Inflammation and Repair — MCQs

Inflammation and Repair Indian Medical PG Practice Questions and MCQs

Question 261: Which condition does not typically exhibit granuloma formation?

A. Tuberculosis
B. Sarcoidosis
C. Leprosy
D. Infarction (Correct Answer)

Explanation: **Explanation:** **1. Why Infarction is the Correct Answer:** Infarction refers to tissue death (necrosis) resulting from ischemia. The typical response to an acute infarct is **Coagulative Necrosis** (except in the brain, where it is liquefactive). This process triggers **Acute Inflammation**, characterized by neutrophil infiltration, followed by chronic non-specific inflammation and eventual repair by fibrosis (scarring). It does not involve the formation of granulomas, which are a hallmark of **Chronic Granulomatous Inflammation** [4]. **2. Analysis of Incorrect Options:** * **Tuberculosis (A):** The classic example of granulomatous inflammation [4]. It features **caseating granulomas** with a central zone of necrosis, surrounded by epithelioid cells, Langhans giant cells, and a peripheral rim of lymphocytes [3]. * **Sarcoidosis (B):** Characterized by **non-caseating granulomas** [1]. High-yield histological findings include **Schumann bodies** and **Asteroid bodies** within giant cells. * **Leprosy (C):** Caused by *Mycobacterium leprae*. Tuberculoid leprosy presents with well-formed granulomas [5], while lepromatous leprosy shows foamy macrophages (Virchow cells) due to a poor T-cell response. **3. NEET-PG Clinical Pearls:** * **Definition of a Granuloma:** A microscopic aggregation of **epithelioid cells** (activated macrophages) surrounded by a collar of mononuclear leukocytes (lymphocytes and plasma cells) [3]. * **Epithelioid cells** are the diagnostic hallmark; they are modified macrophages with abundant pink cytoplasm resembling epithelial cells [3]. * **Common Causes of Granulomas (Mnemonic: "SPECKS"):** **S**arcoidosis [1], **P**rimary Biliary Cholangitis, **E**xogenous (Foreign body) [2], **C**at Scratch Disease, **K** (C)rohn’s Disease, **S**yphilis/Schistosomiasis [4]. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 198-200. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 196-197. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, p. 109. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, p. 360. [5] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 385-386.

Question 262: A patient with previously good muscle mass now presents with decreased muscle mass after being bedridden for 6 months following a road traffic accident. What is the best explanation for this decrease in muscle mass?

A. Metaplasia
B. Dysplasia
C. Hypertrophy
D. Atrophy (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Atrophy** **Concept:** Atrophy is defined as the shrinkage in the size of cells by the loss of cell substance [2]. When a sufficient number of cells are involved, the entire organ or tissue decreases in size. In this clinical scenario, the patient is bedridden, leading to **disuse atrophy** [1]. The lack of physical activity and mechanical loading on the skeletal muscles results in a decrease in protein synthesis and an increase in protein degradation (primarily via the **Ubiquitin-proteasome pathway**) [2]. Additionally, increased autophagy (self-eating) contributes to the reduction in cell components [2]. **Why other options are incorrect:** * **A. Metaplasia:** This is a reversible change in which one adult cell type (epithelial or mesenchymal) is replaced by another adult cell type (e.g., Squamous metaplasia in the lungs of smokers). It does not involve a loss of mass. * **B. Dysplasia:** This refers to disordered growth and maturation of an epithelium, characterized by a loss of architectural uniformity and cellular pleomorphism. It is often a precursor to malignancy. * **C. Hypertrophy:** This is the opposite of atrophy; it is an increase in the size of cells resulting in an increase in the size of the organ, usually due to increased functional demand (e.g., a bodybuilder’s muscles). **NEET-PG High-Yield Pearls:** * **Mechanism of Atrophy:** The hallmark biochemical pathway is the **Ubiquitin-proteasome pathway** [2]. Nutrient deficiency and disuse activate ubiquitin ligases, which tag proteins for degradation in proteasomes. * **Brown Atrophy:** In chronic wasting diseases, the accumulation of **Lipofuscin** (wear-and-tear pigment) in atrophied organs (like the heart) is termed "Brown Atrophy." * **Common Causes of Atrophy:** Disuse (immobilization), denervation (loss of nerve supply), diminished blood supply (ischemia), inadequate nutrition, and loss of endocrine stimulation [1], [2]. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 90-91. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Cellular Responses to Stress and Toxic Insults: Adaptation, Injury, and Death, pp. 47-49.

Question 263: Proliferation of mature fibroblasts occurs in which of the following conditions?

A. Keloid (Correct Answer)
B. Hypertrophic scar
C. Both of the above
D. None of the above

Explanation: **Explanation:** The correct answer is **A. Keloid**. The fundamental distinction between a keloid and a hypertrophic scar lies in the cellular composition and the organization of the collagen matrix. 1. **Why Keloid is correct:** A keloid is characterized by the **proliferation of mature fibroblasts** and the deposition of thick, eosinophilic, "glassy" type I and III collagen bundles (hyalinized collagen) [1]. Unlike normal wound healing, keloids extend **beyond the boundaries** of the original injury and rarely regress [1], [2]. The persistent activity of mature fibroblasts leads to an overabundance of extracellular matrix. 2. **Why Hypertrophic Scar is incorrect:** While hypertrophic scars also involve increased collagen, they primarily consist of **younger, active myofibroblasts** arranged in a parallel fashion [3]. Crucially, hypertrophic scars remain **confined to the borders** of the original wound and frequently undergo spontaneous regression over time as the myofibroblasts disappear. 3. **Why "Both" is incorrect:** Because the question specifically highlights the presence of *mature* fibroblasts as a distinguishing pathological feature, it points toward the stable, exuberant growth of a keloid rather than the transient, myofibroblast-driven nature of a hypertrophic scar. **High-Yield NEET-PG Pearls:** * **Keloids:** Common in dark-skinned individuals (African descent); predilection for the earlobes, shoulders, and sternum; high recurrence rate after surgery [1]. * **Collagen Type:** Both involve Type I and III collagen, but keloids have a much higher ratio of Type I to Type III. * **Microscopy:** Look for "thick, wavy, hyalinized collagen bundles" (Keloid) vs. "parallel collagen fibers and myofibroblasts" (Hypertrophic scar) [2]. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 106-107. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, p. 121. [3] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 105-106.

Question 264: Delayed prolonged leakage following tissue injury is due to:

A. Cytokine-mediated vasodilation
B. Histamine
C. Endothelial retraction
D. Direct effect of the injuring agent (Correct Answer)

Explanation: ### Explanation Increased vascular permeability is the hallmark of acute inflammation, leading to the formation of exudate. The pattern of leakage depends on the severity and nature of the injury. **Why "Direct effect of the injuring agent" is correct:** Delayed prolonged leakage (starting after 2–12 hours and lasting for several days) is typically caused by **direct endothelial cell injury** [1]. This occurs in conditions like thermal burns, radiation (e.g., sunburn), or certain bacterial toxins [1]. The delay occurs because the damage, while immediate, takes time to manifest as cellular necrosis and detachment. Since the vessels must be repaired or replaced, the leakage is prolonged. **Analysis of Incorrect Options:** * **A. Cytokine-mediated vasodilation:** While cytokines (like TNF and IL-1) increase blood flow, they are not the primary drivers of the *leakage* mechanism itself; they usually induce endothelial activation rather than direct leakage [2]. * **B. Histamine:** Histamine causes the **Immediate Transient Response** [1]. It acts on H1 receptors to cause endothelial contraction in post-capillary venules. This response starts immediately and lasts only 15–30 minutes [1]. * **C. Endothelial retraction:** This is a reversible process mediated by cytokines (IL-1, TNF) and hypoxia. It involves the reorganization of the cytoskeleton, leading to gaps. While it can be delayed, it is distinct from the "prolonged" leakage caused by cell death/necrosis. **NEET-PG High-Yield Pearls:** 1. **Immediate Transient Response:** Most common pattern; mediated by Histamine/Bradykinin; affects **venules** only [1]. 2. **Delayed Prolonged Leakage:** Caused by direct injury (e.g., Sunburn); affects **capillaries and venules**. 3. **Immediate Sustained Response:** Seen in severe burns or lytic bacterial infections; leakage starts immediately and continues until the vessel thromboses or is repaired. 4. **Leukocyte-mediated injury:** Occurs during the late stages of inflammation due to the release of ROS and proteolytic enzymes by adherent neutrophils [2]. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 187-188. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, p. 101.

Question 265: Which one of the following statements about chemical mediators of inflammation is NOT true?

A. Leukotrienes are formed by the lipoxygenase pathway.
B. Histamine is a preformed chemical mediator.
C. Prostaglandins cause vasodilation at the site of inflammation. (Correct Answer)
D. Thromboxane A2 is associated with platelet aggregation.

Explanation: ### Explanation This question tests your knowledge of the **Arachidonic Acid (AA) pathway** and the properties of vasoactive amines [1]. **Why Option C is the "Correct" (False) Statement:** While the statement "Prostaglandins cause vasodilation" is physiologically true for many prostaglandins (like $PGE_2$, $PGD_2$, and $PGI_2$) [1], in the context of this specific question format, it is often considered the "least accurate" or "incorrect" if the examiner is looking for a specific exception or if the option is phrased too broadly. However, in standard pathology (Robbins), prostaglandins are indeed potent vasodilators [1]. *Note: In some competitive exams, if this is the keyed answer, it may be due to a technicality regarding specific subtypes (e.g., $PGF_{2\alpha}$ causes vasoconstriction) or a potential error in the question's source key. However, based on standard medical literature, Options A, B, and D are indisputably true.* **Analysis of Other Options:** * **Option A (True):** Arachidonic acid is converted by **5-Lipoxygenase** into Leukotrienes ($LTB_4$, $LTC_4$, $LTD_4$, $LTE_4$). $LTB_4$ is a potent chemotactic agent [1]. * **Option B (True):** **Histamine** and Serotonin are "preformed" mediators stored in mast cell granules [1], allowing for an immediate response during the early phase of inflammation. * **Option D (True):** **Thromboxane $A_2$ ($TXA_2$)** is produced by platelets via the cyclooxygenase pathway; it is a powerful vasoconstrictor and a potent inducer of platelet aggregation [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Vasodilation:** Prostaglandins ($PGE_2$, $PGI_2$), Histamine, Nitric Oxide [1]. * **Vasoconstriction:** Thromboxane $A_2$, Leukotrienes ($C_4, D_4, E_4$), Endothelin [1]. * **Chemotaxis:** $LTB_4$, $C5a$, IL-8, and Bacterial products (N-formyl methionine) [1]. * **Pain & Fever:** $PGE_2$ is the primary mediator responsible for pain (sensitizes nerve endings) and fever (hypothalamic action) [1]. * **Aspirin/NSAIDs:** Act by inhibiting Cyclooxygenase (COX), thereby blocking Prostaglandin synthesis [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 93-101.

Question 266: Chemotaxis in response to activation of cells results in what type of movement?

A. Random multidirectional movement
B. Unidirectional motion (Correct Answer)
C. Adhesion to endothelium
D. Augmented oxygen dependent bactericidal effect

Explanation: **Explanation:** **1. Why Option B is Correct:** Chemotaxis is defined as the **unidirectional movement** of cells (such as neutrophils and macrophages) along a chemical gradient toward the site of injury [1]. When inflammatory mediators (chemoattractants) bind to G-protein coupled receptors (GPCRs) on the leukocyte surface, it triggers actin polymerization at the leading edge (lamellipodia). This allows the cell to move purposefully toward the highest concentration of the attractant, rather than wandering aimlessly [4]. **2. Why Other Options are Incorrect:** * **Option A (Random movement):** This describes *chemokinesis*, where the speed of movement increases but the direction is random. Chemotaxis, by contrast, is strictly directional. * **Option C (Adhesion to endothelium):** This refers to the "pavementing" or "stable adhesion" phase of leukocyte extravasation, mediated by **Integrins** (ICAM-1/VCAM-1), which occurs before chemotaxis begins [3]. * **Option D (Augmented oxygen-dependent effect):** This describes the **Respiratory Burst**, which occurs during the killing phase of phagocytosis via NADPH oxidase, not during the migration phase [2]. **3. High-Yield Clinical Pearls for NEET-PG:** * **Exogenous Chemoattractants:** Most common are bacterial products (e.g., N-formylmethionine peptides). * **Endogenous Chemoattractants (The "Big Four"):** 1. **C5a** (Complement system) [2] 2. **LTB4** (Leukotriene B4) 3. **IL-8** (The primary chemokine for neutrophils) 4. **PAF** (Platelet Activating Factor) * **Defect in Chemotaxis:** Seen in **Chediak-Higashi Syndrome** (due to microtubule dysfunction) and **Lazy Leukocyte Syndrome**. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 190-191. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 163-164. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Migration in the tissues toward a chemotactic stimulus, pp. 86-87. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 87-89.

Question 267: A 59-year-old man suffers a massive heart attack and expires 24 hours later due to ventricular arrhythmia. Histologic examination of the affected heart muscle at autopsy would show an abundance of which of the following inflammatory cells?

A. Fibroblasts
B. Lymphocytes
C. Macrophages
D. Neutrophils (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Neutrophils** **Concept:** The timeline of myocardial infarction (MI) is a high-yield topic in pathology. Following an acute ischemic injury, the heart muscle undergoes **coagulative necrosis**. This triggers an acute inflammatory response. * **0–24 hours:** The earliest changes include wavy fibers and contraction bands. By the end of 24 hours, the inflammatory cascade begins [2]. * **1–3 days:** This period is characterized by a **dense infiltrate of neutrophils** [1]. These are the first responders to acute inflammation and are responsible for clearing the necrotic debris [2]. **Why the other options are incorrect:** * **A. Fibroblasts:** These appear during the **repair phase (1–2 weeks)**. They lay down collagen to form a stable scar (granulation tissue). * **B. Lymphocytes:** These are typically seen in chronic inflammation or viral myocarditis, not in the acute phase of a sterile infarct. * **C. Macrophages:** While they arrive shortly after neutrophils, their peak concentration occurs between **3–7 days** post-MI to phagocytose dead myocytes [2]. This is also the period when the ventricular wall is weakest (risk of rupture). **NEET-PG High-Yield Pearls:** * **Earliest gross change (2–12 hrs):** Occasional mottling; can be visualized using **Triphenyl Tetrazolium Chloride (TTC) stain** (infarct appears pale/white as it lacks LDH) [3]. * **Most common cause of death (0–24 hrs):** Ventricular Arrhythmia (as seen in this patient). * **Most common cause of death (3–7 days):** Ventricular wall rupture leading to cardiac tamponade. * **Final Outcome:** A healed MI results in a **collagenous scar** (completed by 6–8 weeks). **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, p. 89. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Heart, p. 552. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Heart, pp. 552-554.

Question 268: Which of the following is NOT a chemoattractant?

A. Leukotriene B4
B. IL8
C. C5a
D. C3 (Correct Answer)

Explanation: **Explanation:** Chemotaxis is the process by which leukocytes migrate toward the site of injury along a chemical gradient. For a molecule to act as a **chemoattractant**, it must bind to specific G protein-coupled receptors on the surface of leukocytes to induce motility. **Why C3 is the correct answer:** Complement **C3** is an inactive precursor molecule. It must be cleaved into its active fragments, **C3a** and **C3b**, to exert biological effects. While C3a acts as an anaphylatoxin (increasing vascular permeability) and C3b acts as an opsonin (enhancing phagocytosis) [1], neither C3 nor its fragments are potent chemoattractants for neutrophils. **Analysis of Incorrect Options:** * **Leukotriene B4 (LTB4):** A product of the lipoxygenase pathway of arachidonic acid metabolism. It is one of the most potent endogenous chemoattractants for neutrophils. * **IL-8 (Interleukin-8):** A major chemokine secreted by macrophages and endothelial cells. It specifically recruits and activates neutrophils. * **C5a:** A powerful chemotactic agent and anaphylatoxin [1]. It is the only component of the complement system that acts as a significant chemoattractant for neutrophils, monocytes, and eosinophils [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Exogenous Chemoattractants:** The most common are bacterial products, specifically those containing **N-formylmethionine** termini. * **Endogenous Chemoattractants (The "Big Four"):** Remember the mnemonic **"C-I-L-B"** — **C**5a, **I**L-8, **L**eukotriene **B**4, and Bacterial products. * **Opsonins:** The most important are **C3b** and **IgG** (Fc fragment). Do not confuse opsonization (tagging) with chemotaxis (recruiting). **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 163-164.

Question 269: Vasodilatation secondary to trauma is mediated by?

A. Histamine (Correct Answer)
B. IL-2
C. TGF-b
D. FGF

Explanation: **Explanation:** **1. Why Histamine is Correct:** Vasodilation is the earliest hemodynamic change in acute inflammation [2]. Following a transient vasoconstriction (lasting seconds), vasodilation occurs, resulting in increased blood flow (hyperemia). This process is primarily mediated by **Histamine** [1]. Histamine is pre-formed and stored in the granules of **mast cells**, basophils, and platelets. Upon trauma or physical injury, mast cells degranulate, releasing histamine which acts on H1 receptors on vascular smooth muscle cells to cause rapid vasodilation and increased vascular permeability [3]. **2. Why Other Options are Incorrect:** * **IL-2 (Interleukin-2):** Produced by T-cells, it primarily functions as a T-cell growth factor and is involved in the adaptive immune response, not the immediate vascular phase of acute inflammation. * **TGF-̢ (Transforming Growth Factor-beta):** This is a potent anti-inflammatory cytokine and a key mediator of **fibrosis and wound healing**. It stimulates collagen synthesis and inhibits inflammation. * **FGF (Fibroblast Growth Factor):** Involved in angiogenesis and fibroblast proliferation during the **repair/proliferative phase** of healing, rather than the initial vasodilatory response. **Clinical Pearls for NEET-PG:** * **Sequence of events in Acute Inflammation:** Vasoconstriction (transient) → Vasodilation (Histamine) → Increased Permeability (Exudation) → Stasis → Leukocyte Margination. * **Triple Response of Lewis:** Induced by histamine release following skin trauma, consisting of **Flush** (capillary dilation), **Flare** (arteriolar dilation), and **Wheal** (exudation/edema) [1]. * **Other Vasodilators:** Nitric Oxide (NO) and Prostaglandins (PGI2, PGE2) [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, p. 101. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 84-85. [3] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 187-188.

Question 270: Which of the following chemical mediators is a product of arachidonic acid metabolism via the cyclooxygenase pathway?

A. Leukotriene A4 (LTA4)
B. Leukotriene B4 (LTB4)
C. 5-Hydroxyeicosatetraenoic acid (5-HETE)
D. Prostaglandin H2 (PGH2) (Correct Answer)

Explanation: ### Explanation Arachidonic acid (AA) is a 20-carbon polyunsaturated fatty acid derived from membrane phospholipids via the enzyme **Phospholipase A2** [1]. Once released, AA is metabolized through two primary enzymatic pathways: the **Cyclooxygenase (COX)** pathway and the **Lipoxygenase (LOX)** pathway [2]. **Why the Correct Answer is Right:** * **Prostaglandin H2 (PGH2):** The COX pathway (involving COX-1 and COX-2 enzymes) converts arachidonic acid into the unstable intermediate **PGG2**, which is rapidly converted to **PGH2** [2]. PGH2 serves as the common precursor for all other prostaglandins (PGE2, PGD2, PGF2α), Prostacyclin (PGI2), and Thromboxane A2 (TXA2) [2]. **Analysis of Incorrect Options:** * **Leukotriene A4 (LTA4) & Leukotriene B4 (LTB4):** These are products of the **5-Lipoxygenase (5-LOX)** pathway. LTA4 is the initial precursor, which is then converted to LTB4 (a potent chemotactic agent) or the cysteinyl leukotrienes (LTC4, LTD4, LTE4) [2]. * **5-HETE:** This is an intermediate metabolite produced by the action of **5-LOX** on arachidonic acid [1]. It is a precursor to leukotrienes and acts as a chemoattractant for neutrophils [2]. **NEET-PG High-Yield Pearls:** 1. **Steroids** inhibit Phospholipase A2, thereby blocking *both* COX and LOX pathways [1]. 2. **NSAIDs (like Aspirin/Ibuprofen)** selectively inhibit the COX pathway, blocking prostaglandin synthesis [2]. 3. **Prostacyclin (PGI2)** causes vasodilation and inhibits platelet aggregation, while **Thromboxane A2 (TXA2)** causes vasoconstriction and promotes aggregation (the "Homeostatic Balance") [2]. 4. **LTC4, LTD4, and LTE4** are potent bronchoconstrictors and are significantly more powerful than histamine in inducing vascular permeability [2]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, p. 95. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 95-96.

Practice by Chapter

Acute Inflammation: Vascular Events

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Acute Inflammation: Cellular Events

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Chemical Mediators of Inflammation

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Chronic Inflammation

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Granulomatous Inflammation

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Systemic Effects of Inflammation

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Wound Healing

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Tissue Regeneration

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Fibrosis and Repair

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Resolution of Inflammation

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