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22 Cards in this Set

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  • Back
What chemical element is required for normal thyroid function?
Iodine
Where are thyroid hormones synthesized?
Follicular cells of the thyroid gland
Name the 2 active thyroid hormones.
T4(thyroxine) most produced,
T3 3,5, 3-triiodothyronine, most active.
What protein synthesizes and stores thyroid hormones?
Throglobulin- contains the iodotyrosyl residues;
monoiodotyrosine(MIT) and diiodotyrosine(DIT).
What are the steps of thyroid hormone synthesis?
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).
What are the steps of thyroid hormone secretion?
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.
Where else are thyroid hormones produced?
80% of T3 is converted from T4 in peripheral tissues, including liver and kidney.
What else does T4 form peripherally?
T4---deiodinated---inactive rT3
How do thyroid hormones circulate?
>99% in circulation are bound to proteins(thyroxin binding globulins(TBG), albumin and prealbumin.
What are the half lives of T3 and T4?
T3-1 day
T4-7 days
What is the action of T3 and T4 on metabolism?
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
What are the actions of T3 and T4 on the cardiac apparatus?
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.
WQhat factors regulate thyroid hormone synthesis and secretion?
TSH
TRH
What is TSH?
A glycoprotein with alpha and beta subunit.
Where is TSH synthesized?
Anterior pituitary.
How are the effects of TSH mediated?
Through TSH receptor on follicular cells.
What is TSH' second messenger system?
cAMP
What is TRH?
A polypeptide hormone
Where is TRH synthesized?
Hypothalamus
How are the effects of TRH mediated?
Through TRH receptor on pituitary cells.
What is the 2nd messenger system of TRH?
IP3
Name the actions of TRH?
Increase pituitary secretion of TSH.