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July 12, 2023 8 min read

Your thyroid and thymus might not be something you think about often, but these two glands play an essential role in keeping your body running smoothly. The thyroid plays a major role in your metabolism and growth, while the thymus is important for your immune system. Though their functions are quite different, they share some similarities in structure and development. Here, we will compare and contrast the thymus and thyroid, looking at their functions, similarities, and differences.

What is Thymus?

The thymus gland is a part of the lymphatic system, which plays an important part in your immune function. Without the thymus, your immune system can't function properly. It produces white blood cells called T cells, which help to protect the body from infection. In addition, the thymus also produces hormones that help to regulate the immune system.
The thymus is the largest at birth and continues to grow until puberty when it begins to shrink.

What role does the thymus play in the body?

The thymus is in charge of maturing white blood cells, or lymphocytes. These include the T cells (also known as T lymphocytes or thymocytes), which are responsible for helping the body fight infection. 

Lymphocytes make their way to the thymus from the bone marrow. In your thymus, they undergo a maturation process, multiply, and become specialized T cells with different jobs. After the T cells have completed their maturation, they enter the bloodstream. After that, they will make their way to lymph nodes and other organs in the lymphatic system, where they will help defend your body and fight against disease and infection.

Aside from being an essential part of the lymphatic system, the thymus is also a part of the endocrine system. Your endocrine system is responsible for producing and releasing hormones, which regulate how your body works. Thymus secretes thymosin, thymulin, thymopoietin, and the thymic humoral factor.

When is the thymus at its most active stage in human development?

Your thymus is active from the time you are born until you hit puberty. The thymus is at its peak activity level during childhood and adolescence. Most T cells are created in your thymus before you're even born. The remaining T cells are produced during childhood. By the time you reach adolescence, you will have enough for the remainder of your life. After you hit puberty, the thymus gradually becomes less active and begins to shrink. This process is known as involution. Eventually, the tissues in the thymus are replaced by fat.

Where is the thymus located?

The thymus is mostly located at your upper chest, just behind the breastbone (sternum). It's right in front of your heart and between your lungs, in an area called the mediastinum. In some people, however, it sits in the neck.

What is the anatomy of the thymus?

Shape and appearance

The thymus is a triangular-shaped soft gland with a rosy-gray color. It's made up of two lobes: the cortex and the medulla. The cortex is the outer layer of the thymus and is where T cells mature. The medulla is the inner layer and contains more mature T cells. 


In infants and young children, the thymus is quite big. During puberty, it reaches its maximum weight of approximately 1 ounce. It starts to decrease in size after puberty. When you reach adulthood, it becomes very small and largely replaced by fat.

What conditions can affect the thymus?

A few conditions can affect the thymus, ranging from genetic birth defects to diseases found in adults. Here are some of the conditions that can affect your thymus:

DiGeorge syndrome

DiGeorge syndrome is a genetic condition present from birth or early childhood. The condition is characterized by the absence or underdevelopment of the thymus.

Graft-versus-host disease 

A thymus can be transplanted from a stillborn to an infant with DiGeorge syndrome to help repair the infant's immune system. Sometimes, however, the transplanted thymus may produce cells that attack the recipient's cells.

Thymoma and thymic carcinoma (thymus cancer)

Thymic carcinoma and thymoma are rare cancers that can develop in the cells that cover the outside of your thymus. Thymomas resemble normal thymus cells, develop slowly, and seldom extend beyond the thymus. Thymic carcinoma, on the other hand, differs from normal thymus cells because it grows faster and spreads to other body parts more frequently. Therefore, thymoma is less severe than thymic carcinoma.

Will you survive without a thymus?

The answer to this question depends on how old you are. The thymus won't function throughout your lifetime, but it has a big responsibility when it's still active.

Since it produces your T cells before you are born and then makes the rest during childhood and adolescence, it's a vital part of your body in your early development. Therefore, a baby or toddler may experience health problems if their thymus needs to be removed. The removal can increase the risk of cancer, infection, autoimmune diseases, and allergies. 

Adults, however, don't need the thymus because it's no longer active after puberty.

What is the thyroid gland?

The thyroid gland is an important part of the endocrine system. It plays a major role in your body's growth, development, and metabolism. Your thyroid produces thyroid hormones, which are spread throughout the body via the bloodstream. Thyroid hormones help the body use energy, stay warm and keep the brain, heart, muscles, and other organs working properly.

The thyroid gland consists of two lobes, the right lobe, and the left lobe, which are about the size of a plum cut in half. The two lobes are connected by a thin band of thyroid tissue called an isthmus. Located on the front of the neck, it has a butterfly shape.

What are the functions of thyroid hormones?

Thymus vs thyroid: What are their functions?

Using iodine for the foods you eat, the thyroid produces two main hormones: triiodothyronine (T3) and thyroxine (T4), as well as calcitonin. T3 is the more active hormone, while T4 is inactive until it is converted to T3 in the body. They are the most important hormones in your body and are responsible for regulating metabolism, growth, and development.

T3 and T4 levels must be balanced, neither too high nor too low. To produce the right amount of hormones according to your body's needs, this gland works with the pituitary gland. The pituitary gland produces a thyroid stimulating hormone (TSH), which instructs your thyroid on how much thyroid hormone it has to create.

What is thyroid stimulating hormone (TSH)?  

Thyroid stimulating hormone (TSH) is a hormone that regulates the production and release of T3 and T4 hormones. It's created and produced in the pituitary gland, a tiny endocrine gland that sits at the base of your brain and controls the functions of the other endocrine glands. 

How is the thyroid stimulating hormone regulated?

TSH levels are regulated by a feedback loop between the pituitary gland and the hypothalamus.

The hypothalamus, an area in the brain, continuously monitors the thyroid hormone levels in your blood. If it detects that too few thyroid hormones are in your blood, it'll prompt the pituitary gland release more TSH, which signals your thyroid to produce more T3 and T4. Conversely, if it detects that there's too much T3 or T4 in the blood, the pituitary gland will slow down the production of TSH. This system keeps your thyroid hormone levels within the healthy range.

What are the main thyroid problems?

The majority of thyroid problems are caused by abnormal T3 and T4 hormone production. These include:

Hypothyroidism (underactive thyroid)

This is a conditionwhen your thyroid gland doesn't produce and release enough thyroid hormones, causing your metabolism to slow down and affect your entire body. This condition is possibly the most common thyroid problem.

Hyperthyroidism (overactive thyroid)

Hyperthyroidism occurs when too much thyroid hormones are produced and released. 

In some cases, thyroid problems can lead to thyroid cancer. However, thyroid cancer is very rare.

What causes thyroid problems?

Hypothyroidism and hyperthyroidism are caused by different medical conditions and situations. The following conditions may cause hypothyroidism:

  • Hashimoto's disease is the most common cause of hypothyroidism. It's a condition in which your immune system attacks your thyroid, a small gland at the base of your neck that produces hormones that regulate your metabolism.

  • Thyroiditisis a condition that causes your thyroid gland to become inflamed.

  • Hyperthyroidism treatment, such as radiation and surgical thyroid removal (thyroidectomy).

Hyperthyroidism, on the other hand, is caused by the following conditions:

  • Graves diseaseis when the body produces antibodies that attack the thyroid gland, causing it to overproduce hormones.

  • Thyroid nodulesare a growth or lump on the thyroid gland that may produce more hormones than your body needs.

What are the most common signs of thyroid problems?

There are many different symptoms of thyroid problems. They can vary depending on the individual. In general, symptoms of thyroid problems fall into one of two categories: those associated with hypothyroidism and those associated with hyperthyroidism.

If you have hypothyroidism, you might experience fatigue, body weight gain, forgetfulness, impaired focus, dry and coarse hair, hair loss, and a hoarse voice.

If you have hyperthyroidism, you might experience anxiety, sleeping trouble, body weight loss, tremors, and vision problems. You might also have a goiter or an enlarged thyroid gland.

How are thyroid problems identified?

There are a few different ways that doctors can identify whether or not a person has a thyroid problem. One way is to simply check the person's symptoms. However, they can also identify thyroid problems by doing blood tests. This test will measure the levels of thyroid hormones in the blood. If the levels are abnormal, it could be an indication of a thyroid problem. A single blood test is usually enough to confirm the diagnosis, but sometimes, further tests are needed.

Doctors may also use imaging tests, known as a thyroid scan, to look at the thyroid gland itself.

Are thyroid problems treatable?

Yes, thyroid problems and diseases are treatable. And most people with thyroid problems can lead normal, healthy lives. The goal of treatment is to get your thyroid hormone levels back to normal. The type of treatment you'll get depends on the cause of your thyroid problems.

For hypothyroidism, the main treatment option is thyroid replacement medication. Your main options include levothyroxine and natural desiccated thyroid (NDT). Levothyroxine is a synthetic version of T4 that replaces the missing or deficient thyroid hormone in the body. NDT is a type of hypothyroidism medication containing natural forms of T4 and T3. NDT is available in supplement form. One great brand to try is VitaliThy, a natural desiccated thyroid you can buy online.

If you have hyperthyroidism, the first line of treatment is radioactive iodine. It involves taking a pill that contains a small amount of radioactive iodine. The iodine will destroy the overactive thyroid cells, which will help to reduce symptoms. Other options include anti-thyroid medications and surgery.

Conclusion: Thymus vs. Thyroid Difference

Although they share similar names, the thymus and thyroid are actually different glands with different functions. The thymus is an organ in the chest responsible for producing T cells, which are essential for the immune system. The thyroid is a gland located in the neck that produces hormones that regulate metabolism. Although both organs are important for maintaining health, they have different functions.

The thymus produces T cells, which are essential for your immune. T cells help to protect the body from infection and disease. It regulates metabolism and plays a role in many other body functions. Both the thymus and thyroid can be affected by certain conditions that interfere with their optimal function.

Wojciech Majda
Wojciech Majda

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