This set of Molecular Endocrinology Multiple Choice Questions & Answers (MCQs) focuses on “Thyroid Gland and its Hormones”.
1. Which cells in the thyroid gland produces T4, T3 and “reverse” T3 hormones in the thyroid gland?
a) Follicular cells
b) Parafollicular C-cells
c) Sertoli cells
d) Leydig cells
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Explanation: In the thyroid gland, follicular cells develop T4, T3 and “reverse” T3 hormones. Whereas calcitonin is produced by parafollicular C-Cells. The major cell type in the thyroid gland is thyroid follicular cells (also called thyroid epithelial cells or thyrocytes).
2. Which among the following is the correct structure of the hormone 3,5,3’ tri- iodothyronine (T3)?
a)
b)
c)
d)
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Explanation: T4, T3 and “reverse” T3 hormones are iodinated tyrosine amino acids. Iodine in thyroxine is the reason for the 80% of iodine in thyroid venous blood. T3 helps retain muscle regulation, heart and digestive functions, brain function and growth.
3. What are the two raw materials used by thyroid gland to synthesize thyroid hormones?
a) Thyrotoxin and zinc
b) Thyrotoxin and iodine
c) Thyroglobulin and Iodine
d) Thyroglobulin and zinc
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Explanation: The thyroid gland requires two raw materials to synthesize thyroid hormones. They include the protein thyroglobulin and the mineral iodine. The thyroid takes iodine from our diet, combines it with tyrosine, an amino acid, and transforms it to T3 (containing three iodine atoms).
4. The iodination of the tyrosine residues of a large protein called “thyroglobulin” synthesizes thyroid hormones.
a) True
b) False
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Explanation: Thyroid hormones are synthesized by iodinating a large protein called “thyroglobulin” in their tyrosine residues. Thyroglobulin is a 19S-type dimeric glycoprotein with a molecular weight of 660,000.
5. The ratio of the precursors, MIT (mono-iodotyrosine)/DIT (di-iodotyrosine) increases in iodine deficiency.
a) True
b) False
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Explanation: The ratio of the precursors of iodine in thyroglobulin, MIT (mono-iodotyrosine)/DIT (di-iodotyrosine) reduces in iodine deficiency. When there is an adequate supply of iodine, the T4:T3 ratio is around 7:1.
6. What is the name of one of the precursor molecules of iodine in thyroglobulin protein?
a) Macroglobulin
b) Mono-iodotyrosine (MIT)
c) Micro globulin
d) Thyronine
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Explanation: Around 70% of the iodide in thyroglobulin are present as the inactive precursors mono-iodotyrosine (MIT) and di-iodotyrosine ‘(DIT). While the iodothyronyl residues T4 and T3 account for the rest 30 per cent.
7. Besides thyroglobulin which other proteins are present in the thyroid gland?
a) 4S iodoproteins
b) 5S iodoproteins
c) Ovoglobulin
d) Iodoglobulin
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Explanation: In addition to thyroglobulin, hormonally inactive and albumin-like other 4S iodoproteins are also found in the thyroid. In circulating blood, the above can appear and contribute to the protein bound iodine content in the blood.
8. The synthesis of thyroglobulin, which is the major raw material for thyroid hormone production take place in which type of cells?
a) Follicular cells
b) Sertoli cells
c) Parafollicular cells
d) Acinar cells
View Answer
Explanation: Thyroglobulin is synthesized and deposited as colloid in acinar cells. T3 and T4 are separated from the thyroglobulin and these hormones are secreted into the bloodstream. Acinar formation may also be considered to be the thyroid follicles, although in this case the follicles, which are part of an endocrine gland, function as a hormonal deposit instead of promoting secretion.
9. Which hormone of anterior pituitary gland induces the iodide uptake by the thyroid gland?
a) TSH
b) FSH
c) LH
d) MSH
View Answer
Explanation: The anterior pituitary gland secreted thyroid-stimulating hormone (TSH) promotes thyroid gland iodide uptake. Ingested dietary iodine is converted and absorbed from the gut into iodide. A pituitary hormone that activates the thyroid gland to manufacture thyroxine and then triiodothyronine, which stimulates the metabolism of almost every tissue in the body, is the thyroid-stimulating hormone.
10. What is the name of the mechanism by which iodine transport take place in the thyroid gland?
a) Iodine diffusion
b) Iodine trapping
c) Iodine pathway
d) Iodine wave
View Answer
Explanation: The thyroid concentrates iodide by transmitting it from the body to the colloid “actively” and “selectively.” The transport mechanism is called the “iodide-trapping” or “iodide-pump” mechanism.
11. Which transporter is required for the iodine pump to function properly in the plasma membrane?
a) Sodium potassium dependent ATPase
b) Calcium pump
c) ATP pump
d) Potassium pump
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Explanation: In combination with sodium potassium-dependent ATPase, the iodide ‘transporter’ (Pump) is situated in the basal plasma membrane and involves simultaneous ‘sodium-pump’ action. The iodide-pump requires ATP and reveals the specificity of the iodide substrate.
12. Which molecules compete with iodine for its uptake in the iodine trapping mechanism?
a) Thiocyanates
b) Calcium
c) Sulfonates
d) Thiolates
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Explanation: Thiocyanates/or perchlorates fights for the absorption process with iodide. This triggers the accelerated discharge of “exchangeable iodide” from the thyroid gland. Thiocyanate is a competitive sodium iodide symporter (NIS) inhibitor at levels of thiocyanate that are usually present in the blood. In this way, iodine deficiency is worsened by inhibition of the accumulation of thyroid iodide and inhibition of the transport of iodide into breast milk for infant nutrition.
13. Which among the following is an inhibitor of iodine uptake mechanism?
a) Calcium
b) Cyanide
c) Chlorine
d) Perchlorates
View Answer
Explanation: Since the mechanism of iodine absorption is dependent on energy, cyanide or dinitrophenol (DNP) can inhibit it. ‘Ouabain’ that can inhibit ‘sodium-pump’ will also inhibit iodine pump. Also, cyanide inhibits the use of oxygen by the body’s cells. The cells die as this occurs.
14. Which among the following is the extrathyroidal tissue which binds with iodine?
a) Pancreas
b) Liver
c) Mammary gland
d) Pineal gland
View Answer
Explanation: The mammary gland is the only iodine-binding extrathyroidal tissue. “Di-iodotyrosine” (DIT) forms in the mammary gland, but thyroxine and tri-iodothyronine do not form. In addition to its absorption into thyroid hormones, iodine is bound into thyroid antiproliferative iodolipids called iodolactones, which may also play a role in mammary gland proliferative regulation.
15. Which among the following carries out the oxidation of iodine in the thyroid gland?
a) Glutathione
b) Hydrogen peroxide
c) Thyroxin
d) Thyroperoxidase
View Answer
Explanation: A “haem-containing” particulate-bound “peroxidase” catalyzes iodide oxidation and other steps in thyroid hormone synthesis. This is known as thyroperoxidase, which needs hydrogen peroxide for its activity.
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