Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 21: In hypogonadotropic hypogonadism, what is the typical hormonal profile?

A. Both LH and FSH are decreased (Correct Answer)
B. Both LH and FSH are increased
C. LH is increased and FSH is decreased
D. LH is decreased and FSH is increased

Explanation: ### Explanation **Underlying Concept:** The Hypothalamic-Pituitary-Gonadal (HPG) axis operates through a feedback loop. In **Hypogonadotropic Hypogonadism**, the primary defect lies in the **Hypothalamus** (decreased GnRH) or the **Anterior Pituitary** (decreased LH/FSH). Because the "tropic" hormones (LH and FSH) that stimulate the gonads are low, the gonads fail to produce sex steroids (testosterone or estrogen). This is a **secondary** or **central** failure. **Why Option A is Correct:** In this condition, the pituitary fails to secrete adequate Gonadotropins. Therefore, both **Luteinizing Hormone (LH)** and **Follicle-Stimulating Hormone (FSH)** are **decreased** (or inappropriately normal) in the presence of low sex steroids. **Why Other Options are Incorrect:** * **Option B:** Increased LH and FSH with low sex steroids characterize **Hypergonadotropic Hypogonadism** (Primary failure, e.g., Klinefelter syndrome or Turner syndrome). Here, the lack of negative feedback from the gonads causes the pituitary to overproduce gonadotropins. * **Options C & D:** LH and FSH usually move in the same direction in central or primary failure. Isolated elevations or depressions are rare and typically point to specific conditions like PCOS (high LH:FSH ratio) or specific pituitary adenomas, rather than classic hypogonadotropic hypogonadism. **High-Yield Clinical Pearls for NEET-PG:** * **Kallmann Syndrome:** The most common congenital cause of hypogonadotropic hypogonadism, characterized by **anosmia** (failure of GnRH neurons to migrate from the olfactory bulb). * **Differential:** If LH/FSH are high, the problem is in the **Gonads** (Primary). If LH/FSH are low, the problem is in the **Pituitary/Hypothalamus** (Secondary). * **Prostate Cancer Treatment:** GnRH *agonists* (like Leuprolide) initially increase LH/FSH but eventually cause down-regulation of receptors, leading to a state of "chemical" hypogonadotropic hypogonadism.

Question 22: What hormones are secreted by a pheochromocytoma?

A. Epinephrine
B. Norepinephrine
C. Dopamine
D. All of the above (Correct Answer)

Explanation: **Explanation:** Pheochromocytoma is a catecholamine-secreting tumor derived from the **chromaffin cells** of the adrenal medulla (or extra-adrenal paraganglia). To understand why all options are correct, one must look at the biosynthetic pathway of catecholamines: **Tyrosine → L-Dopa → Dopamine → Norepinephrine → Epinephrine.** * **Norepinephrine (B):** This is the **most common** hormone secreted by pheochromocytomas. Most tumors lack the enzyme necessary to convert it fully to epinephrine, leading to sustained or episodic hypertension. * **Epinephrine (A):** While less common than norepinephrine, many tumors secrete epinephrine. This occurs if the tumor cells express **Phenylethanolamine N-methyltransferase (PNMT)**, the enzyme that converts norepinephrine to epinephrine (induced by cortisol in the adrenal medulla). * **Dopamine (C):** Some tumors, particularly malignant or extra-adrenal ones, may secrete dopamine. While often clinically silent regarding blood pressure, elevated dopamine levels are a significant biochemical marker. **Why "All of the above" is correct:** A pheochromocytoma is a tumor of the catecholamine pathway; therefore, it can secrete any combination of these three hormones, though the proportions vary between patients. **High-Yield Clinical Pearls for NEET-PG:** * **Rule of 10s:** 10% are bilateral, 10% are malignant, 10% are pediatric, and 10% are extra-adrenal (Paragangliomas). * **Classic Triad:** Episodic headache, sweating (diaphoresis), and tachycardia. * **Diagnosis:** Best initial screening test is **Urinary/Plasma Metanephrines** (metabolites are more stable than catecholamines). * **Management:** Always give **Alpha-blockers (e.g., Phenoxybenzamine)** before Beta-blockers to prevent a hypertensive crisis.

Question 23: Exposure to darkness leads to increased melatonin secretion. What mechanism brings this about?

A. Decreasing the activity of suprachiasmatic nuclei
B. Increasing the serotonin N-acetyl transferase activity (Correct Answer)
C. Decreasing the hydroxy-indole-o-methyltransferase activity
D. Blocking the release of norepinephrine from sympathetic nerve terminals

Explanation: **Explanation:** The pineal gland acts as a "neuroendocrine transducer," converting light signals from the retina into the hormonal signal of melatonin. **1. Why the correct answer is right:** Melatonin is synthesized from **Tryptophan** via the following pathway: *Tryptophan → 5-Hydroxytryptophan → Serotonin → N-Acetylserotonin → Melatonin.* The rate-limiting enzyme in this pathway is **Serotonin N-acetyltransferase (SNAT)**. In darkness, postganglionic sympathetic fibers release **Norepinephrine**, which acts on **β-adrenergic receptors** in the pineal gland. This increases intracellular cAMP, which significantly activates SNAT. Consequently, serotonin is rapidly converted to N-acetylserotonin, leading to a surge in melatonin production. **2. Why the incorrect options are wrong:** * **Option A:** The Suprachiasmatic Nucleus (SCN) is the "master clock." While light inhibits the SCN's stimulation of the pineal gland, the specific biochemical mechanism for increased melatonin is the *activation* of the enzymatic pathway, not merely a decrease in SCN activity. * **Option C:** Hydroxy-indole-O-methyltransferase (HIOMT) is the final enzyme in the pathway. While it is necessary, it is not the primary regulatory/rate-limiting step triggered by darkness. * **Option D:** Darkness **increases** (rather than blocks) the release of norepinephrine from the superior cervical ganglion to stimulate melatonin synthesis. **High-Yield Facts for NEET-PG:** * **Precursor:** L-Tryptophan. * **Rate-limiting enzyme:** Serotonin N-acetyltransferase (SNAT). * **Light pathway:** Retina → Retinohypothalamic tract → SCN → Intermediolateral column (T1-T2) → Superior Cervical Ganglion → Pineal Gland. * **Clinical Pearl:** Melatonin levels peak between **2 AM and 4 AM**. It is used clinically for jet lag and delayed sleep phase syndrome.

Question 24: Which of the following hormones exerts the least effect on the calcium metabolism of bone tissue?

A. Androgen
B. Estrogen
C. Norepinephrine (Correct Answer)
D. Thyroid hormone

Explanation: ### Explanation The correct answer is **Norepinephrine (Option C)**. **Why Norepinephrine is the correct answer:** Calcium metabolism in bone is primarily regulated by hormones that influence the activity of osteoblasts (bone formation) and osteoclasts (bone resorption). While the sympathetic nervous system does have some receptors in bone, **Norepinephrine** is primarily a neurotransmitter and catecholamine focused on cardiovascular and metabolic "fight or flight" responses. Compared to sex steroids and thyroid hormones, its direct physiological impact on systemic calcium homeostasis and bone mineral density is negligible. **Why the other options are incorrect:** * **Androgens (Option A):** Androgens are crucial for bone health in both males and females. They promote osteoblast activity, increase bone matrix production, and help in the closure of epiphyseal plates. Testosterone deficiency is a major risk factor for male osteoporosis. * **Estrogen (Option B):** Estrogen is a potent regulator of bone metabolism. It inhibits osteoclast activity (by increasing OPG and decreasing RANKL) and promotes osteoclast apoptosis. The loss of estrogen during menopause is the primary cause of rapid bone loss and postmenopausal osteoporosis. * **Thyroid Hormone (Option D):** Thyroxine (T4) and Triiodothyronine (T3) are essential for normal bone growth and remodeling. However, in excess (hyperthyroidism), they significantly increase bone turnover, favoring resorption over formation, which can lead to hypercalcemia and secondary osteoporosis. **High-Yield NEET-PG Pearls:** * **Primary Regulators:** Parathyroid Hormone (PTH), Vitamin D (Calcitriol), and Calcitonin are the "big three" of calcium metabolism. * **RANKL/OPG Pathway:** Estrogen maintains bone density by increasing **Osteoprotegerin (OPG)**, which acts as a decoy receptor for RANKL, thereby preventing osteoclast activation. * **Glucocorticoids:** These are also potent regulators (unlike Norepinephrine); they decrease bone formation by inhibiting osteoblasts and decreasing intestinal calcium absorption.

Question 25: Lactiferous duct contraction is primarily due to the action of which hormone?

A. Progesterone
B. Estrogen
C. Oxytocin (Correct Answer)
D. Prolactin

Explanation: **Explanation:** The correct answer is **Oxytocin**. This question tests the understanding of the "Milk Ejection Reflex" (Let-down reflex). **Why Oxytocin is correct:** Oxytocin is synthesized in the hypothalamus (paraventricular nuclei) and released by the posterior pituitary. In response to suckling, oxytocin causes the contraction of **myoepithelial cells** that surround the alveoli and lactiferous ducts of the mammary gland. This mechanical contraction squeezes synthesized milk from the alveoli into the ducts and out through the nipple. **Why the other options are incorrect:** * **Prolactin:** While essential for lactation, its primary role is **milk production (synthesis)** within the alveolar epithelium, not the mechanical ejection of milk. * **Estrogen:** Responsible for the **ductal growth** and development of the breasts during puberty and pregnancy. It inhibits the actual secretion of milk during pregnancy by antagonizing prolactin. * **Progesterone:** Responsible for the **tubulo-alveolar development** (lobular growth). Like estrogen, high levels during pregnancy inhibit milk secretion. **High-Yield Clinical Pearls for NEET-PG:** * **The "Love Hormone":** Oxytocin also causes uterine contractions during labor (Ferguson reflex) and aids in uterine involution postpartum. * **Conditioned Reflex:** Unlike prolactin, oxytocin release can be stimulated by psychological factors, such as the sound of a baby crying. * **Inhibition:** Oxytocin release can be inhibited by fear, anxiety, or pain (via catecholamines). * **Mnemonic:** **P**rolactin **P**roduces milk; **O**xytocin **O**ozes (ejects) milk.

Question 26: An excess of which of the following hormones may be associated with increased sensitivity to epinephrine?

A. Testosterone
B. Parathyroid hormone
C. Insulin
D. Thyroid hormone (Correct Answer)

Explanation: **Explanation:** The correct answer is **Thyroid hormone**. This phenomenon is primarily due to the **permissive effect** of thyroid hormones on catecholamines (epinephrine and norepinephrine). **Why Thyroid Hormone is Correct:** Thyroid hormones ($T_3$ and $T_4$) increase the expression and sensitivity of **$\beta$-adrenergic receptors** in various tissues, particularly the heart. By increasing the number of these receptors (upregulation), thyroid hormone enhances the body's responsiveness to circulating epinephrine. This explains why patients with hyperthyroidism (thyrotoxicosis) exhibit symptoms resembling sympathetic overactivity, such as tachycardia, palpitations, tremors, and anxiety, even if their catecholamine levels are technically within the normal range. **Why Other Options are Incorrect:** * **Testosterone:** While it has anabolic effects and influences secondary sexual characteristics, it does not significantly modulate adrenergic receptor sensitivity. * **Parathyroid Hormone (PTH):** PTH primarily regulates calcium and phosphate homeostasis via the bones and kidneys; it has no direct role in epinephrine sensitivity. * **Insulin:** Insulin is an anabolic hormone focused on glucose uptake and storage. While hypoglycemia (caused by insulin excess) triggers a sympathetic "counter-regulatory" surge, the hormone itself does not increase the sensitivity of receptors to epinephrine. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Application:** Propanolol (a $\beta$-blocker) is the drug of choice for immediate symptomatic relief in thyrotoxicosis because it blocks the heightened adrenergic response. * **Mechanism:** Thyroid hormone increases the synthesis of $\beta_1$ receptors in the myocardium and $\beta_2$ receptors in skeletal muscle and adipose tissue. * **Thyroid Storm:** This is a life-threatening exaggeration of hyperthyroidism where the extreme sensitivity to catecholamines can lead to fatal arrhythmias and hyperpyrexia.

Question 27: Which of the following conditions or actions increases basal metabolic rate (BMR)?

A. Starvation
B. Obesity
C. Ingestion of food (Correct Answer)
D. Sleep

Explanation: ### Explanation **Correct Answer: C. Ingestion of food** The increase in Basal Metabolic Rate (BMR) following food intake is known as **Specific Dynamic Action (SDA)** or the **Thermic Effect of Food (TEF)**. This phenomenon occurs because the body requires energy for the digestion, absorption, transport, and storage of nutrients. Among macronutrients, **proteins** have the highest SDA (increasing BMR by ~30%), followed by carbohydrates (~6%) and fats (~4%). **Analysis of Incorrect Options:** * **A. Starvation:** During prolonged fasting or starvation, the body undergoes an adaptive decrease in BMR (often by 10–20%). This is a survival mechanism mediated by decreased levels of T3 (triiodothyronine) and sympathetic nervous system activity to conserve energy stores. * **B. Obesity:** While BMR is technically higher in absolute terms in larger individuals due to increased total body mass, the metabolic rate *per unit of surface area* or relative to lean body mass is typically lower or unchanged. In the context of standard physiological factors that "increase" a baseline state, obesity is not a stimulatory factor. * **D. Sleep:** BMR decreases by approximately 10–15% during sleep. This reduction is due to complete muscle relaxation and decreased sympathetic tone. **High-Yield Clinical Pearls for NEET-PG:** 1. **Thyroid Status:** Thyroid hormones are the single most important regulators of BMR. Hyperthyroidism increases BMR, while hypothyroidism decreases it. 2. **Surface Area Rule:** BMR is directly proportional to the body surface area (Rubner’s Law). This is why smaller animals (with larger surface-area-to-volume ratios) have higher mass-specific metabolic rates. 3. **Climate:** BMR is higher in individuals living in cold climates (adaptation to thermogenesis) compared to those in tropical climates. 4. **Gender & Age:** BMR is generally higher in males (due to higher testosterone and muscle mass) and decreases progressively with age as lean muscle is replaced by adipose tissue.

Question 28: Which of the following is the most useful investigation for thyroid function?

A. T3
B. T4
C. TSH (Correct Answer)
D. TRH

Explanation: **Explanation:** **Serum TSH (Thyroid Stimulating Hormone)** is considered the single most useful and sensitive initial screening test for evaluating thyroid function in the general population. **Why TSH is the Correct Answer:** The relationship between Serum TSH and Free T4 is **log-linear**; even a minor change in the concentration of free thyroid hormones results in a much larger, compensatory change in TSH levels from the anterior pituitary. Therefore, TSH is the first parameter to become abnormal in both subclinical hypothyroidism (high TSH) and subclinical hyperthyroidism (low TSH), often before the patient becomes symptomatic or T3/T4 levels fall outside the reference range. **Why Other Options are Incorrect:** * **T3 (Triiodothyronine):** While T3 is the biologically active form, it is the least sensitive for screening. In early hypothyroidism, T3 levels are often maintained within the normal range due to increased TSH stimulation. It is primarily useful for diagnosing T3-toxicosis. * **T4 (Thyroxine):** Total T4 levels are heavily influenced by changes in **Thyroxine-Binding Globulin (TBG)** levels (e.g., pregnancy, OCP use). While Free T4 is more accurate, it is still less sensitive than TSH for early detection of thyroid dysfunction. * **TRH (Thyrotropin-Releasing Hormone):** TRH stimulation tests are rarely used in modern clinical practice. They were historically used to distinguish between secondary and tertiary hypothyroidism but have been largely replaced by high-sensitivity TSH assays and MRI. **High-Yield Clinical Pearls for NEET-PG:** * **Best Screening Test:** TSH. * **Best test to monitor Thyroid Replacement (Levothyroxine):** TSH (wait 6–8 weeks after dose adjustment). * **Exception:** In **Secondary (Central) Hypothyroidism**, TSH is unreliable; **Free T4** is the investigation of choice to monitor treatment. * **Best test for early Hyperthyroidism:** TSH (suppressed).

Question 29: What is the half-life of insulin?

A. 5 minutes (Correct Answer)
B. 1 hour
C. 12 hours
D. 24 hours

Explanation: **Explanation:** The correct answer is **A. 5 minutes**. **Why it is correct:** Insulin is a peptide hormone secreted by the beta cells of the Islets of Langerhans. Once it enters the systemic circulation, it has a very short biological half-life, typically ranging from **3 to 8 minutes** (average 5 minutes). This rapid turnover is physiologically essential because it allows the body to make minute-to-minute adjustments in blood glucose levels. Insulin is primarily degraded by the enzyme **insulinase** in the liver, kidneys, and muscles. **Why other options are incorrect:** * **B. 1 hour:** While some "Short-acting" exogenous insulin formulations (like Regular Insulin) have a peak effect around 2–3 hours, the endogenous hormone itself is cleared much faster. * **C & D. 12 to 24 hours:** These durations are characteristic of "Long-acting" or "Basal" insulin analogues (like Glargine or Degludec), which are pharmacologically modified to delay absorption. No endogenous hormone persists this long in the plasma. **High-Yield NEET-PG Pearls:** * **C-Peptide:** While insulin has a half-life of ~5 minutes, C-peptide has a longer half-life (approx. **30 minutes**). Therefore, C-peptide levels are a more reliable clinical marker of endogenous insulin production (beta-cell function). * **Degradation:** Approximately 50% of insulin is cleared during its "first pass" through the liver. * **Volume of Distribution:** Insulin is distributed in a volume roughly equal to the extracellular fluid volume. * **Mechanism:** Insulin acts via a **Tyrosine Kinase receptor** (enzyme-linked receptor), leading to the translocation of **GLUT-4** transporters to the cell membrane in muscle and adipose tissue.

Question 30: What is the Wolff-Chaikoff effect?

A. Reduced thyroxine synthesis by radiotherapy
B. Reduced thyroxine synthesis by propylthiouracil
C. Reduced thyroxine synthesis by iodides (Correct Answer)
D. None of the above

Explanation: The **Wolff-Chaikoff effect** is an autoregulatory phenomenon where high levels of circulating iodides cause a transient reduction in thyroid hormone synthesis. ### **Explanation of the Correct Answer** * **Mechanism:** When there is an acute excess of inorganic iodide, the thyroid gland protects itself from overproducing hormones by inhibiting the enzyme **thyroid peroxidase (TPO)**. This leads to a decrease in the organification of iodide and a subsequent reduction in the synthesis of $T_3$ and $T_4$. * **Duration:** This effect is temporary, typically lasting about 10–14 days. After this period, the gland "escapes" the effect by downregulating the sodium-iodide symporter (NIS), reducing internal iodide concentration and allowing hormone synthesis to resume. ### **Why Other Options are Incorrect** * **Option A:** Radiotherapy (specifically $I^{131}$) destroys thyroid tissue via beta-particle emission, leading to permanent hypothyroidism, rather than a biochemical autoregulatory inhibition. * **Option B:** Propylthiouracil (PTU) is a pharmacological inhibitor of TPO and peripheral conversion of $T_4$ to $T_3$. While it reduces synthesis, this is a drug-induced action, not the physiological Wolff-Chaikoff effect. ### **High-Yield NEET-PG Pearls** * **Clinical Application:** The Wolff-Chaikoff effect is the rationale behind giving **Lugol’s iodine** or Potassium Iodide (SSKI) before thyroid surgery to decrease the vascularity and size of the gland. * **Jod-Basedow Phenomenon:** The opposite of Wolff-Chaikoff. It occurs when iodine administration leads to *hyperthyroidism* (common in patients with underlying multinodular goiter). * **Amiodarone:** This drug contains high iodine content and can trigger both the Wolff-Chaikoff effect (hypothyroidism) and the Jod-Basedow effect (hyperthyroidism).

Practice by Chapter

Principles of Endocrine Regulation

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Hypothalamus and Pituitary Gland

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Thyroid Physiology

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Adrenal Cortex and Medulla

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Pancreatic Hormones and Glucose Metabolism

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Calcium and Phosphate Homeostasis

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Growth Hormone and Growth Factors

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Endocrine Regulation of Metabolism

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Hormone Receptors and Signaling

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Assessment of Endocrine Function

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