Difference Between Thymus and Thyroid

Main Difference – Thymus vs Thyroid

Thymus and thyroid are two endocrine glands in the animal body. The thymus is located in the upper chest and the thyroid is located in the neck. The main difference between thymus and thyroid is that thymus is mainly involved in the development and differentiation of T cells whereas thyroid is mainly involved in the secretion of thyroxine and triiodothyronine, which govern the metabolism. Thymus secretes thymosin and thymopoietin, which stimulate the development of T cells in the thymus. T cells mediate the cell-mediated immunity, which activates the apoptosis of the infected cells.

Key Areas Covered

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

Key Terms: Cell-Mediated Immunity, Endocrine Glands, Metabolism, T Cells, Thymopoietin, Thymosin, Thymus, Thyroid, Thyroxin, Triiodothyronine

What is Thymus

Thymus is a lymphoid organ, which is located behind the sternum between the lungs of vertebrates and, produces T cells for the immune system. It is a pinkish-gray color organ, consisting of two thymic globes. The thin outer covering of the thymus consists of three cell types: Kulchitsky cells, lymphocytes, and epithelial cells. Klchitskuy cells are the hormone-releasing cells. They are also called neuroendocrine cells. Lymphocytes provide protection against infections. Epithelial cells are tightly-packed and give shape to the organ. The outer region of the thymus is called the cortex and the inner region is called the medulla. The location and the structure of the thymus are shown in figure 1.

Figure 1: Thymus

The most characteristic feature of the vertebrate thymus is the thymic involution in which the shrinking of the thymus occurs with age. The minimal size of the thymus is at puberty. After puberty, the thymus remains inactive and is replaced by fat. The maturation of the T cells occurs in the thymus. The development and differentiation of T cells are governed by two hormones produced by the thymus called thymosin and thymopoietin. The fully-matured T cells migrate to the lymph nodes. This suggests that thymus is involved in both immune function and endocrine function in the body.

What is Thyroid

Thyroid is a large, ductless gland, which is located in the neck and secretes hormones to regulate the growth and development by regulating the rate of metabolism in the body. It is a butterfly-shaped gland, which lies just below the larynx. The two lobes of the thyroid gland are located on either side of the throat. They are connected by a strip of thyroid tissue called the isthmus. The structure and the location of the thyroid gland are shown in figure 2.

Figure 2: Thyroid Gland

The thyroid gland produces, stores, and secretes hormones known as thyroxine (T4) and triiodothyronine (T3). The secretion of the thyroid hormones is regulated by the hypothalamus and the pituitary gland in the brain. Thyroid stimulating hormone (TSH) and the thyroid releasing hormone (TRH) are the two hormones which regulate the production and the secretion of thyroid hormones.

Difference Between Thymus and Thyroid - 3

Figure 3: Thyroid System

The T4 and T3 hormones travel to each cell of the body to regulate metabolism. They regulate breathing, heart rate, body weight, muscle strength, body temperature, cholesterol level etc. The function and the regulation of the thyroid are shown in figure 3.

Similarities Between Thymus and Thyroid

Both thymus and thyroid are endocrine glands that produce hormones.
Both thymus and thyroid are found in vertebrates.
Both thymus and thyroid are composed of two lobes.

Definition

Thymus: Thymus is a lymphoid organ, which is located behind the sternum between the lungs of vertebrates and produces T cells for the immune system.

Thyroid: Thyroid is a large, ductless gland, which is located in the neck and secretes hormones to regulate the growth and development by regulating the rate of metabolism in the body.

Location

Thymus: Thymus is located in the upper chest.

Thyroid: Thyroid is located in the neck.

Size with the Age

Thymus: The size of the thymus becomes smaller compared to the size of the body. The minimal size of the thymus is at the puberty.

Thyroid: The size of the thyroid keeps on increasing with age.

Function

Thymus: Thymus is involved in the development of T cells. It also secretes hormones required by the development of T cells.

Thyroid: Thyroid secretes hormones.

Types of Hormones

Thymus: Thymus secretes thymosin and thymopoietin.

Thyroid: Thyroid secretes thyroxine and triiodothyronine.

Role

Thymus: Thymus provides a proper environment for the development of the T cells.

Thyroid: Thyroid secretes hormones, which governs the metabolism.

Conclusion

Thymus and thyroid are two organs of the body which serve as endocrine glands. Thymus is located in the chest whereas thyroid is located in the neck. Thymus secretes thymosin and thymopoietin. Thyroid secretes thyroxine and triiodothyronine. The hormones of the thymus are involved in the development of the T cells in the thymus. In contrast, thyroid hormones regulate the metabolism of the body. However, thymus performs an immune function as well by providing a site for the maturation of T cells. The main difference between thymus and thyroid is the structure, location, and the function of each organ in the body.

Reference:

1.“An Overview of the Thymus.” EndocrineWeb, Available here. Accessed 3 Oct. 2017.
2. Bailey, Regina. “Learn About the Thymus Gland and How It Functions in the Immune System.” ThoughtCo, Available here, Accessed 3 Oct. 2017.
3.“Thyroid Gland, How it Functions, Symptoms of Hyperthyroidism and Hypothyroidism.” EndocrineWeb, Available here. Accessed 3 Oct. 2017.

Image Courtesy:

1. “2206 The Location Structure and Histology of the Thymus” By OpenStax College – Anatomy & Physiology, Connexions Web site, Jun 19, 2013 (CC BY 3.0) via Commons Wikimedia
2. “Anterior thyroid” By CFCF – Own work (CC BY-SA 3.0) via Commons Wikimedia
3. “Figure 37 04 01” By CNX OpenStax – (CC BY 4.0) via Commons Wikimedia