An Overview of the Thyroid and Thyroid Hormones

What is the thyroid?

The thyroid is a small gland about five centimetres wide. It is an endocrine gland located in the front of the neck. It is in the shape of a bow tie or butterfly. It has two lobes. The isthmus connects its two lobes, which are situated on either side of the trachea near the front of the throat. The isthmus is located just below the cricoid cartilage, and the left and right lobes are attached to the lateral wall of the pharynx. 

The thyroid is typically tiny and delicate, and can hardly be felt by skin contact despite being close to the surface. The entire thyroid gland is surrounded by a connective tissue membrane that is continuous with the neck fascia. As said, the size of the thyroid gland is about 5cm. But the size of the thyroid gland varies from person to person. The weight of the thyroid gland is about 20-40 grams. It is brown in colour and has many small bumps on its surface because the inner tissues of the thyroid are made by numerous follicles. 

Although reticular fibres make up the majority of the thin connective tissue that surrounds and separates each follicle, a network of capillary blood capillaries has formed between the follicles, making it easy to absorb the hormones generated by the follicles. A lymphatic network is also developed between the capillary networks. The follicular cavity is filled with colloids, and the follicular wall is made up of a single layer of cuboidal epithelial cells. When the thyroid gland is stimulated, the height of follicular epithelial cells rises. The height of follicular epithelial cells varies depending on their function. The thyroid gland is the only endocrine gland that can store large amounts of secretion extracellularly. It generates types of hormones, which are known as thyroid hormones.

What are thyroid hormones?

The function of the thyroid gland is to produce, store, and release thyroid hormones depending on the body's ability to extract enough iodine from the food eaten.

Millions of follicular cells secrete iodine-containing hormones into the blood. Thyroxine (T4), makes up 99.9% of the hormones the thyroid produces Triiodothyronine (T3), another hormone, makes up the remaining 0.1% of the thyroid hormones. So, the thyroid produces two types of thyroid hormones:

  • T4: thyroxine (also called tetraiodothyronine)
  • T3: Triiodothyronine

When the thyroid doesn't work properly, it disturbs the secretion of T3 and T4 hormones in the body, causing many problems.

To maintain the property work of the thyroid hormones, a pituitary gland helps. It is a gland under the skull, below the brain. When pituitary glands find a lack of thyroid hormones or overload of thyroid hormones, it produces its own hormones named thyroid stimulating hormone (TSH) which adjusts the amount of the other two types of thyroid hormones. This thyroid stimulating hormone (TSH) is sent to the thyroid gland and instructs it to get back to normal. Hence, thyroid stimulating hormone (TSH) is also an important thyroid hormone.

Thyroid-Related Diseases and Problems

The thyroid holds a number of functions in the body. An abnormal thyroid and abnormal thyroid hormone production cause several problems in the body.

  • Hyperthyroidism: An excess release of thyroid hormones or overactive thyroid causes hyperthyroidism. Numerous issues, such as mood swings, anxiety, exhaustion, and heart palpitations, to mention a few, can be brought on by an excess of hormones.
  • Hypothyroidism: It is a vice-versa of hyperthyroidism. An insufficient thyroid hormone production in the body is known as hypothyroidism. Numerous issues, such as constipation, a chilly sensation, fatigue, and difficulties concentrating. Young people who have hypothyroidism may experience growth issues, delayed puberty, and irregular menstrual cycles.
  • Goitre: An enlarged thyroid gland is termed goitre. It is related to the malfunction of the gland. In some situations, it can cause symptoms including coughing, trouble swallowing, and even breathing difficulties.
  • Thyroid Cancer: The thyroid gland, like other body organs and glands, is prone to cancer. Although it can affect anyone, Asian women between the ages of 25 and 65 experience it the most frequently.
  • Thyroiditis: The general term for an inflamed thyroid is thyroiditis. It can be used to describe a variety of illnesses, such as subacute thyroiditis, postpartum thyroiditis, and Hashimoto's thyroiditis. Although the common symptom of all these disorders is the inflammation of the different body parts, they all affect people of different ages and have unique symptoms.

Function of Thyroid Hormones.

The thyroid hormone is known to have effects on energy metabolism, protein/nucleic acid metabolism, growth, glucose metabolism, fat metabolism, vitamins, etc. Let's known about it in detail-

  1. The primary action of thyroid hormones is to support metabolism in the body. Metabolism is a process which converts the intake of food into energy. It helps to produce energy that is required for the body throughout the day. Thyroids help to produce energy. T4 (thyroxine, which contains four iodine atoms) and T3 (triiodothyronine, which contains three iodide atoms), both help to control the metabolism.
  2. Thyroid hormone also promotes protein and nucleic acid synthesis. Lack of thyroid hormones affects protein synthesis and leads to poor intellectual and physical development. It plays an important role in the growth and development of bone and skeletal muscle. That is why it causes weight loss in the body in the cases of hyperthyroidism.
  3. In hyperthyroidism, the body suffers from abnormal glucose metabolism effects. It causes excess absorption of glucose from the intestinal tract, increased use of sugar, increased protein catabolism/gluconeogenesis, increased conversion of hepatic glycogen to glucose and increased free fatty acids, etc.
  4. Thyroid hormone promotes the synthesis of triglycerides, phospholipids, and cholesterol in the liver. It also encourages the breakdown and excretion of triglycerides, the breakdown of cholesterol, and the release of free fatty acids. Blood cholesterol levels drop in hyperthyroidism and rise in hypothyroidism, most likely as a result of faster or slower cholesterol oxidation, respectively.
  5. The effects of thyroid hormone on intestine absorption, concentration, usage, and rate of conversion of a vitamin's active form vary depending on the kind of vitamin. For instance, carotene must be converted to vitamin A in the liver with the help of thyroid hormones. Therefore with hypothyroidism, blood levels of carotene rise and the skin turns yellow.

Likewise, there are many functions in the body which affect the lack of thyroid hormones and excess thyroid hormones.

What is hyperthyroidism?

Hyperthyroidism is also known as Basedow's disease or Graves' disease. It is a condition in which the thyroid gland is overactive and produces a large amount of thyroid hormone in the blood. By excess hormones, metabolism is overstimulated, affecting mood, weight, physical and mental energy levels and more. When thyroid hormones are more, all body functions speed up and cause a wide range of symptoms to the body.

The use of medication that includes high doses of thyroid hormone (given to treat hypothyroidism) or tumours in the testicles or ovaries may be its causes. Other potential reasons include infections of the thyroid gland, noncancerous tumours in the gland or pituitary gland, and thyroid infections. Hyperthyroidism, often known as Graves' disease, is autoimmune in origin in more than 80% of cases.

Symptoms of hyperthyroidism

  • Difficulty concentrating, restlessness, anxiety, trouble sleeping
  • Tingling hands
  • Insomnia
  • Tiredness, muscle weakness
  • Frequent bowel movements, but not diarrhoea
  • Swelling in the neck (enlarged thyroid)
  • Increased appetite, simultaneously with weight loss
  • Irregularity in menstruation
  • Inflammation of the tissues surrounding the eyes, in the case of Graves' disease.

The following symptoms are less common:

  • Breast development in men
  • Diarrhoea
  • Hair loss
  • Arterial hypertension
  • absence of menstruation
  • generalised itching
  • palpitations

What is Hypothyroidism?

Hypothyroidism is a condition in which the thyroid gland is overactive and produces a large amount of thyroid hormone in the blood. It also causes inflammation in the thyroid gland. The body's natural rhythm slows down, resulting in mental and physical fatigue. In contrast to hyperthyroidism, the lack of thyroid hormone production results in a slowing in metabolism in this situation. The decline in organic activity affects a variety of bodily processes, including metabolic, neurological, cardiovascular, and digestive.

It occurs most frequently in obese individuals, those over 50 who are female, and people who have had thyroid surgery. The condition known as "Postpartum Thyroiditis" affects certain women who have hypothyroidism after giving birth.

Hypothyroidism can manifest as myxedema, which is a medical emergency in its most severe form.

Symptoms of Hypothyroidism

  • Fatigue
  • Bad memory
  • Depression
  • dry and rough skin
  • slow heart rate
  • Weight gain
  • goitre
  • cold intolerance
  • Constipation
  • Drowsiness
  • In extreme situations, it can cause heart failure, respiratory failure and generalised swelling.
  • When myxedema occurs: numbness, decreased breathing, low blood pressure, low blood sugar, and temperature below normal.

How To Diagnose a Thyroid Problem?

There are many ways to diagnose thyroid problems in the body. Here is some of the specific test you can opt for:

  1. Thyroid Blood Test: A blood test which checks the number of hormones in the blood. It is a common test performed to rectify hyperthyroidism or hypothyroidism. Basically, in the test, we look out for the level of T3, T4, and TSH in the blood vessels. The normal level is as followed-
  • TSH Hormone Level - 0.8 - 1.7 nanograms per deciliter (ng/dL)
  • T3 Hormone Level - 60 to 180 nanograms per deciliter (ng/dL)
  • T4 Hormone Level - 0.9 to 2.3 nanograms per deciliter (ng/dL)

To perform this test, visit a laboratory and submit your blood sample

  1. Antibody Test: This is also a blood test. In this test, we measure the antibodies against the thyroid. This is a special test suggested to perform by healthcare professionals.
  2. Thyroid Ultrasound: An ultrasound is performed in the neck or around the thyroid gland to evaluate the size of the gland. In this test, we check the cysts, tumours, goitre, nodules or any types of inflammation around the thyroid gland.
  3. Thyroid Scan: It is a special test to check the position of the thyroid gland. It is an advanced test, in which a small amount of radioactive iodine and a special camera is used to take pictures of the nodule or lump on the thyroid or around the thyroid.  
  4. Thyroid Self-Test: It is a test that you can perform at home. Carefully check the neck to see if there are any nodules or cysts available. It is an inspection to detect the thyroid problem at the initial stage. Check yourself in the mirror and identify the thyroid. Drink a lot of water and observe the movement of the thyroid to check thyroid health. 

Treatments for Thyroid Disease

Depending on the type of disease, many treatments are available for thyroid disorders. Your medical history, physical exam, and numerous thyroid tests are used by medical professionals to identify thyroid illness. A biopsy is also advised in specific circumstances.

Drugs may be prescribed to reduce the number of hormones produced in hyperthyroidism, encourage more hormone production in hypothyroidism, or balance the hormone levels produced by the thyroid gland.

How to maintain a healthy thyroid?

Iodine is an important mineral for a healthy thyroid. An adult body requires ten thousand grams of iodine in a day. This amount is generally provided by the food eaten because iodine is present in the soil and is taken up by plants. A balanced diet that includes fruit, vegetables, and low-processed foods should provide enough iodine to sustain a healthy thyroid.

Iodine can also be found in shellfish, seaweed, fortified cereals, liver, meat (particularly liver), and water. The majority of people don't need to worry about eating too much iodine because any excess is excreted in the urine.

Iodine may be present in some multivitamins, but iodine-only supplements are hard to find and rarely actually necessary. For thyroid-related diseases like hyperthyroidism, hypothyroidism, goitre, etc, it is suggested to consult with the healthcare professional only.

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