Thymus Gland: Function, Location, Hormones, Structure, Anatomy

What Is the Thymus Gland?

The thymus is a small, butterfly-shaped lymphoid organ. It is located in the upper anterior thoracic cavity, behind the sternum, and between the lungs. It plays an important role in immune system development. It produces and matures the T-cells essential in adaptive immunity. It is at peak operation during childhood, then shrinks in size and progressively degenerates in function throughout life.

Anatomy of the Thymus Gland

The anatomy of the thymus gland is discussed below:

Location and Structure

• Located in the upper anterior chest, behind the sternum and between the lungs.

• Extends from the lower edge of the thyroid gland to the fourth rib.

Lobes and Lobules

• Has two lobes connected by an isthmus.

• Each lobe is divided into smaller lobules by fibrous septa.

• Lobules contain a cortex rich in immature T-cells on the outer regions, and medulla with mature T-cells on the inner region.

Growth, Development & Involution

The changes that the thymus gland undergoes during a lifetime include size, structure, and functional changes.

Childhood

• Largest and most active

• Essential for the establishment of a functional immune system.

• High production of T cells to build the immune system.

Puberty And Adulthood

• Thymic involution starts at puberty

• Functional tissue is gradually replaced with fat.

• T-cell output significantly reduced but persistent immune function

Old Age

• Continued involution results in decreased immune responsiveness.

• Increased susceptibility to infections and autoimmune diseases

Functions of the Thymus Gland

The major role of the thymus gland is to provide support for the development of the body's immune system, especially facilitating the process of maturation for T cells.

Role In Immune System

• Site of maturation and differentiation of T-cells

• Critical in generating a diverse and self-tolerant T-cell repertoire.

Thymic Hormones

• Thymosin α1 activates or enhances T-cell function.

• Thymopoietin influences T-cell differentiation.

• Thymulin increases T-cells and natural killer cell activity.

Thymus Gland and Immunity

The proper immune activity is greatly dependent upon the thymus gland because of the production and regulation of the T-cells.

T-helper Cells

• Activate and enable other immune cells to perform their functions.

Cytotoxic T-Cells

• Lyse virus-infected and malignant cells.

Regulatory T-Cells

• Maintain balance in the immune system and prevent autoimmunity.

Disorders of The Thymus Gland

The disorders in the thymus gland include serious immune dysfunctions with developmental abnormalities, tumours, and autoimmune diseases.

Hypoplasia and Aplasia

• Hypoplasia: Poorly developed thymus, which results in immunodeficiency.

• Aplasia: Completely missing thymus, leading to severe immunodeficiency.

Thymomas and Thymic Carcinoma

• Symptoms: Chest pain, cough, difficulty swallowing.

• Diagnosis: Imaging, biopsy

• Treatment: Surgery, radiation, chemotherapy.

Myasthenia Gravis

• Autoimmune disorder where antibodies, in abnormal immune response, attack acetylcholine receptors at the neuromuscular junction.

DiGeorge Syndrome

• A hereditary disorder that causes hypoplasia of the thymus, leading to immunodeficiency.

Thymus Gland NEET MCQs (With Answers & Explanations)

Important questions asked in NEET from this topic are:

• Thymus gland hormones and their functions

• Disorders related to Thymus gland

Practice Questions for NEET

Q1. Which of these glands is large at the time of birth but in adults, it reduces to a very small size?

1. Pineal

2. Thyroid

3. Thymus

4. Spleen

Correct answer: 3) Thymus

Explanation:

At birth and throughout childhood, the thymus is huge but as a person ages it gradually gets smaller. It becomes much smaller and less noticeable in adults. The thymus is essential for the immune system's development, especially for the maturation of lymphocytes (T cells) which are critical for adaptive immunity. The thymus is large and active during infancy and youth but by age its activity diminishes and the tissue is progressively replaced by adipose tissue. For this reason, the thymus is significantly smaller in adults than it was at birth.

Hence, the correct answer is option 3)Thymus.

Q2. The hormone that gives directions to lymphocytes for maturation in the thymus gland

1. Parathyroid hormone

2. Thyroid hormone

3. Thymosin hormone

4. Both A and B work together

Correct answer: 3) Thymosin hormone

Explanation:

The thymus is a crucial organ in the immune system's development. It produces peptide hormones known as thymosins. These hormones significantly influence the maturation of specific white blood cells, which are essential for immunity generation. Thymosin acts as an instructor for lymphocytes, guiding their development within the thymus gland itself.

Hence, the correct answer is option 3) Thymosin hormone.

Q3. The oval and spherical bodies present in the thymus act as phagocytes and provide immunity to the body. These bodies are

1. Zona glomerulosa

2. Hassall's corpuscles

3. Intestinal bodies

4. Zona fasiculata

Correct answer: 2) Hassall's corpuscles

Explanation:

The Thymus gland is derived from the endoderm and is a lobular structure located between the lungs behind the sternum on the ventral side of the aorta which plays a major role in the development of the immune system. It has some corpuscles that act as phagocytes. Hassall's corpuscles (macrophages) are spherical and oval bodies present in the thymus that are phagocytic in function.

Hence, the correct answer is option 2) Hassall's corpuscles.

Also Read:

• MCQs on Thymus Gland

• Mechanism of Hormone Action

• Parathyroid Gland

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