discovery of Calcitonin
Calcitonin was discovered by B. Cheney and Douglas Harold Copp in 1962 at the University of British Columbia. Copp named the hormone calcitonin because of its function in maintaining normal calcium tone.
It was first thought to be secreted from the parathyroid gland, but Iain Macintyre of Royal Postgraduate Medical School, London showed that it is secreted from the parafollicular cells of the thyroid gland.
Synthesis of Calcitonin
Calcitonin is biosynthesised by the proteolytic cleavage of prepropeptide that is released from the CALC1 gene. It functions antagonistically to vitamin D3 and parathyroid hormone. The synthesis or secretion of calcitonin is triggered by high levels of calcium in blood and the presence of pentagastrin and gastrin.
Function of Calcitonin
Calcitonin is a hormone that functions to decrease the calcium levels in our blood by counteracting against parathyroid hormone which increases the calcium levels. It lowers the levels of calcium in our blood by inhibiting osteoclasts in the bone tissue. As a result, the resorption of calcium in the kidney is inhibited and more calcium is excreted from our body.
However, this increased excretion of calcium may cause hypocalcemia. This condition has very little physiological effect, firstly because it has a short-term effect, and secondly because the kidneys soon become resistant to calcitonin.
Another important function of calcitonin is to decrease loss of calcium in high calcium mobilisation situations such as pregnancy and lactation. It also inhibits postprandial hypercalcemia.
Activity of Calcitonin
Calcitonin inhibits osteoclasts to lower the level of calcium in blood. However, osteoblasts do not have calcitonin receptors and are hence not affected by levels of calcitonin. The process of bone formation and bone resorption is a coupled process, therefore inhibition of osteoclasts ultimately leads to inhibition of osteoblasts as a result of indirect effect.
The calcitonin receptor is a G protein-coupled receptor that is located on osteoclasts, brain cells and the kidney. It stimulates cAMP production in target cells and may also affect reproductive structures of men and women.
Clinical Significance
Calcitonin levels are increased in association with lung cancer and certain tumours in the pancreas. Medullary thyroid carcinoma, a cancer of the parafollicular cells, is characterised by elevated levels of serum calcitonin.
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Also Read:
- What Is Bone? – Types and Functions
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- Thyroid Hormones – Functions, Production and More
- Types, Regulation & Growth Hormone Function
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