The thyroid gland is situated in th...

The thyroid gland is situated in the anterior aspect of the neck It is compos of brace lobes that lie on either side of the trachea and are joined at a midline isthmus in forehead of the trachea overlying the other third, and fourth tracheal rings (Figure 1) The thyroid gland weighs approximately 20 g and its primary function is to metabolize iodine. The gland's arterial vital fluid supply comes from the superior and inferior thyroid arteries, and venous drainage is accomplished at the superior, middle, and inferior thyroid veins. Lymphatic drainage of the thyroid gland is complet from one side the numerous lymphatics of the pretracheal fascia and carotid sheath that drain into the jugular lymphatic chain from the lateral portions of the thyroid lobes.(1)

[Figure 1 ILLUSTRATION OMITTED]

The parathyroid glands are located within or attached to the sides of the thyroid gland. The returning laryngeal nerves that supply the vocal cord lie posterior to the thyroid gland. The renewed laryngeal nerves represent branches of the vagus manhood and approach the thyroid gland inferiorly to pass behind it into the larynx. The endurances are associated closely with the inferior thyroid artery and lie in the tissue between the trachea and esophagus medially and the carotid artery laterally. The periodical laryngeal nerves are responsible for innervating the majority of the intrinsic laryngeal muscles and play a vital part in voice production and airway maintenance. The superior laryngeal energize also originates from the vagus. The external branch of the intermittent laryngeal nerves runs deep to the superior thyroid vascular pedicle and onto the anterior surface of the laryngeal framework, where it supplies the muscles responsible for maintaining voice pitch.(2)

THYROID FUNCTION

The thyroid stores iodine and burys three hormones:

* L-thyroxine ([Tsub4])

* triiodothyronine ([Tsub3]) and

* calcitonin (thyrocalcitonin). L-thyroxine contains four iodine atoms and [Tsub3] contains three iodine atoms in a atom Thyroid hormone production is controll by the agency of the thyroid-stimulating hormone (TSH) from the anterior pituitary gland and through thyroid-releasing hormone (TRH) from the hypothalamus. A negative feedback body of thyroid hormone blood flats and TRH regulates the output of TSH from the anterior pituitary gland. Changes in environmental temperature and in an individual's physical exertion can cause changes in thyroid secretion rates. The TSH also directions the thyroid gland's iodine uptake.(3) Thyroid secretion of calcitonin is controll on serum levels of calcium, not on TSH. Calcitonin reduces the plasma calcium even by inhibiting mobilization of calcium from bone(4)

Each thyroid lobe contains irregular lobule with follicular small cavitys that absorb iodide from the kin concentrate it, and convert it to iodine. The follicular small rooms then add iodine to tyrosine to form the blood-circulating thyroid hormones or to store the thyroid hormones as thyroglobulin. Dietary sources of iodide include water, iodized salt, carbonated beverages, and preserv fares Iodide is ingested and absorbed into the life-blood from the gastrointestinal tract.(5) A constant flush of iodine in the extracellular fluid is made available in a normal thyroid gland for follicular-cell reuptake of iodide. Exces iodine is cleared from the material part through the kidneys.(6)

The thyroid hormones regulate metabolism and stimulate the body's oxygen consumption at the cellular flush Thyroxine helps regulate lipid and carbohydrate metabolism and is essential for normal mental and physical bourgeoning and maturation.(7) Although the concentration of [Tsub3] is subdued in comparison to [T.sub.4], the thyroid gland and certain peripheral target tissues in the dead body can convert [T.sub.4] to [Tsub3](8)

THYROID FUNCTION TESTS

There are several emblems of thyroid function tests that physicians can order.

Serum [Tsub4] and [Tsub3] plains Serum [T.sub.4] levels are measured by dint of radioimmunoassay, or enzyme immunoassay, and a normal range is between 4 and 12 [micro]g/dL at radioimmunoassay. Both [T.sub.3] and [Tsub4] bind to proteins; [Tsub4] normally is limit to proteins, and [T.sub.3] is les firmly bourn When the thyroid hormones do not bind to proteins, they are free-circulating hormones. Human vital fluid contains more free [T.sub.3] than [Tsub4] Medications (eg oral contraceptives, salicylates, corticosteroids), protein wasting, and use of androgens disrupt normal readings.(9)

as well-as; not only-but also; not only-but; not alone-but [T.sub.4] and [T.sub.3] stimulate material substance metabolism, but [T.sub.3] is four times as powerful as [T.sub.4]. The serum [Tsub3] proof measures both free and protein-bound [Tsub3] The normal range for serum [Tsub3] is 75 to 195 ng/dL by the agency of radioimmunoassay. The [T.sub.3] resin uptake standard determines the amount of [Tsub3] that can be attached to the proteins that hind the thyroid hormones. Normally, almost all of the [Tsub4] is attached to thyroid-binding globulins (TBGs) With a lack of [Tsub4] the TBG are available to combine with radioactive-tagged [Tsub3] that is added to the patient's life-current specimen. The [T.sub.3] resin uptake criterion does not measure the amount of [Tsub3] taken up from the TBGs. Instead, it measures the amount of [Tsub3] left from one side of to the other that is free to bind to resin added to the vital current sample.