In the neck, near the thyroid, are four small glands known as the parathyroid glands, each about the size of a pea. These glands have the responsibility of regulating the body’s calcium levels. Maintaining a precise calcium balance is important for the proper functioning of the nervous and muscular systems. The glands achieve this regulation by producing a specific hormone that balances calcium in the blood and bones.
The Calcium Regulation Mechanism
The parathyroid glands control calcium by producing and releasing parathyroid hormone (PTH). This system operates on a negative feedback loop, similar to a thermostat. When the calcium concentration in the blood falls too low, the parathyroid glands sense this change and increase their production of PTH. Conversely, when blood calcium levels are sufficient, the glands reduce or stop secreting the hormone.
PTH raises blood calcium levels through a coordinated effort targeting three main areas: the bones, the kidneys, and the intestines. The hormone stimulates specialized cells in the bones to release stored calcium into the bloodstream, providing a rapid source of this mineral. This process, known as bone resorption, ensures that calcium is available for immediate use by the body’s systems when dietary intake is insufficient.
Simultaneously, PTH acts on the kidneys to conserve calcium. As blood is filtered through the kidneys, the hormone enhances the reabsorption of calcium, preventing it from being excreted in urine. This action effectively reduces the amount of calcium lost from the body. This renal process is a direct way the body holds onto its existing calcium stores when blood levels are low.
The hormone’s influence extends to the digestive system through its effect on Vitamin D. PTH stimulates the kidneys to convert Vitamin D into its most active form, a substance called calcitriol. This activated Vitamin D then travels to the intestines, where it significantly increases the absorption of calcium from the food we eat.
Impact of Parathyroid Dysfunction
Hyperparathyroidism (Overactive Glands)
When the parathyroid glands produce too much PTH, it leads to a condition called hyperparathyroidism. This overproduction is often caused by a noncancerous tumor, or adenoma, on one of the glands. The excess hormone causes persistently high levels of calcium in the blood, a state known as hypercalcemia.
The effects of hypercalcemia are often summarized by a memorable phrase: “bones, stones, groans, and psychiatric overtones.”
- Bones: The continuous release of calcium from bones can lead to thinning and weakening, resulting in conditions like osteopenia and osteoporosis, and an increased risk of fractures.
- Stones: In the kidneys, the effort to filter excess calcium can lead to the formation of painful kidney stones and may impair overall kidney function.
- Groans: Abdominal pain and constipation are common gastrointestinal complaints.
- Psychiatric overtones: High calcium levels can affect the nervous system, leading to fatigue, memory loss, depression, and general weakness.
Hypoparathyroidism (Underactive Glands)
Conversely, hypoparathyroidism occurs when the glands produce an insufficient amount of PTH. This lack of hormone results in abnormally low levels of blood calcium, or hypocalcemia, which directly impacts the function of nerves and muscles. This condition is less common than its overactive counterpart and often occurs as a result of neck surgery or other medical issues.
The primary symptoms of hypocalcemia are neuromuscular in nature. Individuals may experience tingling sensations, particularly in the lips, fingers, and feet. Muscle function is also heavily affected, leading to cramps and painful spasms. In more severe cases, the sudden drop in calcium can cause mental fogginess, confusion, and even seizures. These symptoms highlight the direct relationship between calcium availability and the stable electrical signaling required for proper nerve and muscle activity.
Distinguishing Parathyroid from Thyroid Glands
A common point of confusion is the difference between the parathyroid and thyroid glands, due to their proximity in the neck and similar names. The thyroid is a larger, butterfly-shaped gland that sits at the front of the neck, while the four much smaller parathyroid glands are located on its posterior surface. Despite being neighbors, they are anatomically separate and perform entirely different roles.
Their functions are distinct and unrelated. The thyroid gland is the body’s primary regulator of metabolism, controlling energy use, heart rate, and body temperature through the production of hormones like triiodothyronine (T3) and thyroxine (T4). In contrast, the parathyroid glands have the sole purpose of regulating calcium balance by producing Parathyroid Hormone (PTH). The thyroid has no effect on calcium levels, and the parathyroids have no effect on metabolism.
This functional separation is reflected in the hormones they produce. The thyroid secretes thyroid hormones that influence nearly every cell in the body to control metabolic rate. The parathyroid glands secrete PTH, a hormone with a highly specific set of targets—bone, kidneys, and intestines—all geared toward maintaining blood calcium within a narrow, stable range.