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22 Cards in this Set
- Front
- Back
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What chemical element is required for normal thyroid function?
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Iodine
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Where are thyroid hormones synthesized?
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Follicular cells of the thyroid gland
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Name the 2 active thyroid hormones.
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T4(thyroxine) most produced,
T3 3,5, 3-triiodothyronine, most active. |
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What protein synthesizes and stores thyroid hormones?
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Throglobulin- contains the iodotyrosyl residues;
monoiodotyrosine(MIT) and diiodotyrosine(DIT). |
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What are the steps of thyroid hormone synthesis?
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1. Inorganic iodide(I-) actively transported into follicular cell---diffuse into colloid/lumen---oxidized to iodine(I2) via thyroid peroxidase.
2. Thyroglobulin produced in rough ER of follicular cell---secreted into colloid. 3. IN colloid, I2 is incorporated into tyrosine residues of thyroglobulin---MIT and DIT formed 4. Coupling of iodotyrosyl residues inside thyroglobulin occur to form T3(MIT + DIT) or T4(DIT+DIT). |
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What are the steps of thyroid hormone secretion?
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1. Throglobulin is resorbed into follicular cell---fuse with lysosomes hydrolyzed into T3, T4, DIT and MIT.
2. T3 and T4 secreted into plasma 3. DIT and MIT deiodinated---tyrosines. |
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Where else are thyroid hormones produced?
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80% of T3 is converted from T4 in peripheral tissues, including liver and kidney.
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What else does T4 form peripherally?
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T4---deiodinated---inactive rT3
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How do thyroid hormones circulate?
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>99% in circulation are bound to proteins(thyroxin binding globulins(TBG), albumin and prealbumin.
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What are the half lives of T3 and T4?
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T3-1 day
T4-7 days |
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What is the action of T3 and T4 on metabolism?
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1. Increases BMR, O2 consumption, heat production, activates Na+-K+ ATPase
2. Increases glucose absorption, glycogenolysis, gluconeogenesis, glucose oxidation 3. Increases lipolysis and protein degradation |
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What are the actions of T3 and T4 on the cardiac apparatus?
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Increases beta-adrenergic receptors---increases cardiac output(HRXSV)
2. Increases systolic blood pressure only. It increases the respiratory rate and is required for ovary anfd testis maturation. |
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WQhat factors regulate thyroid hormone synthesis and secretion?
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TSH
TRH |
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What is TSH?
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A glycoprotein with alpha and beta subunit.
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Where is TSH synthesized?
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Anterior pituitary.
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How are the effects of TSH mediated?
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Through TSH receptor on follicular cells.
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What is TSH' second messenger system?
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cAMP
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What is TRH?
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A polypeptide hormone
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Where is TRH synthesized?
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Hypothalamus
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How are the effects of TRH mediated?
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Through TRH receptor on pituitary cells.
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What is the 2nd messenger system of TRH?
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IP3
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Name the actions of TRH?
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Increase pituitary secretion of TSH.
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