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27 Cards in this Set
- Front
- Back
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Where is the thyroid gland located anatomically?
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Above the thyroid cartilage
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What part of the thyroid is only in a minority of people? Where does it originate from?
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3rd lobe
Isthmus, or left lobe |
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What are the hormones released from the thyroid?
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T3
T4 |
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Where is T4 made? Is it released in an active form/
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Entirely from the thyroid
Not active when released; it's a pro-hormone |
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What is the source of T3? Is it released actively?
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20% thyroid secretion
80% from T4 5' deiodination in periphery It's active. |
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What enzyme is responsible for converting T4 to T3? Where does this happen?
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Type 1 5' deiodinase
Liver, kidney |
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What are the different types of deiodonases? Where do they act?
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Type 1,2: convert T4 to T3
Type 3: converts T4 to rT3, T3 to T2 |
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Where is D1 found? D2 found?
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D1: liver, kidney. Function: supply plasma T3
D2: pituitary, brain, placenta, brown fat, , muscle, thyroid. T3 for local use |
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What is the activity of the type 3 deiodinase?
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Inactivate thyroid hormone
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What is the functional unit of the thyroid gland?
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THyroid follicle
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What cells within the thyroid are responsible for calcium levels? How do they regulate this?
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Parafollicular (C) cells
They do it via calcitonin |
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What happens in thyroid hoemone synthesis?
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1. Plasma iodide enters through the Na iodide symporter
2. Thyroglobulin, a large, glycoprotein, is synthesized within the thyroid cell 3. Thyroid peroxidase (luminal) iodinates tyrosines in Tg, creating mono and di-iodotyrosinases 4. Iodotyrosines combine to form T3 and T4 within the Tg protien |
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What is more likely to be found inside a mature Tg molecule: T4 or T3?
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T4:
Each contains around 3 T4's, but only 1 in 4 contains a T3 |
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What is colloid? What is contained?
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A large storage deposit of Tg
Storage depot for thyroid hormone |
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What is the activity of TSH on the thyroid?
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Causes pseudopodia formation; endocytosis of a colloid
The colloid fuses with lysosomes, releasing the thyroid hormone TSH also stimulates iodide trapping and thyroid hormone synthesis |
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What is the sodium iodide symporter? How is it used therapeutically/
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Cotransporter of Na and Iodine
Brings iodine into the thyroid Used in radioiodine therap |
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How much iodine do you need/day?
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>200 ug/day
Less than 50 you have PROBLEMS! |
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What are consequences of iodine deficiency?
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Endemic goiters
In the context of pregnancy: kids with endemic cretinism |
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What are the findings in endemic cretinism?
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Hypothyroidism
Mental retardation Abnormalities of: -Hearing -Posture -Gait -Stature |
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Why does maternal hypothyroidism cause endemic cretinism?
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The fetal thyroid doesn't work for the first 10 weeks.
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What is the feedback loop for thyroid hormone regulation?
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It's a fairly sensitive loop; little changes are able to efect change, which means that levels stay relatively stable
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What is the structure of TSH?
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2 chains: alpha and beta
The alpha subunit is shared by: TSH FSH LH CG The beta subunit gives the specificity |
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What is the mechanism of action for TSH?
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Binds to GCPR at the thyroid follicular cell
Acts with cAMP |
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How are thyroid hormones carried in the blood?
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99.9ish proteins are non-covalently bound to proteins in the blood
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What protein is responsible for binding to T4 and T3 in the blood? To which does it bind more strongly?
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Thyrxine binding globulin
BInds more strongly to T4 Others: Transthyretin (T4), albumin (T3) |
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What are the conditions that cause total T4 and T3 to be altered?
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Pregnancy (estrogen)
Acute hepatitis (too much) Chronic liver failure (too little) |
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What is the form of T4 and T3 that acts on feedback loops in the brain?
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Free T4 or T3, not the bound form.
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