Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 271: Excess Aldosterone is associated with all of the following conditions except?

A. Hypokalemia
B. Hyperkalemia (Correct Answer)
C. Sodium retention
D. Hypertension

Explanation: **Explanation:** Aldosterone is a mineralocorticoid secreted by the *zona glomerulosa* of the adrenal cortex. Its primary site of action is the **Principal cells (P cells)** of the late distal tubule and collecting duct. **1. Why Hyperkalemia is the correct answer:** Aldosterone acts by increasing the activity of the Na+/K+ ATPase pump and opening epithelial sodium channels (ENaC). This leads to the reabsorption of Sodium ($Na^+$) and the **secretion of Potassium ($K^+$)** and Hydrogen ions ($H^+$) into the tubular lumen. Therefore, excess aldosterone (as seen in Conn’s Syndrome) leads to **Hypokalemia**, not Hyperkalemia. **2. Analysis of other options:** * **Sodium retention:** Aldosterone promotes $Na^+$ reabsorption. While this initially causes water retention, the "Aldosterone Escape" phenomenon eventually prevents overt edema, though total body sodium remains high. * **Hypertension:** Increased sodium reabsorption leads to increased plasma volume and peripheral resistance, resulting in secondary hypertension. * **Hypokalemia:** As explained, increased $K^+$ secretion into the urine leads to low serum potassium levels. **High-Yield Clinical Pearls for NEET-PG:** * **Conn’s Syndrome:** Primary hyperaldosteronism characterized by the triad of **Hypertension, Hypokalemia, and Metabolic Alkalosis.** * **Aldosterone Escape:** This refers to the spontaneous diuresis of sodium despite high aldosterone levels, mediated by **Atrial Natriuretic Peptide (ANP)**. This explains why patients with Conn’s syndrome have hypertension but **no edema**. * **Spironolactone/Eplerenone:** These are aldosterone antagonists used to treat hyperaldosteronism; they can cause hyperkalemia as a side effect.

Question 272: Which of the following is NOT a feature of glucocorticoid deficiency?

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

Explanation: **Explanation:** The key to answering this question lies in distinguishing between **Glucocorticoid (Cortisol)** deficiency and **Mineralocorticoid (Aldosterone)** deficiency. **Why Hyperkalemia is the correct answer:** Hyperkalemia is primarily a feature of **Mineralocorticoid deficiency**, not isolated glucocorticoid deficiency. Aldosterone acts on the principal cells of the renal collecting ducts to reabsorb Sodium and secrete Potassium/Hydrogen ions. Therefore, a lack of aldosterone leads to potassium retention (hyperkalemia). In conditions like secondary adrenal insufficiency (pituitary failure), aldosterone levels remain normal because they are regulated by the Renin-Angiotensin system, not ACTH; thus, hyperkalemia is absent. **Analysis of incorrect options:** * **Hyponatremia:** Glucocorticoid deficiency causes hyponatremia through two mechanisms: 1) Loss of negative feedback on ADH (Cortisol is a natural inhibitor of ADH), leading to water retention, and 2) Reduced systemic vascular resistance, which triggers baroreceptor-mediated ADH release. * **Hypoglycemia:** Cortisol is a counter-regulatory hormone that promotes gluconeogenesis and antagonizes insulin. Its absence leads to impaired glucose production and increased insulin sensitivity. * **Fever:** Glucocorticoids have potent anti-inflammatory effects and inhibit cytokine release (like IL-1 and IL-6). Deficiency leads to an unregulated inflammatory response, often manifesting as unexplained fever. **High-Yield Clinical Pearls for NEET-PG:** 1. **Primary Adrenal Insufficiency (Addison’s):** Deficient in *both* Glucocorticoids and Mineralocorticoids. Features: Hyponatremia + **Hyperkalemia** + Hyperpigmentation (due to high ACTH/MSH). 2. **Secondary Adrenal Insufficiency:** Deficient in Glucocorticoids *only*. Features: Hyponatremia + **Normal Potassium** + No hyperpigmentation. 3. **Eosinophilia and Lymphocytosis** are classic hematological findings in glucocorticoid deficiency.

Question 273: All of the following are true about Leptin EXCEPT:

A. It increases appetite (Correct Answer)
B. It is increased in obesity
C. Its receptor is located in the hypothalamus
D. It is expressed in adipose tissue

Explanation: **Explanation:** Leptin is a peptide hormone primarily produced by **adipocytes** (white adipose tissue). It acts as a key regulator of long-term energy balance and body weight. **Why Option A is the correct answer (The Exception):** Leptin is an **anorexigenic** hormone, meaning it **decreases appetite** and increases energy expenditure. It achieves this by acting on the arcuate nucleus of the hypothalamus to inhibit NPY/AgRP neurons (which stimulate feeding) and stimulate POMC/CART neurons (which inhibit feeding). Therefore, the statement that it "increases appetite" is false. **Analysis of other options:** * **Option B (Increased in obesity):** Leptin levels are directly proportional to the total amount of body fat. In most cases of human obesity, leptin levels are high, but individuals develop **"leptin resistance,"** where the brain fails to respond to the satiety signal. * **Option C (Receptor in hypothalamus):** The leptin receptor (Ob-R) is a cytokine-family receptor (JAK-STAT pathway) located predominantly in the **arcuate nucleus of the hypothalamus**, which serves as the control center for hunger and satiety. * **Option D (Expressed in adipose tissue):** Leptin is the product of the *ob* (obese) gene and is synthesized and secreted by **adipose tissue** in proportion to fat stores. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Stimulates POMC (Anorexigenic) and inhibits NPY (Orexigenic). * **Congenital Leptin Deficiency:** A rare cause of severe, early-onset hyperphagia and morbid obesity. * **Ghrelin vs. Leptin:** Remember **G**hrelin makes you **G**row hungry (stomach), while **L**eptin makes you **L**ean (adipose). * **Sleep Deprivation:** Leads to decreased leptin and increased ghrelin, contributing to weight gain.

Question 274: Which of the following is a lipophilic hormone that acts on nuclear receptors, while the others are hydrophilic hormones that act on cytosolic receptors?

A. Thyroxine (Correct Answer)
B. Epinephrine
C. Growth Hormone (GH)
D. Adrenocorticotropic Hormone (ACTH)

Explanation: ### Explanation The classification of hormones based on their chemical nature and receptor location is a high-yield topic for NEET-PG. **Correct Answer: A. Thyroxine** Thyroxine ($T_4$) and Triiodothyronine ($T_3$) are amine-derived hormones, but unlike other amines, they are highly **lipophilic** (lipid-soluble). This property allows them to cross the cell membrane via transporters and bind to **nuclear receptors** (specifically TR$\alpha$ and TR$\beta$). Once bound, they act as transcription factors to modulate gene expression. **Analysis of Incorrect Options:** * **B. Epinephrine:** Although also an amine (derived from tyrosine), epinephrine is **hydrophilic**. It cannot cross the lipid bilayer and must bind to **G-protein coupled receptors (GPCRs)** on the cell surface. * **C. Growth Hormone (GH):** This is a large peptide hormone. Being hydrophilic, it binds to **extracellular receptors** (specifically JAK-STAT linked receptors) on the plasma membrane. * **D. ACTH:** This is a polypeptide hormone. Like GH, it is water-soluble and acts via **cell surface receptors** (specifically MC2R, which uses the cAMP second messenger system). **High-Yield Clinical Pearls for NEET-PG:** * **Exceptions to the Rule:** Most amine hormones (Catecholamines) are hydrophilic, but **Thyroid hormones** are the notable lipophilic exception. * **Receptor Locations:** * **Cytosolic Receptors:** Primarily Steroid hormones (e.g., Cortisol, Aldosterone, Vitamin D). * **Nuclear Receptors:** Thyroid hormones ($T_3/T_4$), Retinoic acid, and Estrogen (partially). * **Speed of Action:** Surface-acting hormones (Epinephrine) act within seconds via second messengers, while nuclear-acting hormones (Thyroxine) take hours to days to show effects due to the time required for protein synthesis.

Question 275: Calcium absorption from the gut is enhanced by which of the following?

A. Parathyroid hormone
B. Calcitonin
C. 1,25-dihydroxycholecalciferol (Correct Answer)
D. All of the above

Explanation: **Explanation:** The correct answer is **1,25-dihydroxycholecalciferol (Calcitriol)**. **1. Why 1,25-dihydroxycholecalciferol is correct:** Calcitriol is the active form of Vitamin D. Its primary function is to increase plasma calcium levels by enhancing intestinal absorption. It acts on the enterocytes of the duodenum and jejunum to increase the synthesis of **Calbindin-D9k** (a calcium-binding protein), **TRPV6** (calcium channels), and **Ca-ATPase**. These proteins facilitate the active transport of calcium from the gut lumen into the bloodstream. **2. Why the other options are incorrect:** * **Parathyroid Hormone (PTH):** While PTH is the master regulator of calcium, it does **not** have a direct effect on the gut. Instead, it acts on the kidneys to stimulate the enzyme **1-alpha-hydroxylase**, which converts 25-hydroxyvitamin D into active 1,25-dihydroxycholecalciferol. Thus, PTH increases gut absorption *indirectly* via Vitamin D. * **Calcitonin:** Secreted by the parafollicular (C-cells) of the thyroid, calcitonin is a "hypocalcemic" hormone. It inhibits osteoclast activity and increases renal calcium excretion. It has no significant role in enhancing gut absorption. **High-Yield Clinical Pearls for NEET-PG:** * **Rate-limiting step:** The conversion of 25(OH)D to 1,25(OH)₂D in the kidney is the rate-limiting step in Vitamin D activation. * **Vitamin D Receptors (VDR):** These are nuclear receptors; therefore, Vitamin D acts by altering gene transcription. * **Other factors increasing absorption:** Acidic pH (Gastric acid), Lactose, and Amino acids (Arginine, Lysine). * **Factors decreasing absorption:** Oxalates, Phytates, Phosphates, and Glucocorticoids.

Question 276: Which of the following is NOT a hydrophilic hormone acting on cytosolic receptors?

A. Thyroxine (Correct Answer)
B. Epinephrine
C. Growth Hormone (GH)
D. Atrial Natriuretic Peptide (ANP)

Explanation: To answer this question correctly, one must understand the relationship between a hormone's chemical nature (solubility) and its receptor location. ### **Explanation of the Correct Answer** **A. Thyroxine (T4):** This is the correct answer because it is **lipophilic** (lipid-soluble), not hydrophilic. Although derived from the amino acid tyrosine, thyroid hormones are unique because they cross the cell membrane via transporters and bind to **nuclear receptors** (not cytosolic) to alter gene transcription. ### **Analysis of Incorrect Options** * **B. Epinephrine:** This is a catecholamine and is **hydrophilic**. It cannot cross the lipid bilayer and must act on **cell surface receptors** (G-protein coupled receptors). * **C. Growth Hormone (GH):** This is a large peptide hormone and is **hydrophilic**. It acts on **cell surface receptors** (specifically JAK-STAT linked receptors). * **D. Atrial Natriuretic Peptide (ANP):** This is a peptide hormone and is **hydrophilic**. It acts on **cell surface receptors** associated with particulate guanylyl cyclase. **Note on the Question Stem:** The question asks for a hormone that is *NOT* hydrophilic acting on *cytosolic* receptors. While options B, C, and D are hydrophilic, they act on **membrane** receptors. Thyroxine is the "most" correct answer because it is fundamentally hydrophobic/lipophilic. ### **High-Yield NEET-PG Pearls** 1. **Lipophilic Hormones (Intracellular Receptors):** * **Cytosolic Receptors:** Steroids (Glucocorticoids, Mineralocorticoids, Progesterone, Testosterone). *Mnemonic: "C" for Cortisol and Cytosol.* * **Nuclear Receptors:** Thyroid hormones (T3/T4), Estrogen, Vitamin D, and Retinoic Acid. 2. **Hydrophilic Hormones (Cell Surface Receptors):** * **cAMP pathway:** ACTH, Glucagon, TSH, PTH. * **IP3/DAG pathway:** Oxytocin, GnRH, TRH. * **Tyrosine Kinase pathway:** Insulin, IGF-1. * **JAK-STAT pathway:** GH, Prolactin, Erythropoietin.

Question 277: Gigantism is due to:

A. Increased secretion of cortisol
B. Decreased secretion of cortisol
C. Increased secretion of growth hormone (Correct Answer)
D. Decreased secretion of growth hormone

Explanation: ### Explanation **Correct Answer: C. Increased secretion of growth hormone** **Medical Concept:** Gigantism is a clinical condition caused by the **excessive secretion of Growth Hormone (GH)**, typically due to a somatotroph adenoma of the anterior pituitary. The defining feature of Gigantism is that this hypersecretion occurs **before the fusion of the epiphyseal plates** (pre-puberty). Because the long bones still have active growth plates, the excess GH (acting via IGF-1) stimulates dramatic linear bone growth, leading to tall stature and increased body proportions. **Analysis of Incorrect Options:** * **Options A & B (Cortisol):** Cortisol is a glucocorticoid from the adrenal cortex. Excess cortisol leads to **Cushing’s Syndrome** (characterized by weight gain and stunted growth in children), while a deficiency leads to **Addison’s Disease**. Neither causes gigantism. * **Option D (Decreased GH):** A deficiency of growth hormone during childhood leads to **Pituitary Dwarfism**, characterized by short stature and delayed skeletal maturation. **NEET-PG High-Yield Pearls:** * **Gigantism vs. Acromegaly:** Both are caused by GH excess. If it occurs *before* epiphyseal fusion, it is **Gigantism** (increased height). If it occurs *after* fusion, it is **Acromegaly** (thickening of bones, enlarged hands/feet, and soft tissue overgrowth, but no increase in height). * **Mediator:** GH does not act directly on bones for linear growth; it stimulates the liver to produce **IGF-1 (Somatomedin C)**, which is the actual mediator of bone growth. * **Screening Test:** The best initial screening test for GH excess is measuring **Serum IGF-1 levels** (due to its stable half-life). * **Confirmatory Test:** The gold standard is the **Oral Glucose Tolerance Test (OGTT)**; failure of GH to suppress below 1 ng/mL after glucose load confirms the diagnosis.

Question 278: Normal testicular development requires which of the following?

A. XY chromosomes
B. XX chromosomes
C. Y chromosome (Correct Answer)
D. X chromosome

Explanation: The development of the male phenotype is a genetically programmed process initiated by specific genetic material rather than the entire chromosomal complement. ### **Explanation of the Correct Answer** The correct answer is the **Y chromosome** because it contains the **SRY gene** (Sex-determining Region of the Y chromosome). This gene encodes the **Testis-Determining Factor (TDF)**, a protein that acts as a master switch. In the presence of TDF, the undifferentiated primordial gonads develop into **testes** during the 7th week of gestation. Once formed, the testes secrete Testosterone (from Leydig cells) and Anti-Müllerian Hormone (from Sertoli cells) to complete male internal and external genital development. ### **Analysis of Incorrect Options** * **XY chromosomes (A):** While this is the normal male genotype, the *entire* set is not the absolute requirement for testicular initiation. Individuals with **47, XXY (Klinefelter Syndrome)** still develop testes because the presence of a single Y chromosome (and its SRY gene) is sufficient to trigger testicular differentiation. * **XX chromosomes (B):** This is the normal female genotype. In the absence of the Y chromosome, the default pathway leads to the development of ovaries. * **X chromosome (D):** The X chromosome is essential for viability but does not determine testicular development. In **45, XO (Turner Syndrome)**, the absence of a Y chromosome results in streak ovaries, not testes. ### **High-Yield Clinical Pearls for NEET-PG** * **Default Pathway:** In the absence of the SRY gene, the indifferent gonad naturally differentiates into an **ovary**. * **Swyer Syndrome:** A 46, XY individual with a mutation/deletion of the SRY gene will develop as a phenotypic female with streak gonads. * **Müllerian Inhibitory Substance (MIS):** Produced by **Sertoli cells**, it causes regression of paramesonephric ducts. * **Testosterone:** Produced by **Leydig cells**, it stimulates the development of Wolffian (mesonephric) ducts into the epididymis, vas deferens, and seminal vesicles.

Question 279: Decreased activity of type I 5’-monodeiodinase could lead to which physiologic effect?

A. Increased plasma triiodothyronine (T3)
B. Increased plasma reverse T3 (Correct Answer)
C. Decreased plasma thyroxine T4
D. Increased TSH

Explanation: ### Explanation **Concept:** The thyroid gland primarily secretes **Thyroxine (T4)**, which is a pro-hormone. To become biologically active, T4 must be converted into **Triiodothyronine (T3)**. This conversion is mediated by **5’-monodeiodinase** enzymes (Type I and Type II), which remove an iodine atom from the *outer* ring of T4. Alternatively, T4 can be converted into **reverse T3 (rT3)**—an inactive metabolite—by the action of **5-deiodinase**, which removes an iodine from the *inner* ring. **Why Option B is Correct:** When the activity of **Type I 5’-monodeiodinase** decreases (seen in starvation, severe illness, or due to drugs like PTU and propranolol), the peripheral conversion of T4 to active T3 is inhibited. Consequently, the metabolic pathway shifts: more T4 is diverted toward the production of **reverse T3 (rT3)**. Additionally, since rT3 is also normally degraded by 5’-monodeiodinase, its clearance decreases, leading to significantly **increased plasma rT3 levels**. **Analysis of Incorrect Options:** * **A. Increased plasma T3:** Incorrect. Decreased deiodinase activity directly reduces the production of T3 from T4, leading to *decreased* T3 levels. * **C. Decreased plasma T4:** Incorrect. T4 levels usually remain normal or slightly elevated because its peripheral conversion into T3 is blocked. * **D. Increased TSH:** Incorrect. In conditions where 5’-monodeiodinase is inhibited (like Euthyroid Sick Syndrome), TSH typically remains within the normal range or is paradoxically low/normal, rather than elevated as seen in primary hypothyroidism. **High-Yield Pearls for NEET-PG:** * **Type I Deiodinase:** Found in liver, kidney, and thyroid; inhibited by **Propylthiouracil (PTU)**, **Propranolol**, and **Glucocorticoids**. * **Type II Deiodinase:** Found in the pituitary and brain; maintains local T3 levels and is *not* inhibited by PTU. * **Euthyroid Sick Syndrome:** Characterized by low T3, high rT3, and normal TSH/T4. It is the most common clinical scenario involving decreased 5’-monodeiodinase activity. * **Amiodarone** also inhibits 5’-monodeiodinase, leading to increased rT3.

Question 280: Which steroid hormone is primarily involved in regulating water balance in the body?

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

Explanation: **Explanation:** **Aldosterone** is the correct answer because it is the primary mineralocorticoid secreted by the *zona glomerulosa* of the adrenal cortex. Its fundamental role is the maintenance of extracellular fluid volume and blood pressure. It acts on the **principal cells** of the distal convoluted tubule and collecting ducts to increase sodium reabsorption and potassium secretion. Since water follows sodium osmotically (obligatory water reabsorption), aldosterone effectively increases water retention, thereby regulating the body's water balance. **Analysis of Incorrect Options:** * **Estrogen:** While estrogens can cause some salt and water retention (often noticed during menstrual cycles), their primary role is the development of female secondary sexual characteristics and reproductive regulation. * **Testosterone:** This is an androgen responsible for male secondary sexual characteristics and spermatogenesis; it has negligible effects on acute water balance. * **Vitamin D (Calcitriol):** Though structurally a steroid hormone, its primary function is the regulation of **calcium and phosphate** homeostasis by increasing intestinal absorption, not water balance. **NEET-PG High-Yield Pearls:** * **Mechanism of Action:** Aldosterone binds to intracellular mineralocorticoid receptors (MR), leading to the up-regulation of **ENaC** (Epithelial Sodium Channels) and the **Na+/K+ ATPase** pump. * **Primary Stimulus:** The most potent stimulators of aldosterone secretion are **Hyperkalemia** (increased K+) and **Angiotensin II**. * **Conn’s Syndrome:** Primary hyperaldosteronism characterized by the triad of hypertension, hypokalemia, and metabolic alkalosis. * **Spironolactone:** A potassium-sparing diuretic that acts as a competitive antagonist to the aldosterone receptor.

Practice by Chapter

Principles of Endocrine Regulation

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Hypothalamus and Pituitary Gland

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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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