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= Behavioral Endocrinology =

Thyroid Hormones
Thyroid hormones are responsible for controlling metabolism, nervous system, body temperature and development of several organ systems such as the reproductive system. The overproduction and under secretion of the thyroid hormones changes the function of the thyroid. Hyperthyroidism and hypothyroidism are the two major dysfunctions associated to behavioral and brain chemistry changes due to the imbalances in the thyroid hormones, triiodothyronine (T3) and thyroxine (T4).

Thyroxine (T4) and triiodothyronine (T3)
''thyroxine (T4) and triiodothyronine (T3) are the main hormones released in the thyroid gland. They are synthesized from tyrosine and iodine in the bloodstream. These hormones travel via the bloodstream to almost every cell throughout the body and function to regulate their target cell's metabolism. These hormones are a product of the hypothalamic–pituitary–adrenal axis (HPA axis or HTPA axis). These organs function together as the hypothalamus releases thyrotropin-releasing hormone (TRH), which cause the pituitary gland to secrete thyrotropin that signals the thyroid gland to process and release thyroxine and triiodothyronine to the body. These hormones play a major role in the Neuroendocrine system which regulates the vital body functions of breathing, body weight, heart rate, muscle strength, cholesterol levels, especially body temperature. When your body has too much or too little of these hormones it has abnormal effect throughout your body:''

Hyperthyroidism
The overproduction of thyroxine and triiodothyronine result in hyperthyroidism which increases metabolic activity. In Grave's disease, an autoimmune condition which is another cause of hyperthyroidism, excessive production of hormones occur due to the production of antibodies that stimulate the thyroid gland. Exophthalmos, bulging of the eyes, is quite prominent in Grave's disease. There are other medical conditions like goiter, visible swelling of the thyroid gland, that can also lead to this dysfunction. Thyroiditis, the inflammation of the thyroid, also contributes to thyrotoxicosis. The overactive activity of the thyroid induces these symptoms of Hyperthyroidism:


 * Anxiety
 * Irritability or moodiness
 * Hyperactivity and nervousness
 * Excessive sweating and sensitivity to higher temperatures
 * Hand Trembling
 * Missed or light menstrual periods
 * weight loss
 * Itching and dryness of skin
 * difficulty in sleeping

Hyperthyroidism occurs more in women than in men. Due to the genetic factors associated with the dysfunction, it has the propensity to run in families.

Hyperthyroidism in Pregnancy:
Thyrotoxicosis does not exacerbate during pregnancy and about 1 percent of women experience thyroid dysfunction in pregnancy. Hyperthyroidism constitutes to various effects during pregnancy. Hyperthyroidism has been shown to induce high blood pressure in pregnant women. Among that, it could also lead to premature birth, where the baby is born in fewer weeks than the 37 weeks' gestational period, and is at risk of dying and having several disabilities due to low birth weight. Also alarmingly high levels of thyroid hormones causes thyroid storm, a life-threatening form of hyperthyroidism.

Diagnosis
The methods presently used for detecting hyperthyroidism are blood-test and physical examination.


 * Thyroid-stimulating hormone (TSH) concentrations along with the thyroid hormones T3 and T4 are measured from biological samples. Increased levels of thyroid hormone thyroxine (FT4), with low levels of thyroid-stimulating hormone in blood plasma by immunometric assays of an individual is a common indicator of an overactive thyroid gland.
 * The analysis of an ultrasound and nuclear scans of the thyroid provides a clear image of the thyroid to identify if there are nodules present. Enlarged or inflamed thyroid indicate an overactive thyroid.
 * The measurement of thyroid-stimulating hormone receptor antibodies, is an important diagnostic tool to know whether over activity is associated to Graves' disease . Individuals with the autoimmune disorder thyroiditis show high levels of antibodies, thus increased amount thyroid stimulating immunoglobulins constitutes to hyperthyroidism.

Treatment
Treatment of hyperthyroidism pertains to each individual due to the consideration of factors like age, medical conditions, and type of hyperthyroidism.


 * Antithyroid medication:

Antithyroid drugs that affect the production of thyroid hormones is the preferred choice for treating pregnant women and children. Drugs such as methimazole or tapazole and propylthiouracil serve as antagonist on the receptors of the thyroid glands reducing its production of thyroid hormones. Propylthiouracil is predominantly used for pregnant women in their first trimester of pregnancy. The use of methimazole has been associated with birth defects. The length of treatment depends on the severity of the hyperthyroidism.

Include side effects of medication?


 * Surgical procedure:

Another treatment of hyperthyroidism is the removal of the thyroid gland. Prior to surgical removal of the thyroid gland, patients with persistent over-activity are treated with antithyroid drugs. Removal of the thyroid gland could potentially lead to hypothyroidism, hence patients will be required to take thyroid hormone agonists such as levothyroxine.


 * Radioactive iodine:

Radioactive iodine (RAI) therapy is one of the safest treatment for hyperthyroidism with little to no potential side effects. For decades radioactive iodine therapy has been used to patients over 60 years due to its low risk rate. The process involves the eradication of the thyroid cells that obtain iodine from the bloodstream needed for the synthesis of thyroid hormones. Radioactive iodine capsules are given to patients and taken orally. Once ingested the radioactive iodine flows through the bloodstream to target the thyroid cell that are overactive. The radioactive iodine causes the thyroid nodules to reduce in size, in turn restoring thyroid hormone levels. Women that have undergone radioactive iodine treatment, and desire to get pregnant are required to wait for a year after therapy.


 * Use of Beta blockers:

Beta blocker are prescribed to patients regardless of the treatments listed above. They help alleviate the symptoms of hyperthyroidism before any of the treatments are given based on the type of hyperthyroidism.

Hypothyroidism
In the situation where the thyroid gland does not produce adequate amount of thyroid hormones, hypothyroidism can develop. The deficiency of the thyroid hormone leads to a generalized plunge in metabolic processes. There are permanent consequences such as mental retardation in infants and children due to the slowing of growth and development. Myxedema, a deposition of glycosaminoglycans in intracellular spaces like skin and muscle, is a severe onset of hypothyroidism in adults.

The underactivity of the thyroid gland has major implications on physiological and psychological wellbeing.

Some potential side effects are:


 * Trouble sleeping
 * Fatigue
 * Dry skin or hair
 * Concentration difficulties
 * depression
 * Sensitivity to cold temperatures
 * Frequent and heavy menstrual periods
 * Joint and muscle pain

Causes
Causes of hypothyroidism varies based on geographic and environmental factors. Age distribution of a population and dietary iodine can be classified as common factors that cause hypothyroidism. Classification of hypothyroidism can be categorized in 4 groups:


 * 1) Thyroid failure
 * 2) Pituitary TSH deficit
 * 3) Hypothalamic deficiency of TRH
 * 4) Peripheral resistance to action of thyroid hormones

Hypothyroidism in younger patients is associated with goiter, while in older patients there is deterioration of the gland due to immunological processes involving inflammation (autoimmune thyroiditis).

Detailed description of causes, diagnosis, and treatments can be found at the Hypothyroidism wiki article page.

= Citation =