Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 191: The alpha chain of human chorionic gonadotropin (HCG) is identical to which of the following hormones except?

A. Luteinizing hormone (LH)
B. Thyroid-stimulating hormone (TSH)
C. Follicle-stimulating hormone (FSH)
D. Adrenocorticotropic hormone (ACTH) (Correct Answer)

Explanation: **Explanation:** The correct answer is **Adrenocorticotropic hormone (ACTH)**. **The Underlying Concept:** In human physiology, there is a specific family of **glycoprotein hormones** that share a common structural blueprint. This family includes **hCG, TSH, LH, and FSH**. These hormones are heterodimers, meaning they consist of two non-covalently linked subunits: 1. **Alpha (α) subunit:** This is **identical** in all four hormones (coded by the same gene on chromosome 6). 2. **Beta (β) subunit:** This is **unique** to each hormone and determines the specific biological activity and receptor specificity. **Why ACTH is the correct answer:** ACTH is a polypeptide hormone derived from the precursor molecule **Pro-opiomelanocortin (POMC)**. It is not a glycoprotein and does not share the alpha-beta dimeric structure. Therefore, it does not possess the common alpha chain shared by the others. **Analysis of Incorrect Options:** * **LH, TSH, and FSH:** These are all members of the glycoprotein hormone family. They all contain the exact same 92-amino acid alpha subunit. Their functional differences arise solely from their distinct beta subunits. **NEET-PG High-Yield Pearls:** * **Cross-reactivity:** Because hCG and LH have highly similar beta subunits (sharing ~80% sequence identity), hCG can bind to LH receptors. This is why hCG is used clinically to trigger ovulation or treat cryptorchidism. * **Pregnancy & Thyroid:** High levels of hCG during the first trimester can weakly stimulate TSH receptors (due to the identical alpha chain), sometimes leading to a physiological decrease in TSH levels (Gestational Transient Thyrotoxicosis). * **Diagnostic Tip:** Pregnancy tests and tumor marker assays specifically measure the **beta-hCG** subunit to avoid cross-reactivity with LH, FSH, or TSH.

Question 192: Polar bodies are formed during which process?

A. Spermatogenesis
B. Organogenesis
C. Oogenesis (Correct Answer)
D. Morphogenesis

Explanation: **Explanation:** **Correct Answer: C. Oogenesis** Polar bodies are small, non-functional cells produced during the process of **oogenesis**. In females, meiosis is characterized by **unequal cytoplasmic division**. * **Meiosis I:** The primary oocyte divides to produce one large secondary oocyte and the **first polar body**. * **Meiosis II:** The secondary oocyte (arrested in metaphase II until fertilization) divides to produce one large mature ovum and the **second polar body**. The purpose of polar body formation is to discard extra sets of chromosomes while conserving the maximum amount of cytoplasm and organelles for the potential zygote. **Why other options are incorrect:** * **A. Spermatogenesis:** Unlike oogenesis, spermatogenesis involves **equal cytoplasmic division**. One primary spermatocyte yields four functional, equal-sized spermatozoa; no polar bodies are formed. * **B. Organogenesis:** This is the phase of embryonic development where germ layers differentiate into specific organs (e.g., neurulation). * **D. Morphogenesis:** This refers to the biological process that causes an organism to develop its shape, involving cell growth and differentiation. **NEET-PG High-Yield Pearls:** 1. **Meiotic Arrests:** Oogenesis arrests twice—first in **Prophase I (Diplotene stage)** at birth, and second in **Metaphase II** at ovulation (completed only if fertilization occurs). 2. **Number of Polar Bodies:** Usually, two polar bodies are formed. However, if the first polar body also undergoes meiosis II, a total of three may be present. 3. **Clinical Utility:** Polar body biopsy is sometimes used in Preimplantation Genetic Testing (PGT) to detect maternal genetic abnormalities without damaging the embryo.

Question 193: Regarding the action of insulin, which of the following is true?

A. Decreased K+ uptake in adipose tissue
B. Increased protein catabolism in muscle
C. Activation of hormone-sensitive lipase
D. Decreased ketogenesis in the liver (Correct Answer)

Explanation: **Explanation:** Insulin is the body’s primary **anabolic hormone**, secreted by the beta cells of the pancreas. Its overarching function is to promote energy storage and inhibit the mobilization of fuel reserves. **Why Option D is Correct:** Insulin **decreases ketogenesis** in the liver through two main mechanisms: 1. It inhibits **Hormone-Sensitive Lipase (HSL)** in adipose tissue, reducing the supply of free fatty acids (FFAs) to the liver. 2. It inhibits **Carnitine Palmitoyltransferase-1 (CPT-1)**, the rate-limiting enzyme for beta-oxidation, thereby preventing the conversion of fatty acids into ketone bodies. This is why insulin deficiency leads to Diabetic Ketoacidosis (DKA). **Analysis of Incorrect Options:** * **Option A:** Insulin **increases K+ uptake** into cells (muscle and adipose) by stimulating the Na+/K+ ATPase pump. This is why insulin/glucose infusion is a standard treatment for hyperkalemia. * **Option B:** Insulin is anabolic; it **increases protein synthesis** and **decreases protein catabolism** in muscle. * **Option C:** Insulin **inhibits Hormone-Sensitive Lipase (HSL)** to prevent lipolysis and instead activates **Lipoprotein Lipase (LPL)** to promote triglyceride storage in adipocytes. **High-Yield Clinical Pearls for NEET-PG:** * **GLUT-4:** The only insulin-dependent glucose transporter, found in skeletal muscle and adipose tissue. * **Enzyme Regulation:** Insulin dephosphorylates enzymes (usually activating them, except for HSL and Glycogen Phosphorylase, which are inactivated). * **Antagonism:** Glucagon, Epinephrine, Cortisol, and Growth Hormone are "counter-regulatory" hormones that oppose insulin's actions.

Question 194: Which of the following has the highest glycemic index?

A. Corn flakes (Correct Answer)
B. White rice
C. Ice cream
D. Whole wheat bread

Explanation: **Explanation:** The **Glycemic Index (GI)** is a ranking of carbohydrates on a scale of 0 to 100 based on how quickly and significantly they raise blood glucose levels after consumption. Foods with a high GI (>70) are rapidly digested and absorbed, causing a sharp spike in blood sugar. **Why Corn Flakes is Correct:** **Corn flakes** have one of the highest glycemic indices (approximately **81–93**) among common breakfast cereals. This is due to the extensive processing (extrusion and high-heat treatment) which gelatinizes the starch, making it extremely easy for pancreatic amylase to break it down into glucose rapidly. **Analysis of Incorrect Options:** * **White Rice (GI ~70-73):** While high, it is generally lower than corn flakes. The GI can vary based on the amylose content; however, it typically sits at the lower end of the "high GI" category. * **Whole Wheat Bread (GI ~71-74):** Despite containing more fiber than white bread, the finely ground flour used in most commercial whole wheat bread allows for quick enzymatic digestion, resulting in a high GI, but still lower than processed corn flakes. * **Ice Cream (GI ~50-60):** Surprisingly, ice cream has a **low to medium GI**. This is because its high **fat and protein content** slows down gastric emptying and delays the absorption of sugars into the bloodstream. **High-Yield Clinical Pearls for NEET-PG:** 1. **Factors lowering GI:** High fiber content, presence of fat/protein, and acidity (e.g., vinegar/lemon) all lower the GI of a meal by slowing digestion. 2. **Glycemic Load (GL):** This is a more accurate clinical measure than GI as it accounts for the **portion size** (GL = GI × grams of carbohydrate / 100). 3. **Clinical Application:** Low GI diets are preferred in managing **Diabetes Mellitus** and **PCOS** to prevent postprandial hyperinsulinemia.

Question 195: Which one of the following cell types is found in the least numbers in the pituitary gland?

A. Lactotrophs
B. Thyrotrophs (Correct Answer)
C. Gonadotrophs
D. Corticotrophs

Explanation: The anterior pituitary (adenohypophysis) contains five distinct cell types that secrete specific hormones. These cells are distributed in varying proportions, which is a high-yield topic for NEET-PG. ### **Why Thyrotrophs are the Correct Answer** **Thyrotrophs** are the least abundant cell type in the anterior pituitary, accounting for only **3–5%** of the total cell population. They secrete Thyroid-Stimulating Hormone (TSH). Despite their small number, they are highly efficient in maintaining systemic metabolic homeostasis. ### **Analysis of Incorrect Options** * **Lactotrophs (Option A):** These make up about **15–25%** of the gland. They secrete Prolactin. Their numbers can significantly increase (hyperplasia) during pregnancy and lactation due to estrogen stimulation. * **Gonadotrophs (Option C):** These constitute approximately **10–15%** of the cells. They are unique because a single cell type typically secretes two different hormones: LH and FSH. * **Corticotrophs (Option D):** These make up about **15–20%** of the cells and secrete ACTH. They are usually the first cells to recover after pituitary suppression. *(Note: **Somatotrophs**, which secrete Growth Hormone, are the **most abundant** cell type, comprising about 40–50% of the gland.)* ### **High-Yield NEET-PG Pearls** 1. **Abundance Hierarchy:** Somatotrophs (50%) > Lactotrophs (20%) > Corticotrophs (15%) > Gonadotrophs (10%) > **Thyrotrophs (5%)**. 2. **Staining Characteristics:** * **Acidophils:** Somatotrophs and Lactotrophs (Mnemonic: **GPA** – **G**rowth hormone, **P**rolactin are **A**cidophils). * **Basophils:** Corticotrophs, Thyrotrophs, and Gonadotrophs (Mnemonic: **B-FLAT** – **B**asophils are **F**SH, **L**H, **A**CTH, **T**SH). 3. **Location:** Thyrotrophs are primarily located in the **anteromedial** portion of the pituitary.

Question 196: Insulin secretion is inhibited by all of the following, EXCEPT:

A. Somatostatin
B. Beta-adrenergic blockers
C. Beta-ketoacids (Correct Answer)
D. Diazoxide

Explanation: **Explanation:** Insulin secretion from the pancreatic beta cells is a highly regulated process. To answer this question, one must distinguish between factors that inhibit insulin release and those that stimulate it. **Why Beta-ketoacids is the correct answer:** Beta-ketoacids (such as acetoacetate and beta-hydroxybutyrate) actually **stimulate** insulin secretion. This serves as a crucial physiological negative feedback loop: as ketone bodies rise (e.g., during fasting or starvation), they trigger a modest release of insulin to prevent runaway ketogenesis and the development of ketoacidosis. Therefore, they do not inhibit insulin; they promote it. **Analysis of incorrect options (Inhibitors of Insulin):** * **Somatostatin:** Known as the "universal endocrine off-switch," paracrine secretion of somatostatin from delta cells directly inhibits both insulin and glucagon release. * **Beta-adrenergic blockers:** Beta-2 receptors on pancreatic beta cells stimulate insulin release. Therefore, blocking these receptors (or alpha-adrenergic stimulation) results in the **inhibition** of insulin secretion. * **Diazoxide:** This drug is a potassium channel opener. By keeping the ATP-sensitive $K^+$ channels open, it hyperpolarizes the beta cell membrane, preventing calcium influx and thereby **inhibiting** insulin release. It is clinically used to treat hyperinsulinism. **NEET-PG High-Yield Pearls:** * **The "Incretin Effect":** Oral glucose stimulates more insulin than IV glucose due to GIP and GLP-1. * **Rate-limiting step:** The phosphorylation of glucose by **Glukokinase** is the glucose-sensor in beta cells. * **Alpha vs. Beta:** Alpha-2 adrenergic stimulation **inhibits** insulin, while Beta-2 stimulation **increases** it. In a "fight or flight" response, alpha-dominance ensures insulin is suppressed to keep blood glucose high for the brain and muscles.

Question 197: Which immunoglobulin lacks a hinge region?

A. IgA
B. IgG
C. IgD
D. IgE (Correct Answer)

Explanation: **Explanation:** The structure of an immunoglobulin molecule consists of two heavy chains and two light chains. In certain classes of antibodies, a flexible **hinge region** (rich in proline and cysteine) exists between the $C_H1$ and $C_H2$ domains of the heavy chains, allowing the Fab arms to move freely to bind antigens. **Why IgE is the Correct Answer:** Immunoglobulins are divided based on their heavy chain structure. **IgE and IgM** do not have a hinge region. Instead of a hinge, they possess an **extra constant domain ($C_H4$)** in their heavy chains. This additional domain provides the structural integrity that the hinge region would otherwise provide. Since IgE is the only option listed among the two that lack a hinge, it is the correct choice. **Analysis of Incorrect Options:** * **IgA, IgG, and IgD:** These three isotopes possess a distinct **hinge region** between the $C_H1$ and $C_H2$ domains. They consist of only three constant domains ($C_H1, C_H2, C_H3$). The hinge region provides these antibodies with segmental flexibility, which is crucial for binding to epitopes spaced at varying distances. **High-Yield Facts for NEET-PG:** * **Mnemonic:** "E and M have an Extra domain" (IgE and IgM have 4 constant domains and no hinge). * **IgE:** Mediates Type I Hypersensitivity (allergic reactions) and provides immunity against helminthic parasites by activating mast cells and basophils. * **IgM:** The largest antibody (pentamer) and the first to appear in a primary immune response. * **IgG:** The only antibody that crosses the placenta and is the most abundant in serum. * **IgA:** The primary secretory antibody found in colostrum, saliva, and tears.

Question 198: Parathormone (PTH) increases calcium levels and reduces phosphate levels by acting on which part of the nephron?

A. Proximal tubules
B. Distal tubules
C. Thick ascending limb of Loop of Henle
D. All of the above (Correct Answer)

Explanation: **Explanation:** Parathormone (PTH) is the primary regulator of calcium and phosphate homeostasis. Its action on the kidney is multi-segmental, aimed at increasing serum calcium and decreasing serum phosphate. 1. **Proximal Tubule (PT):** This is the primary site for phosphate regulation. PTH binds to its receptors and inhibits the **Na⁺-PO₄³⁻ cotransporter (NPT2a)**, leading to phosphaturia (decreased phosphate levels). It also stimulates **1-alpha-hydroxylase** here, converting Vitamin D to its active form. 2. **Distal Convoluted Tubule (DCT):** This is the major site for PTH-mediated **calcium reabsorption**. PTH increases the opening of apical calcium channels (TRPV5), effectively raising serum calcium levels. 3. **Thick Ascending Limb (TAL):** PTH enhances the activity of the **Na⁺-K⁺-2Cl⁻ symporter**, which increases the positive luminal potential, thereby driving the paracellular reabsorption of calcium and magnesium. **Why "All of the above" is correct:** While textbooks often emphasize the PT for phosphate and the DCT for calcium, PTH receptors are present across all these segments. It acts on the PT to decrease phosphate and on the TAL and DCT to increase calcium reabsorption. Therefore, its net effect on the nephron involves all three segments. **Clinical Pearls for NEET-PG:** * **Mnemonic for PTH:** "P"TH = **P**hosphate **T**rash (increases phosphate excretion in the urine). * **Site of Action:** The most potent site for calcium reabsorption is the DCT, but the TAL also contributes significantly. * **Cyclic AMP:** PTH action on the proximal tubule increases urinary cAMP, which is a clinical marker for PTH activity. * **Hypoparathyroidism:** Results in hypocalcemia and hyperphosphatemia due to the loss of these renal actions.

Question 199: Which of the following statements can be regarded as the primary action of inhibin?

A. It inhibits the secretion of prolactin.
B. It stimulates the synthesis of estradiol.
C. It stimulates the secretion of TSH.
D. It inhibits the secretion of FSH. (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. It inhibits the secretion of FSH.** **Mechanism of Action:** Inhibin is a glycoprotein hormone belonging to the **transforming growth factor-beta (TGF-β) superfamily**. It is produced primarily by the **Sertoli cells** in males and the **Granulosa cells** in females. Its primary physiological role is the **selective negative feedback inhibition** of Follicle-Stimulating Hormone (FSH) secretion from the anterior pituitary. Unlike GnRH or sex steroids, inhibin does not significantly affect the secretion of Luteinizing Hormone (LH), making it a specific regulator of the FSH axis. **Analysis of Incorrect Options:** * **A & C (Prolactin and TSH):** Inhibin has no physiological role in regulating the secretion of Prolactin or Thyroid-Stimulating Hormone (TSH). These are regulated by Dopamine/TRH and TRH/Somatostatin, respectively. * **B (Estradiol Synthesis):** Inhibin does not stimulate estradiol synthesis. In fact, **Activin** (another member of the TGF-β family) is the hormone that stimulates FSH secretion and promotes granulosa cell aromatase activity, leading to increased estradiol. **High-Yield Clinical Pearls for NEET-PG:** * **Inhibin B vs. Inhibin A:** Inhibin B is the primary form in males (marker of spermatogenesis) and the early follicular phase in females. Inhibin A is dominant in the luteal phase and during pregnancy (produced by the corpus luteum and placenta). * **Clinical Marker:** Inhibin B levels are used as a clinical marker for **ovarian reserve** and **Sertoli cell function**. * **Tumor Marker:** Elevated Inhibin levels are a highly specific marker for **Granulosa Cell Tumors** of the ovary. * **The "Counter-Hormone":** Remember **Activin** as the functional antagonist to Inhibin; it stimulates FSH release.

Question 200: Which of the following hormones are produced by the endocrine pancreas?

A. Insulin
B. Somatostatin
C. Glucagon
D. All of the above (Correct Answer)

Explanation: The endocrine pancreas consists of clusters of cells known as the **Islets of Langerhans**, which constitute about 1–2% of the total pancreatic mass. These islets contain several distinct cell types, each secreting a specific hormone directly into the bloodstream to regulate glucose homeostasis and metabolic functions. **Explanation of the Correct Answer:** The correct answer is **D (All of the above)** because the Islets of Langerhans produce all three listed hormones: * **Insulin:** Secreted by **Beta (β) cells** (the most abundant, ~60–70% of islet cells). It is an anabolic hormone that lowers blood glucose. * **Glucagon:** Secreted by **Alpha (α) cells** (~20–25%). It is a catabolic hormone that raises blood glucose via glycogenolysis and gluconeogenesis. * **Somatostatin:** Secreted by **Delta (δ) cells** (~5–10%). It acts primarily as a paracrine inhibitor, suppressing the secretion of both insulin and glucagon. **Why individual options are insufficient:** While A, B, and C are all correct, selecting any single one would be incomplete. The endocrine pancreas is a multi-hormonal organ that also secretes **Pancreatic Polypeptide (PP cells/F cells)** and small amounts of **Ghrelin (Epsilon cells)**. **High-Yield NEET-PG Clinical Pearls:** * **Blood Flow Pattern:** Blood flows from the center of the islet (rich in β-cells) to the periphery. This means insulin can inhibit glucagon secretion directly via intra-islet microcirculation. * **Markers:** **C-peptide** is a clinical marker used to assess endogenous insulin production, as it is secreted in a 1:1 molar ratio with insulin. * **Tumor Association:** Pancreatic neuroendocrine tumors (PNETs) like Insulinomas (hypoglycemia) or Gastrinomas (Zollinger-Ellison Syndrome) often arise from these cell types. * **Innervation:** Parasympathetic stimulation (Vagus) increases insulin secretion, while Sympathetic stimulation (α2 receptors) inhibits it.

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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