This Small Organ Is Very Important, But You Might Not Know Much About It

Hidden within your neck, its two lobes sandwiching your trachea, is a gland that’s only a little longer than a paperclip but has an outsized impact on the whole of your body. It’s your thyroid, and chances are you’ve never really stopped to think about it – unless you’ve experienced it going wrong, that is. So, let’s introduce you to this unassuming organ, the two hormones it produces, and how they affect the body.

What is the thyroid?

The thyroid is a gland, a type of organ that’s responsible for producing a substance – in this case, hormones, making it part of the endocrine system.

Situated towards the front of the neck below the larynx , the thyroid is divided into left and right lobes that sit on either side of the trachea or windpipe, linked by a connecting strip of tissue called the isthmus. Ordinarily, you can’t see it or feel it.

The thyroid responds to signals from the pituitary gland at the base of the brain. Throughout the day, the pituitary secretes thyroid-stimulating hormone (TSH), which sends a chemical message to the thyroid to ensure that it, in turn, is producing the right levels of two different hormones to meet the body’s changing needs.

The hormones produced by the thyroid are thyroxine, often called T4, and triiodothyronine, or T3. As well as these, a small subset of cells within the thyroid produces calcitonin.

What do the thyroid hormones do?

T4 is the main hormone secreted by the thyroid, but also the least active. It travels to various different tissues within the body where the bulk of it is then converted to T3. About 80 percent of T3 is produced in this way, with the remaining 20 percent being directly secreted from the thyroid into the bloodstream.

Both T3 and T4 are essential for the correct functioning of the body’s metabolism , and also play roles in digestion, brain development, bone and muscle health, and the heart.

Calcitonin helps to regulate calcium and phosphate in the blood. It works in two different ways to control calcium levels: by inhibiting the breakdown of bone by osteoclasts, thus preventing extra calcium from being released; and by decreasing the reabsorption of calcium in the kidneys.

However, it’s not completely clear how important this function is – people with very high or very low calcitonin don’t seem to show any adverse effects.

What happens when the thyroid doesn’t work correctly?

Keeping the balance of T3 and T4 just right is essential for lots of bodily systems to work properly. But what happens when things go wrong?

Hypothyroidism

Hypothyroidism, or an underactive thyroid, is the most common disorder affecting the organ. It’s not considered preventable – most cases are caused by an autoimmune reaction ( Hashimoto’s disease ) or are a side effect of treatment for other disorders. Sometimes the condition is inherited, but babies born in many countries (including the US and UK) are screened for this shortly after birth.

The symptoms tend to come on slowly, sometimes over a period of years, so it can be tricky to spot the problem. The major signs include:

• Fatigue
• Weight gain
• Depression
• Muscle aches
• Dry skin and hair
• Increased sensitivity to the cold

Hypothyroidism is more common in women than men. Treatment involves taking a synthetic form of thyroxine hormone to bring levels back up to where they should be. While treatment is generally required to continue for life, bringing the hormone levels back into balance generally relieves the symptoms.

Hyperthyroidism

The opposite condition is hyperthyroidism , an overactive thyroid. The symptoms typically include:

• Increased appetite
• Weight loss
• Rapid or irregular heartbeat
• Irritability
• Sweating
• Shaky hands
• Frequent bowel movements

With either an under or overactive thyroid, some people also develop a goiter , which is where the thyroid swells and becomes visible in the neck. This doesn't necessarily cause a major problem, but it may interfere with swallowing and breathing.

Sometimes, hyperthyroidism can result when too much synthetic thyroxine is prescribed to treat hypothyroidism – it can take a bit of trial and error to get the dosage just right. Other causes include an autoimmune condition called Graves’ disease , inflammation of the thyroid, or consuming excessive iodine in your diet.

A common treatment option for hyperthyroidism is radioiodine therapy. This involves taking a capsule or liquid containing the radioactive isotope iodine-131, which selectively destroys the cells in the thyroid that produce thyroxine. This doesn’t damage other tissues in the body, but in almost everyone, it does have the effect of reducing thyroxine production enough that they later develop hypothyroidism.

Since hypothyroidism can be treated with synthetic hormones and doesn’t cause as many long-term health problems, it’s considered preferable to treat hyperthyroidism in this way, even if it goes too far.

Another option that’s sometimes used is surgery to remove part or most of the thyroid, which can again result in hypothyroidism afterward.

Thyroid cancer

Various types of cancer can arise in the thyroid gland. The most common is papillary thyroid cancer, which usually affects people between the ages of 30 and 50. Most papillary thyroid tumors are small, develop very slowly, and respond well to treatment.

Often, surgery will be needed to remove the thyroid. As we’ve seen, that will cause hypothyroidism, which will then need to be treated with medication. Radiotherapy or radioactive iodine treatment may also be used, but chemotherapy is not commonly required unless the cancer recurs.

Researchers still aren’t totally sure what causes thyroid cancer . One major risk factor is radiation exposure , which is why cases of this cancer have been observed to increase in populations exposed to nuclear disasters like Chernobyl .

Postpartum thyroiditis

Postpartum thyroiditis is a complication affecting about 5-10 percent of pregnant people in which the immune system attacks the thyroid shortly after childbirth, causing inflammation. It’s more common in people who already have an autoimmune thyroid condition.

The condition starts with a hyperthyroid phase, where excess thyroid hormone leaks into the bloodstream, and then swings to a hypothyroid phase that can persist for several months or even become permanent. Treatment depends on the severity of the symptoms, and whether your hormone levels eventually normalize.

The bottom line

Keeping the myriad hormones that the human body produces in just the right delicate balance is a full-time job. Even when things are thrown off just a little, it can have far-reaching consequences. For a small organ, the thyroid has a huge role to play in that – so if you haven’t before, maybe now you’ll spare it a thought once in a while.