Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 101: All are true about the Hypothalamus-pituitary-Adrenal axis except?

A. Corticotropin-releasing hormone (CRH) stimulates the zona fasciculata leading to increased cortisol production. (Correct Answer)
B. CRH and vasopressin are released from neurosecretory nerve terminals at the median eminence.
C. Cortisol produced in the adrenal cortex will negatively feedback.
D. Epinephrine and norepinephrine will positively feedback to the pituitary.

Explanation: ### Explanation The Hypothalamic-Pituitary-Adrenal (HPA) axis is a tightly regulated neuroendocrine system. Understanding the specific site of action for each hormone is crucial for NEET-PG. **Why Option A is the Correct Answer (The False Statement):** Corticotropin-releasing hormone (CRH) **does not** act directly on the adrenal cortex. CRH is secreted by the paraventricular nucleus of the hypothalamus and travels via the hypophyseal portal system to the **anterior pituitary**, where it stimulates Corticotrophs to release **ACTH** (Adrenocorticotropic Hormone). It is ACTH, not CRH, that acts on the **zona fasciculata** of the adrenal cortex to stimulate cortisol production. **Analysis of Other Options:** * **Option B:** CRH and Arginine Vasopressin (AVP) are indeed synthesized in the hypothalamus and released into the primary capillary plexus at the **median eminence** to regulate the pituitary. * **Option C:** Cortisol exerts **negative feedback** at both the hypothalamic level (inhibiting CRH) and the anterior pituitary level (inhibiting ACTH) to maintain homeostasis. * **Option D:** Systemic stressors, including the release of catecholamines (Epinephrine/Norepinephrine), act as **positive stimulators** of the HPA axis to ensure adequate cortisol release during the "fight or flight" response. **High-Yield Clinical Pearls for NEET-PG:** * **Rate-limiting step:** ACTH stimulates the conversion of Cholesterol to Pregnenolone (via the enzyme *Desmolase*) in the mitochondria. * **Diurnal Variation:** Cortisol levels are highest in the early morning (approx. 8 AM) and lowest at midnight. * **Primary vs. Secondary:** In Addison’s disease (Primary), ACTH is high; in Pituitary insufficiency (Secondary), ACTH is low. * **Dexamethasone Suppression Test:** Used to differentiate causes of Cushing’s syndrome by testing the integrity of the negative feedback loop.

Question 102: Sympathetic stimulation of nerves innervating the islets of the pancreas will:

A. Have no effect
B. Increase secretion of insulin from B cells
C. Decrease secretion of insulin from B cells
D. Increase secretion of glucagon from A cells (Correct Answer)

Explanation: **Explanation:** The autonomic nervous system plays a critical role in regulating pancreatic endocrine secretions to maintain glucose homeostasis, especially during stress or exercise (the "fight or flight" response). **Why Option D is Correct:** Sympathetic stimulation primarily aims to increase blood glucose levels to provide energy for vital organs. It achieves this through the release of **Norepinephrine**, which acts on **$\alpha_2$-adrenergic receptors** on Beta cells and **$\beta_2$-adrenergic receptors** on Alpha cells. Stimulation of Alpha cells leads to an **increase in glucagon secretion**, which promotes glycogenolysis and gluconeogenesis in the liver, raising blood sugar levels. **Analysis of Incorrect Options:** * **Option A:** Incorrect. The islets are richly innervated by both sympathetic and parasympathetic fibers; they are not autonomous. * **Option B & C:** While sympathetic stimulation involves a dual effect on Beta cells ($\alpha_2$ inhibits, $\beta_2$ stimulates), the **$\alpha_2$-mediated inhibitory effect is dominant**. Therefore, sympathetic activity actually **decreases** insulin secretion to prevent glucose storage during stress. Option D remains the most definitive positive action described. **High-Yield NEET-PG Pearls:** * **Parasympathetic (Vagal) Stimulation:** Increases both insulin and glucagon secretion (anticipatory phase of digestion). * **Receptor Specificity:** * **$\alpha_2$ receptors:** Inhibit insulin release (Dominant sympathetic effect). * **$\beta_2$ receptors:** Stimulate insulin and glucagon release. * **Clinical Correlation:** Somatostatin (from Delta cells) acts as a universal inhibitor, paracrinely inhibiting both insulin and glucagon. * **Exercise:** During intense exercise, sympathetic drive ensures insulin is suppressed and glucagon is elevated to maintain fuel supply to skeletal muscles.

Question 103: Glucocorticoids lead to an increase in the blood levels of which of the following?

A. Neutrophils (Correct Answer)
B. Eosinophils
C. Basophils
D. Lymphocytes

Explanation: **Explanation:** Glucocorticoids (like cortisol) have a profound effect on the distribution and count of circulating white blood cells. The correct answer is **Neutrophils** because glucocorticoids induce **neutrophilia** through three primary mechanisms: 1. **Demargination:** They decrease the expression of adhesion molecules (L-selectin) on neutrophils, causing them to detach from the vascular endothelium and enter the circulating pool. 2. **Increased Bone Marrow Release:** They stimulate the release of mature neutrophils from the bone marrow. 3. **Reduced Egress:** They inhibit the movement of neutrophils from the blood into the tissues. **Why the other options are incorrect:** Glucocorticoids generally cause a decrease in the circulating levels of most other leukocytes (Leukopenia): * **Eosinophils & Basophils:** Glucocorticoids cause **eosinopenia** and **basopenia** by sequestering these cells into the lymphoid tissues and inhibiting their release from the bone marrow. * **Lymphocytes:** They cause **lymphopenia** by redistributing T and B cells from the blood into the lymphoid compartments (spleen, lymph nodes, and bone marrow) and, at high doses, inducing apoptosis of lymphoid cells. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic:** Glucocorticoids cause "Neutrophilia, but everything else goes down" (Eosinopenia, Lymphopenia, Monocytopenia, Basopenia). * **Clinical Correlation:** In patients with Cushing’s Syndrome or those on exogenous steroids, a CBC will typically show a high TLC with a shift toward neutrophils. * **Exception:** While most cells decrease, **Red Blood Cell (RBC)** and **Platelet** counts may actually increase with glucocorticoid administration.

Question 104: Which of the following statements is true regarding luteinizing hormone (LH)?

A. The alpha-subunit is similar in LH and FSH.
B. The alpha-subunit is specific for LH.
C. The beta-subunit provides functional specificity.
D. It is a homodimer consisting of glycoproteins. (Correct Answer)

Explanation: ### Explanation Luteinizing Hormone (LH) is a member of the **glycoprotein hormone family**, which also includes Follicle-Stimulating Hormone (FSH), Thyroid-Stimulating Hormone (TSH), and Human Chorionic Gonadotropin (hCG). **1. Why the Correct Answer is Right:** LH is a **heterodimer** (though often referred to in broader terms as a dimer) composed of two glycosylated polypeptide chains: an alpha ($\alpha$) and a beta ($\beta$) subunit. These subunits are non-covalently linked. The presence of carbohydrate side chains (glycoproteins) is essential for its biological activity and circulating half-life. **2. Analysis of Incorrect Options:** * **Option A & B:** The **alpha-subunit is identical** across LH, FSH, TSH, and hCG. It is encoded by the same gene. Therefore, it is not specific to LH. * **Option C:** This statement is actually **clinically true**; the beta-subunit is unique to each hormone and dictates biological/receptor specificity. However, in the context of the provided key, the question emphasizes the structural nature of the hormone as a glycoprotein dimer. *(Note: In many standard physiological texts, Option C is also considered a "correct" fact, but Option D defines the biochemical class of the molecule).* * **Option D (Corrected Concept):** While the provided key marks "homodimer" as correct, it is important to note for NEET-PG that LH is technically a **heterodimer** (different $\alpha$ and $\beta$ subunits). If "homodimer" is the keyed answer, it refers to the two-part glycoprotein structure. **3. Clinical Pearls for NEET-PG:** * **LH Surge:** Triggered by high levels of estrogen (positive feedback), leading to ovulation. * **Target Cells:** In males, LH acts on **Leydig cells** (L for L) to produce testosterone. In females, it acts on **Theca cells** to produce androgens (precursors to estrogen). * **hCG Mimicry:** Because hCG and LH share a very similar beta-subunit, hCG can be used clinically to trigger ovulation or stimulate testosterone production as it binds to the same LH receptor.

Question 105: About Neuropeptide Y, all are true except?

A. It is mediated through melanocorticotropin hormone
B. Decreases thermogenesis
C. Its level decreases during starvation (Correct Answer)
D. Contains 36 aminoacid residues

Explanation: **Explanation:** **Neuropeptide Y (NPY)** is one of the most potent **orexigenic** (appetite-stimulating) peptides found in the brain, primarily synthesized in the arcuate nucleus of the hypothalamus. **1. Why Option C is the Correct Answer (The "Except" Statement):** In states of negative energy balance, such as **starvation or fasting**, the body attempts to restore energy stores by increasing hunger. Therefore, **NPY levels increase significantly during starvation** to stimulate food intake. The statement that it decreases is physiologically incorrect, making it the right choice for this "except" question. **2. Analysis of Other Options:** * **Option A:** NPY acts as an antagonist to the melanocortin system. It inhibits the release of Pro-opiomelanocortin (POMC) derivatives and competes with the melanocortin signaling pathway to promote feeding. * **Option B:** To conserve energy during periods of perceived food scarcity, NPY **decreases thermogenesis** (specifically by inhibiting brown adipose tissue activity) and lowers sympathetic nervous system activity. * **Option D:** Structurally, NPY is a member of the pancreatic polypeptide family and consists of **36 amino acid residues**. **Clinical Pearls for NEET-PG:** * **Orexigenic (Hunger) Signals:** NPY, Agouti-related peptide (AgRP), Ghrelin ("Hunger hormone"). * **Anorexigenic (Satiety) Signals:** Leptin, Insulin, POMC, CART (Cocaine-and-amphetamine-regulated transcript), and CCK. * **Leptin Connection:** Leptin normally **inhibits** NPY. In obesity, leptin resistance leads to a failure to suppress NPY, contributing to overeating. * **NPY Receptors:** Primarily acts via Y1 and Y5 receptors to stimulate feeding.

Question 106: Basal metabolic rate (BMR) is decreased in which of the following conditions?

A. Exposure to cold temperature
B. Hyperthyroidism
C. Exercise
D. Hypothyroidism (Correct Answer)

Explanation: **Explanation:** **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 in a post-absorptive state. **1. Why Hypothyroidism is Correct:** Thyroid hormones ($T_3$ and $T_4$) are the primary determinants of BMR. They increase oxygen consumption and heat production in almost all tissues by increasing the activity of the $Na^+-K^+$ ATPase pump. In **hypothyroidism**, there is a deficiency of these hormones, leading to a significant decrease in cellular metabolism and oxygen consumption, thereby **decreasing the BMR** (often by 30-40%). **2. Why Incorrect Options are Wrong:** * **Exposure to cold temperature:** Cold exposure **increases** BMR as the body generates heat through shivering and non-shivering thermogenesis (activation of brown adipose tissue) to maintain core temperature. * **Hyperthyroidism:** Excess thyroid hormones stimulate metabolic pathways, leading to a marked **increase** in BMR (up to 60-100% above normal). * **Exercise:** Physical activity involves muscular contraction, which significantly **increases** energy expenditure and metabolic rate. **High-Yield Clinical Pearls for NEET-PG:** * **Surface Area Rule:** BMR is directly proportional to the surface area of the body (Rubner’s Law). * **Gender & Age:** BMR is higher in males (due to testosterone and higher muscle mass) and decreases with advancing age. * **Specific Dynamic Action (SDA):** Protein has the highest SDA (30%), meaning it increases metabolic rate the most during digestion. * **Starvation:** BMR **decreases** during prolonged fasting or starvation as an adaptive mechanism to conserve energy.

Question 107: Which of the following substances is the most potent androgen?

A. Dehydroepiandrosterone
B. Dihydrotestosterone (Correct Answer)
C. Androstenedione
D. Testosterone

Explanation: ### Explanation **Correct Answer: B. Dihydrotestosterone (DHT)** **Why it is correct:** In terms of biological activity, **Dihydrotestosterone (DHT)** is the most potent naturally occurring androgen. It is synthesized from testosterone by the enzyme **5α-reductase** in peripheral tissues (such as the prostate and skin). DHT has a significantly higher affinity (approximately 2–3 times) for the androgen receptor compared to testosterone and dissociates from the receptor much more slowly. This results in a more stable and potent hormone-receptor complex, amplifying the androgenic signal. **Why the other options are incorrect:** * **Testosterone (D):** While it is the primary circulating androgen secreted by the Leydig cells, it acts as a "pro-hormone" for DHT in many tissues. It is less potent than DHT but more potent than adrenal androgens. * **Androstenedione (C) and Dehydroepiandrosterone (A):** These are weak adrenal androgens. They have minimal intrinsic activity and primarily serve as precursors that must be converted into testosterone or estrogens in peripheral tissues to exert significant biological effects. **High-Yield Clinical Pearls for NEET-PG:** * **Potency Hierarchy:** DHT > Testosterone > Androstenedione > DHEA. * **5α-reductase Deficiency:** Leads to ambiguous genitalia in males at birth (pseudohermaphroditism) because DHT is essential for the development of external male genitalia. * **Pharmacology Link:** **Finasteride** is a 5α-reductase inhibitor used to treat Benign Prostatic Hyperplasia (BPH) and male pattern baldness by reducing DHT levels. * **Site of Action:** DHT is responsible for the growth of the prostate, male pattern baldness, and facial hair, whereas testosterone is responsible for internal genitalia (Wolffian duct development) and muscle mass.

Question 108: Thyroid peroxidase is required for all of the following steps in thyroid hormone synthesis except?

A. Iodide uptake (Correct Answer)
B. Oxidation of iodide
C. Iodination of tyrosine
D. Synthesis of iodothyronines

Explanation: **Explanation:** **Thyroid Peroxidase (TPO)** is a multifunctional enzyme located on the apical membrane of follicular cells. It is essential for the synthesis of thyroid hormones, but it plays no role in the initial transport of iodide into the cell. 1. **Why "Iodide Uptake" is the correct answer:** Iodide uptake (trapping) is the first step in thyroid hormone synthesis. It is mediated by the **Sodium-Iodide Symporter (NIS)**, an active transport mechanism located on the basolateral membrane. This process is driven by the Na+/K+ ATPase pump and is regulated primarily by TSH, not TPO. 2. **Why the other options are incorrect:** TPO is a heme-containing enzyme that catalyzes three distinct reactions: * **Oxidation of Iodide (B):** TPO converts iodide ($I^-$) into reactive iodine ($I^0$) using hydrogen peroxide ($H_2O_2$). * **Iodination of Tyrosine (C):** Also known as **Organification**, where iodine is attached to tyrosine residues on thyroglobulin to form Monoiodotyrosine (MIT) and Diiodotyrosine (DIT). * **Synthesis of Iodothyronines (D):** Also known as **Coupling**, where TPO facilitates the joining of MIT and DIT to form $T_3$ and $T_4$. **High-Yield Clinical Pearls for NEET-PG:** * **Wolf-Chaikoff Effect:** An autoregulatory phenomenon where high levels of circulating iodide inhibit TPO, leading to a temporary decrease in thyroid hormone synthesis. * **Propylthiouracil (PTU) & Methimazole:** These antithyroid drugs work primarily by inhibiting the enzyme **Thyroid Peroxidase**. * **Pendred Syndrome:** Caused by a defect in the **Pendrin** transporter (iodide-chloride exchanger) on the apical membrane, leading to sensorineural hearing loss and goiter.

Question 109: What are the important metabolic effects of thyroxine?

A. Increases the basal metabolic rate.
B. Reaction time of stretch reflexes is shortened by hyperthyroidism.
C. Potentiates the effects of catecholamines.
D. All of the above. (Correct Answer)

Explanation: Thyroid hormones (T3 and T4) are the primary determinants of the body’s metabolic pace. The correct answer is **Option D** because thyroxine exerts pleiotropic effects across multiple organ systems. **Explanation of Options:** * **A. Increases Basal Metabolic Rate (BMR):** Thyroxine increases oxygen consumption and heat production (thermogenesis) in almost all active tissues (except the brain, testes, and anterior pituitary). It achieves this by increasing the number and activity of mitochondria and upregulating Na+-K+ ATPase pumps. * **B. Shortened Stretch Reflexes:** Thyroid hormones are essential for normal neuromuscular function. In hyperthyroidism, the reaction time of stretch reflexes (e.g., the Achilles tendon reflex) is shortened (brisk), whereas in hypothyroidism, it is characteristically prolonged ("hung-up" reflex). * **C. Potentiates Catecholamines:** Thyroxine increases the expression and sensitivity of **beta-adrenergic receptors** in the heart and other tissues. This explains why hyperthyroid patients present with tachycardia, tremors, and anxiety, and why beta-blockers (Propranolol) are used for symptomatic relief. **High-Yield NEET-PG Pearls:** * **Lipid Metabolism:** Thyroxine decreases blood cholesterol levels by increasing the expression of **LDL receptors** in the liver (Hypothyroidism leads to hypercholesterolemia). * **Carbohydrate Metabolism:** It is diabetogenic; it increases glucose absorption from the GI tract and potentiates glycogenolysis. * **Growth:** It acts synergistically with Growth Hormone (GH) for skeletal maturation; deficiency in utero/infancy leads to **Cretinism** (mental retardation and stunted growth).

Question 110: What is the most active form of vitamin D?

A. Calcefedial
B. Calcitriol (Correct Answer)
C. 7-dehydrocholesterol
D. Vitamin D3

Explanation: **Explanation:** **1. Why Calcitriol is correct:** Vitamin D undergoes two successive hydroxylations in the body to become biologically active. The first occurs in the liver to form 25-hydroxyvitamin D [25(OH)D]. The second and most critical step occurs in the **proximal convoluted tubules of the kidney**, catalyzed by the enzyme **1-alpha-hydroxylase**. This produces **1,25-dihydroxyvitamin D3**, also known as **Calcitriol**. Calcitriol is the most potent and active metabolite because it has the highest affinity for the Vitamin D Receptor (VDR), through which it regulates calcium and phosphate homeostasis. **2. Why the other options are incorrect:** * **A. Calcifediol:** This is 25-hydroxyvitamin D3. It is the major circulating form of Vitamin D and the clinical marker used to measure a patient's Vitamin D status, but it is a pro-hormone with low biological activity. * **C. 7-dehydrocholesterol:** This is the precursor molecule found in the skin. Upon exposure to UV-B radiation, it is converted into Cholecalciferol (Vitamin D3). It has no hormonal activity. * **D. Vitamin D3 (Cholecalciferol):** This is the inactive form obtained from diet or skin synthesis. It must be hydroxylated twice (in the liver and then the kidney) before it can exert any physiological effect. **3. High-Yield Clinical Pearls for NEET-PG:** * **Rate-limiting step:** The conversion of Calcifediol to Calcitriol by **1-alpha-hydroxylase** is the rate-limiting step, regulated by PTH (stimulates) and Phosphate/FGF-23 (inhibits). * **Storage form:** 25-hydroxyvitamin D (Calcifediol) has a long half-life (2-3 weeks), making it the best indicator of body stores. * **Active form:** 1,25-dihydroxyvitamin D (Calcitriol) has a short half-life (4-6 hours). * **Chronic Kidney Disease (CKD):** Patients with CKD lack 1-alpha-hydroxylase activity, leading to secondary hyperparathyroidism and renal osteodystrophy. They require treatment with pre-activated Vitamin D (Calcitriol).

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

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