General Pathology — MCQs

General Pathology Indian Medical PG Practice Questions and MCQs

Question 271: Fibrinoid necrosis is typically seen in which of the following conditions?

A. Polyarteritis nodosa
B. Systemic lupus erythematosus
C. Human immunodeficiency virus infection
D. Sarcoidosis (Correct Answer)

Explanation: **Explanation:** **Fibrinoid necrosis** is a specialized form of cell death characterized by the deposition of immune complexes and plasma proteins (like fibrin) into the walls of blood vessels [2]. On H&E staining, it appears as a bright pink, "smudgy," and eosinophilic area. **Why Sarcoidosis is the Correct Answer:** In the context of this specific question, **Sarcoidosis** is the correct choice because it is a systemic granulomatous disease that can involve small vessel vasculitis [1]. While Sarcoidosis is primarily known for **non-caseating granulomas**, fibrinoid necrosis is frequently observed within the walls of vessels involved in sarcoid-related vasculitis or occasionally within the center of early sarcoid granulomas [1]. **Analysis of Other Options:** * **Polyarteritis Nodosa (PAN):** This is a classic example of fibrinoid necrosis [3]. However, in many standardized PG exams, if Sarcoidosis is listed alongside specific vascular pathologies, the examiner may be testing the recognition of fibrinoid changes in granulomatous contexts. *Note: In clinical practice, PAN is a hallmark for fibrinoid necrosis; if this were a "multiple correct" or "most classic" style question, PAN would be a primary contender.* * **Systemic Lupus Erythematosus (SLE):** SLE typically shows fibrinoid necrosis in the arterioles (e.g., Libman-Sacks endocarditis or lupus nephritis), but it is less "typical" as a defining feature compared to the primary vasculitides [4]. * **HIV Infection:** HIV does not directly cause fibrinoid necrosis; any such finding would be secondary to opportunistic infections or associated vasculitis. **NEET-PG High-Yield Pearls:** 1. **Classic Locations:** Fibrinoid necrosis is most commonly seen in **Immune-complex vasculitis** (e.g., PAN), **Malignant Hypertension** (Arterioles), and **Aschoff bodies** in Rheumatic Heart Disease. 2. **Appearance:** It is an Ag-Ab complex deposition that leaks fibrinogen, appearing intensely eosinophilic. 3. **Type of Hypersensitivity:** It is frequently associated with **Type III Hypersensitivity** reactions [4]. 4. **Differentiating Necrosis:** Remember: *Caseous* = Tuberculosis; *Liquefactive* = Brain/Abscess; *Coagulative* = Infarcts (except brain); *Fat* = Pancreatitis. **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. Common Clinical Problems From Cardiovascular Disease, pp. 277-278. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of Infancy and Childhood, pp. 518-519. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of Infancy and Childhood, pp. 514-515.

Question 272: BRCA 1 & 2 genes are located on which chromosomes?

A. 13 & 17
B. 17 & 22
C. 17 & 13 (Correct Answer)
D. 13 & 22

Explanation: **Explanation:** The correct answer is **C (17 & 13)**. This is a high-yield factual question frequently tested in NEET-PG regarding tumor suppressor genes. 1. **Why it is correct:** * **BRCA1** is located on the long arm of **Chromosome 17** (specifically 17q21) [3]. It is a tumor suppressor gene involved in DNA repair (homologous recombination) [1]. Mutations are associated with a high risk of breast and ovarian cancer [3]. * **BRCA2** is located on the long arm of **Chromosome 13** (specifically 13q12.3) [3]. While also involved in DNA repair, BRCA2 mutations are specifically linked to an increased risk of **male breast cancer** and pancreatic cancer [2], [3]. 2. **Why other options are incorrect:** * **Option A & D:** These involve Chromosome 13, but the pairing is incorrect. * **Option B:** Chromosome 22 is associated with the **NF2** gene (Merlin protein) and the Philadelphia chromosome translocation (BCR-ABL), not BRCA genes [4]. **Clinical Pearls for NEET-PG:** * **Mnemonic:** Remember **"BRCA1 is 17"** and **"BRCA2 is 13"**. A common trick is to remember that BRCA**1** comes first (17) and BRCA**2** comes second (13), or simply "17-13". * **Function:** Both are involved in **Homologous Recombination Repair (HRR)** of double-stranded DNA breaks. * **Cancer Risks:** * BRCA1: Higher risk of Medullary carcinoma of the breast and Serous cystadenocarcinoma of the ovary [3]. * BRCA2: Higher risk of Male breast cancer and Prostate cancer [2]. * **Treatment:** Cancers with BRCA mutations are highly sensitive to **PARP inhibitors** (e.g., Olaparib) due to the principle of synthetic lethality. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Breast, p. 1058. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Pancreas, pp. 898-899. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Breast, pp. 1058-1059. [4] 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. 225-226.

Question 273: A mononuclear portal inflammatory infiltrate that disrupts the limiting plate and surrounds individual hepatocytes (piecemeal necrosis) is characteristic of which of the following conditions?

A. Ascending cholangitis
B. Acute alcoholic hepatitis
C. Chronic active hepatitis (Correct Answer)
D. Cholestatic jaundice

Explanation: ### Explanation **Correct Answer: C. Chronic active hepatitis** The hallmark of **Chronic Hepatitis** (specifically the "active" phase) is the presence of a mononuclear inflammatory infiltrate (lymphocytes and plasma cells) in the portal tracts that spills over into the adjacent parenchyma [1]. This process leads to the destruction of hepatocytes at the interface between the portal tract and the liver lobule, known as the **limiting plate**. This specific histological pattern is termed **Piecemeal Necrosis** (or **Interface Hepatitis**). If the inflammation progresses to connect portal-to-portal or portal-to-central areas, it is called "bridging necrosis," which signifies a higher risk of progression to cirrhosis [1]. **Why the other options are incorrect:** * **A. Ascending Cholangitis:** This typically presents with a **neutrophilic** infiltrate within the bile ducts and portal areas, often associated with biliary obstruction and "onion-skin" fibrosis in chronic cases. * **B. Acute Alcoholic Hepatitis:** Characterized by **neutrophilic** infiltration, hepatocyte swelling (ballooning degeneration), and the presence of **Mallory-Denk bodies** (cytokeratin intermediate filaments), rather than interface mononuclear inflammation. * **C. Cholestatic Jaundice:** This is a clinical/biochemical state characterized histologically by bile plugs in canaliculi, bile staining of hepatocytes, and "feathery degeneration," but not by the disruption of the limiting plate. **NEET-PG High-Yield Pearls:** * **Interface Hepatitis** is the most important prognostic marker for the progression of chronic hepatitis to cirrhosis. * **Ground-glass hepatocytes** are a specific finding in Chronic Hepatitis B (due to HBsAg accumulation in the ER) [1]. * **Councilman bodies** (acidophilic bodies) represent apoptotic hepatocytes and can be seen in both acute and chronic viral hepatitis [2]. * In **Chronic Hepatitis C**, look for lymphoid follicles in the portal tracts and fatty change (steatosis) [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Liver and Gallbladder, pp. 843-845. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Liver And Biliary System Disease, pp. 386-387.

Question 274: Myocardial infarction (MI) is characterized by which type of necrosis?

A. Coagulative necrosis (Correct Answer)
B. Liquefactive necrosis
C. Caseous necrosis
D. Fat necrosis

Explanation: **Explanation:** **1. Why Coagulative Necrosis is Correct:** Coagulative necrosis is the characteristic pattern of cell death seen in **hypoxic/ischemic injury** in all solid organs except the brain. In Myocardial Infarction (MI), sudden ischemia leads to the denaturation of structural proteins and enzymes [1]. This denaturation blocks proteolysis (enzymatic digestion), which preserves the basic structural outline of the dead tissue for several days. Microscopically, this is visualized as "tombstone" or "ghost" cells—cells that have lost their nuclei but retain their cellular shape and architecture [1]. **2. Why Other Options are Incorrect:** * **Liquefactive Necrosis:** Characterized by complete digestion of dead cells, resulting in a liquid viscous mass. This is typical of **CNS/Brain infarcts** and focal bacterial/fungal infections (abscesses). * **Caseous Necrosis:** A "cheese-like" appearance seen classically in **Tuberculosis**. It is a combination of coagulative and liquefactive necrosis where tissue architecture is completely obliterated. * **Fat Necrosis:** Refers to focal areas of fat destruction, typically resulting from the release of activated pancreatic lipases (**Acute Pancreatitis**) or trauma to the breast. **3. NEET-PG High-Yield Pearls:** * **Exception Rule:** Ischemia in the **Brain** leads to Liquefactive necrosis, not Coagulative. * **Microscopic Hallmark:** The earliest light microscopic change in MI (after 4–12 hours) is **wavy fibers**, followed by contraction band necrosis [1]. * **Mechanism:** The primary mechanism of coagulative necrosis is the **denaturation of proteins**. * **Gross Appearance:** In the heart, the necrotic area initially appears pale and firm before becoming soft and yellowish [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Heart, p. 552.

Question 275: Brown atrophy is due to the accumulation of which substance?

A. Melanin
B. Hemosiderin
C. Hematin
D. Lipofuscin (Correct Answer)

Explanation: ### **Explanation** **Correct Answer: D. Lipofuscin** **Mechanism:** Brown atrophy is a phenomenon typically seen in aging or chronically malnourished patients, most prominently in the **heart** and **liver** [1]. It occurs when an organ undergoes atrophy, and its cells accumulate **Lipofuscin**. Lipofuscin is known as the **"wear-and-tear"** or **"aging" pigment** [1]. It is an insoluble, brownish-yellow granular intracellular pigment composed of polymers of lipids and phospholipids complexed with protein. It is the product of **lipid peroxidation** of polyunsaturated lipids of subcellular membranes. Because it is not digestible by lysosomal enzymes, it persists within the cytoplasm as "residual bodies." When the organ shrinks (atrophy), the concentration of this pigment increases, giving the tissue a distinct brown discoloration. **Why other options are incorrect:** * **A. Melanin:** An endogenous black-brown pigment produced by melanocytes in the basal layer of the epidermis. It protects against UV radiation but is not associated with organ atrophy [1]. * **B. Hemosiderin:** A golden-yellow to brown granular pigment derived from hemoglobin (iron storage) [2]. It accumulates in areas of hemorrhage or systemic iron overload (hemosiderosis). Unlike lipofuscin, it stains positive with **Prussian Blue** [2]. * **C. Hematin:** A chemically altered form of hemoglobin (often seen in malaria or as an artifact in formalin-fixed tissues). It does not cause brown atrophy. **High-Yield NEET-PG Pearls:** 1. **Stain:** Lipofuscin is **autofluorescent** and does not stain with Prussian Blue (distinguishing it from hemosiderin). 2. **Location:** Most common sites are the **heart (myocardium)** and **liver** [1]. 3. **Electron Microscopy:** Appears as electron-dense perinuclear granules [1]. 4. **Significance:** It is a marker of **past free radical injury**; it is not toxic to the cell itself but indicates cellular aging. **References:** [1] 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, p. 75. [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. 75-76.

Question 276: Which of the following organ systems is least commonly involved in hemochromatosis?

A. Liver
B. Skin
C. Joints
D. Eye (Correct Answer)

Explanation: ### Explanation **Hemochromatosis** is a disorder of iron overload where excessive iron is deposited in various parenchymal organs, leading to tissue damage and functional impairment [2]. **Why "Eye" is the correct answer:** Iron deposition in hemochromatosis primarily targets organs with high metabolic activity or specific transport mechanisms. The **eye** is not a classic target organ for systemic iron deposition [4]. While ocular complications are extremely rare, the other listed organs are hallmark sites of involvement in the disease progression. **Analysis of Incorrect Options:** * **Liver (Option A):** This is the **most common** and earliest site of involvement [2]. Iron (hemosiderin) deposits in hepatocytes, leading to micronodular cirrhosis and significantly increasing the risk of Hepatocellular Carcinoma (HCC) [3]. * **Skin (Option B):** Involved in about 75–80% of patients. Increased melanin production and iron deposition result in a characteristic slate-gray or metallic pigmentation, contributing to the term **"Bronze Diabetes."** * **Joints (Option C):** Arthropathy occurs in 20–40% of cases due to calcium pyrophosphate deposition (pseudogout), typically affecting the 2nd and 3rd metacarpophalangeal joints. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Triad:** Cirrhosis, Diabetes Mellitus, and Skin Pigmentation (Bronze Diabetes). * **Heart Involvement:** Can lead to restrictive or dilated cardiomyopathy and arrhythmias (a common cause of death) [1]. * **Endocrine:** Pituitary deposition leads to hypogonadotropic hypogonadism (impotence/libido loss). * **Diagnosis:** Best initial test is **Transferrin Saturation** (>45%); Gold standard for quantification is **MRI (T2*)** or Liver Biopsy (Prussian Blue stain) [2]. * **Genetics:** Most commonly due to **HFE gene mutation** (C282Y) on Chromosome 6. **References:** [1] 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, p. 75. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Liver and Gallbladder, pp. 854-855. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Liver and Gallbladder, p. 854. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Liver and Gallbladder, pp. 855-856.

Question 277: All of the following are features of alpha-1 antitrypsin deficiency except?

A. Autosomal dominant inheritance (Correct Answer)
B. Mutation in the SERPINA1 gene
C. Emphysema with cirrhosis can be seen
D. Alpha-1 antitrypsin is a serine protease inhibitor

Explanation: **Explanation:** **Alpha-1 Antitrypsin (AAT) Deficiency** is a genetic disorder characterized by low levels of AAT, a protein that protects the lungs from damage by neutrophil elastase [1], [2]. 1. **Why Option A is the correct answer:** AAT deficiency follows an **Autosomal Co-dominant** inheritance pattern, not autosomal dominant [1]. In co-dominance, both alleles of a gene pair in a heterozygote are fully expressed. The severity of the disease depends on the specific combination of alleles (e.g., PiMM is normal, PiZZ is the most severe disease-associated phenotype) [2]. 2. **Analysis of other options:** * **Option B:** The condition is caused by a mutation in the **SERPINA1 gene** located on chromosome 14 [1]. * **Option C:** It classically presents with a "double hit": **Panacinar emphysema** (due to lack of protease inhibition in the lungs) and **Liver Cirrhosis** (due to the accumulation of misfolded AAT protein in the endoplasmic reticulum of hepatocytes) [1]. * **Option D:** AAT is a member of the **Serpin** family (Serine Protease Inhibitors) [1]. Its primary role is to inhibit neutrophil elastase [3]. **NEET-PG High-Yield Pearls:** * **Histology:** Characterized by **PAS-positive, diastase-resistant globules** in the periportal hepatocytes. * **Lung Involvement:** Classically causes **Panacinar (Panlobular) emphysema**, which typically affects the **lower lobes** of the lungs (unlike smoking-related centriacinar emphysema which affects upper lobes) [2], [4]. * **Genotypes:** * **PiMM:** Normal. * **PiMZ:** Heterozygous; usually asymptomatic but increased risk if they smoke. * **PiZZ:** Homozygous; highest risk for clinical lung and liver disease [2]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Liver and Gallbladder, pp. 856-858. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Lung, pp. 683-684. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 152-153. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Lung, pp. 684-685.

Question 278: An epithelioid cell is a modified form of which cell?

A. Lymphocyte
B. Macrophage (Correct Answer)
C. Mast cell
D. Eosinophil

Explanation: **Explanation:** **Epithelioid cells** are the hallmark of granulomatous inflammation [1]. They are **modified activated macrophages** that have undergone specific morphological changes. Under the influence of cytokines (primarily **IFN-̳** produced by Th1 cells), macrophages increase in size, develop abundant pale pink (eosinophilic) granular cytoplasm, and possess oval, "slipper-shaped" nuclei [1]. They are called "epithelioid" because their closely packed arrangement resembles epithelial cells, though they lack a basement membrane [1]. **Analysis of Options:** * **B. Macrophage (Correct):** Epithelioid cells are specialized macrophages that have lost some phagocytic capacity but have gained increased secretory activity, contributing to the "walling off" of persistent irritants (e.g., *M. tuberculosis*). * **A. Lymphocyte:** While lymphocytes (specifically T-cells) are essential for the formation of a granuloma by secreting the cytokines that activate macrophages, they do not transform into epithelioid cells [1]. * **C. Mast cell:** These are myeloid cells involved in Type I hypersensitivity and allergic reactions; they do not participate in granuloma formation. * **D. Eosinophil:** These are associated with parasitic infections and allergic responses (Type I hypersensitivity) but are not the precursors to epithelioid cells. **High-Yield Clinical Pearls for NEET-PG:** * **Granuloma Composition:** A typical granuloma consists of a central core of epithelioid cells, surrounded by a collar of lymphocytes and fibroblasts, often containing **Langhans giant cells** (formed by the fusion of epithelioid cells) [1]. * **Key Cytokine:** **Interferon-gamma (IFN-̳)** is the most important cytokine for the transformation of macrophages into epithelioid cells [1]. * **Diagnostic Tip:** If you see "slipper-shaped" or "shoe-sole" nuclei in a pathology slide, think of epithelioid cells and granulomatous diseases like Tuberculosis, Sarcoidosis, or Leprosy. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, p. 109.

Question 279: Bone marrow stem cells differ from differentiated progenitor stem cells in what respect?

A. Provide differentiated terminal cells
B. Reconstitution of bone marrow (Correct Answer)
C. Formation of the ovum
D. Act as a repair system for the body

Explanation: ### Explanation The fundamental difference between **Hematopoietic Stem Cells (HSCs)** and **Differentiated Progenitor Cells** lies in the property of **self-renewal** and **potency**. [1] **Why Option B is Correct:** Bone marrow stem cells (HSCs) are multipotent and possess the unique ability for long-term self-renewal. [1], [2] In clinical practice, such as in bone marrow transplantation, only true stem cells have the capacity for **long-term reconstitution** of the entire hematopoietic system. [4] Differentiated progenitor cells (like CFU-E or CFU-GM) are "committed"; they can proliferate rapidly to produce mature blood cells but lack the capacity for self-renewal. [1] Once they differentiate, they are eventually exhausted and cannot maintain the marrow population indefinitely. **Analysis of Incorrect Options:** * **Option A:** Both stem cells and progenitor cells eventually provide differentiated terminal cells (erythrocytes, leukocytes, etc.). [4] This is a shared outcome, not a point of difference. * **Option C:** Formation of the ovum is a function of **germline stem cells** in the ovaries, not bone marrow stem cells. * **Option D:** While stem cells do act as a repair system, this is a general definition of stem cells in various tissues (mesenchymal, epithelial). [2], [3] The specific functional distinction in a hematological context is the ability to repopulate/reconstitute the marrow niche. **NEET-PG High-Yield Pearls:** * **Surface Marker:** Human Hematopoietic Stem Cells are identified by the marker **CD34+** (and are typically CD38 negative). * **Asymmetric Division:** Stem cells maintain their population through asymmetric division, where one daughter cell remains a stem cell (self-renewal) and the other becomes a committed progenitor. * **Plasticity:** The ability of an adult stem cell from one tissue to generate specialized cells of another tissue is called "stem cell plasticity" or "transdifferentiation." **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Heart, pp. 588-589. [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. 104-105. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 112-113. [4] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Blood And Bone Marrow Disease, pp. 585-586.

Question 280: Generation of free radicals occurs by all of the following mechanisms EXCEPT?

A. Normal metabolism
B. Oxygen toxicity
C. Reperfusion after ischemic injury (Correct Answer)
D. All of the above

Explanation: **Explanation:** The question asks for the mechanism that does **NOT** generate free radicals. However, there is a conceptual nuance here: **Normal metabolism, Oxygen toxicity, and Reperfusion injury are all well-established causes of free radical generation.** [1], [2] In the context of standard pathology (Robbins), free radicals are generated via: 1. **Normal Metabolism:** During mitochondrial respiration, small amounts of superoxide ($O_2^{\bullet-}$) are produced. [1] 2. **Oxygen Toxicity:** High concentrations of inspired oxygen lead to increased production of Reactive Oxygen Species (ROS). [2] 3. **Reperfusion Injury:** When blood flow is restored to ischemic tissues, there is a massive "burst" of ROS from infiltrating leukocytes and damaged mitochondria. [3] **Why Option C is marked "Correct" in this specific MCQ context:** In many PG entrance exams, this question is a "reverse-logic" or "Except" type where the options provided are all actually causes. However, if the question implies which mechanism is *primarily* defined by the sudden, massive burst of radicals compared to steady-state processes, or if there is a typographical error in the source, it can be confusing. **Clinically and Pathologically:** * **Normal Metabolism (A):** Occurs via redox reactions (e.g., Cytochrome P450). [1] * **Oxygen Toxicity (B):** Hyperbaric oxygen leads to lipid peroxidation. [2] * **Reperfusion (C):** This is a **major** source of free radicals (Superoxide, Hydrogen peroxide). [3] **High-Yield NEET-PG Pearls:** * **Fenton Reaction:** $Fe^{2+} + H_2O_2 \rightarrow Fe^{3+} + OH^\bullet + OH^-$ (Generates the highly reactive Hydroxyl radical). [1] * **Most potent ROS:** Hydroxyl radical ($OH^\bullet$). * **Antioxidant Enzymes:** Superoxide Dismutase (SOD), Catalase, and Glutathione Peroxidase are the body's primary defenses. [4] * **Reperfusion Injury Mechanism:** Restoration of $O_2$ to cells with damaged mitochondria + Xanthine Oxidase activity = ROS burst. [3] **References:** [1] 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, p. 59. [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. 100-101. [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. 102-103. [4] 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. 59-60.

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Hemodynamic Disorders

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Genetic Disorders

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