Parathyroid vs. thyroid: How they function

The thyroid and parathyroid glands are two parts of the human endocrine system.

Glands in a person’s endocrine system are responsible for secreting specific hormones that can affect a variety of functions, such as metabolism, blood sugar (glucose), and reproduction. Other common examples include the adrenal and pituitary glands.

While sometimes discussed in similar conversations because of their proximity to one another in the neck, the thyroid and parathyroid glands have completely separate functions. Aside from functional distinctions, irregular activity with these glands can also lead to different health issues.

This article explains the key differences between the thyroid and parathyroid glands, as well as what happens when they lose normal function and treatment options for such cases.

The thyroid is a small butterfly-shaped gland that’s located at the bottom and front of a person’s neck.

While weighing just 20 to 60 grams, the thyroid gland does a lot of work despite its small size. It releases two main types of hormones: triiodothyronine (T3) and thyroxine (T4). These hormones travel to cells and organs throughout the body.

The pituitary gland, located in the brain, produces thyroid-stimulating hormone (TSH). TSH controls T4 production.

The parathyroid glands are four glands located directly behind the thyroid. There are two glands on each side of the thyroid gland that produce parathyroid hormone (PTH).

A person’s parathyroid glands are responsible for maintaining normal blood calcium levels. They work with the bones, as well as the kidneys and intestines, to help ensure the body sustains the correct level of calcium.

When blood calcium is low, the parathyroid glands stimulate PTH secretion. This can occur in bones, as well as in the intestines with the help of vitamin D. In some cases, the parathyroid glands tell the kidneys to stop releasing excess calcium in the urine.

The thyroid and parathyroid glands release different types of hormones that help regulate different body functions.

Despite both glands having the term “thyroid” in their names, parathyroid glands are not related to the thyroid gland, functionally speaking. Instead, the “para” prefix in “parathyroid” means “beyond” or “beside.” It points to their location by the thyroid gland only.

In fact, the parathyroid glands do not affect thyroid gland function at all, and vice versa. Rather than influencing thyroid hormone levels and related body functions, the parathyroid glands help regulate calcium levels in the blood.

Both types of glands can release too much or not enough hormone.

Thyroid diseases are commonly classified as overactive or underactive thyroid gland (hyperthyroidism and hypothyroidism, respectively). They can result from autoimmune diseases that attack the thyroid gland, such as Graves’ or Hashimoto’s disease.

Due to the complexity of hormonal conditions, thyroid diseases can also be non-autoimmune in nature. Pituitary gland issues can also contribute to low TSH production.

When the thyroid produces too little or too much hormone, cascading effects can occur throughout the body. For example, hypothyroidism can cause sluggishness, reduced metabolism, and cold skin, while hyperthyroidism can lead to insomnia, increased heart rate, and irritability.

Parathyroid dysfunction can also cause its own separate issues. Without enough calcium in the blood, a person can develop hypoparathyroidism. Too much blood calcium is known as hyperparathyroidism, and it’s much more common than low blood calcium.

Signs and symptoms of hyperparathyroidism can include weakness, gastrointestinal upset, and joint pain.

Given their distinct nature, when the thyroid and parathyroid glands lose normal function, very different treatment approaches are required. In both cases, the goal is to help support the glands to ensure the respective hormone levels are normalized in the body.

When a person has a thyroid disease, an endocrinologist will need to order a blood test to determine whether the results point to overactivity or underactivity. Depending on their findings, they may also order antibody tests to rule out autoimmune diseases.

Thyroid hormone therapies, such as levothyroxine (brand name Synthroid), may be a treatment option for hypothyroidism. These can help supplement the lack of T4 in the bloodstream to help offset the effects of low hormone production from the thyroid gland.

On the flipside, since producing too much hormone causes hyperthyroidism, treatment focuses on reducing overactivity in the thyroid gland. It may include antithyroid drugs, radioactive iodine, or beta-blockers.

Similarly, parathyroid disease treatment options depend on whether a person has hypoparathyroidism or hyperparathyroidism.

Oral calcium and vitamin D supplementation are typical treatments for the condition.

While hyperparathyroidism is more common, it’s also more difficult to treat and manage. Treatment options include diuretics or other calcium-lowering drugs such as bisphosphonates. A healthcare professional may also recommend intravenous fluids.

Both the parathyroid and thyroid glands are important parts of the human endocrine system. Each releases hormones that help regulate specific functions to support a person’s health. While the thyroid gland governs metabolic functions, the parathyroid gland regulates calcium.

Sometimes certain medical conditions can affect the release of hormones from the thyroid and parathyroid glands. The exact symptoms a person might experience depend on which gland is affected and whether the gland releases too little or too much hormone.

A doctor can order blood tests to help diagnose thyroid and parathyroid issues by confirming whether any related hormone levels are out of range. From there, they can then recommend further diagnostic testing or prescribe medications to help regulate hormone levels.

If a person experiences any unusual symptoms, it is important that they consider contacting a doctor. Early diagnosis and treatment can help individuals with either type of glandular issues feel better while also reducing the risk of further complications.