A 32-year-old woman has weight gain, purple striae and hypertension. After 1 mg dexamethasone at night, her 8 am cortisol is 14 µg/dL (normal suppression below 1.8 µg/dL). Plasma ACTH is 85 pg/mL (reference 10-50 pg/mL). After an 8 mg overnight dexamethasone test, her cortisol falls by 70% from baseline. What is the most likely source of the disorder?

Cortisol-secreting adrenal adenoma

A 27-year-old woman at 14 weeks of pregnancy has a thyroid profile done at her antenatal visit. Total T4 is 15 µg/dL (reference 5-12), while free T4 and TSH are within the trimester-specific ranges. She has no symptoms. What best explains the raised total T4?

Oestrogen-induced rise in thyroxine-binding globulin

Reduced conversion of T4 to T3 in tissues

Early Graves disease of pregnancy

An 18-month-old boy, exclusively breastfed and kept indoors, has wide wrists and bowed legs. Results: calcium 8.0 mg/dL (reference 8.8-10.8), phosphate 2.6 mg/dL (reference 4.0-6.5), alkaline phosphatase markedly raised, PTH 180 pg/mL (reference 15-65) and 25-hydroxyvitamin D 6 ng/mL. What mainly explains his low serum phosphate?

Secondary hyperparathyroidism causing phosphaturia

Lack of phosphate in breast milk

Excess FGF23 secreted by osteocytes

Proximal tubulopathy of Fanconi type

Endocrine physiology and feedback axes

23 NEET-PG practice questions on Endocrine physiology and feedback axes, part of Physiology. The first 23 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Hard
A 32-year-old woman has weight gain, purple striae and hypertension. After 1 mg dexamethasone at night, her 8 am cortisol is 14 µg/dL (normal suppression below 1.8 µg/dL). Plasma ACTH is 85 pg/mL (reference 10-50 pg/mL). After an 8 mg overnight dexamethasone test, her cortisol falls by 70% from baseline. What is the most likely source of the disorder?
1. ALong-term topical steroid use
2. BEctopic ACTH from lung cancer
3. CPituitary corticotroph adenoma
4. DCortisol-secreting adrenal adenoma
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Answer: C · Pituitary corticotroph adenoma
Failure to suppress with 1 mg dexamethasone confirms endogenous hypercortisolism. A raised ACTH makes it ACTH-dependent, which rules out an adrenal tumour and exogenous steroids, both of which suppress ACTH. Pituitary corticotroph adenomas keep some sensitivity to glucocorticoid feedback, so a high dose suppresses cortisol by more than 50%, whereas ectopic ACTH sources usually do not suppress. Pituitary MRI follows, with inferior petrosal sinus sampling if the MRI is not conclusive.
- A: Exogenous steroids suppress both ACTH and the patient's own cortisol.
- B: Ectopic ACTH usually fails to suppress even with high-dose dexamethasone, and ACTH is often much higher.
- D: An adrenal adenoma suppresses pituitary ACTH, so ACTH would be low.
Question 2 · Medium
A 27-year-old woman at 14 weeks of pregnancy has a thyroid profile done at her antenatal visit. Total T4 is 15 µg/dL (reference 5-12), while free T4 and TSH are within the trimester-specific ranges. She has no symptoms. What best explains the raised total T4?
1. AOestrogen-induced rise in thyroxine-binding globulin
2. BhCG acting on the TSH receptor
3. CReduced conversion of T4 to T3 in tissues
4. DEarly Graves disease of pregnancy
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Answer: A · Oestrogen-induced rise in thyroxine-binding globulin
Oestrogen increases hepatic synthesis of thyroxine-binding globulin and slows its clearance, so total (bound) T4 and T3 rise in pregnancy. The free hormone, which is what acts on tissues and is sensed by the pituitary, stays normal, and so does TSH. She is euthyroid and needs no treatment. Women already on thyroxine usually need a higher dose in pregnancy.
- B: hCG stimulation in the first trimester lowers TSH and can raise free T4; both are normal here.
- C: Reduced deiodination would not raise total T4 with a normal free T4 and TSH.
- D: Graves disease would raise free T4 and suppress TSH.
Question 3 · Medium
An 18-month-old boy, exclusively breastfed and kept indoors, has wide wrists and bowed legs. Results: calcium 8.0 mg/dL (reference 8.8-10.8), phosphate 2.6 mg/dL (reference 4.0-6.5), alkaline phosphatase markedly raised, PTH 180 pg/mL (reference 15-65) and 25-hydroxyvitamin D 6 ng/mL. What mainly explains his low serum phosphate?
1. ALack of phosphate in breast milk
2. BExcess FGF23 secreted by osteocytes
3. CProximal tubulopathy of Fanconi type
4. DSecondary hyperparathyroidism causing phosphaturia
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Answer: D · Secondary hyperparathyroidism causing phosphaturia
This is nutritional vitamin D deficiency rickets. Low vitamin D reduces calcium absorption, the fall in calcium raises PTH, and PTH both mobilises calcium from bone and reduces phosphate reabsorption in the proximal tubule. Calcium is thus partly defended while phosphate falls, and the low calcium-phosphate product impairs mineralisation of growth plates. Vitamin D with calcium corrects it, and ALP falls as healing occurs.
- A: Breast milk provides enough phosphate for a growing infant.
- B: FGF23 excess (as in X-linked hypophosphataemic rickets) gives low phosphate with normal calcium and PTH.
- C: A Fanconi tubulopathy would also cause glycosuria, aminoaciduria and acidosis, with normal vitamin D.
Question 4 · Medium
A 9-year-old boy with Langerhans cell histiocytosis, diagnosed from lytic skull lesions, has started drinking water through the night and wetting the bed; he passes about 4 litres of pale urine a day and serum Na+ is 148 mmol/L. During supervised fluid restriction, plasma osmolality reaches 302 mOsm/kg while urine osmolality is 150 mOsm/kg; after desmopressin, urine osmolality climbs to 540 mOsm/kg. What is the diagnosis?
1. APrimary polydipsia
2. BCentral diabetes insipidus
3. CNephrogenic diabetes insipidus
4. DOsmotic diuresis
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Answer: B · Central diabetes insipidus
Urine stays dilute despite a high plasma osmolality, so ADH is either missing or ineffective. A large rise in urine osmolality (more than 50%) after desmopressin shows the kidney responds to ADH and the hormone itself is lacking: central diabetes insipidus, here from injury to the hypothalamus or pituitary stalk. Desmopressin, a V2-selective analogue, is the treatment, with careful monitoring of sodium.
- A: In primary polydipsia, water deprivation concentrates the urine and sodium is not high.
- C: In nephrogenic DI, urine osmolality hardly rises after desmopressin.
- D: Osmotic diuresis gives urine osmolality near or above plasma, not 140 mOsm/kg.
Question 5 · Easy
A 35-year-old woman with a thyroid nodule undergoes scintigraphy with technetium-99m pertechnetate. Which transporter carries the tracer into the thyroid follicular cells?
1. ASodium-iodide symporter
2. BDual oxidase 2 (DUOX2)
3. CPendrin anion exchanger
4. DThyroid peroxidase
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Answer: A · Sodium-iodide symporter
Pertechnetate has a similar size and charge to iodide, so it is taken up by the sodium-iodide symporter (NIS) on the basolateral membrane of follicular cells, driven by the sodium gradient of Na+/K+-ATPase. Unlike iodide it is not organified, so it shows trapping only. Perchlorate and thiocyanate competitively block NIS, and TSH increases its expression.
- B: DUOX2 generates the hydrogen peroxide that peroxidase needs; it does not transport iodide.
- C: Pendrin moves iodide from the cell into the colloid across the apical membrane.
- D: Thyroid peroxidase oxidises and organifies iodide; it is not a transporter.
Question 6 · Medium
A 12-year-old girl with short stature, a round face and short fourth and fifth metacarpals is brought with a seizure. Calcium is 6.9 mg/dL, phosphate 7.2 mg/dL and PTH 260 pg/mL (reference 15-65); magnesium and renal function are normal. What is the mechanism of her hypocalcaemia?
1. AAbsent parathyroid glands from birth
2. BMagnesium deficiency suppressing PTH release
3. CDefective Gs-alpha signalling from the PTH receptor
4. DDeficiency of hepatic 25-hydroxylase
Answer and explanation in LearnFree account
Question 7 · Medium
A 50-year-old man has chewed mulethi (liquorice root) daily for a year for a chronic cough. His BP is 168/100 mmHg and K+ is 2.8 mmol/L; plasma renin and serum aldosterone are both low. What is the mechanism of his hypertension?
1. AInhibition of adrenal 11-beta-hydroxylase
2. BInhibition of renal 11-beta-HSD2 by glycyrrhetinic acid
3. CActivating mutation of the ENaC sodium channel
4. DAldosterone secretion by an adrenal adenoma
Answer and explanation in LearnFree account
Question 8 · Hard
A 34-year-old woman has central obesity, purple striae, proximal myopathy and hypertension. Her 24-hour urinary free cortisol and late-night salivary cortisol are both raised. Plasma ACTH is 78 pg/mL (reference 10-50). A high-dose (8 mg) dexamethasone test suppresses her cortisol by 70%, and ACTH rises after CRH. What is the most likely source of her cortisol excess?
1. AEctopic ACTH from a lung tumour
2. BCortisol-secreting adrenal adenoma
3. CExogenous glucocorticoid use
4. DPituitary corticotroph adenoma
Answer and explanation in LearnFree account
Question 9 · Hard
A 27-year-old pharmacy graduate who lives with her insulin-treated diabetic father is admitted after being found unresponsive at home for the second time this month. Before dextrose was given, plasma glucose was 36 mg/dL, serum insulin 85 µU/mL (raised) and C-peptide 0.1 ng/mL (reference 0.8-3.1). A sulfonylurea screen and insulin antibodies are negative. What is the most likely cause?
1. ASurreptitious injection of insulin
2. BAutoimmune insulin syndrome
3. CCovert sulfonylurea ingestion
4. DInsulinoma of the pancreas
Answer and explanation in LearnFree account
Question 10 · Medium
A 19-year-old engineering student's pre-employment blood tests show serum calcium 11.2 mg/dL (reference 8.5-10.5) and PTH 70 pg/mL (reference 15-65). He feels well, has never had stones, and his calcium/creatinine clearance ratio from a 24-hour urine is 0.004, which is very low. His father had a neck exploration years ago that did not lower his calcium. What is the most likely mechanism?
1. AVitamin D intoxication from supplements
2. BTumour secretion of PTH-related peptide
3. CInactivating mutation of the calcium-sensing receptor
4. DParathyroid adenoma secreting excess PTH
Answer and explanation in LearnFree account
Question 11 · Easy
A 40-year-old woman has permanent hypoparathyroidism after total thyroidectomy. She is prescribed calcitriol rather than cholecalciferol alone. What is the physiological reason?
1. AHepatic 25-hydroxylation needs PTH
2. BThyroxine is needed to absorb vitamin D
3. CCholecalciferol is poorly absorbed after surgery
4. DRenal 1-alpha-hydroxylation needs PTH
Answer and explanation in LearnFree account
Question 12 · Medium
A 48-year-old obese man newly diagnosed with type 2 diabetes in an NCD clinic is started on a GLP-1 agonist. While counselling him, the intern reviews insulin physiology. Consider four statements: 1. Oral glucose releases more insulin than the same rise in plasma glucose given intravenously. 2. Insulin moves GLUT4 transporters to the surface of skeletal muscle and fat cells. 3. Glucose entry into hepatocytes through GLUT2 requires insulin. 4. Insulin shifts potassium into cells. Which statements are correct?
1. A1, 2 and 3 only
2. B1, 2 and 4 only
3. C1 and 2 only
4. D1 and 3 only
Answer and explanation in LearnFree account
Question 13 · Medium
A 38-year-old man treated for pulmonary tuberculosis 2 years ago has fatigue, weight loss and dark pigmentation of his palmar creases and buccal mucosa. BP is 86/60 mmHg, Na+ 126 mmol/L, K+ 5.8 mmol/L and random glucose 64 mg/dL. Which test best confirms the likely diagnosis?
1. AOvernight dexamethasone suppression test
2. BWater deprivation test
3. CShort Synacthen (ACTH stimulation) test
4. DOral glucose tolerance test
Answer and explanation in LearnFree account
Question 14 · Medium
A 72-year-old man with type 2 diabetes and chronic kidney disease on glibenclamide is found drowsy and sweating at home; capillary glucose is 42 mg/dL. Which action of the drug on beta cells explains this hypoglycaemia?
1. AActivation of GLP-1 receptors
2. BClosure of ATP-sensitive K+ channels
3. CDirect opening of L-type Ca2+ channels
4. DInhibition of plasma DPP-4
Answer and explanation in LearnFree account
Question 15 · Easy
A 30-year-old woman with known Graves disease is brought to casualty with fever of 40 °C, atrial fibrillation at 150/min and agitation. Propylthiouracil is chosen over carbimazole. What added action makes propylthiouracil preferred here?
1. AIt also blocks TSH receptor antibodies
2. BIt also blocks peripheral T4 to T3 conversion
3. CIt also stops release of stored hormone
4. DIt also inhibits the iodide trapping pump
Answer and explanation in LearnFree account
Question 16 · Medium
A 45-year-old man has noticed his shoe and ring sizes increasing, with coarse facial features, heavy sweating and a raised serum IGF-1. Which dynamic test confirms autonomous growth hormone secretion?
1. AGH measured after a 75 g oral glucose load
2. BA single random serum GH measurement
3. CSerum prolactin measured after TRH
4. DGH measured after insulin-induced hypoglycaemia
Answer and explanation in LearnFree account
Question 17 · Easy
The adrenal medulla converts noradrenaline to adrenaline efficiently because the enzyme PNMT is induced by high local levels of:
1. AAndrostenedione
2. BCortisol
3. CDopamine
4. DAldosterone
Answer and explanation in LearnFree account
Question 18 · Hard
A 58-year-old man with end-stage kidney disease on haemodialysis has calcium 8.0 mg/dL, phosphate 7.0 mg/dL, PTH 650 pg/mL and a raised alkaline phosphatase. Consider four statements about his mineral disorder: 1. The high phosphate suppresses PTH secretion. 2. FGF23 rises early in CKD and lowers renal phosphate reabsorption. 3. Reduced renal 1-alpha-hydroxylation lowers calcitriol. 4. Calcitriol therapy may raise his serum phosphate further. Which statements are correct?
1. A1, 3 and 4 only
2. B2 and 3 only
3. C2, 3 and 4 only
4. D1, 2, 3 and 4
Answer and explanation in LearnFree account
Question 19 · Medium
A 45-year-old woman with rheumatoid arthritis took prednisolone 20 mg daily for 8 months and stopped it abruptly 10 days ago. She now has fatigue, dizziness and anorexia; BP is 92/60 mmHg, Na+ 131 mmol/L and K+ 4.2 mmol/L, and there is no pigmentation. Why is her potassium normal, unlike in Addison disease?
1. ALow CRH acts directly on the kidney to hold K+
2. BZona glomerulosa remains under renin-angiotensin control
3. CResidual prednisolone still acts on her kidneys
4. DCortisol, not aldosterone, controls potassium
Answer and explanation in LearnFree account
Question 20 · Medium
A 29-year-old woman had a massive postpartum haemorrhage needing 6 units of blood 3 months ago. She could not breastfeed and her periods have not returned; she feels tired and cold. Free T4 is 0.5 ng/dL (reference 0.8-1.8) and TSH is 1.2 mIU/L (reference 0.4-4.0). What is the best interpretation of her thyroid tests?
1. AHypothyroid phase of postpartum thyroiditis
2. BCentral hypothyroidism from pituitary failure
3. CEarly primary hypothyroidism
4. DSubclinical hypothyroidism
Answer and explanation in LearnFree account
Question 21 · Medium
A 36-year-old woman has tingling around her lips and spasm of her hand when a BP cuff is inflated, 24 hours after total thyroidectomy. Serum calcium is 6.8 mg/dL with normal albumin. Why does a low ionised calcium cause these features?
1. ANeuronal membranes become more permeable to sodium
2. BAcetylcholinesterase at the end plates is inhibited
3. CMuscle releases more calcium from its stores
4. DMore acetylcholine is released at end plates
Answer and explanation in LearnFree account
Question 22 · Hard
A 36-year-old schoolteacher has palpitations, heat intolerance and a diffuse goitre, with no eye signs; for 6 months she has also had headaches. Free T4 is 3.1 ng/dL (reference 0.8-1.8), free T3 is raised and TSH is 5.4 mIU/L (reference 0.4-4.0) on two samples. TSH receptor antibodies are negative, serum glycoprotein alpha-subunit is raised and she takes no biotin. What is the most likely diagnosis?
1. AGraves disease
2. BTSH-secreting pituitary adenoma
3. CPainless lymphocytic thyroiditis
4. DResistance to thyroid hormone
Answer and explanation in LearnFree account
Question 23 · Easy
A 26-year-old woman with schizophrenia has been on risperidone for 3 months. She now has milky nipple discharge and has missed her periods; serum prolactin is 110 ng/mL and pituitary MRI is normal. What is the mechanism?
1. ABlockade of D2 receptors on lactotrophs
2. BStimulation of hypothalamic TRH release
3. CBlockade of serotonin 5-HT2A receptors
4. DA direct oestrogen-like action on the breast
Answer and explanation in LearnFree account

Endocrine physiology and feedback axes

A 27-year-old woman at 14 weeks of pregnancy has a thyroid profile done at her antenatal visit. Total T4 is 15 µg/dL (reference 5-12), while free T4 and TSH are within the trimester-specific ranges. She has no symptoms. What best explains the raised total T4?

A 35-year-old woman with a thyroid nodule undergoes scintigraphy with technetium-99m pertechnetate. Which transporter carries the tracer into the thyroid follicular cells?

A 12-year-old girl with short stature, a round face and short fourth and fifth metacarpals is brought with a seizure. Calcium is 6.9 mg/dL, phosphate 7.2 mg/dL and PTH 260 pg/mL (reference 15-65); magnesium and renal function are normal. What is the mechanism of her hypocalcaemia?

A 50-year-old man has chewed mulethi (liquorice root) daily for a year for a chronic cough. His BP is 168/100 mmHg and K+ is 2.8 mmol/L; plasma renin and serum aldosterone are both low. What is the mechanism of his hypertension?

A 40-year-old woman has permanent hypoparathyroidism after total thyroidectomy. She is prescribed calcitriol rather than cholecalciferol alone. What is the physiological reason?

A 38-year-old man treated for pulmonary tuberculosis 2 years ago has fatigue, weight loss and dark pigmentation of his palmar creases and buccal mucosa. BP is 86/60 mmHg, Na+ 126 mmol/L, K+ 5.8 mmol/L and random glucose 64 mg/dL. Which test best confirms the likely diagnosis?

A 72-year-old man with type 2 diabetes and chronic kidney disease on glibenclamide is found drowsy and sweating at home; capillary glucose is 42 mg/dL. Which action of the drug on beta cells explains this hypoglycaemia?

A 30-year-old woman with known Graves disease is brought to casualty with fever of 40 °C, atrial fibrillation at 150/min and agitation. Propylthiouracil is chosen over carbimazole. What added action makes propylthiouracil preferred here?

A 45-year-old man has noticed his shoe and ring sizes increasing, with coarse facial features, heavy sweating and a raised serum IGF-1. Which dynamic test confirms autonomous growth hormone secretion?

The adrenal medulla converts noradrenaline to adrenaline efficiently because the enzyme PNMT is induced by high local levels of:

A 36-year-old woman has tingling around her lips and spasm of her hand when a BP cuff is inflated, 24 hours after total thyroidectomy. Serum calcium is 6.8 mg/dL with normal albumin. Why does a low ionised calcium cause these features?

A 26-year-old woman with schizophrenia has been on risperidone for 3 months. She now has milky nipple discharge and has missed her periods; serum prolactin is 110 ng/mL and pituitary MRI is normal. What is the mechanism?