Endocrine pharmacology: thyroid hormone action MCQs With Answer

Endocrine pharmacology: thyroid hormone action MCQs With Answer

This question set is designed for M.Pharm students studying Advanced Pharmacology-II and focuses on the molecular, cellular and systemic actions of thyroid hormones. The questions explore genomic and non‑genomic mechanisms, receptor isoforms, deiodinase biology, transport proteins, physiological effects on metabolism, cardiovascular and bone systems, developmental roles, and important drug interactions that modify thyroid hormone action. Each MCQ engages higher‑order understanding relevant for therapeutics, drug interactions and clinical interpretation of thyroid function. Answers are provided to facilitate self‑assessment and deeper study of the mechanisms underlying thyroid hormone physiology and pharmacology.

Q1. Which of the following best describes the primary mechanism by which thyroid hormones exert long‑term biological effects?

• Activation of G protein‑coupled receptors on the cell surface
• Binding to nuclear thyroid hormone receptors and modulation of gene transcription
• Direct activation of mitochondrial electron transport chain enzymes
• Inhibition of cytosolic kinases to reduce protein phosphorylation

Correct Answer: Binding to nuclear thyroid hormone receptors and modulation of gene transcription

Q2. Which thyroid hormone is considered the most biologically active at the receptor level?

• Thyroxine (T4)
• Triiodothyronine (T3)
• Reverse T3 (rT3)
• Thyroid stimulating hormone (TSH)

Correct Answer: Triiodothyronine (T3)

Q3. Which enzymatic activity is primarily responsible for converting circulating T4 into the more active T3 in peripheral tissues?

• 5′-deiodinase (outer‑ring deiodinase)
• Thyroid peroxidase
• Deiodinase type III (inner‑ring deiodinase)
• Sulfotransferase

Correct Answer: 5′-deiodinase (outer‑ring deiodinase)

Q4. Reverse T3 (rT3) is generated predominantly by which biochemical process?

• Outer‑ring deiodination of T3
• Inner‑ring deiodination of T4
• Oxidative deamination of T4
• Glucuronidation in the liver

Correct Answer: Inner‑ring deiodination of T4

Q5. Which thyroid hormone receptor (TR) isoform is most abundant in cardiac tissue and mediates many cardiac effects of thyroid hormone?

• TRβ1
• TRβ2
• TRα1
• TRγ

Correct Answer: TRα1

Q6. Rapid non‑genomic actions of thyroid hormones at the cell membrane are often mediated by which protein?

• Glycoprotein hormone receptors in the nucleus
• Integrin αvβ3 leading to activation of MAPK signaling
• Mitochondrial ATP synthase
• Voltage‑gated potassium channels exclusively

Correct Answer: Integrin αvβ3 leading to activation of MAPK signaling

Q7. Thyroid hormones increase basal metabolic rate primarily by which combined cellular actions?

• Decreasing mitochondrial biogenesis and lowering Na+/K+‑ATPase activity
• Increasing mitochondrial number and expression of uncoupling proteins and Na+/K+‑ATPase
• Blocking glycolysis and increasing fatty acid uptake into adipose tissue
• Reducing protein synthesis and promoting autophagy

Correct Answer: Increasing mitochondrial number and expression of uncoupling proteins and Na+/K+‑ATPase

Q8. How do thyroid hormones affect plasma LDL cholesterol levels mechanistically?

• Decrease hepatic LDL receptor expression, raising LDL levels
• Increase hepatic LDL receptor expression, enhancing LDL clearance
• Inhibit HMG‑CoA reductase directly in the liver
• Increase intestinal cholesterol absorption without changing hepatic clearance

Correct Answer: Increase hepatic LDL receptor expression, enhancing LDL clearance

Q9. Chronic excess thyroid hormone has which predominant effect on bone metabolism?

• Stimulates osteoblastic bone formation exclusively
• Enhances osteoclastic bone resorption, increasing risk of osteoporosis
• Inhibits both osteoclasts and osteoblasts equally
• Causes increased bone mineralization and reduced fracture risk

Correct Answer: Enhances osteoclastic bone resorption, increasing risk of osteoporosis

Q10. Which molecular change contributes to the positive chronotropic and inotropic effects of thyroid hormone on the heart?

• Downregulation of β1‑adrenergic receptors in cardiomyocytes
• Upregulation of β1‑adrenergic receptors, increasing heart rate and contractility
• Inhibition of Ca2+ channel expression in the sinoatrial node
• Suppression of sarcoplasmic reticulum Ca2+ ATPase (SERCA)

Correct Answer: Upregulation of β1‑adrenergic receptors, increasing heart rate and contractility

Q11. In the hypothalamic‑pituitary‑thyroid axis, which hormone exerts the principal negative feedback on TRH and TSH secretion?

• Thyroxine (T4) only
• Triiodothyronine (T3) acting on pituitary and hypothalamus
• Thyroid peroxidase
• Reverse T3 (rT3)

Correct Answer: Triiodothyronine (T3) acting on pituitary and hypothalamus

Q12. Which plasma protein binds the majority of circulating thyroid hormones and determines total hormone levels?

• Albumin
• Thyroxine‑binding globulin (TBG)
• Transferrin
• High‑density lipoprotein (HDL)

Correct Answer: Thyroxine‑binding globulin (TBG)

Q13. Amiodarone frequently alters thyroid function because it:

• Stimulates thyroid hormone synthesis by activating thyroid peroxidase
• Inhibits peripheral conversion of T4 to T3 and supplies a high iodine load
• Acts as a selective T3 receptor agonist in peripheral tissues
• Enhances renal clearance of thyroid hormones

Correct Answer: Inhibits peripheral conversion of T4 to T3 and supplies a high iodine load

Q14. Which distinction in mechanism is true when comparing propylthiouracil (PTU) and methimazole?

• PTU inhibits thyroid peroxidase only; methimazole inhibits deiodinases only
• PTU inhibits thyroid peroxidase and peripheral 5’‑deiodinase; methimazole inhibits thyroid peroxidase only
• Both drugs exclusively block TSH receptors
• Methimazole enhances peripheral T4 to T3 conversion while PTU blocks it

Correct Answer: PTU inhibits thyroid peroxidase and peripheral 5’‑deiodinase; methimazole inhibits thyroid peroxidase only

Q15. In the absence of ligand (T3), thyroid hormone receptors bound to DNA preferentially recruit which proteins to repress transcription?

• Histone acetyltransferases and coactivators
• Corepressors such as NCoR/SMRT
• RNA polymerase II activators
• Ubiquitin ligases that degrade the receptor

Correct Answer: Corepressors such as NCoR/SMRT

Q16. Thyroid hormone effects on carbohydrate metabolism include which of the following?

• Suppression of hepatic gluconeogenesis and increased peripheral glucose uptake only
• Stimulation of hepatic gluconeogenesis and glycogenolysis, increasing blood glucose
• Complete inhibition of pancreatic insulin secretion
• Exclusive promotion of adipose glucose uptake with no hepatic effect

Correct Answer: Stimulation of hepatic gluconeogenesis and glycogenolysis, increasing blood glucose

Q17. The deiodinase enzymes that convert T4 to T3 require which micronutrient cofactor?

• Iodine
• Selenium as a component of selenoproteins
• Iron as a heme prosthetic group
• Vitamin D

Correct Answer: Selenium as a component of selenoproteins

Q18. Early fetal brain development depends critically on which source of thyroid hormone?

• Fetal thyroid gland secretion of T3 from conception
• Maternal T4 crossing the placenta and local fetal conversion to T3
• Placental synthesis of TSH delivering T3 to the fetus
• Reverse T3 produced by the mother

Correct Answer: Maternal T4 crossing the placenta and local fetal conversion to T3

Q19. Which statement best describes the integrin αvβ3 thyroid hormone binding sites?

• It is a nuclear receptor that binds only T3 to alter gene transcription
• It is a cell surface receptor with distinct sites where T4 preferentially activates MAPK signaling
• It transports T4 across the blood‑brain barrier by endocytosis
• It is an intracellular deiodinase enzyme that generates rT3

Correct Answer: It is a cell surface receptor with distinct sites where T4 preferentially activates MAPK signaling

Q20. Which laboratory pattern is most consistent with primary hypothyroidism due to thyroid gland failure?

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

Correct Answer: High TSH, low free T4

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