Thyroid gland is the largest endocrine organ its function is to secrete thyroxin (T4) & triiodothyronine (T3).
The thyroid is a butterfly (pear)-shaped gland, it consists of 2 symmetrical lobes joined by a central isthmus that normally covers the 2nd & 3rd tracheal rings.
The isthmus of the thyroid gland is located midway between apex of thyroid cartilage & suprasternal notch.
- Wt: 10-20 gm in adulthood
- Width: 1.5-2 cm
- Length: 2.4-4 cm
- Thickness: 1-1.5 cm
Thyroid gland has a rich blood supply & the blood flow to thyroid gland is about 5ml/gm/min so it’s very high blood supply.
The thyroid gland is palpable in about 50% of women and 30% of men. It is located in the neck, inferior to the larynx and cricoid cartilage. It has two lobes, each about 5 cm long and joined by a narrow isthmus. The lobes lie either side of the trachea and oesophagus, and the isthmus crosses the trachea anteriorly, usually over the second and third tracheal cartilages.
The thyroid gland is surrounded by a fibrous capsule derived from the pretracheal layer of the deep cervical fascia. Extensions of this capsule into the body of the thyroid create septae, which divide the gland into lobules. This connective tissue firmly connects the thyroid to the larynx and explains why the thyroid moves on swallowing.
The thyroid is highly vascular, and a bruit (the sound of turbulent blood flow) is sometimes heard in overactive glands. It is supplied by two arteries that anastomose (join) within the gland: the inferior and superior thyroid arteries. The inferior thyroid artery is a branch of the thyrocervical trunk that arises from the subclavian arteries. It ascends behind the carotid sheath to enter the thyroid posteriorly. The right recurrent laryngeal nerve is intimately related to this artery near the inferior pole of the thyroid gland. Surgery to the thyroid gland can damage this nerve, causing temporary difficulty with speaking. To minimize the risk to this nerve, the artery is ligated far away from the thyroid gland during thyroidectomy.
Interesting Questions about Thyroid:
What are hot and cold nodules?
Thyroid nodules do not function like normal thyroid tissue. A thyroid image (scan) done with a radioactive chemical shows the size, shape, and function of the gland and of thyroid nodules. A nodule that takes up more of the radioactive material than the rest of the gland is called a hot nodule.
A nodule that takes up less radioactive material is a cold nodule. Hot nodules are seldom cancerous, but less than 10% of all nodules are hot. Cold nodules may or may not be cancerous. All lumps should be checked by your doctor.
How do doctors test nodules for cancer?
Your doctor can use several tests to find out whether or not a thyroid lump is cancerous.
- A thyroid image or scan shows the size, shape, and function of the gland. It uses a tiny amount of a radioactive chemical, usually iodine or technetium, which the thyroid absorbs from the blood. A special camera then creates a picture, showing how much iodine was absorbed by each part of the gland.
- In needle aspiration biopsy, a small needle is inserted into the nodule in an effort to suck out (aspirate) cells. If the nodule is a fluid-filled cyst, the aspiration often removes some or all of the fluid. If the nodule is solid, several small samples are removed for examination under the microscope. In over 90% of all cases, this testing tells the doctor whether the lump is benign or malignant.
- Ultrasound uses high-pitch sound waves to find out whether a nodule is solid or filled with fluid. About 10% of lumps are fluid-filled cysts, and they are usually not cancerous. Ultrasound may also detect other nodules that are not easily felt by the doctor. The presence of multiple nodules reduces the likelihood of cancer.
How are nodules treated?
Nodules that are thought to be benign are usually observed at regular intervals. Some patients may be advised to take thyroid hormone pills. In certain instances, the nodule may be surgically removed because of continuing growth, pressure symptoms in the neck, or for cosmetic reasons.
Fluid-filled cysts that come back after several aspirations may need to be removed.
If the testing shows a nodule that is, or might be, malignant (cancerous), your doctor will recommend surgery. (You should discuss special situations, such as pregnancy, with your doctor.) The goal of surgery is to remove as much of the cancerous tissue as possible. If the cancer is found in the early stages when it is still confined to the thyroid gland, the surgery is almost always successful. With papillary cancer, patients usually do well after treatment, even if the cancer has spread to the lymph nodes in the neck.
The surgeon starts by removing one lobe of the thyroid. This specimen is tested during surgery (frozen section) to tell the surgeon whether it is benign or malignant. If it is malignant, most or all of the thyroid is removed. If the cancer has spread, lymph nodes in the neck may also have to be removed. In addition, in patients with either papillary or follicular cancer, radioactive iodine therapy may be needed six weeks after surgery to destroy any remaining cancerous tissue.
What happens after surgery?
After surgery, patients must stay in the hospital for one to three days. They may also need to take some time off from work (one to two weeks for a desk job; three to four weeks for physical labor). Most patients do not have any trouble speaking or swallowing, and they report minimal pain after the surgery. In patients with thyroid cancer, a scan may be done approximately six weeks after surgery to detect any residual thyroid tissue that needs to be treated with radioactive iodine.
Patients with thyroid cancer will need to take thyroid hormone their entire lives. Some patients who have had a noncancerous nodule removed will also be advised to take thyroid hormone pills. These may prevent new nodules from forming in the remaining portion of the thyroid gland.
Why are women more likely to get thyroid disease?
Women are also more vulnerable to autoimmune diseases. Two of the most common thyroid diseases, Hashimoto’s thyroiditis and Graves’ disease, are caused by problems with the body’s immune system. Normally, the immune system defends the body against germs and viruses. In autoimmune diseases, the system attacks the body’s own tissues. Diseases of the immune system tend to run in families.
What about thyroid disease and pregnancy?
Hyperthyroidism or hypothyroidism can affect a woman’s ability to become pregnant. They may also cause a miscarriage if they are not quickly recognized and properly treated.
Women who become pregnant may not notice signs of thyroid disease because similar symptoms can occur in a normal pregnancy. For example, patients may feel warm, tired, nervous, or shaky. In addition, enlargement of the thyroid (goiter) commonly occurs during pregnancy.
A pregnant woman is treated differently than is a non-pregnant woman or a man. For example, radioactive materials commonly used in diagnosing and treating many thyroid diseases are never used in pregnant women. The timing of a biopsy or surgery for a thyroid nodule and the choice of drugs for hyperthyroidism may be different in a pregnant woman. These issues require careful consultation with your doctor.
What is postpartum thyroiditis?
Postpartum thyroiditis is a temporary form of thyroiditis. It occurs in 5%-9% of women soon after giving birth (postpartum period). The effects are usually mild. However, the disease may recur with future pregnancies.
The symptoms usually last for six to nine months. First, the damaged thyroid gland may release its stored thyroid hormones into the blood, causing hyperthyroidism. During this time, you can develop a goiter, have a fast heart rate, and feel warm or anxious. Then, a few months later, you will either return to normal or become hypothyroid. Hypothyroidism occurs because the thyroid has been damaged and its hormone reserves used up. If this happens, you may feel tired, weak, or cold. The hypothyroidism usually lasts a few months until the thyroid gland completely recovers. Occasionally, the hypothyroidism may be permanent.
How do doctors test for thyroid disease during pregnancy?
As with any disease, it is important that you watch for the early warning signs of thyroid disease. However, only your doctor can tell for sure whether or not you have the disease. Your doctor may examine:
- your history and physical appearance
- the amount of thyroid hormones, thyroid stimulating hormone (TSH), and thyroid antibodies in your blood.
How is thyroid disease treated during pregnancy?
Pregnancy places some limits on the treatments which you can receive, because your doctor must also look out for the safety of your child. A common treatment for hyperthyroidism is radioactive iodine, but it must be avoided by women who are pregnant or nursing a baby. Surgery to remove a goiter or cancer may also be delayed until after the pregnancy. However, needle aspiration biopsy of a thyroid nodule may be safely done during pregnancy.
Treatments which may be used for thyroid disease during pregnancy include:
- antithyroid drugs, which block the production of thyroid hormone
- thyroid hormone pills, which provide the body with the right amount of thyroid hormone when the gland is not able to produce enough by itself.
Postpartum thyroiditis may or may not be treated during the hyperthyroid stage, depending upon its severity. If the patient later becomes hypothyroid, her doctor may prescribe thyroid hormone pills.
If you or a blood relative has Hashimoto’s thyroiditis or Graves’ disease, there is a chance that your children will inherit the problem. These diseases are also linked to other autoimmune conditions, such as premature gray hair, diabetes mellitus, arthritis, and patchy loss of skin pigment (vitiligo). You should tell your child’s doctor, so that the appropriate examinations can be performed.
Also, one out of every 4,000 infants is born without a working thyroid gland. If the problem is not corrected, the child will become mentally and physically retarded. Therefore, all newborns in the United States are tested for the disease. Once the problem is discovered and corrected, the child can grow up normally.
Have more questions? Need more answers? Check our Full Thyroid FAQ
The superior thyroid artery is usually the first branch of the external carotid artery. The external laryngeal nerve is related to this artery, but it is at less risk than the recurrent laryngeal during thyroid surgery. The superior thyroid artery is ligated close to the thyroid gland to reduce this risk. A third artery, called the thyroid ima artery, is present in 10% of people. It supplies the isthmus and it arises near the aortic arch, although the exact origin varies.
The thyroid gland is drained by three veins:
- Superior thyroid vein.
- Middle thyroid vein.
- Inferior thyroid vein.
The first two veins drain into the internal jugular, whereas the inferior vein drains into the brachio-cephalic veins.
Thyroid lymphatics drain into four groups of nodes:
- Prelaryngeal lymph nodes.
- Pretracheal lymph nodes.
- Paratracheal lymph nodes.
- Deep cervical lymph nodes.
The thyroid is composed of about one million spherical follicles or acini. Each follicle is lined by a single layer of secretory epithelial cells (follicular cells) around a colloid-filled space. These cells secrete thyroglobulin into the lumen of the follicle, and thyroid hormones are synthesized from thyroglobulin at the cell–colloid boundary. When the thyroid gland is not actively secreting hormones, the size of the colloid store and the follicle itself increase in diameter. When the follicular cells enter an active secretory phase, microvilli form on their inner surface and thyroglobulin is absorbed. The colloid store shrinks as a result. The absorbed thyroglobulin is broken down to release thyroid hormon. Another type of secretory cell is found between the follicles. These parafollicular cells (C cells) synthesize and secrete calcitonin.
Thyroid FAQ & Links to Related Articles
|There are four parathyroid glands that are normally having the size of a single rice grain. In some normal cases, they can be as big as the size of a pea.|
|Also called underactive thyroid, hypothyroidism is a disorder that is characterized by abnormal level of thyroid hormones in the body, which is too low.|
|The thyroid is a butterfly (pear)-shaped gland, it consists of 2 symmetrical lobes joined by a central isthmus that normally covers the 2nd & 3rd tracheal rings.|
|Congenital hypothyroidism is a thyroid gland disorder that may lead to deafness or mental retardation if left undetected.|
|Hypothyroidism can cause depression. Most people don?t realize that this feeling is depression caused by the thyroid gland not functioning as it should.|
|Papillary thyroid cancer is one of the thyroid cancer types. This type of thyroid cancer arises from the follicles in the thyroid gland.|
|The thyroid gland is located immediately below the larynx on each side of and anterior to the trachea. It is one of the largest of the endocrine glands|
|These thyroid hormones are responsible in regulating the body?s metabolism, which is how much food will be broken down into useful energy for consumption.|
|When the thyroid gland produces too much thyroid hormone, one may suffer from hyperthyroidism.|
|The thyroid stimulating hormone is produced by the pituitary gland. The thyroid stimulating hormone promotes the growth of the thyroid gland.|
|Thyroid hormones are chemical substances produced by the thyroid gland. The thyroid gland is located in the front of the neck.|
|Natural thyroid supplements are helpful as a remedy to thyroid disorders. Its natural ingredients assure one of its safeties in taking it.|
|The thyroid gland is an endocrine gland that is the primary responsible in regulating the body?s metabolism.|
|Thyroid surgery is used to treat people with thyroid problems such as thyroid cancer, thyroid nodules and hyperthyroidism.|
|Thyroid tests or thyroid function tests are done to check the thyroid function in one?s body. A doctor will be able to determine and diagnose the thyroid disorder.|
|Treatment for thyroid disorders should be done to prevent unwanted results caused by the severity of the condition. Consult a physician for more of these treatments.|
|Thyroidectomy is a surgical process wherein the whole or a part of the thyroid gland is removed. This surgical process is used to treat thyroid disorders.|
|Having an underactive thyroid is a minor problem but it seeks proper attention to avoid further health problems. Consult a physician about any thyroid problem.|
|Low thyroid, also known as hypothyroidism, is a condition where the thyroid gland is under active.|
|Following a healthy meal plan, exercise and proper medication goes hand in hand to treat hypothyroidism. Consult a physician for a more individualized plan.|
|Each thyroid cancer treatment depends on the type of thyroid cancer and the extent or stage of the thyroid cancer one is suffering from.|
|Parathyroid hormones are considered to be the most important endocrine regulator. It basically regulates the calcium and phosphorus concentration in the body.|
|Studies show that since 1925, the standard treatment for parathyroid disease is to surgically remove the parathyroid gland(s) which are overproducing parathyroid hormones.|
|Parathyroid adenoma is a small tumor of the parathyroid gland and is known to be the most common disorder of the gland.|
|Medullary thyroid cancer is one of the types of thyroid cancer. This type of thyroid cancer is more common in women than in men.|
|Most people don?t feel any symptoms. Others can just lose weight and just feel depressed for no reason at all.|
|Suppose you go in for a routine checkup and your doctor decides to test your thyroid function. You?ve experienced no thyroid disease symptoms|
|Hypothyroidism develops for over a long period of time. It?s normally from several months to even several years.|
|People who are suffering from hypothyroidism are advised to get plenty of exercise and have a balanced and healthy diet. The diet must be rich in protein and iodine.|
|Self medicating one?s thyroid disorder with hypothyroidism diet pills without proper information of the diet pill does not address the problem.|
|Hyperthyroidism is when the thyroid gland is overactive and produces too much thyroid hormones more than the body needs.|
|Hypothyroidism is one of the chronic diseases in the world. Hypothyroidism is also known as underactive thyroid; hypo means under or below normal.|
|Anaplastic thyroid cancer is a type of thyroid cancer that is rare and aggressive. It affects the thyroid gland and most especially its function.|
|Problems arise if the thyroid gland is overactive or underactive. There are three common thyroid disorders. These are hypothyroidism, hyperthyroidism and the thyroid nodules.|
|Hair loss may happen for so many reasons but it is commonly associated to thyroid problems such as hyperthyroidism and hypothyroidism.|
|Thyroid Function Tests are the different tests conducted to assess and determine the cause of an individual?s thyroid problems.|