Question

Increased activity of the parathyroid gland leads to A. an increase in blood \(\mathrm{Ca}^{2+}\) concentration. B. a decrease in the rate of bone resorption. C. a decrease in metabolic rate. D. a decrease in blood glucose levels.

Short answer

A. an increase in blood \text{Ca}^{2+} concentration.

Step-by-step solution

- Understand the Role of the Parathyroid Glands

The parathyroid glands are responsible for regulating calcium levels in the blood. They secrete parathyroid hormone (PTH) which increases blood calcium levels by promoting calcium release from bones, increasing calcium absorption in the intestines, and increasing calcium reabsorption in the kidneys.

- Identify Effects of Increased PTH

Increased activity of the parathyroid gland results in more PTH being produced. More PTH would lead to higher blood calcium levels, as well as increased bone resorption to release calcium into the bloodstream.

- Eliminate Incorrect Options

Option B, stating that bone resorption decreases, is incorrect because increased PTH actually increases bone resorption. Options C and D are unrelated to calcium regulation and are not directly affected by PTH levels.

- Select the Correct Option

Given that PTH increases blood calcium levels, the correct answer is: Option A.

Key concepts

Calcium Regulation

Calcium regulation is crucial for maintaining various bodily functions. It involves balancing the levels of calcium in the blood and tissues. The parathyroid glands play a key role in this process.
When blood calcium levels drop, the parathyroid glands release parathyroid hormone (PTH). PTH acts to increase the calcium levels by:

• Stimulating the release of calcium from bones
• Increasing calcium absorption in the intestines
• Promoting calcium reabsorption in the kidneys

These actions help maintain the necessary level of calcium in the blood, which is vital for muscle function, nerve signaling, and bone health.

Parathyroid Hormone (PTH)

Parathyroid hormone (PTH) is a hormone secreted by the parathyroid glands, which are small glands located behind the thyroid. PTH is essential for managing calcium levels in the blood.
When calcium levels are low, PTH is released. Its primary functions include:

• Increasing calcium release from bones (through a process known as bone resorption)
• Enhancing calcium absorption in the intestines by activating vitamin D
• Reducing the amount of calcium excreted by the kidneys

By performing these actions, PTH helps ensure that the body has sufficient calcium to perform vital functions. Without proper PTH function, calcium balance can be disrupted, leading to various health issues.

Bone Resorption

Bone resorption is a natural process where bone tissue is broken down, and minerals like calcium are released into the bloodstream. This process is primarily regulated by parathyroid hormone (PTH).
During bone resorption, specialized cells called osteoclasts break down the bone matrix. When PTH is released due to low blood calcium levels, it increases the activity of osteoclasts.
This leads to:

• Release of calcium from bones into the bloodstream
• Maintaining proper calcium levels in the blood

However, excessive bone resorption over time can weaken bones, leading to conditions like osteoporosis. Therefore, bone resorption must be carefully balanced with bone formation.

Blood Calcium Levels

Blood calcium levels are tightly regulated by the body, primarily through the actions of parathyroid hormone (PTH).
Calcium is vital for many bodily functions, including:

• Muscle contraction
• Nerve transmission
• Blood clotting
• Bone health

When blood calcium levels are low, the parathyroid glands release PTH, which increases calcium levels by promoting its release from bones and enhancing absorption and reabsorption in the intestines and kidneys.
Conversely, when calcium levels are too high, less PTH is produced to prevent excess calcium release. This dynamic regulation ensures that blood calcium levels remain within a narrow, optimal range to support overall health.