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Thyroid Embryology and Anatomy
Where does the thyroid gland originate during fetal development?
From the base of the tongue.
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Regulation of Thyroid Hormone Production
What is the role of TSH in thyroid hormone production?
It stimulates the release of T3 and T4 into the bloodstream.
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Regulation of Thyroid Hormone Production
What is the feedback loop involved in regulating thyroid hormone production?
The hypothalamus releases TRH, stimulating the pituitary to secrete TSH, which acts on the thyroid.
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Key Enzymes and Proteins in Thyroid Function
What do Deiodinases (D1, D2, D3) do?
They remove iodine atoms from thyroid hormones, converting T4 to T3 or rT3.
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Thyroid Hormone Synthesis
What role does Reverse Triiodothyronine (rT3) play in the body?
It is an inactive metabolite of T4 that may help conserve energy during illness or fasting.
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Thyroid Hormone Synthesis
What is the role of the sodium/iodide symporter (NIS) in the thyroid?
It actively transports iodide from the blood into follicular cells.
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Thyroid Hormone Synthesis
How are T3 and T4 formed from iodinated tyrosines?
Iodinated tyrosines on thyroglobulin are coupled to form T3 and T4.
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Key Enzymes and Proteins in Thyroid Function
What is the function of the Sodium/Iodide Symporter (NIS)?
It actively transports iodide from the blood into thyroid follicular cells.
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Thyroid Hormone Synthesis
What stimulates follicular cells to take up iodinated thyroglobulin?
Thyroid-stimulating hormone (TSH).
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Thyroid Hormone Deiodination
What is reverse T3 (rT3)?
An inactive form of T3 produced during deiodination.
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Thyroid Hormone Action and Regulation
What are the effects of T3 and T4 on metabolism?
They regulate metabolism, growth, and development, influencing carbohydrate, protein, and lipid metabolism.
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Regulation of Thyroid Hormone Production
What hormone stimulates the thyroid gland to produce T3 and T4?
Thyroid-Stimulating Hormone (TSH).
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Thyroid Hormone Synthesis
What are the products formed when iodinated tyrosines couple within thyroglobulin?
T4 (thyroxine) and T3 (triiodothyronine).
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Thyroid Hormone Synthesis
How is dietary iodide transported to the thyroid gland?
Via the bloodstream after absorption in the small intestine.
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Thyroid Hormone Synthesis
What is thyroglobulin and its significance in thyroid hormone production?
Thyroglobulin is synthesized and secreted into the follicle lumen, serving as a precursor for T3 and T4.
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Hypothalamic-Pituitary-Thyroid (HPT) Axis
How does the Hypothalamic-Pituitary-Thyroid (HPT) Axis regulate thyroid hormone production?
Through a negative feedback loop involving TRH, TSH, and the levels of free T4 and T3.
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Key Enzymes and Proteins in Thyroid Function
What is the function of Thyroid Peroxidase (TPO)?
It catalyzes the oxidation of iodide to iodine and the iodination of tyrosine residues on thyroglobulin.
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Regulation of Thyroid Hormone Production
What type of feedback regulation maintains thyroid hormone levels?
Negative feedback from free T4 and T3 to the pituitary gland and hypothalamus.
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Thyroid Hormone Synthesis
What is thyroglobulin and where is it synthesized?
A glycoprotein containing tyrosine residues, synthesized in follicular cells.
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Regulation of Thyroid Hormone Production
What role does TSH play in thyroid hormone synthesis?
TSH stimulates each step of the thyroid hormone synthesis process.
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Clinical Significance of Thyroid Disorders
What are the symptoms of hyperthyroidism?
Increased metabolism, weight loss, rapid heartbeat, anxiety, heat intolerance, and other symptoms.
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Impact of Thyroid Dysfunction
What is the impact of hyperthyroidism?
Excess thyroid hormone affecting metabolism, growth, and organ systems.
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Thyroid Hormone Synthesis
What is the role of the sodium/iodide symporter (NIS) in thyroid hormone synthesis?
It facilitates iodide absorption and transport into follicular cells.
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Thyroid Hormone Transport and Action
What percentage of T3 and T4 exists in a free (unbound) form?
Only a tiny fraction; approximately 0.02% of T4 and 0.2% of T3 are free.
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Thyroid Hormone Deiodination
What converts T4 to the more active T3 in peripheral tissues?
Enzymes called deiodinases (D1, D2, D3).
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Regulation of Thyroid Hormone Production
Which hormone stimulates the anterior pituitary to produce TSH?
Thyrotropin-Releasing Hormone (TRH).
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Thyroid Hormone Deiodination
How is T4 converted to the more active T3 in peripheral tissues?
By deiodinase enzymes (D1 and D2).
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Clinical Significance of Thyroid Disorders
What is congenital hypothyroidism and its significance?
A deficiency of thyroid hormones that can cause severe developmental delays if untreated, highlighting the importance of early diagnosis.
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Thyroid Hormone Synthesis
What enzyme catalyzes the iodination of tyrosine residues on thyroglobulin?
Thyroid peroxidase (TPO).
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Thyroid Hormone Transport and Action
Why do T3 and T4 require transport proteins in the blood?
Because they are hydrophobic and have limited solubility in aqueous environments like blood plasma.
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Key Enzymes and Proteins in Thyroid Function
What is the role of Thyroglobulin (TG) in thyroid hormone synthesis?
It acts as a scaffold for thyroid hormone synthesis and contains tyrosine residues that become iodinated.
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Key Enzymes and Proteins in Thyroid Function
What is the function of DUOX2 in thyroid hormone synthesis?
It generates hydrogen peroxide, which is required by TPO for iodide oxidation.
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Key Enzymes and Proteins in Thyroid Function
What is the role of selenium in thyroid hormone metabolism?
Selenium is a crucial cofactor for all deiodinases.
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Thyroid Hormone Transport and Action
What is the role of Thyroxine-Binding Globulin (TBG)?
It binds to and transports T4 and, to a lesser extent, T3 in the blood.
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Thyroid Hormone Transport and Action
What happens to T3 and T4 after they are released from follicular cells?
They bind to transport proteins and travel to target tissues.
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Thyroid Hormone Deiodination
What is the function of deiodinase enzymes?
They convert T4 to the more active T3 or the inactive rT3 in peripheral tissues.
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Clinical Significance of Thyroid Disorders
What are the symptoms of hypothyroidism?
Slowed metabolism, weight gain, fatigue, cold intolerance, and other symptoms.
