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25 Cards in this Set
- Front
- Back
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What are the two goals of thyroid drugs?
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(1) Prevent excessive Thyroid production - hyperthyroidism
(2) Supplement poor thyroid production - hypothryoidism |
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What is the thyroid hormone derived from?
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Two tyrosine amno acids - this basic structure is called Thyromine. If the 3 and 5 position of the first phenyl group and the 3' and 5' postion of the second phenyl group all have I's this is Thyroxine (T4). If the 5' I is missing, this is Triiodoxine (T3). If the 5 I is missing, this is Reverse T3.
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Which is more potent, T3 or T4?
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T4 is the principle hormone made by the thyroid but is less potent when compared to T3. T3 is 3-4 times more active. Reverse T3 is inactive.
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What is the thyroid gland's structure histologically?
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In the thyroid gland, the cells form a follicle and there are cells that surround the interspace and in this space is a colloidal material. A lot of the important things are going to go on between the interspace and the cells surrounding it.
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What is Thyroid Peroxidases (TPO) role?
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nzyme on the luminal border is called Thyroid Peroxidase (TPO) uses peroxide to convert the I- to hypoiodine. This is a reactive form of iodine (I+ or IO-). This enzyme also takes the hypoiodine and attaches it to the protein.
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Where is thyroglobulin made?
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Thyroglobulin is made in the cell and is secreted out into the colloid of the lumen.
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The thyroglobulin iodinated tyrosines. Some of these are next to one another - diiodotyrosines and others are monoiodotyrosines. How do these pair to form T4 and T3?
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T4 is formed from two diiodotyrosines and T3 is formed from one diiodotryosine and one monotryosine.
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What is the ratio of T4 to T3?
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4:1 BUT T3 is about four times as potent as T3.
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What happens if you are deficient of Iodine in your diet?
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In people who are deficient in iodine in their diet, there is a decrease in thyroid hormone production. As a result of this decrease, the body tries to stimulate this through the anterior pituitary hormone, TSH. This stimulation makes the thyroid gland produce more cells and to enlarge. This is called GOITER. There are areas in the country that have this deficiency - the GOITER BELT.
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What is the final step of T3 synthesis? Where does this occur?
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○ The final step in all of this occurs in the periphery. It occurs in the liver and other tissues. And what occurs is there is an enzyme called iodothryonine deiodinase and this enzyme in the peripheral tissue will now take T4 and by removing the 5' iodo group will convert this to T3.
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Quick recap of the synthesis of thyroid hormones.
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(1) Thyroid Peroxidase (TPO)
(2) Thyroglobulin (3) Diiodotyrosines and Monoiodotyrosines (4) Lysosomes --> T3 and T4 (5) Iodothyronine deiodinase - to make T3 from T4. |
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What is the purpose of the Thyroid Hormone Binding Globulin?
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As it turns out, most of the circulating thyroid hormone, 0.04 % T4 or 0.03% T3 are actually free hormone. What this does is it buffers to help level the concentration of free hormone. So most of it is bind but this allows for good regulation.
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What are the major purposes of the thyroid hormone?
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(1) Growth and development - especially the brain
(2) Increases heat production |
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What are typical signs of hyperthyroidism or thyrotoxisis?
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(1) Increased Heart Rate
(2) Increased Cardiac Output (3) Peripheral resistance decreases because of Beta 2 receptors. |
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What is one non-drug txt for hyperthyroidism?
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I131-beta emitted. 6-7 times the concentration of what it is in the plasma. Will destroy thyroid gland if concentrated there.
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How do PTU and methimazole work?
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The major actions of both drugs is inhibiting the thyroid peroxidase and blocking the addition of iodine to the tyrosines. They will also block the coupling of iodotryrosines.
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What is the advantage of PTU?
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Prefered sometimes to txt Thyroid storm because it has a quicker effect - it will also inhibit the deiodinase.
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What is the advantage of Methimazole?
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Isually preferred becaue it only requires one dose per day and is more potent and has very infrequent adverse effects compared to PTU
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What are possible toxicities of PTU and methimazole?
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(1) Agranulocytosis (reversible)
(2) Liver Failure |
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Which hyperthyroid drug is used to treat pregnant women?
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PTU becuas Methimazole is a teratogen.
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What are two other drugs used to treat hyperthyroidism?
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(1) Beta Blocker
(2) Dexamethasone |
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What is the rationale for using dexamethasone in the txt of hyerthyroidism - especially grave's disease?
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Dexamethasone is a long acting glucocorticoid. In Grave's disease, hyperthyroidism is usually caused by an antibody(A6) that binds to the TSH receptor on the thyroid cells - the TSH stimulates thyroid hormone production - this antibody binds to the same receptor to stimulate production. It suppresses the formation of an antibody.
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What are signs of hypothyroidism?
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(1) Increased vascular resisitance
(2) Decreased Heart Rate (3) Decreased Cardiac Output |
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Who are most at risk for hypothyroidism?
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7% of the population has it.
Women who are over 50 or more, this figure goes up to 50% |
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What is the treatment for hypothyroidism?
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The treatment includes replacing the thyroid hormone - Give T4 because it has a higher half life (7 days) this is compared to T3 with a half life of 1 day.
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