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.
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.|