Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 531: Which hormone is released during increased stress?

A. Cortisol (Correct Answer)
B. Thyroxine
C. Growth hormone
D. Somatostatin

Explanation: **Explanation:** **1. Why Cortisol is Correct:** Cortisol is the primary glucocorticoid produced by the **Zona Fasciculata** of the adrenal cortex. It is famously known as the "stress hormone" because its secretion increases significantly during physical, emotional, or physiological stress (e.g., trauma, infection, extreme heat/cold). Under the influence of **ACTH** from the anterior pituitary, cortisol helps the body cope with stress by mobilizing energy stores through **gluconeogenesis**, proteolysis, and lipolysis, ensuring adequate glucose supply for the brain and heart. **2. Why Other Options are Incorrect:** * **Thyroxine (T4):** Primarily regulates the Basal Metabolic Rate (BMR) and long-term growth. While thyroid function can be affected by chronic stress, it is not the acute hormonal mediator of the stress response. * **Growth Hormone (GH):** Although GH can rise during acute physical stress (like exercise or hypoglycemia), it is primarily a hormone of growth and metabolism. Cortisol is the more definitive and classic answer for the general stress response. * **Somatostatin:** This is an inhibitory hormone (Growth Hormone Inhibiting Hormone) produced by the hypothalamus and delta cells of the pancreas. It inhibits the release of GH, TSH, and insulin, rather than being a mediator of stress. **3. NEET-PG Clinical Pearls:** * **HPA Axis:** Stress triggers the Hypothalamic-Pituitary-Adrenal axis: CRH → ACTH → Cortisol. * **Diurnal Variation:** Cortisol levels are highest in the early morning (approx. 8 AM) and lowest at midnight. This rhythm is often lost in **Cushing’s Syndrome**. * **Permissive Action:** Cortisol is essential for the vasoconstrictive action of catecholamines (epinephrine/norepinephrine) on blood vessels. * **Immunosuppression:** High levels of cortisol inhibit phospholipase A2, leading to the anti-inflammatory effects used in clinical practice.

Question 532: In which of the following ways does aldosterone interact with renal tubular cells?

A. Increases translocation of ENaCs from the cytoplasm to the cell membrane (Correct Answer)
B. Binds to a steroid receptor inside the nucleus of renal tubular cells
C. Binds to ENaCs on the cell membrane and increases sodium transport
D. Binds to G-protein coupled receptors on the cell surface

Explanation: **Explanation:** Aldosterone, a mineralocorticoid secreted by the adrenal cortex, acts primarily on the **Principal cells** of the late distal tubule and collecting ducts. Its mechanism of action is divided into rapid (non-genomic) and classic (genomic) phases. **Why Option A is correct:** The "early response" of aldosterone involves the activation and **translocation of pre-formed Epithelial Sodium Channels (ENaCs)** from the cytoplasmic vesicles to the apical (luminal) membrane. This increases the membrane's permeability to sodium, allowing for rapid reabsorption. In the "late phase," aldosterone induces the synthesis of *new* ENaCs, SGK-1 (Serum-glucocorticoid regulated kinase), and Na+/K+ ATPase pumps. **Analysis of Incorrect Options:** * **Option B:** Aldosterone is a steroid hormone; it binds to the **Mineralocorticoid Receptor (MR) in the cytoplasm**, not the nucleus. The hormone-receptor complex then translocates into the nucleus to act as a transcription factor. * **Option C:** Aldosterone does not bind directly to ENaCs. It regulates their expression and insertion via intracellular signaling and protein synthesis. * **Option D:** Aldosterone primarily uses intracellular receptors. While some rapid non-genomic effects via membrane receptors are researched, the classic physiological mechanism taught for NEET-PG is via cytoplasmic steroid receptors. **High-Yield Clinical Pearls for NEET-PG:** * **Liddle’s Syndrome:** A genetic mutation causing "constitutively active" ENaCs, leading to hypertension and hypokalemia (mimics hyperaldosteronism but with low renin/aldosterone). * **Spironolactone/Eplerenone:** Competitive antagonists of the Mineralocorticoid Receptor. * **Amiloride/Triamterene:** Direct blockers of the ENaC channel. * **Net Effect of Aldosterone:** Sodium reabsorption, Water reabsorption (via ENaC/osmosis), and secretion of Potassium ($K^+$) and Hydrogen ($H^+$) ions.

Question 533: What is true about glucagon?

A. Hyperglycemia stimulates its release
B. Has no effect on muscle glycogenolysis (Correct Answer)
C. Stimulates glycolysis
D. Inhibits gluconeogenesis

Explanation: **Explanation:** Glucagon is a catabolic hormone secreted by the **alpha cells of the pancreas**, primarily acting to increase blood glucose levels during fasting or hypoglycemia. **Why Option B is correct:** Glucagon acts specifically on the liver because **skeletal muscle lacks glucagon receptors**. While muscle contains significant glycogen stores, these are reserved for local energy production during exercise. Muscle glycogenolysis is stimulated by epinephrine (via $\beta_2$ receptors) and calcium ions, but not by glucagon. In contrast, glucagon is the primary driver of **hepatic glycogenolysis**. **Analysis of Incorrect Options:** * **A. Hyperglycemia stimulates its release:** Incorrect. Glucagon is inhibited by hyperglycemia and stimulated by **hypoglycemia**. Its primary role is to prevent blood glucose from falling too low. * **C. Stimulates glycolysis:** Incorrect. Glucagon **inhibits glycolysis** (the breakdown of glucose for energy) in the liver to conserve glucose for release into the bloodstream. It does this by decreasing levels of Fructose-2,6-bisphosphate. * **D. Inhibits gluconeogenesis:** Incorrect. Glucagon **stimulates gluconeogenesis** (the synthesis of glucose from non-carbohydrate sources like amino acids) to maintain euglycemia during prolonged fasting. **High-Yield NEET-PG Pearls:** * **Mechanism of Action:** Glucagon acts via a **G-protein coupled receptor (Gs)**, increasing intracellular **cAMP** and activating Protein Kinase A. * **Amino Acids:** Arginine and Alanine *stimulate* glucagon release (this prevents hypoglycemia during a pure protein meal). * **Clinical Use:** Glucagon is the treatment of choice for **Beta-blocker overdose** because it increases cAMP in cardiac tissue independently of beta-receptors.

Question 534: Mineralocorticoid receptors are present in all except?

A. Hippocampus
B. Colon
C. Liver (Correct Answer)
D. Kidney

Explanation: **Explanation:** Mineralocorticoid receptors (MR), also known as Type I glucocorticoid receptors, are nuclear receptors that primarily mediate the effects of aldosterone. Their distribution is specific to tissues involved in electrolyte balance or specific neural signaling. **Why Liver is the Correct Answer:** The **Liver** does not express mineralocorticoid receptors. While the liver is the primary site for the metabolism and conjugation of aldosterone (converting it to tetrahydroaldosterone-3-glucuronide for excretion), it is not a target organ for its physiological action. Therefore, it lacks the receptors to initiate a mineralocorticoid response. **Analysis of Incorrect Options:** * **Kidney:** This is the primary site of MR expression. Receptors are located in the **principal cells** of the late distal tubule and collecting duct, where they promote sodium reabsorption and potassium/hydrogen secretion. * **Colon:** MRs are present in the distal colon, where they stimulate the absorption of sodium and water and the secretion of potassium, similar to their action in the kidney. * **Hippocampus:** This is a high-yield neuro-endocrine fact. The hippocampus expresses high levels of MRs (Type I), where they bind corticosterone/cortisol with high affinity to modulate mood, memory, and the HPA axis feedback loop. **NEET-PG High-Yield Pearls:** 1. **Specificity:** In epithelial tissues (Kidney/Colon), the enzyme **11β-HSD2** converts cortisol to inactive cortisone, preventing cortisol from flooding the MR and allowing aldosterone to bind selectively. 2. **Other Sites:** MRs are also found in **salivary glands** and **sweat glands** (to conserve sodium) and the **myocardium** (where excess activation leads to fibrosis). 3. **Antagonist:** Spironolactone and Eplerenone are the primary clinical MR antagonists used in heart failure and hypertension.

Question 535: Which thyroid hormone receptor is predominantly expressed in the CNS/Brain?

A. TR alpha-1
B. TR alpha-2
C. TR beta-1 (Correct Answer)
D. TR beta-2

Explanation: **Explanation:** Thyroid hormone receptors (TR) are nuclear receptors encoded by two primary genes: **THRA** (alpha) and **THRB** (beta). The distribution of these receptors is tissue-specific, which dictates the physiological effects of T3 in different organs. **Why TR beta-1 is correct:** **TR beta-1** is the most widely distributed isoform of the beta receptor. It is the **predominant thyroid receptor expressed in the Central Nervous System (Brain)**, as well as in the liver and kidneys. It plays a crucial role in brain development and the maintenance of metabolic homeostasis within neural tissues. **Analysis of Incorrect Options:** * **TR alpha-1:** This is the primary isoform found in the **heart** and skeletal muscle. It mediates the chronotropic and inotropic effects of thyroid hormones. * **TR alpha-2:** Although widely expressed in the brain, this isoform is unique because it **cannot bind T3**. It acts as an antagonist or a dominant-negative regulator, modulating the activity of other TR isoforms. * **TR beta-2:** Expression is highly restricted. It is primarily found in the **hypothalamus and anterior pituitary**, where it mediates the negative feedback inhibition of TRH and TSH. It is also found in the cochlea and retina. **High-Yield Clinical Pearls for NEET-PG:** * **Resistance to Thyroid Hormone (RTH):** Most commonly caused by mutations in the **TR beta** gene. Patients typically have high levels of T3/T4 and inappropriately normal or elevated TSH (due to impaired negative feedback at the pituitary). * **Heart vs. Liver:** Remember **Alpha = Heart** (tachycardia in hyperthyroidism) and **Beta = Brain/Liver** (metabolic control). * **T3 vs. T4:** TRs have a much higher affinity (approx. 10 times) for **T3** than T4, which is why T3 is the biologically active form.

Question 536: Melatonin is:

A. Serotonergic (Correct Answer)
B. Dopaminergic
C. Adrenergic
D. Estrogenic

Explanation: **Explanation:** **Melatonin** is a hormone synthesized and secreted primarily by the **pineal gland**. The correct answer is **Serotonergic** because melatonin is biochemically derived from the neurotransmitter **Serotonin** (5-hydroxytryptamine). **The Synthesis Pathway:** 1. **Tryptophan** (Amino acid precursor) → 5-Hydroxytryptophan. 2. 5-Hydroxytryptophan → **Serotonin**. 3. Serotonin is then converted to N-acetylserotonin (via *N-acetyltransferase*, the rate-limiting enzyme). 4. N-acetylserotonin is converted to **Melatonin** (via *Hydroxyindole-O-methyltransferase*). **Why other options are incorrect:** * **Dopaminergic:** Refers to dopamine, a catecholamine involved in the reward pathway and motor control. While dopamine and melatonin have an antagonistic relationship in the retina, melatonin is not derived from dopamine. * **Adrenergic:** Refers to epinephrine/norepinephrine. These are derived from Tyrosine, not Tryptophan. * **Estrogenic:** Refers to steroid hormones derived from cholesterol. Melatonin is an amine hormone, not a steroid. **High-Yield Clinical Pearls for NEET-PG:** * **Circadian Rhythm:** Melatonin secretion is stimulated by darkness and inhibited by light. It regulates the sleep-wake cycle by acting on the **Suprachiasmatic Nucleus (SCN)** of the hypothalamus (the master biological clock). * **Rate-limiting Enzyme:** Serotonin N-acetyltransferase (SNAT). Its activity peaks at night. * **Precursor:** Tryptophan is the essential amino acid required for its production. * **Clinical Use:** Exogenous melatonin is used for **Jet lag** and delayed sleep phase syndrome. * **Other functions:** It is a potent antioxidant and plays a role in inhibiting gonadotropin secretion (antigonadotropic effect).

Question 537: Which of the following hormones does not contain alpha and beta subunits?

A. FSH
B. HCG
C. Prolactin (Correct Answer)
D. Insulin

Explanation: **Explanation:** The correct answer is **Prolactin**. This question tests your knowledge of the structural classification of hormones, specifically the **Glycoprotein family**. **1. Why Prolactin is the correct answer:** Prolactin is a single-chain polypeptide hormone (containing 199 amino acids) synthesized by the lactotrophs of the anterior pituitary. It belongs to the **Somatotropin family**, which also includes Growth Hormone (GH) and Human Placental Lactogen (hPL). These hormones consist of a single polypeptide chain stabilized by disulfide bridges and do not possess a dimeric alpha-beta subunit structure. **2. Analysis of Incorrect Options:** * **FSH and hCG (Options A & B):** These belong to the **Glycoprotein hormone family**, which also includes LH and TSH. All members of this family are dimers consisting of two subunits: * **Alpha (α) subunit:** Identical in all four hormones (FSH, LH, TSH, and hCG). * **Beta (β) subunit:** Unique to each hormone, providing biological and receptor specificity. * **Insulin (Option D):** While Insulin is not a glycoprotein, it **does** consist of two chains (Alpha and Beta) linked by disulfide bonds. Therefore, it technically contains alpha and beta subunits, making it an incorrect choice for a hormone that "does not" contain them. **Clinical Pearls for NEET-PG:** * **Cross-reactivity:** Because hCG and TSH share the same alpha subunit and have similar beta subunits, very high levels of hCG (as seen in Hydatidiform mole) can stimulate TSH receptors, leading to hyperthyroidism. * **Pregnancy Tests:** Immunological pregnancy tests specifically detect the **beta-subunit of hCG** to avoid cross-reactivity with LH or FSH. * **Prolactin Inhibition:** Unlike most pituitary hormones, Prolactin is under tonic **inhibition by Dopamine** (Prolactin Inhibiting Hormone) from the hypothalamus.

Question 538: Which of the following hormones are increased due to stress during surgery, especially in patients with Diabetes Mellitus?

A. Epinephrine
B. Growth Hormone (GH)
C. Glucocorticoids
D. All of the above (Correct Answer)

Explanation: **Explanation:** The surgical procedure acts as a potent physical and psychological stressor, triggering a complex neuroendocrine response aimed at maintaining homeostasis and mobilizing energy substrates. This is often referred to as the **"Stress Response to Surgery."** **Why "All of the above" is correct:** During surgery, the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic nervous system are activated, leading to a surge in **counter-regulatory hormones**. These hormones oppose the action of insulin, leading to hyperglycemia—a significant concern in patients with Diabetes Mellitus. 1. **Epinephrine (Option A):** Stress triggers the sympathetic-adrenal medullary axis, releasing catecholamines. Epinephrine increases glycogenolysis and gluconeogenesis while inhibiting insulin secretion. 2. **Growth Hormone (Option B):** GH levels rise rapidly during surgical stress. It contributes to insulin resistance and stimulates lipolysis, providing alternative fuel sources. 3. **Glucocorticoids (Option C):** Cortisol levels rise significantly due to ACTH stimulation. Cortisol promotes protein catabolism and gluconeogenesis, further elevating blood glucose levels. **Clinical Pearls for NEET-PG:** * **The "Diabetes of Injury":** Surgical stress induces a state of transient insulin resistance and hyperglycemia even in non-diabetic patients; however, in diabetics, this can lead to severe metabolic derangements like DKA or HHS. * **Insulin is the "Odd One Out":** While counter-regulatory hormones (Glucagon, GH, Cortisol, Epinephrine) increase, insulin secretion is often suppressed or its peripheral action is impaired during the acute stress phase. * **ADH (Vasopressin):** Also increases during surgery to maintain blood volume, often leading to postoperative fluid retention. * **Cytokines:** IL-6 is the primary cytokine responsible for stimulating the acute-phase response during surgery.

Question 539: GLUT 4 receptors are primarily found in which tissues?

A. Brain, red blood cells
B. Liver, Kidney, Ileum
C. Neurons and placenta
D. Skeletal muscle, fat, and cardiac tissue (Correct Answer)

Explanation: **Explanation:** The core concept behind this question is the distinction between **insulin-independent** and **insulin-dependent** glucose transport. **Why Option D is correct:** **GLUT 4** is the only glucose transporter that is **insulin-dependent**. It is sequestered in intracellular vesicles and only translocates to the cell membrane in response to insulin or exercise. It is primarily expressed in tissues that serve as major sites for glucose disposal and storage: **skeletal muscle** (the largest consumer of glucose), **adipose tissue** (fat), and **cardiac muscle**. **Why other options are incorrect:** * **Option A (Brain, RBCs):** These tissues require a constant supply of glucose regardless of insulin levels. RBCs and the Blood-Brain Barrier use **GLUT 1** (basal uptake). * **Option B (Liver, Kidney, Ileum):** The liver and pancreatic beta cells use **GLUT 2**, a high-capacity, low-affinity bidirectional transporter. The ileum and kidneys primarily use **SGLT 1/2** (active transport) and GLUT 2. * **Option C (Neurons and Placenta):** Neurons primarily use **GLUT 3**, which has a very high affinity for glucose to ensure the brain is prioritized during hypoglycemia. **High-Yield Clinical Pearls for NEET-PG:** * **Exercise & GLUT 4:** Exercise can trigger GLUT 4 translocation in skeletal muscle *independent* of insulin, which is why exercise helps manage blood sugar in Type 2 Diabetes. * **GLUT 2:** Acts as a "glucose sensor" in pancreatic beta cells. * **SGLT vs. GLUT:** SGLTs (Sodium-Glucose Linked Transporters) use secondary active transport (against gradient), while GLUTs use facilitated diffusion (down gradient). * **Mnemonic:** "BRICK L" (Brain, RBCs, Intestine, Cornea, Kidney, Liver) are insulin-independent.

Question 540: The last step of spermatogenesis takes place in which of the following cells?

A. Leydig cells
B. Interstitial cells
C. Sertoli cells (Correct Answer)
D. Stromal cells

Explanation: **Explanation:** The correct answer is **Sertoli cells**. The "last step" of spermatogenesis refers to **spermiogenesis**, the process where non-motile, spherical spermatids transform into mature, motile spermatozoa. This critical maturation occurs while the spermatids are physically embedded within the apical membranes of **Sertoli cells**. Sertoli cells provide the necessary nutrients, hormonal signals, and structural support for this remodeling. The final release of mature sperm into the lumen of the seminiferous tubule is called **spermiation**. **Why other options are incorrect:** * **Leydig cells (and Interstitial cells):** These are the same cell type located in the connective tissue between seminiferous tubules. Their primary function is the production of **testosterone** in response to LH. They do not participate directly in the physical maturation of sperm. * **Stromal cells:** These are general connective tissue cells that provide structural support to the testes but do not have a direct functional role in the stages of spermatogenesis. **High-Yield Clinical Pearls for NEET-PG:** * **Blood-Testis Barrier:** Formed by tight junctions between adjacent Sertoli cells; it protects developing germ cells from the immune system. * **Inhibin B:** Secreted by Sertoli cells, it provides negative feedback to the anterior pituitary to inhibit **FSH** secretion. * **Androgen Binding Protein (ABP):** Also secreted by Sertoli cells, it ensures high local concentrations of testosterone within the tubules, which is essential for spermatogenesis. * **Mnemonic:** **S**ertoli cells **S**upport **S**permatogenesis and are stimulated by **FSH** (FSH acts on Sertoli; LH acts on Leydig).

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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