What is the Difference Between Calcitonin and Parathyroid Hormone

The main difference between calcitonin and parathyroid hormone is that calcitonin reduces the calcium concentration in the blood, whereas parathyroid hormone increases calcium concentration in the blood. Furthermore, calcitonin is produced by the thyroid gland, while parathyroid hormone is produced by the parathyroid gland. Additionally, calcitonin indirectly increases the mineralization and the synthesis of the bone matrix while parathyroid hormone increases the formation of osteoclasts, increasing bone resorption.  

Calcitonin and parathyroid hormone are two peptide hormones responsible for the calcium homeostasis in the body. 

Key Areas Covered 

1. What is Calcitonin
     – Definition, Secretion, Function
2. What is Parathyroid Hormone
     – Definition, Secretion, Function
3. What are the Similarities Between Calcitonin and Parathyroid Hormone
     – Outline of Common Features
4. What is the Difference Between Calcitonin and Parathyroid Hormone
     – Comparison of Key Differences

Key Terms

Calcitonin, Calcium Levels, Parathyroid Gland, Parathyroid Hormone, Thyroid Gland

What is Calcitonin 

Calcitonin is a peptide hormone primarily produced by the parafollicular cells of the thyroid gland. Generally, high levels of calcium in the blood stimulate calcitonin production and secretion. Moreover, the main function of calcitonin is to reduce the calcium ion concentration in the blood plasma. Therefore, it stimulates bone-forming cells known as osteoblasts to synthesize bone matrix. Typically, 80% of the bone tissue is composed of the mineral phase, mostly containing calcium phosphate in the crystalline form, which is hydroxyapatite. Hence, bone tissue serves as a reservoir of calcium in the body.

Figure 1: Thyroid and Parathyroid Glands

Furthermore, low levels of calcitonin result in osteopenia, which is a preliminary stage of osteoporosis. Therefore, doctors prescribe calcitonin as a drug for patients with osteoporosis. On the other hand, high levels of calcitonin result in hypocalcemia. Also, it increases the excretion of calcium and phosphorus through urine. 

What is Parathyroid Hormone 

Parathyroid hormone is the peptide hormone with the opposing effect of calcitonin. Generally, it is produced by the parathyroid gland in response to low calcium concentrations in the blood. Therefore, the main function of parathyroid hormone is to increase the calcium level in the blood. It stimulates osteoclasts, which are the cells responsible for bone resorption. Also, it releases calcium ions to the blood, increasing its concentration.

Figure 2: Calcium Regulation

Moreover, lower levels of parathyroid hormone lead to hypothyroidism, which results in lower calcium levels in the blood. On the other hand, higher levels of parathyroid hormone lead to hyperthyroidism, which results in higher calcium levels in the blood. 

Similarities Between Calcitonin and Parathyroid Hormone 

• Calcitonin and parathyroid hormone are the two types of hormones responsible for the regulation of calcium levels in the blood. 
• Both are peptide hormones. 
• However, both have opposing effects on the calcium level in the blood. 
• Moreover, they have a function in bone remodelling. 
• Nevertheless, abnormal levels of these hormones give rise to different clinical conditions. 

Difference Between Calcitonin and Parathyroid Hormone 

Definition 

Calcitonin refers to a peptide hormone secreted by parafollicular cells (also known as C cells) of the thyroid gland in humans, and in many other animals while parathyroid hormone refers to a hormone secreted by the parathyroid glands, regulating the serum calcium through its effects on bone, kidney, and intestine. Thus, this is the main difference between calcitonin and parathyroid hormone.

Secreted by 

Moreover, the thyroid gland secretes calcitonin while parathyroid gland secretes parathyroid hormone. 

Secretion 

The secretion of calcitonin is stimulated by the elevated calcium levels in the blood while the secretion of parathyroid hormone is stimulated by low calcium levels in the blood. Hence, this is another difference between calcitonin and parathyroid hormone.

Influence on the Calcium Level 

Calcitonin reduces the calcium concentration in the blood, while parathyroid hormone increases the calcium concentration in the blood. 

Effect on the Bone Matrix 

Furthermore, the calcitonin indirectly increases the mineralization and the synthesis of the bone matrix, while the parathyroid hormone increases the formation of osteoclasts, increasing bone resorption.  

Low Levels 

Low levels of calcitonin lead to osteopenia, while low levels of parathyroid hormone lead to hypothyroidism. 

High Levels 

High levels of calcitonin lead to hypocalcemia, while high levels of parathyroid hormone lead to hyperthyroidism. 

Conclusion 

Basically, calcitonin is a peptide hormone secreted by the thyroid gland in response to high calcium levels in the blood. Moreover, it is responsible for reducing the calcium levels in the blood by increasing bone mineralization and the synthesis of bone matrix. On the other hand, parathyroid hormone is the peptide hormone secreted by the parathyroid gland with the opposing effect to the calcitonin. Generally, it is secreted in response to low calcium levels in the blood. It increases calcium levels through the breakdown of bones. Therefore, the main difference between calcitonin and parathyroid hormone is the effect on calcium levels in blood and bones. 

References:

1. Mandal, Ananya. “What Is Calcitonin?” News MEDICAL LIFE SCIENCES, 26 Feb. 2019, Available Here.
2. “ The Parathyroid Glands.” Boundless Anatomy and Physiology, Lumen, Available Here.

Image Courtesy:

1. “Illu thyroid parathyroid” (Public Domain) via Commons Wikimedia  
2. “Calcium regulation” By Mikael Häggström (Public Domain) via Commons Wikimedia