The thymus gland is a pyramid shaped endocrine gland located in the region between the superior mediastinum and lower neck. Its main function is to produce T-lymphocytes or T-cells, thereby making it a vital cog in the immune system. However, there is no substantial dysfunction of the immune system if the thymus gland is surgically removed, even during childhood.

Anatomy and Location of the Thymus gland

The thymus gland is a pinkish-gray organ that is located in the front section of the upper thoracic area, below the breast bone or the sternum, and behind the sternum’s manubrium.

It starts from the lower section of the neck and continues till the upper section of the mediastinum present in the chest cavity. The thymus tends to vary in size from one person to another; hence in some people, it may extend to just under the sternal angle or into the upper section of the lower mediastinum. Thus, in a larger picture, the thymus gland lies around the level of the vertebrae T4 and T6. It connects to the front section of the chest wall. The airways, aorta, and esophagus are located behind the gland.

The activities and growth of the thymus gland begin in the fetus and continue post birth. It keeps growing and becomes most active during puberty. Due to the importance of the thymus gland and its increased function during early life, it weighs around 20 to 30 grams in newborns and about 30 to 50 grams at puberty.It measures around 40 mm in width and 50 mm in length, during birth, with thickness that varies in the range of 7 mm.

A completely developed thymus gland is a covered lobar organ. Post puberty, the organ undergoes slow involution and typically gets substituted by fat tissues. Involution is a process marked by reversal in growth and shrinkage in size of the gland. Hence, elderly people feature a thymus gland that is about 5 to 15 grams and primarily made of connective tissues, fat, and/or some adipose.

The thymus gland consists of 2 lobes and each of these lobes are subdivided into many lobes or lobules by the thymus capsule’s fibrous extensions, i.e., a wall or a septum. The lobules are surrounded by a capsule and known as thymic lobules.The thymus consists of 2 parts, i.e., the peripheral/outer cortex and the central/inner medulla.

• The cortex is full of immature T-lymphocytes which later pass to the medulla to mature. Here, the T-cells understand the differentiation between body structures and foreign germs, which then helps prevent incorrect immune responses. The thymus gland also has other cells, although in low amounts, such as eosinophils, neutrophils, B-lymphocytes, and macrophages.
• Oxygenated blood arrives in the thymus gland via arteries from the front mediastinal and back intercostal branching of the thoracic internal arteries.
• The lymphatic vessels from the gland are received by the parasternal, tracheobronchial, and brachiocephalic lymph nodes.
• The blood from veins gets drained into the internal thyroid, left brachiocephalic, and thoracic internal veins.

Thymus gland – Functions

The thymus gland tends to be most active during childhood and is vital to the development and enhancement of the immune system in kids.

Some of the functions of thymus gland are listed below:

• Production and processing of T-cells or lymphocytes is the primary function of the thymus gland. Also called leukocytes, lymphocytes are WBCs or white blood cells. After maturing, the T-cells travel from the thymus gland to the lymph nodes and the spleen, where new lymphocytes are made. These WBCs are a vital part of the immune system; they produce antibodies that fight against viruses, bacteria, and other pathogens, and stop them, thereby protecting the body from varied diseases. The T-cells also make sure that the body functions efficiently and restore organs’ wear and tear.
• The thymus gland secretes a hormone known as thymopoietin, which is a protein occurring in messenger RNA or the mRNA and gets encoded by the TMPO gene.Thymus also produces the thymosin hormone which is responsible for stimulating lymphocytes and other lymphatic organs to become mature.
• The thymus gland also helps prevent anomalous cell growth that may lead to malignancy, tumors, and cancer. The T-cells migrate from bone marrow to the gland and remain in the thymus till they become active. After maturing, the cells pass into the bloodstream from where they move to other lymphatic organs, thereby helping the defense mechanisms of the body against varied illnesses.

Thymus gland disorders

The thymus gland can suffer from varied conditions. Thymus gland disorders are usually accompanied by symptoms like chest pain, fever, wheezing, fatigue, night sweats, breathing problems, loss of weight, coughing, and reduced immunity marked by frequent infections and sickness.

Some of the common thymus gland disorders are listed below:

• SCID/Severe Combined Immunodeficiency: It is a genetic immunodeficiency disorder marked by reduced levels of immune cells that may cause the thymus gland to atrophy and impair the immune system. As stated above, thymus gland is instrumental in helping cells mature and function efficiently. SCID inhibits this major function of the gland. Treatment involves intake of antibiotics and other medications and diet and lifestyle changes to improve the immune system.
• Absent or underdeveloped thymus gland: DiGeorge syndrome is a genetic disorder caused due to short-selection or deletion of chromosome 22. This chromosome plays a major role in the development of the thymus gland and other parts of the body. Hence, DiGeorge syndrome patients feature an absent or underdeveloped thymus gland, which in turn leads to a weakened immune system. Other symptoms of DiGeorge syndrome include developmental delays, heart defects, bluish skin hue, cleft palate, weakness, behavioral problems, recurrent infections, parathyroid gland issues, learning difficulties, poor muscle tone, and twitching of the hands, mouth, arms, and throat.
• Thymoma: It is a benign tumor made of adipose and thymic tissues that can become very large and may affect thymus gland function. It typically affects people in the age group of 40 to 60 years.It can be treated with surgery.
• Thymus cancer/thymic carcinoma: It is marked by growth of cancerous tumors that grow very fast, metastasize, and attack and harm healthy tissues. It is treated with surgery.
• Other disorders: Myasthenia gravis is an autoimmune condition caused by acetylcholine receptors by antibodies. Thymic hypertrophy is considered as one of its causes. Another thymus disorder is thymic hyperplasia or thymus enlargement.