Structure and functions of thyroid gland MCQs With Answer

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Introduction:

The structure and functions of thyroid gland MCQs with answer provide B. Pharm students a focused way to master thyroid anatomy, histology, hormone synthesis (T3, T4), regulation by TSH/TRH, and clinical pharmacology. This topic covers iodide transport (NIS), thyroid peroxidase reactions, deiodinases, hormone transport proteins (TBG), and key disorders such as Graves’ disease, Hashimoto’s thyroiditis, goiter, and thyroid cancers. Drug-related aspects include levothyroxine, liothyronine, methimazole, propylthiouracil, iodides, and radioactive iodine therapy. These MCQs emphasize pathophysiology, diagnostic tests, and therapeutics to strengthen exam preparation and clinical application. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Where is the thyroid gland located?

  • In the anterior neck overlying the trachea
  • In the posterior neck adjacent to the cervical vertebrae
  • In the superior mediastinum behind the sternum
  • In the retroperitoneal space near the kidneys

Correct Answer: In the anterior neck overlying the trachea

Q2. Which cells of the thyroid gland synthesize thyroid hormones T3 and T4?

  • Parafollicular (C) cells
  • Follicular epithelial cells
  • Endothelial cells of capillaries
  • Colloid macrophages

Correct Answer: Follicular epithelial cells

Q3. Which transporter mediates active iodide uptake from blood into thyroid follicular cells?

  • Pendrin located on apical membrane
  • Sodium-iodide symporter (NIS) on basolateral membrane
  • Thyroglobulin receptor on luminal surface
  • Glucose transporter (GLUT) on basolateral membrane

Correct Answer: Sodium-iodide symporter (NIS) on basolateral membrane

Q4. Which enzyme catalyzes iodination and coupling reactions in thyroid hormone synthesis?

  • Thyroid peroxidase (TPO)
  • Thyroglobulin synthase
  • Deiodinase type 1
  • Sulfotransferase

Correct Answer: Thyroid peroxidase (TPO)

Q5. Combination of which iodotyrosine residues produces active T3?

  • DIT + DIT
  • MIT + MIT
  • MIT + DIT
  • Thyroglobulin + iodide

Correct Answer: MIT + DIT

Q6. Which form of hormone is predominantly secreted by the thyroid gland?

  • Triiodothyronine (T3)
  • Thyroxine (T4)
  • Reverse T3 (rT3)
  • Calcitonin

Correct Answer: Thyroxine (T4)

Q7. Which enzymes convert T4 to the more active T3 in peripheral tissues?

  • Thyroid peroxidases
  • Deiodinases (D1 and D2)
  • Sulfatases
  • Monooxygenases

Correct Answer: Deiodinases (D1 and D2)

Q8. What is the major plasma carrier protein for thyroid hormones?

  • Albumin
  • Thyroxine-binding globulin (TBG)
  • Transferrin
  • Haptoglobin

Correct Answer: Thyroxine-binding globulin (TBG)

Q9. Which hypothalamic hormone stimulates TSH release from the anterior pituitary?

  • Corticotropin-releasing hormone (CRH)
  • Growth hormone-releasing hormone (GHRH)
  • Thyrotropin-releasing hormone (TRH)
  • Gonadotropin-releasing hormone (GnRH)

Correct Answer: Thyrotropin-releasing hormone (TRH)

Q10. Which thyroid hormone exerts the strongest negative feedback on pituitary TSH secretion?

  • Reverse T3 (rT3)
  • Thyroxine (T4)
  • Triiodothyronine (T3)
  • Calcitonin

Correct Answer: Triiodothyronine (T3)

Q11. Primary action of thyroid hormones on cellular metabolism includes:

  • Decreasing Na+/K+ ATPase expression
  • Increasing basal metabolic rate and mitochondrial activity
  • Inhibiting protein synthesis globally
  • Reducing oxygen consumption

Correct Answer: Increasing basal metabolic rate and mitochondrial activity

Q12. How do thyroid hormones affect the cardiovascular system?

  • Decrease heart rate and contractility
  • Increase beta-adrenergic receptor expression, heart rate, and contractility
  • Cause coronary vasoconstriction without affecting rate
  • Produce bradycardia and low cardiac output

Correct Answer: Increase beta-adrenergic receptor expression, heart rate, and contractility

Q13. Hypothyroidism typically causes which change in lipid profile?

  • Decreased LDL cholesterol
  • Increased LDL cholesterol
  • Marked decrease in triglycerides only
  • No change in lipid levels

Correct Answer: Increased LDL cholesterol

Q14. Untreated congenital hypothyroidism in infants can lead to:

  • Cretinism with intellectual disability and growth retardation
  • Precocious puberty
  • Hyperactivity and increased IQ
  • Excessive growth and tall stature

Correct Answer: Cretinism with intellectual disability and growth retardation

Q15. The most common global cause of endemic goiter is:

  • Autoimmune thyroid disease
  • Iodine deficiency
  • Excessive TSH suppression
  • Radiation exposure

Correct Answer: Iodine deficiency

Q16. Which antibody stimulates the TSH receptor causing hyperthyroidism in Graves’ disease?

  • Anti-thyroglobulin antibody
  • Anti-thyroid peroxidase antibody
  • Thyroid-stimulating immunoglobulin (TSI)
  • Anti-TSH antibody that blocks receptor

Correct Answer: Thyroid-stimulating immunoglobulin (TSI)

Q17. Which autoantibodies are most commonly associated with Hashimoto’s thyroiditis?

  • Anti-TSI only
  • Anti-thyroid peroxidase (anti-TPO) and anti-thyroglobulin
  • Anti-insulin antibodies
  • Anti-parietal cell antibodies

Correct Answer: Anti-thyroid peroxidase (anti-TPO) and anti-thyroglobulin

Q18. Which antithyroid drug inhibits thyroid peroxidase and peripheral conversion of T4 to T3 (used in pregnancy first trimester cautiously)?

  • Methimazole
  • Potassium iodide
  • Propylthiouracil (PTU)
  • Levothyroxine

Correct Answer: Propylthiouracil (PTU)

Q19. Radioactive iodine (I-131) therapy primarily treats which thyroid condition?

  • Hypothyroidism due to Hashimoto’s
  • Graves’ disease and toxic nodular goiter to ablate thyroid tissue
  • Thyroid hormone replacement
  • Acute thyroiditis with low uptake

Correct Answer: Graves’ disease and toxic nodular goiter to ablate thyroid tissue

Q20. Administration of high-dose iodide (Lugol’s solution) before thyroid surgery works primarily by:

  • Stimulating new hormone synthesis
  • Inducing the Wolff-Chaikoff effect to temporarily inhibit hormone release
  • Blocking TSH receptor antibodies
  • Enhancing peripheral conversion of T4 to T3

Correct Answer: Inducing the Wolff-Chaikoff effect to temporarily inhibit hormone release

Q21. Which beta blocker is frequently used to control hyperthyroid symptoms and reduces peripheral T4 to T3 conversion?

  • Atenolol
  • Metoprolol
  • Propranolol
  • Bisoprolol

Correct Answer: Propranolol

Q22. Which drug is synthetic thyroxine used for replacement therapy in hypothyroidism?

  • Liothyronine
  • Levothyroxine
  • Propylthiouracil
  • Methimazole

Correct Answer: Levothyroxine

Q23. In primary hypothyroidism, typical laboratory findings are:

  • Low TSH, low T4
  • High TSH, low T4
  • High TSH, high T4
  • Low TSH, high T4

Correct Answer: High TSH, low T4

Q24. Which diagnostic test best reflects the active unbound hormone level?

  • Total T4
  • Total T3
  • Free T4 (FT4)
  • Thyroglobulin

Correct Answer: Free T4 (FT4)

Q25. Thyroid storm is best treated initially with which combination of therapies?

  • Levothyroxine and radioiodine
  • Beta blockers, antithyroid drugs, iodide, and glucocorticoids
  • Thyroid hormone replacement only
  • Calcium supplementation and diuretics

Correct Answer: Beta blockers, antithyroid drugs, iodide, and glucocorticoids

Q26. Which antibody is most specific for Graves’ disease and stimulates thyroid hormone production?

  • Anti-TPO
  • Anti-thyroglobulin
  • TSH receptor-stimulating antibodies (TSI)
  • Anti-TSH blocking antibodies

Correct Answer: TSH receptor-stimulating antibodies (TSI)

Q27. Which thyroid carcinoma is most commonly associated with prior radiation exposure and shows psammoma bodies histologically?

  • Medullary carcinoma
  • Follicular carcinoma
  • Papillary carcinoma
  • Anaplastic carcinoma

Correct Answer: Papillary carcinoma

Q28. Medullary thyroid carcinoma originates from which cell type and secretes which marker?

  • Follicular cells; thyroglobulin
  • Parafollicular C cells; calcitonin
  • Endothelial cells; chromogranin A
  • Stromal fibroblasts; thyroxine

Correct Answer: Parafollicular C cells; calcitonin

Q29. Follicular thyroid carcinoma most commonly spreads by which route?

  • Lymphatic spread to regional nodes
  • Hematogenous spread to bone and lung
  • Transcoelomic spread to pleura
  • Direct extension only without metastasis

Correct Answer: Hematogenous spread to bone and lung

Q30. Anaplastic thyroid carcinoma is characterized by:

  • Indolent behavior with excellent prognosis
  • Highly aggressive local invasion in elderly patients
  • Origin from parafollicular cells producing calcitonin
  • Exclusive occurrence in children

Correct Answer: Highly aggressive local invasion in elderly patients

Q31. TSH acts on thyroid follicular cells mainly via which intracellular pathway?

  • Gi-protein decreasing cAMP
  • Gs-protein increasing cAMP
  • Tyrosine kinase receptor activating MAPK directly
  • Ion channel-mediated depolarization

Correct Answer: Gs-protein increasing cAMP

Q32. Approximate recommended daily iodine intake for an adult is closest to:

  • 10 micrograms
  • 150 micrograms
  • 1,500 micrograms
  • 5,000 micrograms

Correct Answer: 150 micrograms

Q33. Which deiodinase primarily generates reverse T3 (rT3) and inactivates thyroid hormone?

  • Deiodinase type 1 (D1)
  • Deiodinase type 2 (D2)
  • Deiodinase type 3 (D3)
  • Thyroid peroxidase (TPO)

Correct Answer: Deiodinase type 3 (D3)

Q34. Elevated reverse T3 (rT3) is most commonly seen in which clinical state?

  • Hyperthyroidism due to Graves’ disease
  • Euthyroid sick syndrome (non-thyroidal illness)
  • Primary hypothyroidism with very high TSH
  • Congenital hypothyroidism only

Correct Answer: Euthyroid sick syndrome (non-thyroidal illness)

Q35. Which measurement is least affected by changes in thyroid-binding proteins (e.g., pregnancy, estrogen therapy)?

  • Total T4
  • Total T3
  • Free T4 (FT4)
  • Thyroxine-binding globulin concentration

Correct Answer: Free T4 (FT4)

Q36. During pregnancy, thyroid hormone requirements often increase because of:

  • Decrease in TBG levels
  • Increased thyroid-binding globulin (TBG) and increased thyroid hormone demands
  • Suppression of maternal thyroid by placenta only
  • Exclusive increase in peripheral deiodinase activity reducing demands

Correct Answer: Increased thyroid-binding globulin (TBG) and increased thyroid hormone demands

Q37. Which drug is well-known to cause hypothyroidism by inhibiting thyroid hormone release?

  • Amiodarone
  • Rifampin
  • Metformin
  • Warfarin

Correct Answer: Amiodarone

Q38. Lithium therapy can induce which thyroid abnormality?

  • Hyperthyroidism due to increased T3 synthesis
  • Hypothyroidism by inhibiting hormone release
  • Increased peripheral conversion of T4 to T3
  • No effect on thyroid function

Correct Answer: Hypothyroidism by inhibiting hormone release

Q39. After total thyroidectomy for differentiated thyroid cancer, which tumor marker is useful for follow-up?

  • Calcitonin
  • Thyroglobulin
  • Thyroid-stimulating immunoglobulin (TSI)
  • Anti-TPO antibody

Correct Answer: Thyroglobulin

Q40. How is iodinated thyroglobulin returned from the colloid to follicular cells for hormone release?

  • Simple diffusion across membrane
  • Receptor-mediated endocytosis and lysosomal proteolysis
  • Active transport via pendrin into blood
  • Secretion through exocytosis without internalization

Correct Answer: Receptor-mediated endocytosis and lysosomal proteolysis

Q41. Embryologically, the thyroid gland descends from which anatomical region?

  • First branchial arch
  • Foramen cecum at the base of the tongue (thyroglossal duct)
  • Third pharyngeal pouch endoderm only
  • Lateral pharyngeal pouches forming ultimobranchial body

Correct Answer: Foramen cecum at the base of the tongue (thyroglossal duct)

Q42. Failure of thyroid migration can result in which ectopic thyroid tissue location?

  • Lingual thyroid at the base of the tongue
  • Axillary thyroid tissue
  • Thyroid tissue inside the kidneys
  • Thyroid only in the mediastinum postnatally

Correct Answer: Lingual thyroid at the base of the tongue

Q43. Which laboratory pattern is most consistent with primary hyperthyroidism?

  • High TSH, high T4
  • Low TSH, high T4
  • Low TSH, low T4
  • High TSH, low T4

Correct Answer: Low TSH, high T4

Q44. TRH stimulation test is used to evaluate which level of dysfunction in the hypothalamic–pituitary–thyroid axis?

  • Primary thyroid failure only
  • To distinguish secondary (pituitary) from tertiary (hypothalamic) hypothyroidism
  • To diagnose Graves’ disease specifically
  • To screen for thyroid cancer

Correct Answer: To distinguish secondary (pituitary) from tertiary (hypothalamic) hypothyroidism

Q45. Major adverse effect of methimazole that requires monitoring is:

  • Hypokalemia
  • Agranulocytosis
  • Nephrolithiasis
  • Hyperglycemia

Correct Answer: Agranulocytosis

Q46. Thyroid radioactive iodine uptake scan shows diffuse increased uptake in which condition?

  • Subacute thyroiditis
  • Graves’ disease
  • Exogenous thyroid hormone ingestion
  • Thyroid adenoma with cold nodule

Correct Answer: Graves’ disease

Q47. Calcitonin secreted by C cells primarily acts to:

  • Increase bone resorption and blood calcium
  • Decrease bone resorption and lower blood calcium
  • Stimulate parathyroid hormone release
  • Increase renal calcium reabsorption

Correct Answer: Decrease bone resorption and lower blood calcium

Q48. Tertiary hypothyroidism refers to dysfunction at which anatomical level?

  • Thyroid gland itself
  • Anterior pituitary
  • Hypothalamus (TRH deficiency)
  • Peripheral deiodination only

Correct Answer: Hypothalamus (TRH deficiency)

Q49. Thyroid hormone receptors are located in which cellular compartment to mediate genomic effects?

  • Plasma membrane ion channels
  • Cytosolic surface of mitochondria only
  • Nucleus as ligand-activated transcription factors
  • Extracellular matrix

Correct Answer: Nucleus as ligand-activated transcription factors

Q50. Which biochemical marker commonly increases in untreated hypothyroidism due to muscle involvement?

  • Alkaline phosphatase only
  • Creatine kinase (CK)
  • Bilirubin
  • Amylase

Correct Answer: Creatine kinase (CK)

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