Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 591: Insulin stimulates glucose entry in which of the following tissues?

A. Cardiac muscles (Correct Answer)
B. Smooth muscles
C. Brain
D. Intestines

Explanation: **Explanation:** The entry of glucose into cells is mediated by a family of glucose transporters (GLUT). The correct answer is **Cardiac muscles** because they primarily express **GLUT-4**, which is the only insulin-dependent glucose transporter. 1. **Why Cardiac Muscle is Correct:** Insulin binds to its receptor, triggering a signaling cascade that causes the translocation of GLUT-4 vesicles from the cytoplasm to the cell membrane. This mechanism is specific to **skeletal muscle, cardiac muscle, and adipose tissue**. Without insulin, these tissues are relatively impermeable to glucose. 2. **Why Other Options are Incorrect:** * **Brain:** Most neurons utilize **GLUT-3**, while the blood-brain barrier uses **GLUT-1**. Both are insulin-independent, ensuring the brain receives a constant glucose supply regardless of insulin levels. * **Intestines:** Glucose absorption in the intestinal mucosa occurs via **SGLT-1** (secondary active transport with Sodium) on the apical membrane and **GLUT-2** (facilitated diffusion) on the basolateral membrane. Neither requires insulin. * **Smooth Muscles:** While some smooth muscles may show minor insulin sensitivity, they primarily rely on insulin-independent pathways compared to the robust GLUT-4 response seen in cardiac and skeletal muscles. **High-Yield NEET-PG Pearls:** * **GLUT-1:** Basal uptake (RBCs, BBB, Placenta). * **GLUT-2:** Bidirectional (Liver, Pancreatic beta cells, Kidney, Small Intestine). Acts as a "glucose sensor." * **GLUT-4:** Insulin-dependent (Skeletal muscle, Cardiac muscle, Adipose tissue). * **Exercise** can also trigger GLUT-4 translocation in skeletal muscle via an insulin-independent pathway (AMPK activation), which is why exercise helps manage Type 2 Diabetes.

Question 592: What is true about insulin action?

A. Causes gluconeogenesis
B. Not useful for growth and development
C. Required for the transport of glucose, amino acids, K+, and Na+ (Correct Answer)
D. Catabolic hormone

Explanation: **Explanation:** Insulin is the primary **anabolic hormone** of the body, secreted by the beta cells of the Islets of Langerhans. Its primary role is to lower blood glucose levels and promote the storage of nutrients. **Why Option C is Correct:** Insulin facilitates the transport of various substances across cell membranes: * **Glucose:** It increases glucose uptake in skeletal muscle and adipose tissue by mobilizing **GLUT-4** transporters. * **Amino Acids:** It stimulates the uptake of amino acids (valine, leucine, isoleucine, tyrosine, and phenylalanine) into muscles, promoting protein synthesis. * **Electrolytes:** Insulin stimulates the **Na+-K+ ATPase pump**, leading to the influx of **Potassium (K+)** and **Sodium (Na+)** into cells. This is the physiological basis for using insulin-dextrose therapy to treat hyperkalemia. **Analysis of Incorrect Options:** * **A & D:** Insulin is an **anabolic** hormone, not catabolic. It **inhibits gluconeogenesis** (formation of glucose from non-carbohydrate sources) and glycogenolysis, while promoting glycogenesis and lipogenesis. * **B:** Insulin is **essential for growth and development**. It has a synergistic effect with Growth Hormone (GH). In fact, insulin-like growth factors (IGFs) are structural homologs of proinsulin. **High-Yield Clinical Pearls for NEET-PG:** * **GLUT-4** is the only insulin-dependent glucose transporter (found in heart, skeletal muscle, and adipose tissue). * **Brain, Liver, and RBCs** do not require insulin for glucose uptake (Insulin-independent). * **Hypokalemia** is a significant side effect of insulin therapy due to the intracellular shift of potassium. * Insulin inhibits **Hormone Sensitive Lipase (HSL)**, thereby preventing lipolysis and ketogenesis.

Question 593: The major regulator of platelet production is the hormone thrombopoietin (THPO), which is produced by which organ(s)?

A. Kidneys
B. Liver
C. Liver and kidneys (Correct Answer)
D. Spleen and lymph nodes

Explanation: **Explanation:** **Thrombopoietin (THPO)** is a glycoprotein hormone that serves as the primary regulator of megakaryocyte differentiation and platelet production. It acts by binding to the **c-Mpl receptor** on the surface of hematopoietic stem cells and megakaryocytes. 1. **Why Option C is correct:** The **liver** is the primary site of thrombopoietin production (constituting approximately 90% of the circulating levels), where it is produced constitutively by parenchymal cells and sinusoidal endothelial cells. The **kidneys** (specifically the proximal convoluted tubule cells) act as the secondary site of production. Small amounts are also produced by the smooth muscle of the bone marrow. 2. **Why other options are incorrect:** * **Option A & B:** While both organs produce THPO, selecting only one is incomplete. The liver is the dominant source, but the renal contribution is physiologically significant. * **Option D:** The spleen and lymph nodes are involved in platelet storage and immune function, respectively, but they do not synthesize thrombopoietin. **High-Yield Clinical Pearls for NEET-PG:** * **Regulation:** Unlike Erythropoietin (which is regulated by hypoxia/gene transcription), THPO levels are largely regulated by **platelet mass**. Platelets have c-Mpl receptors that internalize and degrade THPO; thus, in thrombocytopenia, less THPO is degraded, leading to higher circulating levels that stimulate the bone marrow. * **Clinical Correlation:** In **liver cirrhosis**, decreased THPO production is a major cause of thrombocytopenia. * **Drug Link:** **Romiplostim** and **Eltrombopag** are TPO receptor agonists used to treat ITP and aplastic anemia.

Question 594: Which of the following hormones does not utilize the adenylyl cyclase-cAMP pathway as a second messenger system?

A. TSH
B. Epinephrine
C. Insulin (Correct Answer)
D. Glucagon

Explanation: **Explanation:** The correct answer is **Insulin**. The mechanism of action of a hormone depends on its chemical nature and the type of receptor it binds to. **1. Why Insulin is the correct answer:** Insulin (along with IGF-1 and Growth Hormone) does not use the cAMP pathway. Instead, it binds to a **Receptor Tyrosine Kinase (RTK)**, which is a transmembrane receptor with intrinsic enzymatic activity. Upon binding, the receptor undergoes autophosphorylation, activating the **MAP kinase** pathway (for growth/gene expression) and the **PI3K/Akt** pathway (for metabolic effects like glucose transport via GLUT-4). **2. Why the other options are incorrect:** * **TSH (Thyroid Stimulating Hormone):** As a glycoprotein hormone, it binds to G-protein coupled receptors (GPCRs) that activate the **Gs protein**, stimulating adenylyl cyclase to increase intracellular cAMP. * **Epinephrine:** When acting on **$\beta$-adrenergic receptors** ($\beta_1, \beta_2, \beta_3$), epinephrine activates the Gs-adenylyl cyclase-cAMP pathway. (Note: While it uses the $IP_3/DAG$ pathway via $\alpha_1$ receptors, it is a classic example of a cAMP-utilizing hormone). * **Glucagon:** This is the "prototypical" cAMP-mediated hormone. It binds to GPCRs in the liver to activate adenylyl cyclase, leading to glycogenolysis. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for cAMP hormones:** "FLAT ChAMP" (FSH, LH, ACTH, TSH, CRH, hCG, ADH (V2), MSH, PTH, Glucagon, Calcitonin). * **ANP and Nitric Oxide (NO)** utilize **cGMP** as a second messenger. * **Steroid and Thyroid hormones** are lipophilic and utilize **intracellular/nuclear receptors** to directly alter gene transcription.

Question 595: Adrenal insufficiency is not associated with which of the following?

A. Hyponatremia
B. Hyperkalemia
C. Hypoglycemia
D. Metabolic alkalosis (Correct Answer)

Explanation: **Explanation:** Adrenal insufficiency (Addison’s disease) is characterized by the deficiency of adrenal cortical hormones: **Aldosterone** and **Cortisol**. **Why Metabolic Alkalosis is the Correct Answer:** Aldosterone normally acts on the distal convoluted tubules and collecting ducts to reabsorb sodium and water while secreting Potassium ($K^+$) and Hydrogen ions ($H^+$). In adrenal insufficiency, the lack of aldosterone leads to decreased $H^+$ secretion. This results in the retention of $H^+$ ions, leading to **Metabolic Acidosis** (specifically Normal Anion Gap Metabolic Acidosis), not alkalosis. **Analysis of Incorrect Options:** * **A. Hyponatremia:** Lack of aldosterone leads to "salt wasting" (failure to reabsorb $Na^+$), resulting in low serum sodium levels. * **B. Hyperkalemia:** Without aldosterone, the kidney cannot effectively excrete potassium, leading to its accumulation in the blood. * **C. Hypoglycemia:** Cortisol is a counter-regulatory hormone that promotes gluconeogenesis and antagonizes insulin. Its deficiency leads to impaired glucose production and increased insulin sensitivity, causing low blood sugar. **High-Yield Clinical Pearls for NEET-PG:** * **Primary vs. Secondary:** Hyperpigmentation (due to high ACTH/POMC) and mineralocorticoid deficiency (electrolyte imbalances) are features of **Primary** Adrenal Insufficiency (Addison’s), but are absent in Secondary (Pituitary) insufficiency. * **The "Addisonian Triad":** Hyponatremia, Hyperkalemia, and Metabolic Acidosis. * **Eosinophilia:** A common but often overlooked hematological finding in adrenal insufficiency. * **Gold Standard Test:** ACTH Stimulation Test (Cosyntropin test).

Question 596: Prostaglandin was discovered from which bodily fluid?

A. Tear
B. Saliva
C. Seminal fluid (Correct Answer)
D. Blood

Explanation: **Explanation:** **Correct Option: C (Seminal fluid)** Prostaglandins were first discovered and isolated from human **seminal fluid** in the 1930s. The discovery is credited to **Ulf von Euler**, who mistakenly believed these lipid compounds were produced exclusively by the **prostate gland**, hence the name "Prostaglandin." However, it was later discovered that the majority of prostaglandins in semen are actually secreted by the **seminal vesicles**. **Analysis of Incorrect Options:** * **A (Tear) & B (Saliva):** While prostaglandins are ubiquitous and can be found in almost all nucleated cells and various body fluids (acting as autacoids), they were not discovered in these fluids. Their concentration in tears and saliva is significantly lower than in semen. * **D (Blood):** Prostaglandins are present in the blood, particularly during inflammatory responses or platelet aggregation (e.g., Thromboxane A2). However, they function primarily as local hormones with a very short half-life in circulation, making blood an unlikely source for their initial discovery. **High-Yield NEET-PG Pearls:** * **Precursor:** All prostaglandins are derived from **Arachidonic acid** (a 20-carbon polyunsaturated fatty acid) via the **Cyclooxygenase (COX) pathway**. * **Function in Semen:** Prostaglandins in seminal fluid react with female cervical mucus to make it more receptive to sperm and induce retrograde peristaltic contractions in the uterus/fallopian tubes to aid sperm transport. * **Inhibition:** **NSAIDs** (like Aspirin) work by inhibiting the COX enzyme, thereby blocking prostaglandin synthesis. * **Alprostadil (PGE1):** Used clinically to maintain a patent ductus arteriosus in neonates with cyanotic heart disease.

Question 597: Osteoclasts have a specific receptor for which hormone?

A. Parathyroid hormone
B. Calcitonin (Correct Answer)
C. Thyroxin
D. Vitamin D3

Explanation: **Explanation:** The correct answer is **Calcitonin**. This is a classic high-yield concept in bone physiology. **1. Why Calcitonin is Correct:** Osteoclasts are the primary target cells for calcitonin. Calcitonin receptors are G-protein coupled receptors located directly on the cell membrane of **osteoclasts**. When calcitonin binds to these receptors, it rapidly inhibits the resorptive activity of osteoclasts and decreases their number, leading to a reduction in bone resorption and a decrease in serum calcium levels. **2. Why the Other Options are Incorrect:** * **Parathyroid Hormone (PTH):** Contrary to popular belief, osteoclasts do **not** have PTH receptors. PTH acts primarily on **osteoblasts**. When PTH binds to osteoblasts, it triggers the release of **RANKL** (Receptor Activator of Nuclear Factor kappa-B Ligand), which then binds to RANK receptors on osteoclast precursors to stimulate bone resorption. * **Vitamin D3 (Calcitriol):** Like PTH, Vitamin D3 receptors (VDR) are primarily found on **osteoblasts**. Vitamin D3 promotes osteoclast differentiation indirectly via the RANKL pathway. * **Thyroxin:** While thyroid hormones influence bone turnover, they do not have specific, primary regulatory receptors on osteoclasts that govern calcium homeostasis in the same direct manner as calcitonin. **Clinical Pearls for NEET-PG:** * **The "Indirect" Rule:** Remember that most bone-resorbing factors (PTH, Vitamin D3, IL-1, TNF) act **indirectly** on osteoclasts via osteoblasts. Calcitonin is the major exception that acts **directly**. * **Marker of Osteoclasts:** Tartrate-resistant acid phosphatase (TRAP) is a key histological marker for osteoclasts. * **Therapeutic Use:** Due to its direct inhibitory effect on osteoclasts, synthetic calcitonin (Salmon calcitonin) is used clinically to treat Paget’s disease and severe hypercalcemia.

Question 598: Which of the following conditions leads to an increase in the secretion of antidiuretic hormone (ADH)?

A. Hypervolemia
B. Hypertension
C. Hypovolemia (Correct Answer)
D. Decreased osmolarity

Explanation: ### Explanation **Correct Answer: C. Hypovolemia** **Mechanism of ADH Secretion:** Antidiuretic Hormone (ADH), also known as Vasopressin, is synthesized in the hypothalamus (supraoptic and paraventricular nuclei) and secreted by the posterior pituitary. Its primary function is to maintain water balance and blood pressure. **Hypovolemia** (decreased blood volume) triggers ADH release through **low-pressure baroreceptors** located in the great veins and atria. When blood volume drops by more than 10%, these receptors decrease their firing rate, which removes the tonic inhibition on the hypothalamus, leading to a potent stimulation of ADH secretion. This is known as the **volumetric control** of ADH. --- ### Analysis of Incorrect Options: * **A. Hypervolemia:** Increased blood volume stretches the atria, increasing baroreceptor firing and stimulating the release of Atrial Natriuretic Peptide (ANP). This **inhibits** ADH secretion to promote water excretion. * **B. Hypertension:** High blood pressure stimulates **high-pressure baroreceptors** in the carotid sinus and aortic arch. This inhibits the vasomotor center and suppresses ADH release to lower blood pressure. * **D. Decreased Osmolarity:** ADH is extremely sensitive to plasma osmolarity. A decrease in osmolarity (hypoosmolarity) causes osmoreceptors in the anterior hypothalamus to swell, which **inhibits** ADH secretion to prevent further water retention. --- ### High-Yield NEET-PG Pearls: * **Primary Stimulus:** The most *sensitive* stimulus for ADH is an increase in **plasma osmolarity** (even a 1% change). * **Potent Stimulus:** **Hypovolemia/Hypotension** is a more *potent* stimulus than osmolarity; in cases of severe volume loss, ADH will be secreted even if osmolarity is low (volume overrides osmolarity). * **V1 vs. V2 Receptors:** ADH acts on **V1 receptors** (Gq) for vasoconstriction and **V2 receptors** (Gs) in the collecting ducts for water reabsorption via **Aquaporin-2** channels. * **SIADH:** Characterized by excessive ADH, leading to hyponatremia and concentrated urine.

Question 599: Which of the following hormones is released from the hypothalamus?

A. Orexin
B. Cortisol releasing hormone (Correct Answer)
C. Neuropeptide
D. Ghrelin

Explanation: The hypothalamus acts as the primary neuroendocrine control center, secreting "releasing" and "inhibiting" hormones that regulate the anterior pituitary gland via the hypophyseal portal system. ### **Explanation of the Correct Answer** **B. Cortisol Releasing Hormone (CRH):** This is the correct answer. CRH (also known as Corticotropin-Releasing Hormone) is synthesized by the parvocellular neurosecretory cells of the **paraventricular nucleus (PVN)** of the hypothalamus. It stimulates the anterior pituitary to release Adrenocorticotropic Hormone (ACTH), which in turn stimulates the adrenal cortex to produce cortisol. ### **Analysis of Incorrect Options** * **A. Orexin (Hypocretin):** While produced in the lateral hypothalamus, it functions primarily as a **neurotransmitter** regulating wakefulness and appetite, rather than a classical endocrine hormone released into the portal circulation. * **C. Neuropeptide Y (NPY):** This is a potent orexigenic (appetite-stimulating) peptide. While found in the arcuate nucleus of the hypothalamus, it is classified as a **neuromodulator/neurotransmitter** involved in energy homeostasis. * **D. Ghrelin:** Known as the "hunger hormone," it is primarily secreted by the **P/D1 cells of the stomach fundus**. It acts on the hypothalamus to increase appetite but is not produced there. ### **High-Yield Clinical Pearls for NEET-PG** * **The "Releasing" Rule:** Almost all hormones with "Releasing" in their name (GHRH, TRH, GnRH, CRH) originate from the hypothalamus. * **Posterior Pituitary Connection:** ADH (Vasopressin) and Oxytocin are *synthesized* in the hypothalamus (Supraoptic and Paraventricular nuclei) but *stored and released* by the posterior pituitary. * **Dopamine:** It is the primary **Prolactin-Inhibiting Hormone (PIH)** secreted by the hypothalamus. A deficiency in hypothalamic dopamine leads to hyperprolactinemia.

Question 600: Which of the following is an orexigenic hormone?

A. Melanocyte-stimulating hormone
B. Cholecystokinin
C. Ghrelin (Correct Answer)
D. Leptin

Explanation: ***Ghrelin (Correct Answer)*** - Ghrelin is often termed the "hunger hormone" as it acts primarily as a powerful **orexigenic signal**, stimulating appetite and food intake. - It is primarily produced by specialized cells in the **stomach**, and its levels typically rise before meals. *Melanocyte-stimulating hormone (Incorrect)* - MSH, specifically **alpha-MSH**, is released from **proopiomelanocortin (POMC) neurons** in the hypothalamus. - It acts to suppress appetite and is classified as an **anorexigenic hormone**. *Cholecystokinin (Incorrect)* - CCK is a **satiety hormone** released in response to fat and protein entering the duodenum and jejunum. - It acts on the brainstem and peripheral nerves to inhibit gastric emptying and induce short-term feelings of **satiety** (anorexigenic effect). *Leptin (Incorrect)* - Leptin is produced mainly by **adipocytes (fat cells)** and signals the brain about long-term energy stores. - High circulating levels of leptin act on the hypothalamus to **inhibit appetite** and increase energy expenditure, making it an **anorexigenic hormone (satiety signal)**.

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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