Endocrinology — MCQs

A 30-year-old male presents with recurrent attacks of sweating and dizziness. Further workup reveals low blood glucose levels with inappropriately elevated insulin and C-peptide levels. Imaging shows a lesion in the pancreas. He is diagnosed with insulinoma and given diazoxide. What is the mechanism of action of diazoxide?

Q348Easy

Which hormone, along with insulin, is produced by the beta cells of the pancreas?

Q349Easy

What are the metabolic effects of insulin on adipose tissue?

Q350Easy

Which of the following decreases the secretion of both insulin and glucagon?

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 341: Inappropriate ADH secretion is characterised by all of the following except?

A. Hypo-osmolar urine (Correct Answer)
B. Water intoxication
C. Expanded fluid volume
D. Hypomagnesemia

Explanation: **Explanation:** The Syndrome of Inappropriate Antidiuretic Hormone (SIADH) is characterized by the excessive, non-physiological release of ADH, leading to water retention and dilutional hyponatremia. **Why Option A is the Correct Answer:** In SIADH, high levels of ADH cause excessive water reabsorption in the collecting ducts of the kidney. This results in the production of highly concentrated urine. Therefore, the urine is **hyper-osmolar** (typically >100 mOsm/kg, and often greater than plasma osmolality), not hypo-osmolar. Finding hypo-osmolar urine in a hyponatremic patient would instead suggest conditions like primary polydipsia. **Analysis of Incorrect Options:** * **B. Water Intoxication:** Excessive ADH leads to free water retention, effectively causing "water intoxication" which manifests as dilutional hyponatremia. * **C. Expanded Fluid Volume:** The retained water leads to ECF volume expansion. However, SIADH is clinically characterized as **euvolemic hyponatremia** because the body compensates via pressure natriuresis (atrial natriuretic peptide release), which excretes sodium and water to prevent overt edema. * **D. Hypomagnesemia:** While hyponatremia is the hallmark, SIADH is frequently associated with other secondary electrolyte disturbances, including hypomagnesemia and hypouricemia, due to increased urinary excretion during the volume-expansion phase. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnostic Criteria:** Hyponatremia + Low plasma osmolality + High urine osmolality (>100 mOsm/kg) + High urine sodium (>40 mEq/L). * **Common Causes:** Small cell carcinoma of the lung (ectopic production), CNS disorders (stroke, trauma), and drugs (SSRIs, Carbamazepine, Cyclophosphamide). * **Treatment:** Fluid restriction is the first-line treatment. For refractory cases, use Vaptans (Vasopressin antagonists) or Demeclocycline. * **Caution:** Rapid correction of hyponatremia can lead to **Osmotic Demyelination Syndrome** (Central Pontine Myelinolysis).

Question 342: Which of the following hormones is NOT produced by the endocrine part of the pancreas?

A. Insulin
B. Somatostatin
C. Glucagon
D. Bombesin (Correct Answer)

Explanation: **Explanation:** The pancreas is a dual-function organ consisting of an exocrine part (acini) and an endocrine part (Islets of Langerhans). The Islets of Langerhans contain several distinct cell types that secrete specific hormones directly into the bloodstream. **Why Bombesin is the correct answer:** Bombesin is a peptide originally isolated from the skin of amphibians. In humans, its equivalent is **Gastrin-Releasing Peptide (GRP)**. It is primarily found in the gastrointestinal tract and the brain, acting as a neurotransmitter and a stimulator of gastrin release. It is **not** a product of the pancreatic Islets of Langerhans. **Why the other options are incorrect:** * **Insulin (Option A):** Produced by the **Beta (β) cells**, which make up about 60-75% of the islet cells. It is the primary anabolic hormone responsible for lowering blood glucose. * **Somatostatin (Option B):** Produced by the **Delta (δ) cells** (approx. 5-10%). It acts locally (paracrine effect) to inhibit the secretion of both insulin and glucagon. * **Glucagon (Option C):** Produced by the **Alpha (α) cells** (approx. 20%). It is a catabolic hormone that increases blood glucose levels via glycogenolysis and gluconeogenesis. **High-Yield Clinical Pearls for NEET-PG:** * **Cell Distribution:** Remember the mnemonic **"BAGS"** for islet cells: **B**eta (Insulin), **A**lpha (Glucagon), **G**amma/PP cells (Pancreatic Polypeptide), and **S**igma/Delta (Somatostatin). * **Epsilon (ε) cells:** A minor cell type in the pancreas that produces **Ghrelin** (the hunger hormone). * **Blood Flow Pattern:** Blood in the islets flows from the center (Beta cells) to the periphery (Alpha/Delta cells), allowing insulin to inhibit glucagon release directly.

Question 343: Continuous administration of testosterone leads to which of the following conditions?

A. Azoospermia (Correct Answer)
B. Increased sperm motility
C. Increased spermatogenesis
D. Increased gonadotrophins

Explanation: **Explanation:** The correct answer is **Azoospermia**. This occurs due to the **negative feedback mechanism** of the Hypothalamic-Pituitary-Gonadal (HPG) axis. 1. **Mechanism of Action:** When exogenous testosterone is administered continuously, it reaches high levels in the systemic circulation. This triggers strong negative feedback on the hypothalamus (inhibiting GnRH) and the anterior pituitary. 2. **Suppression of Gonadotrophins:** This results in a significant decrease in the secretion of **FSH (Follicle Stimulating Hormone)** and **LH (Luteinizing Hormone)**. 3. **Impact on Spermatogenesis:** * Decreased **LH** leads to a drop in endogenous testosterone production by Leydig cells. * Decreased **FSH** impairs the function of Sertoli cells. * Crucially, while systemic testosterone levels are high, the **intratesticular testosterone concentration** (which is normally 100x higher than blood levels and essential for sperm production) falls drastically. Without high local testosterone and FSH stimulation, spermatogenesis halts, leading to **azoospermia** (absence of sperm in the ejaculate). **Why other options are incorrect:** * **B & C:** Since spermatogenesis is inhibited and the intratesticular environment is compromised, sperm motility and production decrease, rather than increase. * **D:** Gonadotrophins (FSH/LH) are **decreased**, not increased, due to the negative feedback loop. **High-Yield Clinical Pearls for NEET-PG:** * **Contraceptive Potential:** This feedback mechanism is the physiological basis for research into male hormonal contraceptives. * **Testicular Atrophy:** Long-term exogenous steroid use leads to shrinking of the testes because the bulk of testicular volume is composed of seminiferous tubules, which atrophy without FSH and local testosterone. * **The "Steroid Paradox":** Bodybuilders using anabolic steroids often present with infertility despite having high muscularity and "normal" or high systemic androgen levels.

Question 344: Which of the following is not controlled by the autonomic nervous system?

A. Aldosterone (Correct Answer)
B. Insulin
C. Growth Hormone (GH)
D. Somatostatin

Explanation: The autonomic nervous system (ANS) plays a significant role in modulating the secretion of several hormones, particularly those involved in metabolism and stress. However, some hormones are regulated strictly by humoral factors or specific feedback loops. ### **Explanation of the Correct Answer** **A. Aldosterone:** This is the correct answer because its secretion is primarily regulated by the **Renin-Angiotensin-Aldosterone System (RAAS)** and **plasma potassium levels**. While sympathetic stimulation can indirectly increase aldosterone by triggering renin release from the juxtaglomerular cells, the direct control of the adrenal cortex (Zona Glomerulosa) is not under autonomic innervation. ### **Analysis of Incorrect Options** * **B. Insulin:** The pancreas is heavily innervated. **Parasympathetic (Vagal)** stimulation increases insulin secretion (anticipatory phase), while **Sympathetic** stimulation (via α2 receptors) inhibits it to maintain blood glucose during stress. * **C. Growth Hormone (GH):** The hypothalamus, which secretes GHRH and Somatostatin to regulate GH, receives extensive input from the ANS. Stress, exercise, and sleep—all mediated or influenced by the ANS—directly alter GH pulsatility. * **D. Somatostatin:** In the pancreas (delta cells) and the GI tract, somatostatin secretion is modulated by vagal activity. In the hypothalamus, it is influenced by central neurotransmitters linked to autonomic pathways. ### **High-Yield Clinical Pearls for NEET-PG** * **Primary Stimulus for Aldosterone:** An increase in **Plasma K+** is the most potent direct stimulus for aldosterone release. * **Adrenal Medulla vs. Cortex:** The Adrenal **Medulla** is essentially a modified sympathetic ganglion (preganglionic sympathetic fibers), whereas the **Cortex** is regulated hormonally (ACTH/Angiotensin II). * **Insulin & Receptors:** Remember that **α2-adrenergic** stimulation inhibits insulin, while **β2-adrenergic** stimulation increases it. The inhibitory α-effect usually dominates during a systemic sympathetic surge.

Question 345: Which of the following can result in the secretion of both insulin and glucagon?

A. Arginine (Correct Answer)
B. Fatty acids
C. Hypoglycemia
D. Hyperglycemia

Explanation: **Explanation:** The secretion of insulin and glucagon is typically reciprocal (one increases while the other decreases) to maintain glucose homeostasis. However, **Arginine** (and other amino acids like lysine) is a unique potent stimulator for **both** hormones. 1. **Why Arginine is Correct:** When a protein-rich meal is consumed, amino acids stimulate **insulin** to promote protein synthesis and glucose uptake. Simultaneously, they stimulate **glucagon** secretion. This "protective" glucagon release prevents hypoglycemia that might otherwise occur if insulin acted alone in the absence of dietary carbohydrates (the "protein-induced hypoglycemia" prevention mechanism). 2. **Why Incorrect Options are Wrong:** * **Fatty Acids:** High levels of free fatty acids primarily stimulate insulin secretion but generally inhibit glucagon. * **Hypoglycemia:** Low blood glucose is the primary stimulus for **glucagon** but strongly inhibits insulin secretion to prevent further glucose drop. * **Hyperglycemia:** High blood glucose is the primary stimulus for **insulin** but inhibits glucagon secretion via paracrine effects (somatostatin and intra-islet insulin). **NEET-PG High-Yield Pearls:** * **Biphasic Response:** Insulin secretion is biphasic; the first phase is the release of pre-formed granules, and the second is the synthesis of new insulin. * **Incretin Effect:** Oral glucose causes a much higher insulin response than intravenous glucose due to GIP and GLP-1 (Incretins). * **Major Inhibitor:** Somatostatin (from Delta cells) inhibits the secretion of both insulin and glucagon. * **Adrenergic Effect:** Alpha-2 stimulation inhibits insulin, while Beta-2 stimulation increases it.

Question 346: Luteinizing hormone (LH) is secreted by which endocrine gland?

A. Ovary
B. Pituitary gland (Correct Answer)
C. Corpus luteum
D. Hypothalamus

Explanation: **Explanation:** Luteinizing Hormone (LH) is a gonadotropin synthesized and secreted by the **gonadotroph cells** of the **Anterior Pituitary Gland**. Its release is stimulated by the pulsatile secretion of Gonadotropin-Releasing Hormone (GnRH) from the hypothalamus. In females, LH triggers ovulation and maintains the corpus luteum; in males, it stimulates Leydig cells to produce testosterone. **Analysis of Options:** * **Pituitary Gland (Correct):** Specifically, the anterior lobe (adenohypophysis) produces LH and FSH. These are glycoprotein hormones consisting of an alpha subunit (common to TSH and hCG) and a hormone-specific beta subunit. * **Ovary (Incorrect):** The ovary is the target organ for LH, not the source. It produces steroid hormones like estrogen and progesterone in response to LH stimulation. * **Corpus Luteum (Incorrect):** This is a temporary endocrine structure formed in the ovary *after* ovulation (triggered by the LH surge). It primarily secretes progesterone. * **Hypothalamus (Incorrect):** The hypothalamus acts as the "master controller" by secreting **GnRH**, which then signals the pituitary to release LH. **High-Yield Clinical Pearls for NEET-PG:** * **The LH Surge:** A positive feedback loop of Estrogen leads to a massive release of LH, which is the immediate trigger for **ovulation** (occurring ~24–36 hours after the surge). * **Alpha Subunit:** LH, FSH, TSH, and hCG share an identical alpha subunit. Specificity is determined by the **beta subunit**. * **LH:FSH Ratio:** An elevated ratio (>2:1 or 3:1) is a classic biochemical marker for **Polycystic Ovary Syndrome (PCOS)**. * **Leydig Cells:** In males, LH is often called Interstitial Cell Stimulating Hormone (ICSH).

Question 347: A 30-year-old male presents with recurrent attacks of sweating and dizziness. Further workup reveals low blood glucose levels with inappropriately elevated insulin and C-peptide levels. Imaging shows a lesion in the pancreas. He is diagnosed with insulinoma and given diazoxide. What is the mechanism of action of diazoxide?

A. Opening of ATP-sensitive K+ channels (Correct Answer)
B. Closing of ATP-sensitive K+ channels
C. Increase in the number of GLUT-4 receptors
D. Opening of voltage-sensitive Ca+2 channels

Explanation: **Explanation:** **Correct Option: A (Opening of ATP-sensitive K+ channels)** In the normal physiology of insulin secretion, glucose enters pancreatic beta cells and increases the ATP/ADP ratio. This causes the **ATP-sensitive K+ channels ($K_{ATP}$)** to close, leading to cell depolarization, calcium influx, and insulin release. **Diazoxide** acts as a **$K_{ATP}$ channel opener**. By keeping these channels open, it allows potassium to exit the cell (hyperpolarization). This prevents the opening of voltage-gated calcium channels, thereby inhibiting the exocytosis of insulin. In patients with insulinoma, diazoxide is used to manage hypoglycemia by suppressing this excessive insulin secretion. **Incorrect Options:** * **B (Closing of ATP-sensitive K+ channels):** This is the mechanism of **Sulfonylureas** (e.g., Glibenclamide). Closing these channels triggers insulin release, which would worsen hypoglycemia in an insulinoma patient. * **C (Increase in GLUT-4 receptors):** This is the mechanism of **Thiazolidinediones** (e.g., Pioglitazone) and is also a secondary effect of exercise and insulin. It increases peripheral glucose uptake but does not address the primary pathology of hyperinsulinism. * **D (Opening of voltage-sensitive Ca+2 channels):** This occurs downstream of $K_{ATP}$ channel closure and directly triggers insulin release. Diazoxide indirectly prevents this step. **NEET-PG High-Yield Pearls:** * **Insulinoma Triad (Whipple’s Triad):** Hypoglycemic symptoms, low plasma glucose (<50 mg/dL), and relief of symptoms after glucose administration. * **C-peptide:** Elevated in insulinoma (endogenous production) but low/absent in exogenous insulin surreptitious use. * **Other uses of Diazoxide:** It was historically used as an IV vasodilator for hypertensive emergencies (though rarely used now due to side effects like sodium retention and hypertrichosis).

Question 348: Which hormone, along with insulin, is produced by the beta cells of the pancreas?

A. Amylin
B. C-peptide
C. Both Amylin and C-peptide (Correct Answer)
D. Neither Amylin nor C-peptide

Explanation: ### Explanation **Correct Answer: C. Both Amylin and C-peptide** **1. Why the answer is correct:** The beta cells of the Islets of Langerhans are responsible for synthesizing and secreting insulin. However, this process involves the co-secretion of two other important molecules: * **C-peptide (Connecting peptide):** Insulin is synthesized as a precursor called **proinsulin**. Inside the secretory granules, proinsulin is cleaved by endopeptidases into equimolar amounts of mature insulin and C-peptide. Therefore, for every molecule of insulin released into the portal circulation, one molecule of C-peptide is also released. * **Amylin (Islet Amyloid Polypeptide - IAPP):** This is a 37-amino acid peptide hormone that is stored in the same secretory granules as insulin and is co-released in response to nutrient stimuli (though in much smaller quantities, roughly 1:100 ratio). Amylin functions to slow gastric emptying and promote satiety. **2. Why other options are incorrect:** * **Option A & B:** While both are produced by beta cells, selecting either individually is incomplete. Since both are co-secreted with insulin, Option C is the most accurate choice. **3. High-Yield Clinical Pearls for NEET-PG:** * **C-peptide Clinical Utility:** Unlike insulin, C-peptide undergoes negligible first-pass metabolism by the liver and has a longer half-life. It is used as a **marker of endogenous insulin production**. It helps distinguish Type 1 DM (low/absent C-peptide) from Type 2 DM (normal/high C-peptide) and is used in the workup of insulinoma. * **Amylin & Pathology:** In Type 2 Diabetes, amylin can aggregate to form **amyloid deposits** in the pancreas, which is a classic histopathological finding. * **Pramlintide:** This is a synthetic analogue of amylin used as an adjunct treatment in both Type 1 and Type 2 DM to control postprandial glucose.

Question 349: What are the metabolic effects of insulin on adipose tissue?

A. Accelerated transport of glucose (Correct Answer)
B. Decreased glucose phosphorylation
C. Decreased lipoprotein lipase
D. Increased cyclic AMP

Explanation: ### Explanation Insulin is an anabolic hormone that promotes energy storage. In adipose tissue, its primary role is to facilitate glucose uptake and promote lipogenesis while inhibiting lipolysis. **Why Option A is Correct:** Insulin stimulates the **GLUT-4** (glucose transporter type 4) translocation from intracellular vesicles to the plasma membrane of adipocytes. This leads to the **accelerated transport of glucose** into the cell. Once inside, glucose provides the glycerol backbone (via α-glycerophosphate) necessary for the esterification of fatty acids into triglycerides. **Analysis of Incorrect Options:** * **B. Decreased glucose phosphorylation:** Incorrect. Insulin actually **increases** glucose phosphorylation by stimulating **hexokinase**, ensuring that glucose entering the cell is trapped and utilized for metabolism. * **C. Decreased lipoprotein lipase:** Incorrect. Insulin **increases** the activity of **endothelial lipoprotein lipase (LPL)**. This enzyme breaks down circulating chylomicrons and VLDLs into free fatty acids, which are then taken up by adipocytes for storage. * **D. Increased cyclic AMP:** Incorrect. Insulin **decreases** intracellular cAMP levels by activating phosphodiesterase. Lower cAMP levels inhibit **hormone-sensitive lipase (HSL)**, thereby decreasing lipolysis (the breakdown of stored fat). **NEET-PG High-Yield Pearls:** * **GLUT-4** is the only insulin-dependent glucose transporter; it is found specifically in **adipose tissue and skeletal muscle**. * Insulin is the most potent **antilipolytic hormone** because it inhibits hormone-sensitive lipase. * In **Diabetes Mellitus**, insulin deficiency leads to increased HSL activity, resulting in high levels of circulating free fatty acids and potential ketoacidosis.

Question 350: Which of the following decreases the secretion of both insulin and glucagon?

A. Epinephrine
B. Somatostatin (Correct Answer)
C. Increased blood glucose
D. None of the above

Explanation: ### Explanation The correct answer is **Somatostatin**. **Mechanism of Action:** Somatostatin is a potent inhibitory hormone produced by the **delta ($\delta$) cells** of the pancreatic islets (as well as the hypothalamus and GI tract). In the pancreas, it acts via **paracrine signaling** to inhibit the secretion of both **Insulin** (from beta cells) and **Glucagon** (from alpha cells). It acts through G-protein coupled receptors (SSTRs) that decrease intracellular cAMP and inhibit calcium influx, effectively "shutting down" islet cell output. **Analysis of Incorrect Options:** * **Epinephrine:** Stimulates glucagon secretion (to increase blood glucose for "fight or flight") but **inhibits** insulin secretion (primarily via $\alpha_2$-adrenergic receptors). It does not decrease both. * **Increased blood glucose:** This is the primary physiological stimulus for **insulin** secretion. While it inhibits glucagon, it significantly increases insulin levels. * **None of the above:** Incorrect, as Somatostatin is the classic "universal inhibitor." **NEET-PG High-Yield Pearls:** * **The "Universal Inhibitor":** Somatostatin inhibits not only pancreatic hormones but also Growth Hormone (GH), Thyroid Stimulating Hormone (TSH), and various GI hormones (Gastrin, CCK, Secretin). * **Clinical Application:** **Octreotide**, a synthetic somatostatin analog, is used clinically to treat acromegaly, carcinoid tumors, and acute variceal bleeding (by reducing splanchnic blood flow). * **Islet Cell Arrangement:** Remember the flow of blood in the islet is usually from the center (Beta cells) to the periphery (Alpha/Delta cells), allowing insulin to inhibit glucagon directly.

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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