Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 301: What is the primary function of Follistatin?

A. Decreases gonadotrope function
B. Increases gonadotrope function
C. Prevents interaction of activin with receptor (Correct Answer)
D. Stimulates FSH beta gene expression

Explanation: **Explanation:** **Follistatin** is a glycoprotein primarily produced by the folliculostellate cells of the anterior pituitary and granulosa cells of the ovary. Its primary physiological role is to act as an **activin-binding protein**. 1. **Why Option C is Correct:** Follistatin functions as an activin antagonist. It binds directly to activin with high affinity, effectively "sequestering" it. This prevents activin from binding to its specific serine/threonine kinase receptors on the cell surface. Since activin is a potent stimulator of FSH synthesis, follistatin’s neutralization of activin leads to a significant reduction in FSH secretion. 2. **Why Other Options are Incorrect:** * **Option A & B:** While follistatin ultimately leads to decreased FSH, its *primary* biochemical mechanism is not a direct modulation of the gonadotrope cell's overall function, but rather the specific inhibition of the activin signaling pathway. * **Option D:** Activin stimulates FSH beta gene expression. Because follistatin inhibits activin, it **suppresses** (rather than stimulates) FSH beta gene expression. **High-Yield NEET-PG Pearls:** * **The TGF-β Superfamily:** Activin, Inhibin, and Follistatin are all part of this family and regulate the HPO axis. * **Activin vs. Inhibin:** Activin *increases* FSH; Inhibin *decreases* FSH. * **Follistatin’s Dual Role:** Beyond the pituitary, follistatin plays a role in muscle growth by binding to and inhibiting **Myostatin** (a negative regulator of muscle mass). * **Clinical Correlation:** Elevated follistatin levels are often observed in Polycystic Ovary Syndrome (PCOS), contributing to the characteristic arrest of follicular development.

Question 302: A person sustains head trauma leading to a transaction of the pituitary stalk. All can be a consequence of this, except?

A. SIADH
B. Diabetes mellitus (Correct Answer)
C. Diabetes insipidus
D. Hyperprolactinemia

Explanation: **Explanation:** Pituitary stalk transection (disruption of the infundibulum) disconnects the hypothalamus from the pituitary gland, leading to significant endocrine disturbances. **Why Diabetes Mellitus is the correct answer:** Diabetes Mellitus is a disorder of insulin deficiency or resistance related to the pancreas. Pituitary stalk injury actually leads to a **deficiency of Growth Hormone (GH) and ACTH (Cortisol)**. Since GH and Cortisol are "diabetogenic" (counter-regulatory) hormones that increase blood glucose, their absence increases insulin sensitivity and can lead to **hypoglycemia**, not Diabetes Mellitus. **Analysis of other options:** * **Diabetes Insipidus (DI):** The posterior pituitary stores ADH produced in the hypothalamus. Stalk transection halts the transport of ADH, leading to Central DI (polyuria and polydipsia). * **Hyperprolactinemia:** Prolactin is the only pituitary hormone under tonic **inhibition** by hypothalamic Dopamine (Prolactin Inhibiting Factor). Disruption of the stalk prevents dopamine from reaching the anterior pituitary, causing "disinhibition" and a rise in prolactin levels. * **SIADH:** While DI is more common, head trauma or the "triphasic response" following stalk injury can cause a transient, inappropriate release of stored ADH from the degenerating posterior pituitary terminals, leading to SIADH. **High-Yield Clinical Pearls for NEET-PG:** * **The Triphasic Response in Stalk Injury:** 1. Initial DI (axonal shock), 2. Transient SIADH (leakage of stored ADH), 3. Permanent DI (death of neurons). * **The "Stalk Effect":** Any lesion compressing the stalk (e.g., Craniopharyngioma) causes hyperprolactinemia, but levels are usually <200 ng/mL (unlike Prolactinomas). * **Panhypopituitarism:** Stalk transection leads to a deficiency of all anterior pituitary hormones *except* Prolactin.

Question 303: All of the following are glycoproteins, EXCEPT:

A. TSH
B. FSH
C. LH
D. GH (Correct Answer)

Explanation: **Explanation:** The hormones of the anterior pituitary are chemically classified into three main groups: Glycoproteins, Pro-opiomelanocortin (POMC) derivatives, and Somatotropic hormones (Polypeptides). **1. Why GH is the correct answer:** **Growth Hormone (GH)** and **Prolactin (PRL)** belong to the Somatotropic hormone family. They are single-chain **polypeptides** (GH has 191 amino acids), not glycoproteins. They do not contain carbohydrate moieties and share structural similarities with human placental lactogen (hPL). **2. Why the other options are incorrect:** Options A, B, and C (**TSH, FSH, and LH**) along with the placental hormone **hCG**, form the **Glycoprotein family**. * These hormones are composed of two subunits: **Alpha (α) and Beta (β)**. * The **α-subunit is identical** in all four hormones. * The **β-subunit is unique** and confers biological and immunological specificity to each hormone. **High-Yield Clinical Pearls for NEET-PG:** * **Common α-subunit:** Because TSH, FSH, LH, and hCG share the same α-subunit, extremely high levels of hCG (as seen in Hydatidiform mole) can cross-react with TSH receptors, leading to hyperthyroidism. * **Acidophils vs. Basophils:** * **Acidophils** secrete GH and Prolactin (Mnemonic: **GPA** - **G**rowth hormone, **P**rolactin are **A**cidophils). * **Basophils** secrete the glycoproteins TSH, FSH, and LH (Mnemonic: **B-FLAT** - **B**asophils: **F**SH, **L**H, **A**CTH, **T**SH). * **Smallest Pituitary Hormone:** Vasopressin/ADH (9 amino acids). * **Largest Pituitary Hormone:** GH (191 amino acids).

Question 304: All of the following hormones accelerate the release of free fatty acids (FFA) from adipose tissue, EXCEPT:

A. Epinephrine
B. Insulin (Correct Answer)
C. Norepinephrine
D. Vasopressin

Explanation: **Explanation:** The mobilization of free fatty acids (FFA) from adipose tissue is primarily regulated by the enzyme **Hormone-Sensitive Lipase (HSL)**. This enzyme catalyzes the breakdown of stored triglycerides into glycerol and FFAs (lipolysis). **1. Why Insulin is the Correct Answer:** Insulin is the most potent **anti-lipolytic** hormone. It inhibits HSL through the activation of phosphodiesterase, which lowers intracellular cAMP levels. Furthermore, insulin promotes glucose uptake into adipocytes (via GLUT-4) and stimulates **alpha-glycerophosphate** production, which favors the re-esterification of FFAs back into triglycerides. Therefore, insulin decreases the release of FFA into the plasma. **2. Why the Other Options are Incorrect:** * **Epinephrine & Norepinephrine (Catecholamines):** These are potent stimulators of lipolysis. They bind to **$\beta_3$-adrenergic receptors** on adipocytes, increasing cAMP levels, which activates Protein Kinase A (PKA). PKA then phosphorylates and activates HSL, accelerating FFA release. * **Vasopressin (ADH):** While its primary role is water reabsorption, at higher concentrations, vasopressin exerts a "pressor" effect and has been shown to stimulate lipolysis in adipose tissue via V1a receptors. **Clinical Pearls for NEET-PG:** * **Lipolytic Hormones (The "Stress" Hormones):** Glucagon, Epinephrine, Norepinephrine, Cortisol, Growth Hormone, and ACTH all increase FFA release. * **Rate-Limiting Enzyme:** Hormone-Sensitive Lipase (HSL) is the rate-limiting step for lipolysis. * **Insulin's Dual Action:** It inhibits HSL (preventing breakdown) and stimulates **Lipoprotein Lipase (LPL)** in capillary walls (promoting storage). * **Ketogenesis Connection:** In states of absolute insulin deficiency (like DKA), unchecked HSL activity leads to a massive influx of FFAs to the liver, providing the substrate for ketone body synthesis.

Question 305: 1,25-dihydroxycholecalciferol is synthesized by:

A. Adrenal cortex
B. Liver
C. Proximal tubules of kidney (Correct Answer)
D. Collecting ducts of kidney

Explanation: **Explanation:** The synthesis of **1,25-dihydroxycholecalciferol** (Calcitriol), the most active form of Vitamin D, occurs through a multi-step hydroxylation process. The final and rate-limiting step takes place in the **proximal convoluted tubules (PCT)** of the kidney. Here, the enzyme **1-alpha-hydroxylase** converts 25-hydroxycholecalciferol (Calcidiol) into 1,25-dihydroxycholecalciferol. This enzyme is tightly regulated; it is stimulated by Parathyroid Hormone (PTH) and low serum phosphate, and inhibited by high calcium and FGF-23. **Analysis of Options:** * **Adrenal cortex (A):** This site is responsible for synthesizing steroid hormones like cortisol and aldosterone, not Vitamin D metabolites. * **Liver (B):** The liver performs the *first* hydroxylation step. It converts Vitamin D3 (Cholecalciferol) into **25-hydroxycholecalciferol** via the enzyme 25-hydroxylase. * **Collecting ducts (D):** While part of the nephron, the collecting ducts are primarily involved in water and electrolyte reabsorption (regulated by ADH and Aldosterone) and do not possess significant 1-alpha-hydroxylase activity. **High-Yield Clinical Pearls for NEET-PG:** * **Sequence of Synthesis:** Skin (UV light) → Liver (25-hydroxylation) → Kidney (1-alpha-hydroxylation). * **Chronic Kidney Disease (CKD):** Loss of PCT mass leads to Calcitriol deficiency, resulting in secondary hyperparathyroidism and renal osteodystrophy. * **Sarcoidosis:** Macrophages in granulomas can express 1-alpha-hydroxylase independently of PTH, leading to hypercalcemia. * **Storage Form:** 25-hydroxycholecalciferol is the major circulating form and the best indicator of Vitamin D status.

Question 306: What is the body's reaction to an atmospheric temperature of 20 degrees centigrade?

A. Cutaneous vasoconstriction
B. Shivering
C. Basal Metabolic Rate (BMR)
D. All of the above (Correct Answer)

Explanation: ### Explanation The human body maintains a core temperature of approximately 37°C. The **Thermoneutral Zone (TNZ)** for a naked adult is typically between **25°C and 30°C**. When the atmospheric temperature drops to **20°C**, it falls below the lower critical temperature, triggering the body’s thermoregulatory mechanisms to prevent heat loss and increase heat production. **1. Why "All of the above" is correct:** At 20°C, the body perceives a cold stress and activates the posterior hypothalamus to initiate the following: * **Cutaneous Vasoconstriction:** This is the immediate response. Sympathetic stimulation causes narrowing of skin blood vessels, shifting blood to the core to reduce heat loss via radiation and conduction. * **Shivering:** This is the most potent mechanism for **involuntary heat production**. Rapid muscle contractions convert chemical energy into thermal energy, increasing heat production by up to 4–5 times. * **Increased BMR:** Cold exposure triggers "non-shivering thermogenesis." This involves the release of thyroxine (long-term) and catecholamines (short-term), which increase the cellular metabolic rate to generate internal heat. **2. Analysis of Options:** * **Option A & B:** These are acute physiological responses. While vasoconstriction happens first, shivering is necessary at 20°C if the person is not adequately clothed. * **Option C:** BMR increases as a compensatory mechanism to maintain homeothermy in colder environments. Since all three mechanisms occur simultaneously or sequentially to maintain homeostasis, "All of the above" is the most accurate choice. ### High-Yield Clinical Pearls for NEET-PG: * **Thermostat Center:** The **Anterior Hypothalamus** (Pre-optic area) senses heat, while the **Posterior Hypothalamus** senses cold. * **Brown Adipose Tissue (BAT):** In neonates, non-shivering thermogenesis occurs primarily in brown fat due to the presence of **Thermogenin (UCP-1)**. * **Hunting’s Reaction:** Prolonged cold exposure causes "Lewis Triple Response" or paradoxical vasodilation to prevent tissue frostbite.

Question 307: Which of the following is secreted by beta cells of the pancreas along with insulin?

A. Somatostatin
B. Amylin (Correct Answer)
C. Pancreatic polypeptide
D. Glucagon-like peptide 1

Explanation: **Explanation:** The correct answer is **Amylin** (also known as Islet Amyloid Polypeptide or IAPP). **Why Amylin is correct:** Insulin and Amylin are co-stored and co-secreted from the **beta cells** of the Islets of Langerhans in a molar ratio of approximately 100:1 (Insulin:Amylin). Amylin functions as a synergistic hormone to insulin; it slows gastric emptying, promotes satiety to prevent post-prandial glucose spikes, and inhibits inappropriate glucagon secretion. **Analysis of Incorrect Options:** * **A. Somatostatin:** This is secreted by the **Delta ($\delta$) cells** of the pancreas. It acts as a universal inhibitor, suppressing the secretion of both insulin and glucagon. * **C. Pancreatic Polypeptide:** This is secreted by the **PP cells (or F cells)** of the pancreas, primarily located in the head of the gland. * **D. Glucagon-like peptide 1 (GLP-1):** This is an **incretin** hormone secreted by the **L-cells of the small intestine** (distal ileum and colon) in response to food intake, not by the pancreatic beta cells. **High-Yield NEET-PG Pearls:** 1. **Pramlintide:** A synthetic analogue of Amylin used as an adjunct treatment in both Type 1 and Type 2 Diabetes Mellitus. 2. **Amyloid Deposits:** In Type 2 Diabetes, Amylin can aggregate to form amyloid deposits in the islets, which is a classic histopathological finding. 3. **C-Peptide:** Remember that C-peptide is also secreted in equimolar amounts with insulin and serves as a marker for endogenous insulin production.

Question 308: Orexins play an important role in eating disorders. All of the following are orexins, EXCEPT?

A. Leptin (Correct Answer)
B. Orexin-A
C. Hypocretin 1
D. Hypocretin 2

Explanation: **Explanation:** The regulation of appetite is controlled by the hypothalamus through two types of signals: **Orexigenic** (appetite-stimulating) and **Anorexigenic** (appetite-suppressing). **Why Leptin is the correct answer:** Leptin is an **anorexigenic** hormone produced by adipocytes (fat cells). It acts on the arcuate nucleus of the hypothalamus to inhibit hunger and stimulate satiety. Therefore, it is not an orexin; rather, it is an "anti-orexin" or satiety factor. **Analysis of incorrect options:** * **Orexin-A and Orexin-B:** These are neuropeptides produced in the lateral hypothalamus (the "feeding center"). They strongly stimulate food intake and play a vital role in regulating wakefulness. * **Hypocretin 1 and 2:** These are alternative names for Orexin-A and Orexin-B, respectively. The terms are used interchangeably in medical literature (Hypocretin-1 = Orexin-A; Hypocretin-2 = Orexin-B). Since they promote feeding, they are true orexins. **High-Yield Clinical Pearls for NEET-PG:** * **Narcolepsy Connection:** A deficiency of orexin (hypocretin) producing neurons in the hypothalamus is the primary cause of **Narcolepsy Type 1** (associated with cataplexy). * **The "Satiety Center":** The **Ventromedial Nucleus (VMN)** of the hypothalamus is the satiety center (lesion leads to obesity). * **The "Feeding Center":** The **Lateral Hypothalamus (LHA)** is the feeding center where orexins are produced (lesion leads to anorexia/starvation). * **Ghrelin:** Known as the "hunger hormone," it is the only peripheral orexigenic hormone (produced by the stomach).

Question 309: What is the primary function of vasopressin?

A. Water absorption in the proximal convoluted tubule (PCT)
B. Water absorption in the loop of Henle
C. Water absorption in the collecting duct (Correct Answer)
D. Sodium (Na+) absorption in the PCT

Explanation: ### Explanation **Correct Answer: C. Water absorption in the collecting duct** **Mechanism:** Vasopressin, also known as **Antidiuretic Hormone (ADH)**, is synthesized in the hypothalamus (supraoptic and paraventricular nuclei) and released from the posterior pituitary. Its primary action is to maintain water homeostasis. It acts on the **V2 receptors** located on the basolateral membrane of the **principal cells** in the **Late Distal Tubule and Collecting Ducts**. This triggers a cAMP-mediated signaling pathway that leads to the insertion of **Aquaporin-2 (AQP2)** water channels into the apical membrane. This increases the permeability of the collecting duct, allowing water to be reabsorbed back into the medullary interstitium via an osmotic gradient. **Why other options are incorrect:** * **Option A & D:** The **Proximal Convoluted Tubule (PCT)** is responsible for the bulk reabsorption (65%) of water and solutes (like Sodium). However, water reabsorption in the PCT is "obligatory" (follows solutes) and is **independent of ADH**. * **Option B:** The **Loop of Henle** (specifically the descending limb) is permeable to water, but this is driven by the countercurrent multiplier system, not by vasopressin. Vasopressin does, however, increase urea recycling in the medullary collecting duct to maintain this gradient. **High-Yield NEET-PG Pearls:** * **V1 Receptors:** Located on vascular smooth muscle; cause vasoconstriction (hence the name "Vasopressin"). * **Diabetes Insipidus (DI):** Deficiency of ADH (Central DI) or resistance to ADH (Nephrogenic DI) leads to polyuria and dilute urine. * **SIADH:** Excessive ADH secretion leads to water retention and **euvolemic hyponatremia**. * **Urea Transport:** ADH also increases the activity of **UT-A1 urea transporters** in the inner medullary collecting duct, contributing to the corticomedullary osmotic gradient.

Question 310: Catecholamine hormones are synthesized in which location?

A. Chromaffin cells of the adrenal medulla (Correct Answer)
B. Zona glomerulosa of the adrenal cortex
C. Zona fasciculata of the adrenal cortex
D. Zona reticularis of the adrenal cortex

Explanation: **Explanation:** **1. Why Option A is Correct:** Catecholamines (Epinephrine, Norepinephrine, and Dopamine) are synthesized in the **Chromaffin cells** of the **adrenal medulla**. These cells are embryologically derived from the **neural crest** and act as modified postganglionic sympathetic neurons. Within these cells, the amino acid Tyrosine is converted into catecholamines through a series of enzymatic steps. The final step (Norepinephrine to Epinephrine) is catalyzed by the enzyme **PNMT** (Phenylethanolamine N-methyltransferase), which is uniquely induced by high concentrations of cortisol draining from the adrenal cortex. **2. Why Other Options are Incorrect:** Options B, C, and D refer to the **Adrenal Cortex**, which is mesodermal in origin and produces **steroid hormones**, not catecholamines. * **Zona Glomerulosa (B):** The outermost layer, responsible for secreting mineralocorticoids (primarily **Aldosterone**). * **Zona Fasciculata (C):** The middle and widest layer, responsible for secreting glucocorticoids (primarily **Cortisol**). * **Zona Reticularis (D):** The innermost layer of the cortex, responsible for secreting adrenal androgens (e.g., **DHEA**). **3. NEET-PG High-Yield Pearls:** * **Rate-limiting enzyme:** Tyrosine hydroxylase is the rate-limiting step in catecholamine synthesis. * **VMAT-2:** This transporter packages catecholamines into granules (inhibited by Reserpine). * **Tumor Correlation:** **Pheochromocytoma** is a tumor of the chromaffin cells, leading to episodic hypertension due to excessive catecholamine release. * **Rule of 10s:** Pheochromocytoma is 10% bilateral, 10% malignant, and 10% extra-adrenal (where they are called Paragangliomas).

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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