Difference between Thyroid and Parathyroid

The endocrine system regulates the body through hormones produced by the thyroid and parathyroid glands. The thyroid is a butterfly-shaped gland under the larynx and is necessary for regulating metabolism and energy levels. The four small parathyroid glands behind the thyroid keep our blood calcium at normal levels.

This article dives into the differences between the thyroid and parathyroid glands, covering their anatomy, functions, hormones, disorders, and more.

Thyroid vs. Parathyroid: Anatomy and Location

Distinct in both structure and function, the thyroid and parathyroid glands play a vital role in the body's regulatory processes.

Thyroid Gland

• Location: Located in the front of the neck, just below the Adam's apple.
• Structure: Butterfly-shaped and consists of two lobes connected by an isthmus.
• Function: Secretes hormones (triiodothyronine and thyroxine) that control metabolism, energy generation, and overall growth and development.

Parathyroid Glands

• Location: Found on the back of the thyroid gland.
• Structure: Consists of four small, pea-sized glands.
• Function: Secretes parathyroid hormone (PTH), which controls calcium concentrations in the bloodstream and influences bone metabolism.

Key Functions of Thyroid and Parathyroid Hormones in the Body

Thyroid hormones maintain metabolic and physiological balance. T3 (triiodothyronine) regulates metabolism, heart rate, and body temperature, while T4 (thyroxine) is a precursor, converting to T3 in tissues. Additionally, calcitonin regulates calcium and phosphate levels, competing with parathyroid hormone activity to maintain mineral homeostasis.

Parathyroid hormone (PTH) helps balance the body’s calcium levels. It enhances calcium absorption from the intestines and increases blood calcium levels through stimulation of bone resorption. In addition, PTH helps reduce calcium excretion through the kidney, keeping enough calcium available for critical physiological processes.

Regulation and Control of Thyroid and Parathyroid Hormones

Here is how thyroid and parathyroid hormone secretion is regulated to maintain metabolic and calcium balance in the body.

Feedback Mechanisms for Thyroid Function

The hypothalamic–pituitary–thyroid (HPT) axis regulates thyroid function. Thyrotropin releasing hormone (TRH) is released from the hypothalamus to stimulate the pituitary gland to secrete thyroid stimulating hormone (TSH), causing the thyroid gland to form T3 and T4. A negative feedback loop elevates T3 and T4 levels, which inhibit TRH and TSH release.

Regulation of Parathyroid Hormone Secretion

A calcium-sensitive mechanism regulates parathyroid hormone (PTH) secretion directly by blood calcium levels. When calcium levels are low, PTH is released to restore balance. However, high calcium levels inhibit PTH secretion to maintain calcium homeostasis.

Thyroid vs. Parathyroid: Disorders and Diseases

Listed below are some common disorders and diseases related to the irregularity of thyroid and parathyroid hormones:

Common Thyroid Disorders

• Hypothyroidism: An underactive thyroid produces insufficient hormones, resulting in a slower metabolism. 
  Hyperthyroidism: The thyroid gland produces excessive hormones that increase metabolism. 
• Goitre: It is an enlargement of the thyroid gland due to hypothyroidism, hyperthyroidism or iodine deficiency.
  Thyroid Nodules: These are small, benign growths on the thyroid gland, leading to excessive hormone production and causing hyperthyroidism.
• Thyroid Cancer: It is a type of cancer originating from thyroid cells. Symptoms include a lump in the neck, hoarseness, and trouble swallowing.
• Hashimoto's Thyroiditis: It is an autoimmune disease in which the immune system creates antibodies against the thyroid, which leads to hypothyroidism.
• Graves' Disease: It is an autoimmune disorder resulting in the production of antibodies that cause excessive production of hormones and hyperthyroidism.

Common Parathyroid Disorders

• Hyperparathyroidism: High blood calcium levels may result from excessive production of parathyroid hormone (PTH), which produces symptoms such as weak bones, kidney stones, and fatigue.
• Hypoparathyroidism: Low blood calcium levels occur from insufficient PTH secretion with muscle cramps, tingling sensations, and, in severe cases, seizures.
• Parathyroid Adenoma: A parathyroid gland tumour, usually benign, can lead to hyperparathyroidism, calcium imbalances, and related symptoms.

Thyroid vs Parathyroid: Symptoms of Dysfunction

When thyroid and parathyroid glands malfunction, they can cause various symptoms that are mentioned below:

Symptoms Associated with Thyroid Dysfunction

• Hypothyroidism: Fatigue, weight gain, cold intolerance, dry skin, constipation, hair thinning, and depression are common signs.
• Hyperthyroidism: The key symptoms include weight loss, heat intolerance, rapid heartbeat, sweating, anxiety, nervousness, insomnia, and bulging eyes in the case of Graves' disease.

Symptoms Associated with Parathyroid Dysfunction

• Hyperparathyroidism: The most common signs are fatigue, weakness, bone pain, kidney stones, abdominal pain, nausea, and frequent urination.
• Hypoparathyroidism: Symptoms include muscle cramps, tingling in the fingers and toes, confusion, dry hair, and brittle nails.

Diagnosis and Testing of Thyroid and Parathyroid Disorders

Below are the methods that help medical professionals diagnose thyroid and parathyroid disorders and assess hormone levels:

Diagnostic Tests for Thyroid Issues

• TSH Test: It measures thyroid-stimulating hormone (TSH) levels, which indicate whether the thyroid is overactive or underactive. A high TSH level suggests hypothyroidism, whereas a low level suggests hyperthyroidism.
• T4 Test: This test measures thyroxine (T4), a thyroid hormone. High levels may suggest hyperthyroidism, while low levels indicate hypothyroidism.
• T3 Test: It is used if hyperthyroidism is suspected, especially in normal T4 levels. It measures triiodothyronine (T3) levels to confirm the diagnosis.
• Thyroid Antibody Tests: It helps assess autoimmune thyroid disorders, such as Graves' disease and Hashimoto's disease, where the immune system attacks the thyroid gland.
• Ultrasound: This procedure examines thyroid nodules and evaluates whether they are benign or malignant.
• Thyroid Scan: This test uses a small amount of radioactive iodine to determine the thyroid's size, shape, and function. It assists in the detection of hyperthyroidism and thyroid nodules.

Radioactive Iodine Uptake Test: This test checks how much iodine the thyroid absorbs to make hormones. It can help identify the cause of hyperthyroidism, including Graves disease and thyroid nodules.

Diagnostic Tests for Parathyroid Issues

• Blood Tests: These tests measure calcium, parathyroid hormone (PTH), and phosphorus to help confirm parathyroid function.
• Imaging Tests: Ultrasound, sestamibi scans, and 4D CT scans can locate abnormal parathyroid glands and identify any issues.
• Bone Density Test: It evaluates bone health and detects bone loss, which can occur due to hyperparathyroidism. 

Treatment and Management of Thyroid and Parathyroid Disorders

Thyroid disorders are treated with a range of options depending on the condition. Hypothyroidism is managed with synthetic thyroid hormone pills, while hyperthyroidism is treated with medications to reduce hormone production or block its release, as well as drugs to control symptoms like rapid heart rate.

If medications are ineffective, radioactive iodine ablation may be used to destroy overactive thyroid tissue. Conditions like large goitres or thyroid cancer often require surgery, and if the thyroid is completely removed, lifelong hormone replacement therapy becomes necessary. Although surgery was once the main treatment for Graves’ disease, it is now less common due to newer alternatives.

Treatment for hyperparathyroidism is primarily surgical, usually consisting of a targeted minimally invasive parathyroidectomy or a four-gland exploration. Hypoparathyroidism is managed with medications, along with calcium and vitamin D supplements, to restore hormonal balance. For parathyroid cancer, surgery is the primary approach, followed by radiation.

Importance of Early Detection and Lifestyle Choices

Early detection of thyroid and parathyroid disorders allows prompt intervention to prevent complications like cardiovascular disease in thyroid disorders and osteoporosis in parathyroid disorders. It also improves the overall quality of life, which reduces the need for more extensive treatments.

To maintain endocrine health, we must ensure a healthy diet with iodine, calcium, and vitamin D to support thyroid and parathyroid function. Regular exercise is important for metabolic health and bone strength and for managing thyroid and parathyroid disorders. Avoiding smoking and limiting alcohol can also reduce risk factors for endocrine-related health issues.

Conclusion

Though located proximally, the thyroid and parathyroid glands serve distinct functions. The thyroid regulates metabolism and energy, and the parathyroids maintain calcium balance. A balanced lifestyle, early detection, and regular monitoring are essential to maintaining optimal thyroid and parathyroid function and health.