Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 91: What is true regarding the renin-angiotensin system?

A. Angiotensin is an octapeptide.
B. Renin splits the leucine-valine bond. (Correct Answer)
C. Aspartic acid is essential for renin activity.
D. All of the above.

Explanation: ### Explanation **Correct Answer: B. Renin splits the leucine-valine bond.** The Renin-Angiotensin-Aldosterone System (RAAS) is a critical hormonal cascade for blood pressure regulation. **Renin**, an aspartyl protease produced by the juxtaglomerular cells of the kidney, acts on its substrate, **Angiotensinogen** (an $\alpha_2$-globulin produced by the liver). Renin specifically cleaves the peptide bond between the **10th (Leucine) and 11th (Valine)** amino acid residues at the amino-terminal of angiotensinogen. This cleavage results in the formation of the decapeptide, Angiotensin I. **Analysis of Options:** * **Option A is incorrect:** Angiotensin I is a **decapeptide** (10 amino acids). It is subsequently converted by Angiotensin-Converting Enzyme (ACE) into Angiotensin II, which is an **octapeptide** (8 amino acids). * **Option C is incorrect:** While renin is classified as an "aspartyl protease" because its catalytic site contains two **aspartic acid residues**, these residues are part of the enzyme's structure, not the substrate's essential activity requirement in the context usually tested. More importantly, the question asks for the most definitive biochemical action, which is the specific bond cleavage. * **Option D is incorrect:** Since A is false, "All of the above" cannot be correct. **High-Yield NEET-PG Pearls:** * **Rate-limiting step:** The reaction catalyzed by Renin (Angiotensinogen $\rightarrow$ Angiotensin I) is the rate-limiting step of the RAAS pathway. * **ACE Location:** ACE is primarily located in the luminal surface of vascular endothelial cells, particularly in the **lungs**. * **Potency:** Angiotensin II is a potent vasoconstrictor and stimulates the **Zona Glomerulosa** of the adrenal cortex to release Aldosterone. * **Degradation:** Angiotensin II is degraded by **Angiotensinases** into Angiotensin III (heptapeptide), which also stimulates aldosterone secretion but has less pressor activity.

Question 92: Growth hormone increases all of the following except?

A. Blood glucose concentration
B. Blood free fatty acid concentration
C. Protein synthesis
D. Metabolism of carbohydrates (Correct Answer)

Explanation: **Explanation:** Growth Hormone (GH) is primarily an anabolic hormone regarding proteins, but it acts as a **"Diabetogenic"** and **"Glucose-sparing"** hormone regarding fuel metabolism. **Why "Metabolism of carbohydrates" is the correct answer:** GH actually **decreases** the peripheral utilization (metabolism) of carbohydrates. It induces insulin resistance by inhibiting the uptake of glucose by skeletal muscle and adipose tissue. By sparing glucose, the body shifts its energy source from carbohydrates to fats. Therefore, saying GH "increases" carbohydrate metabolism is physiologically incorrect. **Analysis of Incorrect Options:** * **A. Blood glucose concentration:** GH increases blood glucose by stimulating gluconeogenesis in the liver and reducing glucose uptake in peripheral tissues (Anti-insulin effect). * **B. Blood free fatty acid concentration:** GH is highly **lipolytic**. It activates hormone-sensitive lipase, breaking down triglycerides into free fatty acids (FFAs) to be used as the primary energy source. * **C. Protein synthesis:** GH is a potent anabolic agent. It increases amino acid transport into cells, enhances DNA transcription/translation, and decreases protein catabolism, leading to a positive nitrogen balance. **NEET-PG High-Yield Pearls:** * **Ketogenic Effect:** Due to excessive mobilization of FFAs, GH is considered ketogenic. * **IGF-1 (Somatomedin C):** Most growth-promoting effects of GH (bone and cartilage growth) are mediated via IGF-1, produced mainly in the liver. * **Pulsatile Secretion:** GH is secreted in pulses, with the largest spike occurring during **Deep Sleep (Stage N3)**. * **Stimuli:** Hypoglycemia, fasting, and exercise are potent stimulators of GH release.

Question 93: Insulin-like growth factor-II (IGF-II) is synthesized in all of the following tissues EXCEPT:

A. Brain
B. Liver
C. Cartilage (Correct Answer)
D. Pancreas

Explanation: **Explanation:** The synthesis of Insulin-like Growth Factors (IGFs) is a critical component of the growth hormone (GH) axis. While **IGF-I** is primarily GH-dependent and synthesized in the liver and peripheral tissues like **cartilage** (where it acts locally via autocrine/paracrine mechanisms to promote bone growth), **IGF-II** follows a different physiological pattern. **Why Cartilage is the Correct Answer:** IGF-II is primarily a **fetal growth factor**. While it is synthesized in various adult tissues, it is notably **not synthesized in cartilage**. In contrast, cartilage is a major site for IGF-I synthesis, which mediates the longitudinal growth effects of Growth Hormone. **Analysis of Incorrect Options:** * **Liver (B):** The liver is the primary site of synthesis for both IGF-I and IGF-II in adults. IGF-II levels in the blood remain relatively high throughout adulthood, though its metabolic role is less dominant than IGF-I. * **Brain (A) and Pancreas (D):** IGF-II is widely expressed in several extrahepatic tissues. It is synthesized in the **brain** (where it plays a role in cognitive function and neurogenesis) and the **pancreas** (involved in beta-cell mass regulation). **High-Yield NEET-PG Pearls:** * **IGF-I (Somatomedin C):** Major mediator of postnatal growth; synthesis is GH-dependent. * **IGF-II:** Major mediator of fetal growth; synthesis is largely GH-independent. * **Receptors:** IGF-I acts via a tyrosine kinase receptor (similar to insulin). The IGF-II receptor is identical to the **Mannose-6-Phosphate receptor**, which is involved in lysosomal enzyme targeting. * **Clinical Correlation:** Excessive IGF-II production by non-islet cell tumors can lead to **hypoglycemia** (Doege-Potter Syndrome).

Question 94: Which of the following acts on nuclear receptors?

A. Glucocorticoids
B. Thyroxine (Correct Answer)
C. Progesterone
D. Insulin

Explanation: **Explanation:** The mechanism of hormone action is determined by the chemical nature of the hormone. Receptors are generally classified into cell surface receptors (for water-soluble hormones) and intracellular receptors (for lipid-soluble hormones). **1. Why Thyroxine (B) is the Correct Answer:** Thyroid hormones (T3 and T4) are unique. Although they are derived from the amino acid tyrosine, they are lipophilic. They enter the cell via carrier-mediated transport and bind directly to **nuclear receptors** (specifically the Thyroid Hormone Receptor, TR). Once bound, they act as hormone-activated transcription factors, altering gene expression. **2. Analysis of Incorrect Options:** * **Glucocorticoids (A) and Progesterone (C):** These are steroid hormones. While they act on intracellular receptors, their primary receptors are located in the **cytoplasm**. Upon binding, the hormone-receptor complex translocates into the nucleus. Therefore, while they have nuclear effects, "Thyroxine" is the classic textbook answer for a receptor that is constitutively located *inside* the nucleus. * **Insulin (D):** This is a peptide hormone. It is water-soluble and cannot cross the lipid bilayer. It binds to a **transmembrane receptor** with intrinsic **Tyrosine Kinase** activity (Enzyme-linked receptor). **High-Yield NEET-PG Pearls:** * **Pure Nuclear Receptors:** Thyroid hormones (T3/T4), Retinoic acid (Vitamin A), and Vitamin D. * **Cytoplasmic Receptors:** Steroid hormones (Glucocorticoids, Mineralocorticoids, Progesterone, Estrogen, Testosterone). * **Mnemonic for Tyrosine Kinase:** "PIG" (Prolactin, Insulin, Growth Hormone). * **Note:** In many recent physiological classifications, both steroids and thyroid hormones are grouped as "Intracellular Receptors," but if "Thyroxine" is an option, it is the most specific answer for a receptor located permanently on the chromatin.

Question 95: All are required for the formation of estradiol except?

A. Lyase
B. 11b-hydroxylase (Correct Answer)
C. Aromatase
D. Hydroxysteroid dehydrogenase

Explanation: The synthesis of **Estradiol** (the primary female sex hormone) follows the steroidogenic pathway starting from Cholesterol. To answer this question, one must distinguish between the synthesis of **Sex Steroids** and **Adrenal Corticosteroids**. ### Why 11β-hydroxylase is the Correct Answer **11β-hydroxylase** is an enzyme exclusively involved in the **Glucocorticoid and Mineralocorticoid pathways**. It converts 11-deoxycortisol to Cortisol and 11-deoxycorticosterone to Corticosterone. It is located in the Zona Fasciculata and Zona Glomerulosa of the adrenal cortex. It plays **no role** in the synthesis of androgens or estrogens. ### Explanation of Incorrect Options * **Lyase (17,20-lyase):** This enzyme is crucial for converting 17-hydroxypregnenolone/progesterone into androgens (DHEA and Androstenedione), which are the direct precursors to estrogens. * **Aromatase (CYP19A1):** This is the **rate-limiting enzyme** for estrogen synthesis. It converts androgens (testosterone and androstenedione) into estrogens (estradiol and estrone) by "aromatizing" the A-ring. * **Hydroxysteroid dehydrogenase (3β-HSD & 17β-HSD):** These enzymes are essential for converting inactive precursors into active hormones. Specifically, **17β-HSD** converts Androstenedione to Testosterone and Estrone to Estradiol. ### High-Yield NEET-PG Pearls * **Two-Cell, Two-Gonadotropin Theory:** LH stimulates **Theca cells** to produce androgens (using Lyase), while FSH stimulates **Granulosa cells** to convert those androgens to estradiol (using Aromatase). * **Congenital Adrenal Hyperplasia (CAH):** A deficiency in **11β-hydroxylase** leads to decreased cortisol but **increased androgens** (virilization), as precursors are shunted away from the corticosteroid pathway toward the sex steroid pathway. * **Aromatase Inhibitors** (e.g., Letrozole, Anastrozole) are clinically used in the treatment of ER-positive breast cancer.

Question 96: Insulin stimulates all of the following except:

A. Glycolysis
B. Lipolysis (Correct Answer)
C. Protein synthesis
D. Lipogenesis

Explanation: **Explanation:** Insulin is the body’s primary **anabolic hormone**, secreted by the beta cells of the pancreas in response to high blood glucose levels. Its fundamental role is to promote energy storage and inhibit the mobilization of stored nutrients. **Why Lipolysis is the correct answer:** Insulin **inhibits** lipolysis. It does this by inhibiting the enzyme **Hormone-Sensitive Lipase (HSL)** in adipose tissue, which prevents the breakdown of triglycerides into free fatty acids and glycerol. By suppressing lipolysis, insulin ensures that the body utilizes glucose for energy rather than fat stores. **Analysis of Incorrect Options:** * **Glycolysis (A):** Insulin stimulates glycolysis (the breakdown of glucose for energy) by increasing the activity of key enzymes like glucokinase, phosphofructokinase, and pyruvate kinase. * **Protein Synthesis (C):** Insulin is highly anabolic for proteins; it increases amino acid uptake by cells and stimulates ribosomal machinery to synthesize new proteins while inhibiting proteolysis. * **Lipogenesis (D):** Insulin promotes the storage of fat. It activates **Acetyl-CoA carboxylase** and increases glucose uptake in adipocytes (via GLUT-4), providing the glycerol backbone for triglyceride synthesis. **High-Yield Clinical Pearls for NEET-PG:** * **GLUT-4:** The only insulin-dependent glucose transporter, found primarily in skeletal muscle and adipose tissue. * **Potassium Shift:** Insulin stimulates the Na+/K+ ATPase pump, driving potassium into cells. This is why insulin/dextrose is used to treat **hyperkalemia**. * **Antagonistic Hormone:** Glucagon is the primary catabolic counterpart to insulin, stimulating lipolysis, glycogenolysis, and gluconeogenesis.

Question 97: Which of the following hormones increases during surgical stress?

A. Cortisol (Correct Answer)
B. Glucagon
C. Insulin
D. Gastrin

Explanation: ### Explanation **Correct Option: A (Cortisol)** Surgical stress triggers the **Neuroendocrine Stress Response**, characterized by the activation of the Hypothalamic-Pituitary-Adrenal (HPA) axis and the Sympathetic Nervous System. The hypothalamus releases Corticotropin-Releasing Hormone (CRH), which stimulates the anterior pituitary to secrete ACTH, leading to a significant rise in **Cortisol** from the adrenal cortex. Cortisol acts as a "stress hormone" to maintain hemodynamic stability, increase blood glucose (via gluconeogenesis), and modulate the inflammatory response during trauma or surgery. **Analysis of Incorrect Options:** * **B. Glucagon:** While glucagon levels do rise during stress to assist in hyperglycemia, **Cortisol** is the primary and most characteristic hormonal marker of the surgical endocrine response cited in standard physiological texts for this context. * **C. Insulin:** Insulin levels typically **decrease** or remain inappropriately low relative to blood glucose levels during the initial "ebb phase" of surgical stress. Furthermore, stress induces peripheral **insulin resistance**, leading to "stress-induced hyperglycemia." * **D. Gastrin:** Gastrin is primarily involved in gastrointestinal regulation (acid secretion) and is not a component of the systemic neuroendocrine stress response. **High-Yield Clinical Pearls for NEET-PG:** * **Hormones that INCREASE in stress:** Cortisol, Catecholamines (Epinephrine/Norepinephrine), Glucagon, Growth Hormone, ADH (Vasopressin), and Renin-Angiotensin-Aldosterone. * **Hormones that DECREASE in stress:** Insulin, Testosterone, and Estrogen. * **The "Ebb Phase":** Occurs immediately after injury (24–48 hours); characterized by decreased metabolic rate, decreased body temperature, and increased catecholamines/cortisol. * **The "Flow Phase":** Follows the ebb phase; characterized by hypermetabolism, catabolism, and persistent elevation of stress hormones.

Question 98: A primary oocyte is formed after which process?

A. First meiotic division
B. Second meiotic division
C. Mitotic division (Correct Answer)
D. None of the above

Explanation: ### Explanation The process of oogenesis begins during fetal life when primordial germ cells migrate to the ovary and undergo multiple rounds of **mitotic division** to form **oogonia**. These oogonia then undergo further mitosis and begin to differentiate into **primary oocytes**. **Why Mitotic Division is Correct:** A primary oocyte is essentially an oogonium that has completed DNA replication and entered the prophase of Meiosis I. This transition from a germ cell to a primary oocyte is driven by mitotic expansion and subsequent differentiation. By the 5th month of intrauterine life, the ovaries contain approximately 7 million oogonia, all formed via mitosis, which then transform into primary oocytes. **Why Other Options are Incorrect:** * **First Meiotic Division:** The completion of the first meiotic division (Meiosis I) occurs just before ovulation, resulting in the formation of a **secondary oocyte** and the first polar body. * **Second Meiotic Division:** The completion of the second meiotic division (Meiosis II) occurs only if fertilization takes place, resulting in a mature **ovum** (ootid) and the second polar body. **High-Yield Clinical Pearls for NEET-PG:** * **Arrest Points:** Primary oocytes are arrested in the **Dictyate stage (Prophase I)** until puberty. Secondary oocytes are arrested in **Metaphase II** until fertilization. * **Timeline:** All primary oocytes are formed before birth; no new oocytes are created postnatally. * **Number:** At birth, there are ~1–2 million primary oocytes; by puberty, only ~400,000 remain due to atresia.

Question 99: What hormone is secreted by the adrenal medulla?

A. Sex hormones
B. Thyroid stimulating hormone
C. Epinephrine (Correct Answer)
D. Glucocorticoid

Explanation: ### Explanation The adrenal gland is divided into two distinct functional units: the outer **adrenal cortex** and the inner **adrenal medulla**. **1. Why Epinephrine is Correct:** The **adrenal medulla** is embryologically derived from the neural crest and acts as a modified sympathetic ganglion. It contains **chromaffin cells** that synthesize and secrete catecholamines directly into the bloodstream in response to sympathetic stimulation (the "fight-or-flight" response). **Epinephrine (Adrenaline)** constitutes about 80% of the medullary secretion, while Norepinephrine (Noradrenaline) makes up the remaining 20%. **2. Why the Other Options are Incorrect:** * **A. Sex hormones (Androgens):** These are secreted by the **Zona Reticularis**, the innermost layer of the adrenal cortex. * **B. Thyroid Stimulating Hormone (TSH):** This is a glycoprotein hormone secreted by the thyrotrophs of the **Anterior Pituitary gland**, not the adrenal gland. * **C. Glucocorticoids (e.g., Cortisol):** These are secreted by the **Zona Fasciculata**, the middle and widest layer of the adrenal cortex. **3. NEET-PG High-Yield Pearls:** * **Mnemonic for Adrenal Cortex:** **G-F-R** (Glomerulosa, Fasciculata, Reticularis) corresponds to **S-S-S** (Salt/Mineralocorticoids, Sugar/Glucocorticoids, Sex/Androgens). * **Rate-limiting enzyme:** Tyrosine hydroxylase is the rate-limiting enzyme for catecholamine synthesis in the medulla. * **PNMT Enzyme:** Phenylethanolamine N-methyltransferase (PNMT) converts Norepinephrine to Epinephrine; its activity is induced by cortisol. * **Clinical Correlation:** A tumor of the chromaffin cells is called a **Pheochromocytoma**, which presents with the classic triad of episodic headaches, sweating, and tachycardia due to excess catecholamine secretion.

Question 100: Which of the following is secreted by the pineal gland?

A. Melanin
B. Melatonin (Correct Answer)
C. ANP
D. GH

Explanation: **Explanation:** The **pineal gland** (epiphysis cerebri) is a small, pine-cone-shaped endocrine gland located in the midline of the brain, behind the third ventricle. Its primary function is the synthesis and secretion of **Melatonin**, a hormone derived from the amino acid **Tryptophan**. **1. Why Melatonin is correct:** Melatonin is synthesized via a pathway involving Serotonin. Its secretion is strictly regulated by the light-dark cycle (circadian rhythm). Light signals from the retina travel via the suprachiasmatic nucleus (SCN) to the pineal gland; darkness stimulates melatonin release, while light inhibits it. It plays a crucial role in regulating the sleep-wake cycle and has antioxidant properties. **2. Why the other options are incorrect:** * **Melanin (A):** This is a pigment produced by **melanocytes** in the skin and hair. It is not a hormone secreted by the pineal gland. (Note: MSH—Melanocyte Stimulating Hormone—is secreted by the anterior pituitary). * **ANP (C):** Atrial Natriuretic Peptide is a hormone secreted by the **atria of the heart** in response to high blood pressure/stretch. * **GH (D):** Growth Hormone is secreted by the somatotrophs of the **Anterior Pituitary gland**. **High-Yield Facts for NEET-PG:** * **Precursor:** Tryptophan → 5-Hydroxytryptophan → Serotonin → Melatonin. * **Rate-limiting enzyme:** N-acetyltransferase (NAT). * **Biological Clock:** The Suprachiasmatic Nucleus (SCN) of the hypothalamus is the master pacemaker that controls the pineal gland. * **Clinical Correlation:** Melatonin is used therapeutically for **jet lag** and delayed sleep phase syndrome. * **Brain Sand:** Calcification of the pineal gland (corpora arenacea) is a common radiological finding in adults, used as a midline marker on X-rays/CT scans.

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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