Difference Between Thyroid and Parathyroid

Main Difference – Thyroid vs Parathyroid

Thyroid and parathyroid are two endocrine glands in the animal body. The thyroid gland is a butterfly-shaped gland, which lies in front of the trachea, just below the larynx. Though it does not possess any functional relationship with the thyroid gland, parathyroid glands are physically attached to the capsule of the thyroid gland at its posterior side. Since they are endocrine glands, both thyroid and parathyroid glands produce hormones that belong to the endocrine system of the body. The main difference between thyroid and parathyroid is that thyroid produces hormones that regulate the metabolism of the body whereas parathyroid produces hormones that control the calcium ion levels in the blood.  

Key Areas Covered

1. What is Thyroid
      – Definition, Anatomy, Physiology, Function
2. What is Parathyroid
      – Definition, Anatomy, Physiology, Function
3. What are the Similarities Between Thyroid and Parathyroid
      – Outline of Common Features
4. What is the Difference Between Thyroid and Parathyroid
      – Comparison of Key Differences

Key terms: Calcium Ion Level, Endocrine Glands, Hormones, Metabolism, Parathyroid, Parathyroid Hormone (PTH), Thyroid, Triiodothyronine (T3), Thyroxine (T4)

What is Thyroid

Thyroid is a large, ductless gland that produces and secretes hormones to regulate growth and development by regulating the rate of metabolism. It is a butterfly-shaped gland, located at the base of the neck. The gland is 2-inches long. The two lobes the thyroid lie on either side of the trachea. These lobes are connected by a structure called isthmus. The anatomy of the thyroid is shown in figure 1.

Figure 1: Thyroid

The main function of the thyroid gland is to regulate the metabolism of the body. For this purpose, the thyroid gland produces, stores, and secretes hormones, acting as an endocrine gland. The production of hormones by the thyroid gland requires iodine. The two hormones produced by the thyroid gland are triiodothyronine (T3) and thyroxine (T4). These two hormones travel through the blood to reach metabolizing cells in the body. The thyroid system is shown in figure 2.

Figure 2: Thyroid System

The breathing, heart rate, body weight, muscle strength, body temperature, cholesterol level, menstrual cycle, etc. are the body functions regulated by the thyroid hormones.

What is Parathyroid

Parathyroid is a gland next to the thyroid, which regulates the calcium levels in the body. The normal size of a parathyroid gland is the size of a rice grain. Normally, parathyroid gland is mustard-yellow color. Ideally, four parathyroid glands occur on the posterior side of the thyroid gland. The anatomy of the parathyroid gland is shown in figure 3.

Figure 3: Parathyroid

The main function of the parathyroid gland is to regulate the calcium level in the blood within a very narrow range. The hormone secreted by the parathyroid is the parathyroid hormone (PTH). The normal calcium ion concentration in blood is 8.5–10.5 mg/dL. In a deficiency of calcium in the blood, the PTH release calcium ions from bones. When the calcium ion concentration is high in the blood, the excess calcium is deposited in the bones. The parathyroid system is shown in figure 4.

Figure 4: Parathyroid system

Calcium is the only type of electrolytes in the body regulated by a hormone. It provides the electrical energy to the nervous system and the muscular system.

Similarities Between Thyroid and Parathyroid

• Both thyroid and parathyroid glands are endocrine glands, which produce hormones.
• Both thyroid and parathyroid glands are located around the trachea, in the neck region.
• Both thyroid and parathyroid glands maintain the homeostasis of the body.

Difference Between Thyroid and Parathyroid

Definition

Thyroid: Thyroid is a large ductless gland that produces and secretes hormones to regulate growth and development by regulating the rate of metabolism.

Parathyroid: Parathyroid is a gland next to the thyroid, which regulates the calcium levels in the body.

Location

Thyroid: Thyroid lies in front of the trachea, just below the larynx.

Parathyroid: Parathyroid glands are physically attached to the capsule of the thyroid gland at its posterior side.

Number of Glands

Thyroid: There is only one thyroid gland in the body.

Parathyroid: There are four parathyroid glands in the body.

Shape

Thyroid: Thyroid is a butterfly-shaped gland.

Parathyroid: Parathyroid is a rice grain-sized gland.

Color

Thyroid: The color of the thyroid gland is brownish-red.

Parathyroid: The color of the parathyroid is mustard-yellow.

Types of Hormones

Thyroid: The two hormones produced by the thyroid gland are triiodothyronine (T3) and thyroxine (T4).

Parathyroid: Parathyroid hormone (PTH) is produced by the parathyroid.

Function

Thyroid: Thyroid hormones regulate the rate of metabolism in the body.

Parathyroid: Parathyroid hormones regulate the concentration of calcium ions in the blood.

Conclusion

Thyroid and parathyroid are two endocrine glands located at the base of the neck. Thyroid gland secretes two hormones that regulate the rate of metabolism of the body. Parathyroid secretes a hormone that regulates the calcium ion concentration in the blood. Therefore, the main difference between thyroid and parathyroid is the function of the hormones which are secreted by each gland.

Reference:

1.“ Thyroid Gland, How it Functions, Symptoms of Hyperthyroidism and Hypothyroidism.” EndocrineWeb, Available here.
2.“Introduction to Parathyroid Glands.” Parathyroid.com and hyperparathyroidism, Available here.

Image Courtesy:

1. “Illu08 thyroid” (Public Domain) via Commons Wikimedia
2. “Thyroid system” By Mikael Häggström  (Public Domain) via Commons Wikimedia
3. “Illu thyroid parathyroid” Public Domain) via Commons Wikimedia
4. “Calcium regulation” By Mikael Häggström – (Public Domain) via Commons Wikimedia