Question

Which of the following hormones affect \(\mathrm{Ca}^{2+}\) ion metabolism? (a) TCT (Thyrocalcitonin) (b) Parathyroid hormone (PTH) (c) Both (a) and (b) (d) Cortisol

Short answer

The correct answer is (c) Both (a) and (b). Both TCT (Thyrocalcitonin) and Parathyroid hormone (PTH) have roles in \(\mathrm{Ca}^{2+}\) ion metabolism, thus impacting calcium levels in the body.

Step-by-step solution

Identify Role of TCT

TCT or Calcitonin is a hormone that is produced in the human thyroid gland. Calcitonin has a direct and key role in calcium metabolism, as it lowers blood \(\mathrm{Ca}^{2+}\) levels by inhibiting osteoclast activity in the bones. This way it stops or slows down the process of bone reabsorption where calcium is released into the bloodstream.

Identify Role of PTH

Parathyroid hormone (PTH) is secreted by the parathyroid glands in the neck. It aids in controlling the levels of calcium within the blood. It is vital for bone remodeling due to its effects on both osteoblasts and osteoclasts. When blood \(\mathrm{Ca}^{2+}\) levels are low, PTH secretion is increased to bring the calcium levels back to normal.

Ignore Role of Cortisol

Cortisol is a steroid hormone, and it mainly helps the body respond to stress. It also affects protein degradation, glucose metabolism, and inflammation suppression but doesn't have a major impact on calcium metabolism.

Combine the Hormonal Effects

Now, considering both TCT and PTH, it can be gathered that they function in a complementary manner to fine-tune calcium homeostasis in the body. When the \(\mathrm{Ca}^{2+}\) ion concentration is high, TCT is secreted to lower it, and when it is low, PTH is secreted to increase it.

Key concepts

Thyrocalcitonin (TCT)

Thyrocalcitonin, abbreviated as TCT and often referred to as Calcitonin, is a hormone produced by the thyroid gland in humans. This hormone plays a significant role in calcium metabolism, which is crucial for maintaining proper calcium levels in the blood.

One of the primary functions of TCT is to decrease the concentration of calcium ions (\(\mathrm{Ca}^{2+}\) ions) in the blood. It achieves this by inhibiting the activity of osteoclasts. Osteoclasts are cells responsible for breaking down bone tissue and releasing calcium ions into the bloodstream. When osteoclast activity is inhibited, less calcium is released from the bones, thereby reducing blood calcium levels.

In this way, TCT serves to protect bones by preventing excessive calcium loss and ensuring that blood calcium levels remain within a healthy range. It is an essential component in the complex system of calcium regulation in the body.

Parathyroid Hormone (PTH)

Parathyroid hormone, abbreviated as PTH, is a hormone secreted by the parathyroid glands located in the neck. It is a crucial player in maintaining calcium homeostasis, which refers to the stable balance and distribution of calcium ions within the body.

When the calcium levels in the blood drop below a certain threshold, the secretion of PTH increases. This hormone then acts on various organs to elevate blood calcium levels:

• PTH increases the activity and number of osteoclasts in the bones, promoting the release of calcium.
• It enhances the reabsorption of calcium in the kidneys, preventing its loss through urine.
• PTH also stimulates the production of active vitamin D, which facilitates calcium absorption from the gut.

With these actions, PTH ensures that the body has sufficient calcium for various physiological processes such as nerve function, muscle contraction, and blood clotting.

Calcium Homeostasis

Calcium homeostasis is the process by which the body maintains stable levels of calcium in the blood and within cells. This balance is vital as calcium plays multiple roles in the body, including forming strong bones and teeth, supporting muscle function, nerve signaling, and aiding in blood clot formation.

To maintain calcium homeostasis:

• The thyroid gland releases TCT when blood calcium levels are high to reduce calcium by targeting osteoclasts.
• Conversely, when blood calcium levels are low, the parathyroid glands release PTH to increase calcium levels through several mechanisms.

These hormones work in tandem to keep calcium concentrations within a narrow and optimal range. Without this tight regulation, various health problems can arise, such as osteoporosis (from low calcium levels) or hypercalcemia (from high levels), affecting bone integrity and other bodily functions.

Osteoclast Activity

Osteoclasts are specialized cells that play an essential role in bone remodeling, a continuous process where old bone tissue is replaced with new bone. They achieve this by dissolving bone tissue, releasing calcium and other minerals into the bloodstream.

The activity of osteoclasts is tightly regulated by hormones such as TCT and PTH:

• TCT inhibits osteoclast activity, reducing calcium release from bones when calcium levels are high.
• PTH increases osteoclast activity, promoting the mobilization of calcium from the bone into the blood when needed.

By regulating osteoclast activity, the body ensures that blood calcium levels remain stable, which is vital for both bone health and overall metabolic functions. The balance between bone resorption by osteoclasts and bone formation by osteoblasts is crucial for maintaining bone density and strength throughout life.