Thyroid
The thyroid is a butterfly-shaped gland that sits low on the front of the neck. Your thyroid lies below your Adam’s apple, along the front of the windpipe. The thyroid has two side lobes, connected by a bridge (isthmus) in the middle. When the thyroid is its normal size, you can’t feel it.
Brownish-red in color, the thyroid is rich with blood vessels. Nerves important for voice quality also pass through the thyroid.
The thyroid secretes several hormones, collectively called thyroid hormones. The main hormone is thyroxine, also called T4. Thyroid hormones act throughout the body, influencing metabolism, growth and development, and body temperature. During infancy and childhood, adequate thyroid hormone is crucial for brain development.
The thyroid gland develops in the floor of the pharynx at the base of the tongue at 3–4 weeks gestation; it then descends in front of the pharyngeal gut, and ultimately over the next few weeks, it migrates to the base of the neck. During migration, the thyroid remains connected to the tongue by a narrow canal, the thyroglossal duct. At the end of the fifth week the thyroglossal duct degenerates, and over the following two weeks the detached thyroid migrates to its final position.
Euthyroid is the term used to describe a state of normal thyroid function in the body. Thyroid disorders include hyperthyroidism, hypothyroidism, thyroid inflammation (thyroiditis), thyroid enlargement (goitre), thyroid nodules, and thyroid cancer. Hyperthyroidism is characterized by excessive secretion of thyroid hormones: the most common cause is the autoimmune disorder Graves' disease. Hypothyroidism is characterized by a deficient secretion of thyroid hormones: the most common cause is iodine deficiency. In iodine-deficient regions, hypothyroidism secondary to iodine deficiency is the leading cause of preventable intellectual disability in children. In iodine-sufficient regions, the most common cause of hypothyroidism is the autoimmune disorder Hashimoto's thyroiditis.
Thyroid Conditions
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Goiter: A general term for thyroid swelling. Goiters can be harmless, or can represent iodine deficiency or a condition associated with thyroid inflammation called Hashimoto’s thyroiditis.
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Thyroiditis: Inflammation of the thyroid, usually from a viral infection or autoimmune condition. Thyroiditis can be painful, or have no symptoms at all.
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Hyperthyroidism: Excessive thyroid hormone production. Hyperthyroidism is most often caused by Graves disease or an overactive thyroid nodule.
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Hypothyroidism: Low production of thyroid hormone. Thyroid damage caused by autoimmune disease is the most common cause of hypothyroidism .
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Graves disease: An autoimmune condition in which the thyroid is overstimulated, causing hyperthyroidism.
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Thyroid cancer: An uncommon form of cancer, thyroid cancer is usually curable. Surgery, radiation, and hormone treatments may be used to treat thyroid cancer.
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Thyroid nodule: A small abnormal mass or lump in the thyroid gland. Thyroid nodules are extremely common. Few are cancerous. They may secrete excess hormones, causing hyperthyroidism, or cause no problems.
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Thyroid storm: A rare form of hyperthyroidism in which extremely high thyroid hormone levels cause severe illness.
Endocrine System
Endocrine systems, also referred to as hormone systems, are found in all mammals, birds, fish, and many other types of living organisms. They are made up of:
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Glands located throughout the body;
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Hormones that are made by the glands and released into the bloodstream or the fluid surrounding cells; and
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Receptors in various organs and tissues that recognize and respond to the hormones.
Glands Associated to Endocrine
Hypothalamus - The hypothalamus links our endocrine and nervous systems together. The hypothalamus drives the endocrine system.
Pituitary gland - The pituitary gland receives signals from the hypothalamus. This gland has two lobes, the posterior and anterior lobes. The posterior lobe secretes hormones that are made by the hypothalamus. The anterior lobe produces its own hormones, several of which act on other endocrine glands.
Thyroid gland - The thyroid gland is critical to the healthy development and maturation of vertebrates and regulates metabolism.
Adrenal glands - The adrenal gland is made up of two glands: the cortex and medulla. These glands produce hormones in response to stress and regulate blood pressure, glucose metabolism, and the body's salt and water balance.
Pancreas - The pancreas is responsible for producing glucagon and insulin. Both hormones help regulate the concentration of glucose (sugar) in the blood.
Gonads - The male reproductive gonads, or testes, and female reproductive gonads, or ovaries, produce steroids that affect growth and development and also regulate reproductive cycles and behaviors. The major categories of gonadal steroids are androgens, estrogens, and progestins, all of which are found in both males and females but at different levels.
How Can Chemicals Affect the Endocrine System?
Scientific research on human epidemiology, laboratory animals, and fish and wildlife suggests that environmental contaminants can disrupt the endocrine system leading to adverse-health consequences. It is important to gain a better understanding of what concentrations of chemicals found in the environment may cause an adverse effect. Various types of scientific studies (epidemiology, mammalian toxicology, and ecological toxicology) are necessary to resolve many of the scientific questions and uncertainty surrounding the endocrine disruptor issue. Many such studies are currently underway by government agencies, industry, and academia.
A thyroidectomy is an operation that involves the surgical removal of all or part of the thyroid gland. In general surgery, endocrine or head and neck surgeons often perform a thyroidectomy when a patient has thyroid cancer or some other condition of the thyroid gland (such as hyperthyroidism) or goiter. Other indications for surgery include cosmetic (very enlarged thyroid), or symptomatic obstruction (causing difficulties in swallowing or breathing). Thyroidectomy is a common surgical procedure that has several potential complications or sequelae including: temporary or permanent change in voice, temporary or permanently low calcium, need for lifelong thyroid hormone replacement, bleeding, infection, and the remote possibility of airway obstruction due to bilateral vocal cord paralysis. Complications are uncommon when the procedure is performed by an experienced surgeon.
The thyroid produces several hormones, such as thyroxine (T4), triiodothyronine (T3), and calcitonin. After the removal of a thyroid, patients usually take a prescribed oral synthetic thyroid hormone—levothyroxine (Synthroid)—to prevent hypothyroidism. Less extreme variants of thyroidectomy include:
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Hemithyroidectomy (or unilateral lobectomy): removing only half of the thyroid
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Isthmectomy: removing the band of tissue (or isthmus) connecting the two lobes of the thyroid
A thyroidectomy should not be confused with a thyroidotomy (thyrotomy), which is a cutting into (‑otomy) the thyroid, not a removal (‑ectomy, literally “out-cutting”) of it. A thyroidotomy can be performed to get access for a median laryngotomy, or to perform a biopsy. (Although technically a biopsy involves removing some tissue, it is more frequently categorized as an ‑otomy than an ‑ectomy because the volume of tissue removed is minuscule.)
Traditionally, the thyroid has been removed through a neck incision that leaves a permanent scar. More recently, minimally invasive and "scarless" approaches such as transoral thyroidectomy have become popular in some parts of the world. In the United States, over 100,000 procedures are performed yearly as it is a common procedure.
Thyroid Surgery
In breast surgery, the surgeon removes breast tumours and lymph nodes while trying to save as much of the breast as possible. An endocrine surgeon specializes in the surgical treatment of endocrine diseases. These usually include the thyroid gland, parathyroid glands and adrenal glands.
Breast Surgery
Parathyroidectomy is the surgical removal of one or more of the (usually) four parathyroid glands. This procedure is used to remove an adenoma or hyperplasia of these glands when they are producing excessive parathyroid hormone (PTH): hyperparathyroidism. The glands are usually four in number and located adjacent to the posterior surface of the thyroid gland, but their exact location is variable. When an elevated PTH level is found, a sestamibi scan or an ultrasound may be performed in order to confirm the presence and location of abnormal parathyroid tissue.