Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 121: What is the primary action of insulin?

A. Gluconeogenesis
B. Increased glucose uptake in muscle (Correct Answer)
C. Glycogenolysis
D. Increased glucose uptake in endothelium

Explanation: **Explanation:** Insulin is the body’s primary anabolic hormone, secreted by the β-cells of the pancreatic islets. Its fundamental role is to lower blood glucose levels by promoting glucose utilization and storage while inhibiting glucose production. **Why Option B is correct:** Insulin facilitates glucose entry into specific tissues—primarily **skeletal muscle** and **adipose tissue**—by triggering the translocation of **GLUT-4** (an insulin-dependent glucose transporter) from intracellular vesicles to the cell membrane. Since skeletal muscle constitutes a large percentage of body mass, its increased glucose uptake is the primary mechanism for lowering postprandial blood glucose. **Why the other options are incorrect:** * **A & C (Gluconeogenesis and Glycogenolysis):** These are catabolic processes that *increase* blood glucose. Insulin **inhibits** these processes in the liver. Glucagon and epinephrine are the hormones that stimulate them. * **D (Glucose uptake in endothelium):** Glucose uptake in the vascular endothelium (as well as the brain, liver, and RBCs) is mediated by **GLUT-1** or **GLUT-2**, which are **insulin-independent**. These tissues do not require insulin to take up glucose. **High-Yield Clinical Pearls for NEET-PG:** * **GLUT-4** is the only insulin-dependent transporter. * **Exercise** can also trigger GLUT-4 translocation in muscles, which is why physical activity helps manage Diabetes Mellitus. * **Brain and RBCs** rely on GLUT-1/3 and do not require insulin for glucose uptake, protecting vital organs during hypoglycemia. * **SGLT-1/2** are involved in active transport (sodium-dependent) in the gut and kidneys, unlike the facilitated diffusion of GLUT transporters.

Question 122: Which of the following is NOT an action of glucagon?

A. Gluconeogenic
B. Lipolytic
C. Ketogenic
D. None of the above (Correct Answer)

Explanation: **Explanation:** Glucagon is a peptide hormone secreted by the **alpha cells of the pancreas**. Its primary physiological role is to prevent hypoglycemia by acting as a "hormone of starvation," increasing blood glucose and fuel availability. **Why "None of the above" is correct:** All three listed actions (Gluconeogenesis, Lipolysis, and Ketogenesis) are primary physiological effects of glucagon. Since the question asks which is NOT an action, and all are indeed actions, "None of the above" is the correct choice. * **Option A: Gluconeogenic:** Glucagon is a potent stimulator of gluconeogenesis (forming glucose from non-carbohydrate sources like amino acids and glycerol) in the liver. It also stimulates glycogenolysis (breakdown of glycogen). * **Option B: Lipolytic:** Glucagon activates hormone-sensitive lipase in adipose tissue, leading to the breakdown of triglycerides into free fatty acids and glycerol, providing alternative fuel sources. * **Option C: Ketogenic:** By increasing the delivery of fatty acids to the liver and shifting hepatic metabolism toward fatty acid oxidation (via inhibition of Malonyl-CoA), glucagon promotes the formation of ketone bodies (acetoacetate and beta-hydroxybutyrate). **High-Yield NEET-PG Pearls:** 1. **Mechanism of Action:** Glucagon acts via a **G-protein coupled receptor (Gs)**, which activates Adenylyl Cyclase to increase **cAMP** levels. 2. **The Insulin/Glucagon Ratio:** The metabolic state of the body is determined more by the ratio of these two hormones than by the absolute concentration of either. 3. **Clinical Use:** Glucagon is used as an emergency treatment for severe hypoglycemia and as an antidote for **Beta-blocker poisoning** (due to its ability to increase cAMP in cardiac myocytes bypassing the beta-receptor). 4. **Inhibitor:** Somatostatin (from delta cells) inhibits the secretion of both insulin and glucagon.

Question 123: Parathormone secretion is stimulated by?

A. Increased serum calcium
B. Decreased serum calcium (Correct Answer)
C. Increased serum potassium
D. Decreased serum potassium

Explanation: **Explanation:** The secretion of **Parathyroid Hormone (PTH)** is primarily regulated by a negative feedback loop involving ionized serum calcium levels. **Why Option B is Correct:** The chief cells of the parathyroid gland possess **Calcium-Sensing Receptors (CaSR)** on their surface. When serum ionized calcium levels drop (**Hypocalcemia**), these receptors are less stimulated, which triggers the rapid release of pre-formed PTH and increases the synthesis of new hormone. PTH then acts to restore calcium levels by increasing bone resorption, enhancing renal calcium reabsorption, and stimulating the synthesis of Calcitriol (Vitamin D3) to increase intestinal absorption. **Why Other Options are Incorrect:** * **Option A:** Increased serum calcium (**Hypercalcemia**) activates the CaSR, which inhibits PTH secretion to prevent further calcium rise. * **Options C & D:** Serum potassium levels do not have a direct regulatory effect on PTH secretion. Potassium is primarily regulated by Aldosterone and Insulin. **High-Yield Clinical Pearls for NEET-PG:** * **Magnesium’s Role:** While hypocalcemia is the primary stimulus, **mild hypomagnesemia** also stimulates PTH. However, **severe, chronic hypomagnesemia** actually inhibits PTH release and causes PTH resistance, leading to refractory hypocalcemia. * **Phosphate:** Hyperphosphatemia indirectly stimulates PTH by lowering ionized calcium and inhibiting Vitamin D activation. * **Target Organs:** PTH acts directly on the **Bone** (RANKL pathway) and **Kidney** (distal tubule), but its effect on the **Intestine** is indirect (via Vitamin D). * **PTH and Phosphorus:** Remember the phrase: *"PTH stands for Phosphate Trashing Hormone"* because it decreases renal phosphate reabsorption (causing phosphaturia).

Question 124: Sucking stimulates the release of which of the following hormones from the anterior pituitary?

A. Prolactin
B. Oxytocin (Correct Answer)
C. Somatostatin
D. Somatomedin

Explanation: **Explanation:** The correct answer is **Oxytocin**. This question tests the understanding of the **Milk Ejection Reflex (Let-down reflex)**. **1. Why Oxytocin is Correct:** Sucking by the infant triggers sensory receptors in the nipple, sending afferent impulses via the spinal cord to the paraventricular and supraoptic nuclei of the **hypothalamus**. This stimulates the posterior pituitary to release **Oxytocin**. Oxytocin causes the contraction of **myoepithelial cells** surrounding the mammary alveoli, resulting in the ejection of milk into the ducts. *Note: While the question asks for "Anterior Pituitary," it is a common examiner "trap" or error in medical entrance exams. Among the choices, Oxytocin is the hormone most directly stimulated by the mechanical act of sucking to facilitate immediate milk flow.* **2. Why Other Options are Incorrect:** * **Prolactin:** While sucking also stimulates Prolactin release, it is responsible for **milk production (synthesis)** rather than immediate ejection. Prolactin is secreted by the anterior pituitary. * **Somatostatin:** This is Growth Hormone Inhibiting Hormone (GHIH); it inhibits the release of GH and TSH and is not involved in lactation. * **Somatomedin:** Also known as Insulin-like Growth Factor (IGF-1), these are produced by the liver in response to Growth Hormone. **High-Yield Clinical Pearls for NEET-PG:** * **Prolactin vs. Oxytocin:** Prolactin = Milk *Production* (Anterior Pituitary). Oxytocin = Milk *Ejection* (Posterior Pituitary). * **Neuroendocrine Reflex:** The milk ejection reflex is a classic example of a neuroendocrine reflex. * **Uterine Effect:** Oxytocin also causes uterine contractions, which helps in **postpartum involution** of the uterus during breastfeeding. * **Inhibition:** The milk ejection reflex can be inhibited by psychological stress or fear (due to increased catecholamines).

Question 125: Males and females show differences in the age of onset of puberty. What explains the difference in the age of onset of puberty amongst males?

A. Increased Activin-A levels
B. Decreased Follistatin levels
C. Increased Inhibin levels (Correct Answer)
D. Easily releasable FSH pool

Explanation: **Explanation:** The onset of puberty is governed by the reactivation of the **Hypothalamic-Pituitary-Gonadal (HPG) axis**. While both sexes follow a similar pattern of increasing GnRH pulsatility, the specific hormonal dynamics differ. **Why "Increased Inhibin levels" is correct:** In males, the onset of puberty is closely linked to the maturation of **Sertoli cells**. As these cells mature under the influence of FSH, they begin to secrete **Inhibin B**. Studies have shown that in boys, there is a significant rise in serum Inhibin B levels during early puberty, which serves as a marker of Sertoli cell proliferation and tubular growth. This increase in Inhibin B is one of the earliest endocrine changes observed in males, often preceding the significant rise in testosterone. **Analysis of Incorrect Options:** * **A & B (Activin and Follistatin):** While Activin stimulates and Follistatin inhibits FSH secretion, their systemic levels do not serve as the primary physiological trigger or the distinguishing factor for the timing of male puberty in the same way Inhibin B does. * **D (Easily releasable FSH pool):** This is more characteristic of the **female** HPG axis. In females, the pituitary has a more "readily releasable" pool of FSH and LH, leading to an earlier clinical onset of puberty (thelarche) compared to males. **High-Yield NEET-PG Pearls:** * **First sign of puberty in males:** Increase in testicular volume (≥ 4 ml), measured by a Prader Orchidometer. * **First sign of puberty in females:** Thelarche (breast bud development). * **Inhibin B** is the primary form in males (marker of spermatogenesis), while **Inhibin A** is more relevant in the female menstrual cycle (secreted by the dominant follicle/corpus luteum). * **Leptin:** A critical "permissive" factor; a minimum body fat percentage is required to initiate the HPG axis.

Question 126: In evaluating the role of the autonomic nervous system related to urinary incontinence that developed in a 67-year-old man after prostatectomy, it is determined that the sympathetic nerves are injured. What is the natural hormone in the catecholamine pathway?

A. Norepinephrine (Correct Answer)
B. Dopamine
C. Vasoactive intestinal peptide (VIP)
D. Isoproterenol

Explanation: **Explanation:** The sympathetic nervous system plays a crucial role in urinary continence by stimulating **alpha-1 adrenergic receptors** at the bladder neck and internal urethral sphincter, causing contraction and preventing urine leakage. In this clinical scenario, post-prostatectomy injury to the sympathetic nerves leads to stress incontinence. **1. Why Norepinephrine is Correct:** Norepinephrine (NE) is the primary **postganglionic neurotransmitter** of the sympathetic nervous system. In the catecholamine biosynthetic pathway (Tyrosine → L-Dopa → Dopamine → Norepinephrine → Epinephrine), NE is the direct "natural hormone" and neurotransmitter responsible for mediating sympathetic effects on the bladder and internal sphincter. **2. Why the other options are incorrect:** * **Dopamine (B):** While it is a natural catecholamine and a precursor to NE, it is not the primary neurotransmitter of the sympathetic nerves supplying the bladder. * **Vasoactive Intestinal Peptide (C):** VIP is a neuropeptide involved in non-adrenergic, non-cholinergic (NANC) transmission, primarily causing smooth muscle relaxation (e.g., in the gut or penis), not sympathetic-mediated sphincter contraction. * **Isoproterenol (D):** This is a **synthetic** catecholamine (potent beta-agonist). It is not naturally produced by the human body. **High-Yield Clinical Pearls for NEET-PG:** * **Micturition Control:** Sympathetic (T11-L2) = Filling/Storage (Relax detrusor via $\beta_3$, contract sphincter via $\alpha_1$). Parasympathetic (S2-S4) = Emptying (Contract detrusor via $M_3$). * **Rate-limiting step in Catecholamine synthesis:** Tyrosine Hydroxylase. * **PNMT Enzyme:** Converts Norepinephrine to Epinephrine; it is primarily found in the adrenal medulla, not in sympathetic nerve endings.

Question 127: Acromegaly is a disorder of:

A. Excess growth hormone secretion during adulthood (Correct Answer)
B. Excess thyroxine secretion
C. Excess ACTH secretion
D. Excess FSH secretion

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** (adulthood). Because the long bones can no longer grow in length, the excess GH stimulates the overgrowth of cancellous bones, soft tissues, and viscera. This leads to characteristic features like frontal bossing, macroglossia, enlargement of hands and feet (spade-like), and prognathism. **Analysis of Options:** * **Option A (Correct):** GH excess in adults causes Acromegaly. If the excess occurs *before* epiphyseal fusion (childhood), it results in **Gigantism**. * **Option B (Incorrect):** Excess thyroxine (T4) secretion leads to **Hyperthyroidism** (e.g., Graves' disease), characterized by weight loss, tachycardia, and heat intolerance. * **Option C (Incorrect):** Excess ACTH secretion (usually from a pituitary tumor) leads to **Cushing’s Disease**, characterized by central obesity, moon facies, and hypertension. * **Option D (Incorrect):** Excess FSH is rare but may be seen in primary gonadal failure or specific gonadotroph adenomas; it does not cause the skeletal changes seen in acromegaly. **High-Yield Clinical Pearls for NEET-PG:** * **Best Screening Test:** Serum **IGF-1** levels (more stable than pulsatile GH). * **Gold Standard Diagnostic Test:** **Glucose Suppression Test** (Failure to suppress GH <1 ng/mL after 75g oral glucose). * **Most Common Cause of Death:** Cardiovascular disease (Cardiomyopathy/Hypertension). * **Associated Metabolic Finding:** Secondary Diabetes Mellitus (GH is a counter-regulatory/diabetogenic hormone).

Question 128: Which of the following is characteristic of a hyperthyroid state?

A. Increased protein synthesis
B. Decreased glycolysis
C. Lipolysis (Correct Answer)
D. Increased cholesterol

Explanation: **Explanation:** Thyroid hormones ($T_3$ and $T_4$) are the primary regulators of the body’s Basal Metabolic Rate (BMR). In a hyperthyroid state, the body enters a **hypermetabolic phase** characterized by the rapid breakdown of energy stores. **Why Lipolysis is Correct:** Thyroid hormones stimulate **lipolysis** by increasing the activity of hormone-sensitive lipase in adipose tissue. This leads to the mobilization of free fatty acids and glycerol into the plasma. While thyroid hormones also stimulate lipogenesis, the rate of lipid catabolism (lipolysis) significantly outweighs synthesis in hyperthyroidism, leading to a decrease in fat stores and body weight. **Analysis of Incorrect Options:** * **A. Increased protein synthesis:** While physiological levels of thyroid hormone are anabolic, **excessive** levels (hyperthyroidism) are **catabolic**. This leads to increased protein breakdown (proteolysis), resulting in negative nitrogen balance and muscle wasting (thyrotoxic myopathy). * **B. Decreased glycolysis:** Hyperthyroidism **increases** all aspects of carbohydrate metabolism, including glycolysis, gluconeogenesis, and glucose absorption from the GI tract, to meet the high energy demands. * **D. Increased cholesterol:** Thyroid hormones increase the expression of **LDL receptors** in the liver. In hyperthyroidism, this leads to rapid clearance of cholesterol from the blood, resulting in **hypocholesterolemia**. **High-Yield Clinical Pearls for NEET-PG:** * **Weight Loss despite Polyphagia:** A classic hallmark of hyperthyroidism due to increased BMR. * **Cholesterol Paradox:** Hypocholesterolemia is seen in hyperthyroidism, while hypercholesterolemia is a key diagnostic marker for hypothyroidism. * **Beta-Adrenergic Sensitivity:** Thyroid hormones increase the number and sensitivity of $\beta$-adrenergic receptors, explaining the tachycardia and tremors treated with Propranolol.

Question 129: Which of the following statements is true about estrogen?

A. Inhibits osteoblasts.
B. Decreases the expression of LDL receptors.
C. Is a C19 steroid.
D. Estradiol is the most potent among estradiol, estriol, and estrone. (Correct Answer)

Explanation: **Explanation:** **1. Why Option D is Correct:** Estrogens are a group of steroid hormones, primarily consisting of **Estradiol (E2), Estrone (E1), and Estriol (E3)**. Among these, **Estradiol (E2)** is the most potent and the predominant estrogen in premenopausal women. In terms of relative potency: **Estradiol > Estrone > Estriol**. Estradiol has the highest affinity for estrogen receptors (ERα and ERβ), making it the primary driver of female secondary sexual characteristics and reproductive functions. **2. Why Other Options are Incorrect:** * **Option A:** Estrogen actually **stimulates osteoblasts** and inhibits osteoclasts (by increasing OPG and decreasing RANKL). This is why estrogen deficiency in menopause leads to osteoporosis. * **Option B:** Estrogen **increases the expression of LDL receptors** in the liver. This enhances the clearance of LDL from the blood, providing a cardioprotective effect by lowering "bad" cholesterol. * **Option C:** Estrogens are **C18 steroids** (18 carbon atoms). C19 steroids refer to Androgens (e.g., Testosterone), and C21 steroids refer to Progesterone and Adrenal Corticosteroids. **3. NEET-PG High-Yield Pearls:** * **Source of Estrogen:** Produced by **Granulosa cells** of the ovary via the enzyme **Aromatase** (which converts androgens to estrogens). * **Predominance:** * **Estradiol (E2):** Reproductive years. * **Estrone (E1):** Post-menopause (produced in peripheral adipose tissue). * **Estriol (E3):** Pregnancy (produced by the feto-placental unit). * **Biphasic Feedback:** Estrogen typically exerts negative feedback on GnRH/FSH, but a sustained high level (LH surge) triggers **positive feedback**, leading to ovulation.

Question 130: Rapid infusion of insulin can cause which of the following electrolyte imbalances?

A. Hyperkalemia
B. Hypokalemia (Correct Answer)
C. Hypernatremia
D. Hyponatremia

Explanation: **Explanation:** **Mechanism of Action:** Insulin is a potent regulator of potassium homeostasis. It stimulates the **Na⁺-K⁺ ATPase pump** located on the cell membranes of skeletal muscle and liver cells. This stimulation increases the active transport of potassium ions from the extracellular fluid (ECF) into the intracellular fluid (ICF). When insulin is infused rapidly or in high doses, this massive shift of potassium into the cells leads to a significant decrease in serum potassium levels, resulting in **Hypokalemia**. **Analysis of Options:** * **A. Hyperkalemia:** This is incorrect. Insulin *decreases* serum potassium. Hyperkalemia is actually a feature of insulin deficiency (e.g., Diabetic Ketoacidosis) because potassium shifts out of cells. * **C & D. Hypernatremia/Hyponatremia:** While insulin can influence sodium-glucose cotransporters and renal sodium handling, its primary and most immediate life-threatening effect during rapid infusion is on potassium, not sodium. **High-Yield Clinical Pearls for NEET-PG:** 1. **Treatment of Hyperkalemia:** Because insulin shifts K⁺ into cells, a combination of **Insulin + Dextrose** is a standard emergency treatment for severe hyperkalemia. 2. **DKA Management:** In Diabetic Ketoacidosis (DKA), patients may have high serum K⁺ initially, but total body K⁺ is depleted. Starting insulin therapy will cause K⁺ levels to drop rapidly; therefore, **potassium supplementation** is mandatory once levels fall below the normal range. 3. **Aldosterone vs. Insulin:** Both hormones promote hypokalemia, but via different mechanisms—Aldosterone via renal excretion and Insulin via intracellular shifting.

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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