Endocrine Physiology (Pituitary, Thyroid, Adrenal, Pancreas) MCQs

Physiology · 82 free questions with answers & explanations.

1. A 35-year-old woman presents with weight gain, cold intolerance, and bradycardia. TSH is markedly elevated and free T4 is low. The most physiologically accurate explanation for the elevated TSH is:
2. Which of the following correctly describes the mechanism by which insulin lowers blood glucose in peripheral tissues?
3. Cortisol is secreted in a diurnal pattern. In healthy individuals, the peak secretion of cortisol occurs at what time relative to waking?
4. Growth hormone secretion is regulated by two opposing hypothalamic hormones. A 14-year-old boy with short stature is found to have a deficiency of the stimulatory hormone. Which hypothalamic hormone is deficient?
5. Mineralocorticoid excess (as in Conn's syndrome) characteristically produces which metabolic abnormality?
6. A 30-year-old woman has amenorrhea and a serum prolactin of 180 ng/mL. A pituitary MRI shows a 12 mm adenoma. Which physiologic mechanism normally keeps prolactin low in non-pregnant women?
7. In the hypothalamic-pituitary-thyroid axis, free T4 exerts negative feedback primarily on which structure, and what is the intracellular mechanism?
8. A 28-year-old man with an adrenal incidentaloma undergoes overnight 1 mg dexamethasone suppression test. Post-dexamethasone morning cortisol is 8 µg/dL (normal < 1.8 µg/dL). Which zone of the adrenal cortex and which enzyme pathway is most likely dysfunctional or autonomous?
9. During a prolonged fast of 48 hours, plasma insulin is 3 µU/mL (low) and glucagon is 180 pg/mL (elevated). Which metabolic shift in the liver is most directly driven by this hormonal milieu?
10. Glucose-stimulated insulin secretion (GSIS) from pancreatic β-cells involves a specific sequence of intracellular events. Which step is MOST DIRECTLY responsible for triggering insulin exocytosis?
11. Glucagon-like peptide-1 (GLP-1), secreted by intestinal L-cells after a meal, stimulates insulin secretion via a mechanism that is distinct from nutrient-stimulated insulin release. The primary intracellular pathway activated by GLP-1 in beta cells is:
12. Thyroid hormone (T3) exerts genomic effects by binding to thyroid hormone receptors (TRs). In the absence of T3, unliganded TR bound to thyroid response elements (TREs) on target gene promoters:
13. In the adrenal stress response, ACTH stimulates cortisol synthesis via multiple intracellular steps. The acute rate-limiting step in cortisol biosynthesis, stimulated within minutes of ACTH signalling, involves:
14. Growth hormone (GH) secretion shows pulsatile nocturnal peaks. The primary hypothalamic peptides regulating GH secretion are GHRH (stimulatory) and somatostatin (inhibitory). Ghrelin, an endogenous GH secretagogue, acts primarily through which receptor and at which site?
15. A woman with Addison's disease has elevated plasma ACTH levels despite receiving daily oral hydrocortisone replacement. She also has markedly elevated MSH (melanocyte-stimulating hormone) levels, explaining her skin hyperpigmentation. Both ACTH and MSH originate from the same precursor because:
16. Thyroid hormone (T3) exerts its primary genomic effects via nuclear receptors. Which isoform of thyroid receptor (TR) has the highest affinity for T3 and is predominantly expressed in cardiac tissue?
17. Glucagon-like peptide-1 (GLP-1) potentiates glucose-stimulated insulin secretion via which intracellular mechanism in pancreatic beta cells?
18. A patient with primary adrenal insufficiency (Addison's disease) develops hyponatremia, hyperkalemia, and hypotension. Aldosterone deficiency causes hyperkalemia primarily by which mechanism?
19. Which second messenger pathway mediates the rapid (non-genomic) action of growth hormone (GH) on hepatocytes to produce IGF-1?
20. A female patient has a pituitary adenoma secreting ACTH (Cushing's disease). Which finding on dynamic testing would MOST reliably distinguish this from ectopic ACTH secretion?
21. Thyroid hormone (T3) exerts most of its effects through nuclear thyroid hormone receptors (TRα, TRβ). What is the molecular mechanism by which T3 converts a transcriptional repressor to an activator?
22. The incretin effect accounts for approximately 50-70% of postprandial insulin secretion. Which receptor/signaling cascade mediates GLP-1's insulinotropic effect on β-cells?
23. In the zona fasciculata, cortisol synthesis requires transport of cholesterol to the inner mitochondrial membrane by which rate-limiting protein?
24. A 28-year-old woman has galactorrhea, amenorrhea, and serum prolactin of 180 ng/mL. Dopamine agonist therapy is initiated. What is the receptor-level mechanism by which dopamine reduces prolactin secretion and causes lactotroph cell shrinkage?
25. Aldosterone exerts its slow (genomic) effect on principal cells by inducing synthesis of which protein(s) that increase renal Na⁺ retention?
26. Glucagon-like peptide-1 (GLP-1) stimulates insulin secretion from pancreatic beta cells through an incretin effect. The intracellular signaling cascade by which GLP-1 augments glucose-stimulated insulin secretion is:
27. A patient with an ACTH-secreting pituitary adenoma (Cushing disease) undergoes inferior petrosal sinus sampling (IPSS). The IPSS central-to-peripheral ACTH ratio is >2 at baseline and >3 after CRH stimulation. This test is used to:
28. Thyroid hormone synthesis requires thyroid peroxidase (TPO) for organification of iodide and coupling of iodotyrosines. Propylthiouracil (PTU) blocks TPO. An additional unique advantage of PTU over methimazole in thyroid storm is:
29. In primary adrenal insufficiency (Addison disease), hyponatremia with hyperkalemia and metabolic acidosis occur due to mineralocorticoid deficiency. The specific ion transport mechanism in the cortical collecting duct that is lost when aldosterone is absent is:
30. Growth hormone (GH) exerts both direct and indirect effects. The indirect effects are mediated by IGF-1, which is produced primarily in the liver. A patient with Laron syndrome has elevated GH but low IGF-1 and short stature. The defect in Laron syndrome is:
31. The sodium-glucose cotransporter in the thyroid follicular cell (NIS — sodium iodide symporter) is the primary mechanism for iodide accumulation in the thyroid. The NIS establishes an iodide concentration gradient of approximately 25–50× plasma. Its activity depends on which electrochemical driving force?
32. A patient with a corticotroph adenoma (Cushing's disease) undergoes bilateral adrenalectomy. Post-operatively, the tumor enlarges and produces excessive MSH along with ACTH, causing hyperpigmentation. This phenomenon is called Nelson's syndrome. The shared precursor molecule for both ACTH and MSH is:
33. Glucose-dependent insulinotropic polypeptide (GIP) and GLP-1 are incretins that potentiate glucose-stimulated insulin secretion. They act via Gs-coupled receptors on beta cells to increase cAMP, which activates PKA. PKA-independent amplification of insulin secretion by incretins also involves activation of which pathway?
34. Mineralocorticoid receptor (MR) is expressed not only in the kidney but also in cardiomyocytes, where aldosterone promotes cardiac fibrosis. The enzyme that protects renal mineralocorticoid receptors from cortisol (which has equal affinity for MR) activation is:
35. In the male, LH acts on Leydig cells to stimulate testosterone synthesis. FSH acts on Sertoli cells and is essential for spermatogenesis. Which specific product of Sertoli cells serves as a paracrine signal from the seminiferous tubule to Leydig cells to amplify steroidogenesis, and which Sertoli cell product provides the direct hormonal feedback to the pituitary to suppress FSH?
36. Thyroid hormone (T₃) acts via nuclear receptors (TRα and TRβ). The unliganded TR-β is bound to a thyroid hormone response element (TRE) in a complex with a corepressor. When T₃ binds, the receptor undergoes conformational change causing:
37. Aldosterone secretion from the zona glomerulosa is stimulated by angiotensin II. The post-receptor signaling mechanism in zona glomerulosa cells predominantly involves:
38. Glucose-stimulated insulin secretion (GSIS) from the pancreatic β-cell involves closure of ATP-sensitive K⁺ (KATP) channels. The KATP channel is a hetero-octameric complex. Which subunit is targeted by sulfonylurea drugs, and which subunit contains the pore?
39. Prolactin secretion is tonically inhibited by dopamine from the tuberoinfundibular pathway. Which receptor subtype on lactotroph cells mediates this inhibition, and what is the principal second messenger mechanism?
40. The hypothalamic osmoreceptors that regulate ADH secretion are located in which specific nucleus and are activated by what mechanism?
41. Wolff-Chaikoff effect describes a transient inhibition of thyroid hormone synthesis that occurs with large iodine loads. The molecular mechanism underlying iodine-mediated inhibition of organification involves:
42. Glucagon-like peptide-1 (GLP-1) potentiates glucose-stimulated insulin secretion (GSIS) through which intracellular pathway in the beta cell?
43. The zona glomerulosa of the adrenal cortex exclusively produces aldosterone because it expresses aldosterone synthase (CYP11B2) but lacks 17α-hydroxylase (CYP17A1). The consequence of the absence of CYP17A1 in zona glomerulosa is that:
44. In central diabetes insipidus, after desmopressin (dDAVP) administration, urinary osmolality rises to >800 mOsm/kg. In nephrogenic DI, it rises by less than 50%. This distinction occurs because dDAVP:
45. Thyroid hormone (T3) exerts its genomic effects by binding nuclear thyroid hormone receptors (TRα/TRβ). The key sequence of events between T3 binding and target gene transcription is:
46. A patient with primary adrenal insufficiency (Addison's disease) is noted to have hyperpigmentation, hyponatremia, and hyperkalemia. The mechanism of hyponatremia in Addison's disease involves primarily:
47. The first-phase insulin secretion in response to IV glucose load is critical for postprandial glucose control. The ionic mechanism triggering this first-phase release from beta cells involves:
48. TSH receptor antibodies (TRAb) in Graves' disease stimulate the TSH receptor, mimicking TSH. This causes hyperthyroidism. The intracellular signaling cascade activated by TSH receptor stimulation and its downstream effects on thyroid hormone synthesis are:
49. During prolonged fasting (72 hours), the brain's fuel utilization shifts. At this stage, which fuel provides the majority of brain energy, and what regulates this shift?
50. The Wolff-Chaikoff effect is a clinically important phenomenon in thyroid physiology. It refers to:
51. Zona glomerulosa of the adrenal cortex is the EXCLUSIVE site of aldosterone synthesis because:
52. In a patient with a glucagonoma, which metabolic consequence is MOST directly attributable to chronic glucagon excess?
53. In primary adrenal insufficiency (Addison's disease), the characteristic skin hyperpigmentation occurs because:
54. A patient with a TSH-secreting pituitary adenoma (thyrotropinoma) has elevated TSH, elevated free T4, and elevated free T3. This differs from Graves' disease in that:
55. The incretin effect accounts for the greater insulin response to oral glucose versus intravenous glucose (at equivalent glucose levels). The two primary incretins and their respective stimulus-secretion patterns are:
56. A 14-year-old girl has no breast development, primary amenorrhea, anosmia, and normal karyotype 46,XX. LH and FSH are very low. Which diagnosis and underlying physiological mechanism is MOST appropriate?
57. During hypoglycemia, plasma glucagon rises while insulin falls. Which additional counter-regulatory mechanism is MOST physiologically important in restoring blood glucose during PROLONGED (> 4 hours) hypoglycemia?
58. A patient with primary adrenal insufficiency (Addison's disease) develops hyperpigmentation of the buccal mucosa and skin creases. Which physiological mechanism explains this finding?
59. A patient undergoes surgical stress. Within 30 minutes, serum cortisol rises from 12 to 38 μg/dL. The acute cortisol secretion in response to ACTH stimulation occurs by which cellular mechanism?
60. A 14-year-old girl has primary amenorrhea. Karyotype is 46,XY. She has normal female external genitalia, absent uterus and fallopian tubes, and bilateral inguinal masses. Serum testosterone is in the male range, and serum LH is markedly elevated. Which hormonal and receptor abnormality is responsible?
61. In a patient with type 2 diabetes mellitus, the incretin effect is markedly reduced. Which of the following correctly explains the incretin effect and its impairment in T2DM?
62. A patient with hyperthyroidism has elevated T3 and T4. Which mechanism explains the increased oxygen consumption and heat production in hyperthyroidism?
63. A 55-year-old man with a known adrenal incidentaloma undergoes a 1 mg overnight dexamethasone suppression test. His 8 AM cortisol is 4.5 µg/dL (normal <1.8 µg/dL). He has no Cushingoid features. What does this finding most likely represent?
64. In type 1 diabetes, loss of first-phase insulin secretion is an early marker. Which cellular mechanism governs first-phase insulin exocytosis?
65. A patient with Addison's disease (primary adrenal insufficiency) is found to have hyperpigmentation, hyponatraemia, hyperkalaemia, and hypoglycaemia. What is the direct physiological mechanism linking loss of cortisol to hypoglycaemia?
66. Thyroid hormone receptor (TR) is a nuclear receptor that binds T3 (not T4) and acts as a transcription factor. The T3–TR complex upregulates certain genes and downregulates others. Which of the following correctly describes the mechanism of negative feedback of T3 on TSH secretion?
67. In the zona fasciculata of the adrenal cortex, cortisol synthesis requires several cytochrome P450 enzymes. The rate-limiting step in adrenal steroidogenesis is:
68. Thyroid hormone (T3) exerts most of its cellular effects through which primary mechanism?
69. A patient with Type 2 diabetes mellitus has elevated fasting glucose despite detectable C-peptide. C-peptide measurement (rather than insulin) is used to assess endogenous insulin secretion because:
70. In primary adrenal insufficiency (Addison's disease), which electrolyte abnormality combination is expected due to combined glucocorticoid and mineralocorticoid deficiency?
71. A 28-year-old woman has a 6 cm pituitary tumour causing bitemporal hemianopia. Biochemistry shows GH 45 ng/mL (elevated), IGF-1 3× upper limit. She has coarsened facial features, enlarged hands, and a 'fish mouth' appearance. The cardiovascular complication most closely correlated with mortality in acromegaly is:
72. Thyroid hormones (T3 and T4) act on nuclear receptors to increase transcription. Which of the following best explains the calorigenic effect (thermogenesis) of thyroid hormones?
73. A 38-year-old man has hypertension, hypokalemia (K+ 2.8 mEq/L), and metabolic alkalosis. Plasma renin activity (PRA) is suppressed and plasma aldosterone is elevated. 24-hour urine aldosterone is 40 μg (elevated). Which physiological concept explains the hypokalemia in this case?
74. Thyroid hormone (T3) exerts its major genomic effects through which mechanism?
75. A 28-year-old woman is found to have elevated 24-hour urine free cortisol and fails to suppress on overnight low-dose dexamethasone (1 mg). High-dose dexamethasone (8 mg) suppresses cortisol by 60%. What is the most likely diagnosis?
76. Glucagon secretion from pancreatic alpha cells is stimulated by which of the following?
77. A 30-year-old woman has serum TSH < 0.01 mU/L, free T4 elevates, free T3 elevated, and a diffuse goitre. Thyroid-stimulating immunoglobulins (TSI) are positive. In Graves' disease, TSI mimics TSH by binding which receptor domain, and what is the intracellular consequence?
78. A patient has Addison's disease (primary adrenal insufficiency). Compared to secondary adrenal insufficiency (pituitary ACTH deficiency), which clinical feature is found in Addison's disease but NOT in secondary AI?
79. Glucagon secretion is increased during fasting. Which cell type in the islets of Langerhans secretes glucagon, and what is its primary receptor signalling cascade in hepatocytes?
80. A patient with Addison's disease on hydrocortisone replacement develops an acute febrile illness. Which physiological principle mandates an immediate doubling or tripling of his hydrocortisone dose?
81. The Wolf-Chaikoff effect and subsequent escape from it are important in thyroid physiology. The initial Wolf-Chaikoff effect (transient inhibition of thyroid hormone synthesis with acute iodine excess) is mediated by:
82. C-peptide is equimolar to insulin in secretion from beta cells. In a patient with insulin-induced hypoglycaemia (factitious hypoglycaemia), what is the expected C-peptide level?