Thymus vs Thyroid – Location, Functions, Disorders, Differences


The word ”thymus” comes from the Greek word ”thymos” which means ”soul,” ”heart,” ”life,” and ”desire.”


It is situated between the lungs, pericardium of the heart, in front of the aorta, behind the breastbone, and below the thyroid.

This gland is divided into 2 lobes that lie on either side of the midline of the body, and into lobules (smaller subdivisions). It has 3 main layers:

  • the capsule is the thin covering over the outside of this gland;
  • the cortex is the layer that surrounds the medulla;
  • the medulla is the inside part of this gland.

The medulla and cortex are made up of a mixture of lymphocytes (a type of white blood cells) and squamous cells (epithelial cells).

The arterial supply to this gland is via small branches of the internal thoracic arteries and the anterior intercostal arteries.


It serves a vital role in the development and training of T-lymphocytes (T cells), a vital type of white blood cells. T-cells are white blood cells that protect against foreign organisms (like – bacteria, fungi, and viruses) that have managed to infect body cells. The production of T-lymphocytes from this gland starts in embryonic life, around the 8th week of gestation.

Despite its important role in immune health, the gland is not active during our entire lifetime. For instance, it is relatively large in infancy (at birth it measures about 4 cm in breadth, 5 cm in length, and 6 mm in thickness), reaches a maximal weight in adolescence between 12 and 19 years, and gradually involutes with age, with a progressive fatty replacement of the cellular components. Regression of the gland is related to hair loss in adults.


Thymus cancer

This type of cancer is very rare, accounting for about 0.2 to 1.5 percent of all malignancies. More than 90% of tumors which develop in this gland are thymomas – tumors that start in the cells which line the outside of the gland and tend to grow slowly. It is very rare for them to spread outside of this gland. Common symptoms include:

Note – about half of these tumors are detected on a plain chest x-ray performed for other reasons and most sufferers have no symptoms.

Myasthenia Gravis

It is a long-term condition that causes weakness in the voluntary muscles. It is a relatively rare condition that affects around 18 out of every 100,000 Americans.


Severe combined immunodeficiency develops when an individual carries a mutation in a gene that regulates the development of T cells.

DiGeorge Syndrome

Congenital thymic hypoplasia, also referred as DiGeorge syndrome, is a rare condition in which a missing portion of chromosome 22 causes a child to be born with an underdeveloped thymus or none at all. Common symptoms may include:

  • behavior problems;
  • learning delays;
  • nasal-sounding speech;
  • delays in rolling over;
  • poor muscle tone;
  • breathing problems;
  • gastrointestinal problems;
  • delayed growth;
  • a gap in the roof of the mouth;
  • wide-set eyes;
  • an underdeveloped chin;
  • frequent infections;
  • a heart murmur.


This is a rare, benign tumor that contains thymic and adipose tissues. It is commonly asymptomatic, however, some people experience chest pain, shortness of breath, or a cough.


It is a butterfly-shaped gland located just below Adam’s apple and in the front of the neck. The two lobes on either side of the windpipe are joined together by a bridge (isthmus), that crosses over the front of a cartilaginous tube that connects the larynx and pharynx to the lungs, called the windpipe.

During development, this gland initially forms on the floor of the primitive pharynx. It descends down the neck to lie in its adult anatomical position.

Its size can vary based on each individual’s size as well as iodine intake, weighing 15 to 20 grams.

The gland nerve supply comes from the superior, middle, and inferior cervical sympathetic ganglia. It gets its blood supply from the inferior and superior thyroid arteries.


It lowers the amount of the active hormone called triiodothyronine and secretes thyroxine (a relatively inactive prohormone). These 2 hormones are called the thyroid hormones. In addition, it produces thyrocalcitonin, a hormone that helps regulate the levels of calcium in the blood.

The thyroid’s hormones regulate important body functions, including:

  • cholesterol levels;
  • breathing;
  • body temperature;
  • heart rate;
  • menstrual cycles;
  • muscle strength;
  • body weight;
  • peripheral and central nervous systems.

Note – it cannot produce hormones on its own, but requires the assistance of the pituitary gland (hypophysis), which creates TSH – thyroid-stimulating hormone.



It is an inflammation of this gland and is commonly caused due to an autoimmune condition or a viral infection. It can have no symptoms or be painful.

Hypothyroid Disorder

It is the inadequate production of thyroid hormone. In the US, this condition affects about 4.6% of people 12 years old and older. Common symptoms may include:

  • loss of hair;
  • elevated cholesterol levels;
  • muscle and joint pain;
  • depression;
  • facial swelling;
  • chronic constipation;
  • unexplained weight gain.


It is a condition in which there is an excessive amount of thyroid hormones. It affects approximately 70% of people with an overactive thyroid. Graves’ disease (also referred as toxic diffuse goiter) is the most frequent cause of hyperthyroidism.

Toxic Adenomas

Nodules develop in this gland and start to secrete thyroid hormones, disrupting the human body’s chemical balance. This condition can be managed by watchful waiting or surgery.

Thyroid Cancer

It is a disease that occurs when abnormal cells start to grow in this gland. Each year, there are more than 56,000 new people with this type of cancer in the United States. As this cancer grows, it may cause:

  • swollen lymph nodes in the neck;
  • pain in the throat and neck;
  • difficulty swallowing;
  • changes to the voice;
  • a lump that can be felt through the skin on the neck.

Thymus vs Thyroid – Differences

The thymus is a gland in the chest and is at its largest in adolescence, then it gradually shrinks away throughout adulthood. As an important part of the lymphatic system, this gland produces white blood cells called T-cells, that help the human body to fight infection.

The thyroid is a butterfly-shaped gland that sits low on the front of the neck. This gland helps coordinate the creation and use of energy.

Images credit – Shutterstock & Getty

READ THIS NEXT: Facts About The Respiratory System


Leave a Comment