Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 441: Where is ADH formed?

A. Pituitary gland
B. Hypothalamus (Correct Answer)
C. Pineal gland
D. None of the above

Explanation: **Explanation:** **1. Why the Correct Answer is Right:** Antidiuretic Hormone (ADH), also known as **Vasopressin**, is synthesized in the cell bodies of magnocellular neurons located in the **Hypothalamus**. Specifically, it is primarily produced in the **Supraoptic nucleus (SON)** (approx. 5/6th) and to a lesser extent in the **Paraventricular nucleus (PVN)** (approx. 1/6th). Once synthesized, ADH is packaged into secretory vesicles and transported down the axons (hypothalamo-hypophyseal tract) to the posterior pituitary for storage and eventual release. **2. Why the Incorrect Options are Wrong:** * **A. Pituitary Gland:** While the **Posterior Pituitary (Neurohypophysis)** stores and releases ADH into the systemic circulation, it does *not* synthesize the hormone. It serves merely as a reservoir. * **C. Pineal Gland:** This gland is responsible for the secretion of **Melatonin**, which regulates circadian rhythms. It has no role in ADH production or water balance. * **D. None of the above:** Incorrect, as the hypothalamus is the definitive site of synthesis. **3. NEET-PG High-Yield Clinical Pearls:** * **Carrier Protein:** ADH is transported along axons bound to a specific carrier protein called **Neurophysin II**. (Oxytocin uses Neurophysin I). * **Primary Stimulus:** The most potent stimulus for ADH release is an increase in **plasma osmolarity** (detected by osmoreceptors in the OVLT/SFO of the hypothalamus). * **Clinical Correlation:** A deficiency in ADH synthesis or release leads to **Central Diabetes Insipidus**, characterized by polyuria and polydipsia. * **V2 Receptors:** ADH acts on V2 receptors in the **Collecting Ducts** of the kidney to insert Aquaporin-2 channels, facilitating water reabsorption.

Question 442: Which of the following can cause hypertension and heart disease?

A. Elevated blood levels of aldosterone and renin resulting from an atherosclerotic plaque in a renal artery. (Correct Answer)
B. Hyperprolactinemia due to a pituitary tumor.
C. Acromegaly due to a GH-producing tumor that developed in adulthood.
D. Cushing syndrome due to an adrenal tumor.

Explanation: **Explanation:** **Correct Option: A (Renovascular Hypertension)** An atherosclerotic plaque in the renal artery causes **Renal Artery Stenosis (RAS)**. This leads to decreased renal perfusion pressure, which triggers the Juxtaglomerular (JG) apparatus to secrete **Renin**. Renin converts Angiotensinogen to Angiotensin I, which is then converted to **Angiotensin II** (a potent vasoconstrictor). Angiotensin II also stimulates the adrenal cortex to release **Aldosterone**, causing sodium and water retention. This "Renin-Angiotensin-Aldosterone System" (RAAS) activation results in secondary hypertension and subsequent hypertensive heart disease. **Analysis of Incorrect Options:** * **B. Hyperprolactinemia:** Primarily causes galactorrhea, amenorrhea, and infertility. It does not have a direct pathophysiological link to hypertension or heart disease. * **C. Acromegaly:** While GH excess *can* cause hypertension and cardiomyopathy, the question asks for the "best" fit based on the provided key. In many clinical scenarios, renovascular causes (Option A) are classic examples of secondary hypertension driven by a dual hormonal surge (Renin + Aldosterone). * **D. Cushing Syndrome:** Cortisol excess causes hypertension via mineralocorticoid effects and increased vascular sensitivity to catecholamines. However, in Cushing syndrome, **Renin levels are typically suppressed** due to volume expansion, unlike Option A where both Renin and Aldosterone are elevated. **NEET-PG High-Yield Pearls:** * **Goldblatt Kidney:** The experimental model for renovascular hypertension. * **Bruit:** A systolic-diastolic abdominal bruit is a specific clinical sign for Renal Artery Stenosis. * **Drug Contraindication:** ACE inhibitors are contraindicated in **bilateral** renal artery stenosis as they can precipitate acute renal failure by decreasing GFR. * **Conn’s Syndrome vs. RAS:** In Primary Hyperaldosteronism (Conn’s), Aldosterone is high but **Renin is low**. In RAS (Secondary), both are high.

Question 443: What is the effect of parathyroid hormone?

A. Decreases bone resorption
B. Increases bone resorption (Correct Answer)
C. Enhances phosphate reabsorption from the kidney
D. Decreases calcium reabsorption from the kidney

Explanation: **Explanation:** Parathyroid Hormone (PTH) is the primary regulator of calcium and phosphate homeostasis in the body. Its main objective is to **increase serum calcium levels** in response to hypocalcemia. 1. **Why Option B is Correct:** PTH stimulates **bone resorption** by indirectly activating osteoclasts (via the RANKL pathway on osteoblasts). This process breaks down the bone matrix, releasing calcium and phosphate into the extracellular fluid (ECF). 2. **Why Option A is Incorrect:** Decreasing bone resorption is the function of **Calcitonin**, which acts as a physiological antagonist to PTH to lower serum calcium. 3. **Why Option C is Incorrect:** PTH actually **decreases phosphate reabsorption** (causes phosphaturia) by inhibiting the sodium-phosphate co-transporter in the **Proximal Convoluted Tubule (PCT)**. This is crucial to prevent calcium-phosphate precipitation in the blood as calcium levels rise. 4. **Why Option D is Incorrect:** PTH **increases calcium reabsorption**, specifically acting on the **Distal Convoluted Tubule (DCT)** of the kidney to minimize calcium loss in urine. **High-Yield NEET-PG Pearls:** * **Kidney Action:** PTH stimulates the enzyme **1-alpha-hydroxylase** in the kidneys, which converts Vitamin D to its active form, Calcitriol ($1,25-(OH)_2D_3$). * **GI Action:** PTH has no direct effect on the gut; it increases intestinal calcium absorption **indirectly** via Vitamin D. * **Mnemonic:** PTH = **P**hosphate **T**rash **H**ormone (it "trashes" phosphate in the urine).

Question 444: A lab technician notes that prolactin levels in a patient's blood sample are high. This could be due to all of the following except:

A. Sleep
B. Pregnancy
C. Stress
D. L-dopa (Correct Answer)

Explanation: **Explanation:** The regulation of **Prolactin (PRL)** is unique among anterior pituitary hormones because it is under **tonic inhibition** by the hypothalamus. The primary Prolactin-Inhibiting Factor (PIF) is **Dopamine**. **Why L-dopa is the correct answer:** L-dopa is a precursor to dopamine. When administered, it increases dopamine levels in the brain. Since dopamine acts on the D2 receptors of the lactotrophs in the anterior pituitary to inhibit prolactin secretion, **L-dopa causes a decrease in prolactin levels**, not an increase. Therefore, it is the exception in this list. **Analysis of incorrect options:** * **Sleep:** Prolactin secretion is pulsatile and follows a diurnal rhythm. Levels rise significantly during sleep (especially non-REM sleep), peaking in the early morning hours. * **Pregnancy:** This is a physiological cause of hyperprolactinemia. High levels of estrogen during pregnancy stimulate the hypertrophy and hyperplasia of lactotrophs, leading to increased prolactin production to prepare the breasts for lactation. * **Stress:** Prolactin is considered a "stress hormone." Physical or emotional stress (including exercise, surgery, or hypoglycemia) triggers the release of prolactin via the suppression of dopamine and the release of Prolactin Releasing Factors (PRFs) like TRH. **NEET-PG High-Yield Pearls:** 1. **Dopamine Agonists** (e.g., Bromocriptine, Cabergoline) are the drugs of choice for Prolactinomas because they mimic dopamine's inhibitory effect. 2. **Antipsychotics** (D2 antagonists) are a common pharmacological cause of hyperprolactinemia/galactorrhea. 3. **TRH** (Thyrotropin-Releasing Hormone) stimulates prolactin; thus, **Primary Hypothyroidism** is a clinical cause of high prolactin levels.

Question 445: Calcitonin is secreted from which of the following cell types?

A. Ancinar cells of thyroid
B. Chief cells of parathyroid
C. C cells of thyroid (Correct Answer)
D. Oxyphil cells of parathyroids

Explanation: **Explanation:** **Correct Answer: C. C cells of thyroid** Calcitonin is a 32-amino acid peptide hormone synthesized and secreted by the **Parafollicular cells (also known as C cells)** of the thyroid gland. These cells are neuroendocrine in origin (derived from the **ultimobranchial body** of the neural crest) and are located in the connective tissue between the thyroid follicles. The primary stimulus for calcitonin secretion is **hypercalcemia**. It acts to lower plasma calcium levels by inhibiting osteoclast activity (decreasing bone resorption) and increasing calcium excretion in the kidneys. **Analysis of Incorrect Options:** * **A. Acinar cells of thyroid:** This is a distractor term. The thyroid consists of **Follicular cells**, which secrete T3 and T4. Acinar cells are typically found in the exocrine pancreas or salivary glands. * **B. Chief cells of parathyroid:** These cells secrete **Parathyroid Hormone (PTH)**, which is the functional antagonist to calcitonin (it increases serum calcium). * **D. Oxyphil cells of parathyroid:** These are larger, eosinophilic cells found in the parathyroid gland. Their exact function is unknown, though they increase in number with age and do not secrete PTH or calcitonin. **High-Yield Clinical Pearls for NEET-PG:** * **Tumor Marker:** Calcitonin is the definitive tumor marker for **Medullary Thyroid Carcinoma (MTC)**, which arises from C cells. * **Hypocalcemic Effect:** Unlike PTH, calcitonin is not essential for day-to-day calcium homeostasis in humans, but it is used pharmacologically to treat **Paget’s disease** and severe hypercalcemia. * **Opposing Actions:** Remember the "3-Ds" of Calcitonin: It **D**eposits calcium in bone, **D**ecreases serum calcium, and **D**erives from C cells.

Question 446: Anterior pituitary gland secretes all of the following except:

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

Explanation: **Explanation:** The anterior pituitary gland (adenohypophysis) synthesizes and secretes six major peptide hormones. The correct answer is **GnRH (Gonadotropin-Releasing Hormone)** because it is a **hypothalamic hormone**, not a pituitary one. **1. Why GnRH is the correct answer:** GnRH is synthesized by neurons in the preoptic area of the **hypothalamus**. It is released into the hypophyseal portal system, where it travels to the anterior pituitary to stimulate the secretion of LH and FSH. Any hormone ending in "-Releasing Hormone" (e.g., TRH, CRH, GHRH) or "-Inhibiting Hormone" (e.g., Somatostatin, Dopamine) is produced by the hypothalamus. **2. Why the other options are incorrect:** * **GH (Growth Hormone):** Secreted by **Somatotrophs** (the most numerous cell type in the anterior pituitary). * **TSH (Thyroid Stimulating Hormone):** Secreted by **Thyrotrophs** to stimulate the thyroid gland. * **FSH (Follicle Stimulating Hormone):** Secreted by **Gonadotrophs** along with LH. **High-Yield NEET-PG Pearls:** * **Embryology:** The anterior pituitary develops from **Rathke’s pouch** (oral ectoderm), while the posterior pituitary develops from **neuroectoderm** (down-growth of the hypothalamus). * **Posterior Pituitary:** It does **not** synthesize hormones; it only stores and releases **Oxytocin** and **ADH (Vasopressin)**, which are produced in the paraventricular and supraoptic nuclei of the hypothalamus, respectively. * **Acidophils vs. Basophils:** Remember the mnemonic **"GPA"** (Growth hormone and Prolactin are secreted by Acidophils) and **"B-FLAT"** (Basophils secrete FSH, LH, ACTH, and TSH).

Question 447: Where is GLUT4 primarily found?

A. Endothelium
B. Liver
C. Cardiac muscle (Correct Answer)
D. Lens

Explanation: **Explanation:** The correct answer is **Cardiac muscle**. GLUT4 is the primary **insulin-dependent** glucose transporter found in the body. Its translocation from intracellular vesicles to the cell membrane is triggered by insulin binding to its receptor or by muscle contraction. **Why Cardiac Muscle is Correct:** GLUT4 is specifically expressed in tissues that require regulated glucose uptake for energy storage or high-metabolic demand. These include: 1. **Skeletal muscle** 2. **Cardiac muscle** 3. **Adipose tissue** **Analysis of Incorrect Options:** * **A. Endothelium:** Glucose uptake in vascular endothelial cells is primarily mediated by **GLUT1**, which is insulin-independent and ensures a basal glucose supply. * **B. Liver:** The liver primarily utilizes **GLUT2**. This is a high-capacity, low-affinity transporter that allows for rapid bidirectional flux of glucose, essential for the liver's role in glucose sensing and glycogen storage. * **C. Lens:** The lens and cornea rely on **GLUT1** and **GLUT3** for insulin-independent glucose uptake to maintain transparency and metabolic homeostasis. **High-Yield NEET-PG Pearls:** * **GLUT1:** Found in RBCs, Blood-Brain Barrier (BBB), and the heart (basal uptake). * **GLUT2:** Found in Liver, Pancreatic beta cells (glucose sensor), and Kidney (PCT). * **GLUT3:** Found in Neurons (highest affinity for glucose) and Placenta. * **GLUT4:** The **only** insulin-dependent transporter. * **GLUT5:** Primarily a **fructose** transporter found in the small intestine and spermatozoa. * **SGLT1/2:** These are active transporters (Sodium-Glucose Co-transporters) found in the gut and kidneys, unlike the GLUT family which facilitates passive diffusion.

Question 448: What effect does insulin have on cellular ion transport?

A. Sodium entry into cells
B. Potassium exit from cells
C. Sodium exit and potassium entry into cells
D. Potassium entry into cells (Correct Answer)

Explanation: **Explanation:** Insulin plays a critical role in maintaining electrolyte balance by stimulating the **Na⁺-K⁺ ATPase pump** located in the cell membranes of skeletal muscle, adipose tissue, and the liver. 1. **Why Option D is correct:** Insulin increases the activity and translocation of the Na⁺-K⁺ ATPase pump. This pump actively transports **three Sodium (Na⁺) ions out** of the cell and **two Potassium (K⁺) ions into** the cell. By shifting potassium from the extracellular fluid (ECF) into the intracellular fluid (ICF), insulin effectively lowers serum potassium levels. 2. **Why other options are incorrect:** * **Option A:** While insulin can influence sodium transporters (like the Na-H exchanger), its primary and most clinically significant acute effect is on potassium sequestration. * **Option B:** Potassium exit (efflux) occurs during cell lysis or acidosis, which is the opposite of insulin’s action. * **Option C:** While the Na⁺-K⁺ pump does move sodium out, the question focuses on the most characteristic and clinically relevant ionic shift associated with insulin therapy, which is the inward movement of potassium. **Clinical Pearls for NEET-PG:** * **Management of Hyperkalemia:** Because insulin shifts K⁺ into cells, a combination of **Insulin + Dextrose** (to prevent hypoglycemia) is a standard emergency treatment for hyperkalemia. * **DKA Management:** In Diabetic Ketoacidosis, patients may have high serum K⁺ but low total body K⁺. Starting insulin therapy will cause a rapid drop in serum K⁺, necessitating careful monitoring and replacement to avoid life-threatening hypokalemia. * **Mechanism:** Insulin binds to its tyrosine kinase receptor, leading to the phosphorylation of IRS-1, which eventually activates the Na⁺-K⁺ ATPase pump.

Question 449: Which of the following is a mineralocorticoid?

A. Cortisone
B. Estrogen
C. Testosterone
D. Aldosterone (Correct Answer)

Explanation: **Explanation:** The adrenal cortex is divided into three zones, each secreting specific steroid hormones (mnemonic: **GFR** – **G**lomerulosa, **F**asciculata, **R**eticularis). 1. **Aldosterone (Correct Answer):** Produced by the **Zona Glomerulosa**, aldosterone is the primary mineralocorticoid in humans. Its main function is to maintain electrolyte balance and blood pressure by promoting **sodium reabsorption** and **potassium/hydrogen ion secretion** in the distal convoluted tubules and collecting ducts of the kidney. 2. **Incorrect Options:** * **Cortisone:** This is a **Glucocorticoid** (along with Cortisol) produced primarily by the Zona Fasciculata. It is involved in glucose metabolism and the stress response. * **Estrogen & Testosterone:** These are **Sex Steroids**. While small amounts of androgens (like DHEA) are produced in the Zona Reticularis of the adrenal cortex, the primary sources of these hormones are the ovaries and testes, respectively. **High-Yield NEET-PG Pearls:** * **Rate-limiting step:** The conversion of cholesterol to pregnenolone by the enzyme **Desmolase** (stimulated by ACTH). * **Regulation:** Unlike glucocorticoids, Aldosterone is primarily regulated by the **Renin-Angiotensin System (RAS)** and plasma **Potassium levels**, rather than ACTH. * **Conn’s Syndrome:** Primary hyperaldosteronism characterized by hypertension, hypokalemia, and metabolic alkalosis. * **Spironolactone:** A potassium-sparing diuretic that acts as a competitive antagonist to the mineralocorticoid receptor.

Question 450: Temperature above which normal hormonal actions fail?

A. 45°C (Correct Answer)
B. 35°C
C. 30°C
D. 25°C

Explanation: **Explanation:** The correct answer is **45°C**. This question tests the fundamental understanding of the biochemical nature of hormones and enzyme kinetics within the human body. **1. Why 45°C is correct:** Most hormones are either proteins (e.g., Insulin, Growth Hormone) or steroids that interact with proteinaceous receptors. Proteins maintain a specific three-dimensional conformation (folding) to function. At temperatures exceeding **45°C**, proteins undergo **denaturation**. This process breaks the hydrogen and disulfide bonds that maintain the protein's shape, rendering the hormone or its receptor biologically inactive. Once the structural integrity is lost, the "lock and key" mechanism of hormone-receptor binding fails. **2. Why the other options are incorrect:** * **35°C:** This is slightly below normal body temperature (37°C). While metabolic processes may slow down (mild hypothermia), hormonal actions do not fail; in fact, the body increases hormonal output (like T3/T4 and Adrenaline) to generate heat. * **30°C & 25°C:** These represent moderate to severe hypothermia. While physiological processes are significantly depressed and enzymatic rates decrease (Q10 effect), the molecular structure of the hormones remains intact. They do not "fail" due to structural breakdown, but rather due to a systemic decrease in metabolic rate. **High-Yield Clinical Pearls for NEET-PG:** * **Optimal Temperature:** Most human enzymes and hormones function optimally at **37°C**. * **Protein Denaturation:** This is generally an irreversible process at high temperatures, which is why hyperpyrexia (fever >41.5°C) is a medical emergency. * **Q10 Coefficient:** This principle states that for every 10°C temperature increase, the rate of biological reactions roughly doubles, but only until the point of protein denaturation (~45°C). * **Thermostability:** Steroid hormones are generally more heat-stable than peptide hormones, but their **receptors** are proteins and will fail at high temperatures.

Practice by Chapter

Principles of Endocrine Regulation

Practice Questions

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

Practice Questions

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