Term
| What two hormones does the thyroid produce? |
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Definition
| Thyroxine (T4), and Triiodothyronine (T3) |
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Term
| What important roles do the thryoid hormones play in? |
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Definition
| Play a critical role in cell differentiation and help maintain thermogenic and metabolic homeostatsis. |
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Term
| In the adult a portion of the thyroid gland persists in the tongue, what is this? |
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Definition
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Term
| Thyroid Development facts |
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Definition
| Thyroid diverticulum in pharynx. Descends down neck remains connected to tongue via thyroglossal duct. 2 lobes connected by isthmus. isthmus just below cricoid cartilage midway between apex of thyroid cartilage. |
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Term
| Blood supply of thyroid (arteries) |
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Definition
| superior thyroid artery arises from common or external artery. Inferior thyroid artery from thyrocervical of subclavian artery, small thyroid artery from brachiocephalic artery of aortic arch. |
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Term
| Venous Drainage of Thyroid gland |
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Definition
| Superior, Lateral, and inferior thyroid veins. |
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Term
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Definition
| a proteinaceous fluid that contains large amounts of thyroglobulin protein precursor of thyroid hormones. |
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Term
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Definition
| polarized- basolateral apposed to bloodstream and apical surface faces follicular lumen. |
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Term
| How does the demand for thyroid hormone get communicated to thyroid gland? |
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Definition
| usually signalled by TSH binding to receptor on the basolateral surface of the follicualr cells. Thyroglobulin reabsorption from follicular lumen and proteolysis wihin cell yield thryoid hormones for secretion. |
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Term
| Perifollicular Endothelial Cells |
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Definition
| responsible for the blood supply to the follicles |
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Term
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Definition
| predominant cells. They have a special affinity for iodine and synthesize the iodothyronine hormones. |
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Term
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Definition
| produce calcitonin hormone involved in calcium metabolism. synthesize and secret the hormone calcitonin. |
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Term
| What does calcitonin do and where is it produced? |
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Definition
| Lowers blood calcium levels by inhibiting bone resorption. Secretion results from elevation of blood calcium above normal levels. |
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Term
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Definition
| fibroblasts and lymphocytes |
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Term
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Definition
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Term
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Definition
| Iodide uptake is mediated by the Na/I-symporter (NIS) which is expressed at the basolateral membrane of thyroid follicular cells. |
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Term
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Definition
| glycoprotein synthesized in the rough endoplasmic reticulum and packaged by Golgi apparatus and released by exocytosis. |
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Term
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Definition
| Iodine combines with tyrosine residues of thyroglobulin form monoiodo- and diiodotyrosine (MIT and DIT. These are inactive forms. |
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Term
| What precursors are coupled to form T3? |
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Definition
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Term
| What is coupled to form T4? |
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Definition
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Term
| What happens to uncoupled MIT and DIT? |
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Definition
| They are deiodniated by the enzyme called deiodinases, recycling iodide not converted into thyroid hormones. |
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Term
| What protein binds to T3 and T4 when they are in circulation? |
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Definition
| Thyroxine binding globulin. this ensures a circulating reserve. readily excreted by the kidneys. |
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Term
| 3 main functions of T4 and T3 |
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Definition
| 1. essential for normal growth, brain development, and development of sex organs 2.Hormones, and particularly T3, control rate of metabolism, and hence the function of practically every organ in the body. 3. exert effects via membrane and nucleus receptors. |
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Term
| Mechanism of action of thyroid hormones on target cells |
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Definition
| They act by binding to nuclear thyroid hormone receptors alpha and beta. |
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Term
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Definition
| has unique amino terminus expressed in the hypthalamus and pituitary where plays role in feedback control of thyroid axis. |
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Term
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Definition
| expressed in most tissues. expression is high in the pituitary and liver. |
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Term
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Definition
| contains a unique carboxy terminus that prevents thyroid hormone binding, may function to block the action of other TR isoforms. |
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Term
| What are the relative affinities for T3 and T4 with the TR receptor. |
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Definition
| T3 is bound with 10-15 times grater affinity than T4 which explains its increased hormonal potency. |
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Term
| How are thyroid hormones regulated? |
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Definition
| TRH-hypothalamus TSH- anterior lobe of pituitary. TSH increases synthesis and secretion of thyroid hormens by follicular cells via cyclic AMP. |
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Term
| What will chronic elevation of TSH cause? |
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Definition
| hypertrophy of the thyroid gland |
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Term
| How do T3 and T4 induce negative feedback? |
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Definition
| They inhibit secretion of TSH from AP by decreasing sensitivity of secretory cells to TRH. |
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Term
| How do the thyroid hormones promote growth? |
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Definition
| act synergistially with growth hormone and somatomedin to promote bone formation. they stimulate bone maturation as a result of ossification and fusion of growth plates. |
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Term
| What vital role does the thryoid hormone play in the development of the CNS? |
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Definition
| during perinatal period. deficiency of thyroid causes irreversible mental retardation. |
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Term
| Adulthood hyperthyroidism |
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Definition
| hyperexcitability and irritability. slowed speech, somnolence, impaired memory, and ecreased mental capacity. |
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Term
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Definition
| has many same actions as B-adrenergic stimulation. useful adjunct therapy for hyperthyroidism is treatment with a B-blockig agent, such as propanolol. |
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Term
| Basal Metabolic Rate tyroid affects |
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Definition
| O2 consumption and BMR are increased by thyroid hormone in all tissues except brain, gonads, and spleen. resulting increase in heat productio underlies the role of thyroid hormone in temperature regulation. |
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Term
| Cardiovascular and respiratory systems |
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Definition
| effects of thyroid hormone on cardiac output and ventilation combine to ensure more O2 delivered to tissues. increased rate and stroke volume=>increased cardiac output. increases ventilation rate. |
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Term
| Metabolic Effects of thyroid hormones. |
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Definition
| increase glucose absorption from GI tract. increase glycogenolysis, gluconeogenesis, and glucose oxidation. increase lipolysis. increase protein synthesis and degradation. |
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Term
| What problems may occur for the mother during pregnancy in regards to idodine? |
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Definition
| As far as the thyroid is concerned, iodine clearance by kidney increases because of glomerular filtration increases and iodine and iodothyronines are transferred to fetus. women living in low iodine develop iodine deficiency and thyroid enlarges. |
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Term
| Placental transfer of thyroid hormones to fetus |
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Definition
| small amounts of maternal T4 is transferred to fetus and is converted to T3 which contributes to T3 concentration in the fetal brain. |
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Term
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Definition
| Test is used to determine total amount of T4 in blood, representing both the bound and unbound portions of T4. |
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Term
| Why is it important to measure the amount of free thyroxine in a free thyroxine index? |
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Definition
| Free T4 is the portion of thyroid hormone available to become active in the body. |
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Term
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Definition
| test is used to test the total amount of T3 in circulation. used in diagnosis of different types of hyperthyroidism such as Graves' disease. |
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Term
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Definition
| It is believed that the amount of free hormone may be the amount that is responsible for the biological activity of thyroid hormones at the cellular level |
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Term
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Definition
| measurement of the TSH in blood stream can help doctor determine whether or not the goiter is making a normal amount of thyroid hormone. |
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Term
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Definition
| having the patient take oral capsules that contain a harmless radioactive tracer. amouont of radioactive iodine taken up can be measured. area does not take up iodine then must be further investigated. |
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Term
| Fine-needle Aspiration Biopsy |
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Definition
| diminished the use of thyroid scans in the evaluation of solitary thyroid nodules. |
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Term
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Definition
| cold nodules which have diminished tracer uptake are benign. |
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