Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 551: Zollinger-Ellison syndrome is due to a tumor of which of the following cell types?

A. Alpha cells
B. Beta cells
C. PP cells
D. G-cells (Correct Answer)

Explanation: **Explanation:** **Zollinger-Ellison Syndrome (ZES)** is characterized by the development of a gastrin-secreting tumor, known as a **Gastrinoma**. 1. **Why G-cells are correct:** Gastrinomas originate from **G-cells**, which are neuroendocrine cells. While G-cells are normally found in the gastric antrum and duodenum, these tumors most commonly arise in the "Gastrinoma Triangle" (bounded by the confluence of the cystic and common bile ducts, the junction of the second and third portions of the duodenum, and the neck of the pancreas). The ectopic secretion of gastrin leads to hypergastrinemia, which causes massive hypersecretion of gastric acid, resulting in severe, recurrent peptic ulcers and secretory diarrhea. 2. **Why other options are incorrect:** * **Alpha cells:** These pancreatic islet cells secrete **glucagon**. A tumor of these cells is a Glucagonoma (presents with necrolytic migratory erythema and diabetes). * **Beta cells:** These secrete **insulin**. A tumor here is an Insulinoma (presents with Whipple’s triad of hypoglycemia). * **PP cells (F-cells):** These secrete **pancreatic polypeptide**. While they can form tumors (PPomas), they do not cause the acid-peptic symptoms seen in ZES. **Clinical Pearls for NEET-PG:** * **Diagnosis:** Best initial screening test is **Fasting Serum Gastrin** (>1000 pg/mL is diagnostic). The most sensitive provocative test is the **Secretin Stimulation Test** (Secretin normally inhibits gastrin but paradoxically increases it in ZES). * **Association:** Approximately 25% of ZES cases are associated with **Multiple Endocrine Neoplasia type 1 (MEN1)**. * **Location:** Most gastrinomas are found in the **duodenum** rather than the pancreas.

Question 552: Where are osmoreceptors located?

A. Anterior hypothalamus (Correct Answer)
B. Renal medulla
C. Carotid body
D. Atrial chamber

Explanation: ### Explanation **1. Why Anterior Hypothalamus is Correct:** Osmoreceptors are specialized sensory neurons primarily located in the **Anterior Hypothalamus**, specifically in the circumventricular organs: the **Organum Vasculosum of the Lamina Terminalis (OVLT)** and the **Subfornical Organ (SFO)**. These areas lack a blood-brain barrier, allowing them to detect changes in plasma osmolality. When osmolality increases (e.g., dehydration), these receptors shrink, firing signals to the **Supraoptic and Paraventricular nuclei** to stimulate the release of **Antidiuretic Hormone (ADH/Vasopressin)** and trigger the thirst mechanism. **2. Why Other Options are Incorrect:** * **Renal Medulla:** While the kidney is the target organ for ADH (acting on V2 receptors in the collecting ducts), it does not sense systemic osmolality. It maintains a hypertonic interstitium to facilitate water reabsorption. * **Carotid Body:** These are **peripheral chemoreceptors** located at the bifurcation of the common carotid artery. They sense changes in arterial $PO_2$, $PCO_2$, and $pH$, not osmolality. * **Atrial Chamber:** The atria contain **baroreceptors (stretch receptors)**. They sense changes in blood volume/pressure and release **Atrial Natriuretic Peptide (ANP)** in response to stretch, rather than sensing osmolality. **3. High-Yield Clinical Pearls for NEET-PG:** * **Sensitivity:** Osmoreceptors are highly sensitive; a change of as little as **1%** in plasma osmolality triggers ADH release. * **Primary Stimulus:** The most potent stimulus for ADH release is increased osmolality, whereas the most potent stimulus for thirst is also osmolality. * **Volume vs. Osmolality:** While osmolality is the primary regulator, a **5-10% decrease in blood volume** (sensed by baroreceptors) can also trigger ADH release, even if osmolality is normal. * **Location Shortcut:** Remember **"OVLT"** as the primary site for osmoreception.

Question 553: Which of the following hormones has a cytoplasmic receptor?

A. Epinephrine
B. Insulin
C. FSH
D. Cortisol (Correct Answer)

Explanation: **Explanation:** The location of a hormone receptor is primarily determined by the hormone's chemical nature (solubility). **1. Why Cortisol is Correct:** Cortisol is a **steroid hormone** derived from cholesterol. Being lipophilic (lipid-soluble), it easily diffuses through the lipid bilayer of the plasma membrane. Once inside the cell, it binds to specific **cytoplasmic receptors** (Type 1 Nuclear Receptors). The hormone-receptor complex then translocates into the nucleus, where it binds to Hormone Response Elements (HRE) on DNA to regulate gene transcription. **2. Why the Other Options are Incorrect:** * **Epinephrine (Option A):** A catecholamine derived from tyrosine. It is water-soluble and cannot cross the cell membrane; it binds to **G-protein coupled receptors (GPCRs)** on the cell surface. * **Insulin (Option B):** A peptide hormone. It binds to a specific **Enzyme-linked receptor** (Receptor Tyrosine Kinase) located on the cell membrane. * **FSH (Option C):** A glycoprotein (peptide) hormone. Like other pituitary hormones, it is large and polar, requiring a **cell surface GPCR** to initiate its action via the cAMP second messenger system. **3. High-Yield NEET-PG Clinical Pearls:** * **Cytoplasmic Receptors:** Primarily used by Steroids (Glucocorticoids, Mineralocorticoids, Androgens, Progesterone). * **Nucleoplasmic (Nuclear) Receptors:** Primarily used by **Thyroid hormones (T3/T4)**, Retinoic acid, and Vitamin D. Note: Though T3/T4 are amino acid derivatives, they act like steroids. * **Mnemonic for Cell Surface Receptors:** All peptide hormones + Catecholamines. * **Exception:** Estrogen receptors are predominantly found in the **nucleus**, unlike most other steroids which start in the cytoplasm.

Question 554: A 35-year-old man presents with a thyroid nodule. Laboratory studies reveal elevated serum calcitonin and normal serum calcium. Which of the following mechanisms best explains the normal calcium levels in this patient despite high serum calcitonin levels?

A. Concurrent parathyroid adenoma
B. Concurrent parathyroid hyperplasia
C. High levels of calcitonin downregulate its receptor (Correct Answer)
D. Increase in parathyroid hormone in response to hypocalcemia

Explanation: ### Explanation **Correct Option: C (High levels of calcitonin downregulate its receptor)** The patient likely has **Medullary Thyroid Carcinoma (MTC)**, which arises from the parafollicular C-cells and secretes excessive **calcitonin**. Under normal physiological conditions, calcitonin lowers serum calcium by inhibiting osteoclast activity. However, in patients with MTC, serum calcium levels remain **normal**. The primary mechanism for this is the **downregulation (internalization) of calcitonin receptors** on target cells (osteoclasts and renal tubular cells) in response to chronically high hormone levels. This renders the body "resistant" to the calcium-lowering effects of calcitonin. Additionally, calcitonin is a relatively weak regulator of calcium homeostasis in humans compared to PTH and Vitamin D. --- ### Why Other Options are Incorrect: * **Options A & B:** While MTC is associated with **MEN 2A** (which includes parathyroid hyperplasia/adenoma), these conditions would typically cause **hypercalcemia**, not "normal" calcium levels. Furthermore, parathyroid involvement is a separate pathology and does not explain the lack of calcitonin effect. * **Option D:** While a transient drop in calcium could theoretically trigger a compensatory rise in PTH, this is not the primary reason for long-term normocalcemia in MTC. The receptor downregulation is the definitive physiological adaptation. --- ### NEET-PG High-Yield Pearls: * **Medullary Thyroid Carcinoma (MTC):** Derived from **neural crest cells** (C-cells). It is a component of **MEN 2A and 2B** (associated with the *RET* proto-oncogene). * **Tumor Marker:** Calcitonin is used for both diagnosis and monitoring recurrence of MTC. * **Amyloid Stroma:** Histology of MTC characteristically shows nests of cells in a prominent **amyloid stroma** (formed by procalcitonin). * **Calcitonin Paradox:** Despite being a "calcium-lowering hormone," neither calcitonin deficiency (after total thyroidectomy) nor calcitonin excess (in MTC) significantly alters serum calcium levels in humans.

Question 555: What is the action of parathormone on the phosphate level in the blood?

A. Decreases phosphate level (Correct Answer)
B. Increases phosphate level
C. No effect
D. Variable effect

Explanation: **Explanation:** Parathyroid Hormone (PTH) is the primary regulator of calcium and phosphate homeostasis. Its net effect on blood phosphate is a **decrease (hypophosphatemia)**. **Why Option A is correct:** PTH acts on the **Proximal Convoluted Tubule (PCT)** of the kidney to inhibit the sodium-phosphate cotransporter (NaPi-IIa). By inhibiting this transporter, PTH decreases the reabsorption of phosphate from the glomerular filtrate, leading to increased urinary excretion of phosphate (**phosphaturia**). Although PTH increases phosphate absorption from the bone (via osteoclasts) and the gut (via Vitamin D activation), the potent phosphaturic effect at the kidney overrides these, resulting in a net decrease in serum phosphate levels. **Why other options are incorrect:** * **Option B:** While PTH increases phosphate release from bone, the renal excretion is much more significant, preventing an increase in blood levels. * **Options C & D:** PTH has a consistent, potent physiological effect on phosphate handling; it is neither variable nor negligible. **High-Yield NEET-PG Pearls:** * **Mnemonic:** "PTH: **P**hosphate **T**hrashing **H**ormone" (It thrashes phosphate out of the body via urine). * **Second Messenger:** PTH acts via the **cAMP** pathway in the renal tubules. An increase in urinary cAMP is a diagnostic marker for PTH activity. * **Calcium Effect:** In contrast to phosphate, PTH **increases** serum calcium by increasing distal tubule reabsorption and bone resorption. * **Clinical Correlation:** In **Hypoparathyroidism**, you will see low calcium and **high** phosphate levels.

Question 556: In Cushing syndrome, which of the following hormones is characteristically elevated?

A. Cortisol (Correct Answer)
B. Aldosterone
C. Epinephrine
D. Norepinephrine

Explanation: **Explanation:** **Cushing Syndrome** is a clinical condition resulting from chronic exposure to excessive levels of glucocorticoids, primarily **Cortisol**. Cortisol is a steroid hormone produced by the *zona fasciculata* of the adrenal cortex. The elevation can be ACTH-dependent (e.g., Pituitary Adenoma/Cushing Disease or Ectopic ACTH) or ACTH-independent (e.g., Adrenal Adenoma or exogenous steroid use). * **Why Cortisol is Correct:** Cortisol is the hallmark hormone of this syndrome. Its elevation leads to the classic metabolic effects: proteolysis (muscle wasting), gluconeogenesis (hyperglycemia), and lipogenesis (central obesity). * **Why Incorrect Options are Wrong:** * **Aldosterone:** Produced by the *zona glomerulosa*. While high cortisol can sometimes cross-react with mineralocorticoid receptors, primary elevation of aldosterone characterizes **Conn Syndrome**, not Cushing Syndrome. * **Epinephrine & Norepinephrine:** These are catecholamines produced by the **adrenal medulla**. Their elevation is characteristic of **Pheochromocytoma**, presenting with episodic hypertension and palpitations rather than the cushingoid habitus. **High-Yield Clinical Pearls for NEET-PG:** * **Screening Tests:** 24-hour urinary free cortisol, Low-dose Dexamethasone Suppression Test (LDDST), or Late-night salivary cortisol. * **Cushing Disease vs. Syndrome:** Cushing *Disease* specifically refers to a **Pituitary Adenoma** secreting ACTH. * **Clinical Signs:** Buffalo hump, moon facies, abdominal purple striae, and proximal muscle weakness. * **Electrolytes:** Hypercortisolism often leads to **Hypokalemic Metabolic Alkalosis** (due to mineralocorticoid cross-reactivity at high concentrations).

Question 557: Acromegaly is due to excess of:

A. Somatomedin
B. Growth hormone (Correct Answer)
C. Somatostatin
D. Insulin

Explanation: **Explanation:** **Acromegaly** is a clinical syndrome resulting from the excessive secretion of **Growth Hormone (GH)**, typically due to a pituitary adenoma, occurring **after the fusion of epiphyseal plates** (post-puberty). 1. **Why Growth Hormone is correct:** GH stimulates the liver to produce Insulin-like Growth Factor-1 (IGF-1). In adults, excess GH leads to the overgrowth of membranous bones (causing frontal bossing and macrognathia) and soft tissues (leading to acral enlargement, visceromegaly, and macroglossia). If this excess occurs before epiphyseal fusion, it results in **Gigantism**. 2. **Why other options are incorrect:** * **Somatomedin (IGF-1):** While GH acts via Somatomedins, the primary pathology is the hypersecretion of GH itself. IGF-1 levels are used for diagnosis, but the "excess" originates from GH. * **Somatostatin (GHIH):** This is a GH-inhibiting hormone produced by the hypothalamus. An excess of somatostatin would lead to a deficiency of GH, not Acromegaly. * **Insulin:** Although GH has anti-insulin effects (diabetogenic), insulin excess causes hypoglycemia and is associated with insulinomas, not skeletal overgrowth. **High-Yield Clinical Pearls for NEET-PG:** * **Best Screening Test:** Serum IGF-1 levels (more stable than GH). * **Gold Standard Diagnostic Test:** Glucose Challenge Test (Failure to suppress GH levels below 1 ng/mL after 75g oral glucose). * **Most Common Cause:** Somatotroph adenoma of the anterior pituitary. * **Characteristic Features:** Spaded hands, increased hat/shoe size, carpal tunnel syndrome, and bitemporal hemianopia (due to optic chiasm compression).

Question 558: Which of the following hormones is stored the longest within a cell?

A. Insulin
B. T3 (Correct Answer)
C. PTH
D. Testosterone

Explanation: **Explanation:** The duration for which a hormone is stored within a cell depends on its chemical nature and the storage mechanism of the gland. **Why T3 is the Correct Answer:** Thyroid hormones (T3 and T4) are unique because they are stored **extracellularly** in the follicular lumen as part of the **thyroglobulin** molecule (colloid). This storage mechanism is exceptionally efficient, allowing the thyroid gland to store enough hormone to supply the body’s requirements for **2 to 3 months**. This is the longest storage duration of any hormone in the human body. **Why Other Options are Incorrect:** * **Insulin (Option A):** As a peptide hormone, insulin is stored in cytosolic secretory granules. However, the pancreas typically stores only about a **5-day supply**, and it is rapidly released in response to glucose. * **PTH (Option B):** Parathyroid hormone is also a peptide hormone stored in granules within chief cells. Its storage is minimal, usually lasting only a **few hours**, as it is synthesized and secreted almost immediately in response to low serum calcium. * **Testosterone (Option D):** Steroid hormones are **not stored** to any significant degree. They are highly lipophilic and would leak through the cell membrane. Instead, they are synthesized de novo from cholesterol precursors on demand. **High-Yield NEET-PG Pearls:** * **Thyroid Exception:** Most endocrine glands store small amounts of hormones; the thyroid is the only gland that stores large quantities in an inactive form (colloid). * **Clinical Correlation:** This long storage explains why patients starting anti-thyroid drugs (like Carbimazole) take several weeks to become euthyroid—the body must first deplete the pre-stored 2-3 month supply of colloid. * **Steroid Rule:** Remember: "Steroids are made on demand, not stored."

Question 559: Ovum is released due to which of the following hormones?

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

Explanation: **Explanation:** The correct answer is **LH (Luteinizing Hormone)**. Ovulation is triggered by a dramatic rise in LH levels, known as the **LH surge**. **Why LH is correct:** Approximately 24–36 hours before ovulation, high levels of estrogen (secreted by the dominant Graafian follicle) exert positive feedback on the anterior pituitary. This results in a massive release of LH. The LH surge is essential because it: 1. Resumes meiosis I in the oocyte (completing it to reach Metaphase II). 2. Stimulates the production of prostaglandins and proteolytic enzymes (like collagenase) that weaken the follicular wall (stigma). 3. Triggers the physical rupture of the follicle and the release of the ovum. **Why other options are incorrect:** * **FSH (Follicle Stimulating Hormone):** While FSH rises slightly during the mid-cycle surge and is crucial for the recruitment and growth of follicles in the early follicular phase, it is not the primary trigger for the release of the ovum. * **Prolactin:** High levels of prolactin actually inhibit the pulsatile release of GnRH, thereby suppressing FSH and LH. This often leads to anovulation (seen in lactational amenorrhea or prolactinomas). * **HCG (Human Chorionic Gonadotropin):** HCG is produced by the syncytiotrophoblast after implantation to maintain the corpus luteum. While HCG is structurally similar to LH and is used *pharmacologically* to induce ovulation in infertility treatments, it is not the endogenous hormone responsible for natural ovulation. **NEET-PG High-Yield Pearls:** * **Timing:** Ovulation occurs **10–12 hours after the LH peak** and **32–36 hours after the onset of the LH surge**. * **Meiotic Arrest:** The primary oocyte is arrested in **Prophase I (Dictyotene stage)** until the LH surge; it then arrests again in **Metaphase II** until fertilization. * **Mittelschmerz:** The clinical term for mid-cycle pelvic pain associated with ovulation.

Question 560: Negative Basal Metabolic Rate (BMR) is observed with which of the following?

A. Pituitary disturbance
B. Thyroid disturbance (Correct Answer)
C. Parathyroid disturbance
D. All of the above

Explanation: **Explanation:** The **Basal Metabolic Rate (BMR)** is the minimum amount of energy required by the body to maintain vital functions (like breathing and circulation) at complete physical and mental rest. The **Thyroid gland** is the primary regulator of BMR. **1. Why Thyroid Disturbance is Correct:** Thyroid hormones (T3 and T4) directly regulate the metabolic activity of almost all tissues in the body by increasing oxygen consumption and mitochondrial activity. * **Hypothyroidism:** Leads to a **negative (decreased) BMR**, often falling 30% to 40% below normal. This results in symptoms like weight gain, cold intolerance, and bradycardia. * **Hyperthyroidism:** Leads to an increased BMR, often 50% to 100% above normal. **2. Why Other Options are Incorrect:** * **Pituitary Disturbance:** While the pituitary gland secretes TSH (which stimulates the thyroid), a pituitary disturbance only affects BMR *indirectly* via the thyroid axis. "Thyroid disturbance" is the more specific and direct physiological answer. * **Parathyroid Disturbance:** Parathyroid hormone (PTH) regulates calcium and phosphate homeostasis. It has no direct clinical impact on the body’s basal metabolic rate. **High-Yield Clinical Pearls for NEET-PG:** * **Surface Area Rule:** BMR is more closely related to surface area than to body weight. * **Specific Dynamic Action (SDA):** Proteins have the highest SDA (30%), meaning they increase metabolic rate significantly during digestion. * **Factors increasing BMR:** Fever (12% increase per 1°C), Pregnancy, Catecholamines (Epinephrine), and Male gender (due to testosterone). * **Gold Standard:** The most accurate way to measure BMR is via indirect calorimetry (measuring oxygen consumption).

Practice by Chapter

Principles of Endocrine Regulation

Practice Questions

Hypothalamus and Pituitary Gland

Practice Questions

Thyroid Physiology

Practice Questions

Adrenal Cortex and Medulla

Practice Questions

Pancreatic Hormones and Glucose Metabolism

Practice Questions

Calcium and Phosphate Homeostasis

Practice Questions

Growth Hormone and Growth Factors

Practice Questions

Endocrine Regulation of Metabolism

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Hormone Receptors and Signaling

Practice Questions

Assessment of Endocrine Function

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