The parathyroid glands are primarily controlled by a negative feedback loop involving blood calcium levels; low calcium triggers parathyroid hormone (PTH) release, while high calcium levels suppress it.
Here’s a more detailed explanation:
Calcium Sensing:
The parathyroid glands, specifically the chief cells, are highly sensitive to changes in serum calcium levels.
Calcium-Sensing Receptor (CaSR):
These cells possess a G protein-coupled transmembrane receptor, the CaSR, which detects low serum calcium.
PTH Release:
When calcium levels are low, the CaSR activates, leading to the synthesis and release of PTH.
PTH’s Role:
PTH then acts on the bones, kidneys, and intestines to increase calcium levels in the blood.
Negative Feedback:
As calcium levels rise, the CaSR senses the increased levels, and PTH release is suppressed, creating a negative feedback loop that maintains calcium homeostasis.
Vitamin D:
Vitamin D also plays a role in calcium regulation, and activated vitamin D can affect the expression of CaSR in the parathyroid gland.
Other Factors:
Other factors, like kidney disease, can also affect parathyroid function and calcium balance.

In hyperparathyroidism, one or more parathyroid glands become overactive, leading to the excessive production and release of parathyroid hormone (PTH)< (high calcium levels in the blood).
Here’s a more detailed explanation:
What are parathyroid glands?
The parathyroid glands are four small, pea-sized glands located on or near the thyroid gland in the neck.
What does the parathyroid hormone do?
PTH plays a crucial role in maintaining calcium balance in the body by increasing blood calcium levels.
How does hyperparathyroidism cause elevated PTH?
Primary Hyperparathyroidism: In this type, one or more parathyroid glands become overactive, often due to a benign tumor (adenoma) or hyperplasia (enlargement) of the glands, leading to excessive PTH production.
Secondary Hyperparathyroidism: In this type, the parathyroid glands become overactive in response to hypocalcemia (low calcium levels), often due to conditions like kidney disease, vitamin D deficiency, or chronic kidney disease, which cause the body to compensate by releasing more PTH to raise calcium levels.
Consequences of elevated PTH:
Hypercalcemia: Excessive PTH causes the release of calcium from bones into the blood, leading to high calcium levels.
Bone thinning (osteoporosis): The constant release of calcium from bones can lead to bone weakening and increased risk of fractures.
Kidney stones: High calcium levels in the blood can lead to the formation of kidney stones.
Other symptoms: Fatigue, muscle weakness, abdominal pain, and changes in mood or concentration can also occur.