Endocrinology Practice Questions

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

Both LH and FSH are decreased. ### 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.

Q: What hormones are secreted by a pheochromocytoma?

All of the above. **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.

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

Increasing the serotonin N-acetyl transferase activity. **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.

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

Oxytocin. **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.

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

TSH. **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).

Q: What is the half-life of insulin?

5 minutes. **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.

Q: What is the Wolff-Chaikoff effect?

Reduced thyroxine synthesis by iodides. 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).

Question 1

In hypogonadotropic hypogonadism, what is the typical hormonal profile?

Accepted Answer

Both LH and FSH are decreased

Answer

Both LH and FSH are increased

Answer

LH is increased and FSH is decreased

Answer

LH is decreased and FSH is increased

Question 2

What hormones are secreted by a pheochromocytoma?

Accepted Answer

All of the above

Answer

Epinephrine

Answer

Norepinephrine

Answer

Dopamine

Question 3

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

Accepted Answer

Increasing the serotonin N-acetyl transferase activity

Answer

Decreasing the activity of suprachiasmatic nuclei

Answer

Decreasing the hydroxy-indole-o-methyltransferase activity

Answer

Blocking the release of norepinephrine from sympathetic nerve terminals

Question 4

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

Accepted Answer

Norepinephrine

Answer

Androgen

Answer

Estrogen

Answer

Thyroid hormone

Question 5

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

Accepted Answer

Oxytocin

Answer

Progesterone

Answer

Estrogen

Answer

Prolactin

Question 6

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

Accepted Answer

Thyroid hormone

Answer

Testosterone

Answer

Parathyroid hormone

Answer

Insulin

Question 7

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

Accepted Answer

Ingestion of food

Answer

Starvation

Answer

Obesity

Answer

Sleep

Question 8

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

Accepted Answer

TSH

Answer

T3

Answer

T4

Answer

TRH

Question 9

What is the half-life of insulin?

Accepted Answer

5 minutes

Answer

1 hour

Answer

12 hours

Answer

24 hours

Question 10

What is the Wolff-Chaikoff effect?

Accepted Answer

Reduced thyroxine synthesis by iodides

Answer

Reduced thyroxine synthesis by radiotherapy

Answer

Reduced thyroxine synthesis by propylthiouracil

Answer

None of the above

Endocrinology — MCQs

Endocrinology — MCQs

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