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Inflammation
1. A 21-year-old man cuts his hand while cooking. Within minutes, vasodilation and increased vascular permeability occur. Which mediator is primarily responsible for these early vascular changes?
A. IL-1
B. Bradykinin
C. Histamine
D. TNF-α
Answer: C. Histamine
Explanation: Histamine is rapidly released from mast cells, basophils, and platelets following tissue injury. It acts almost immediately by causing vasodilation of arterioles (leading to redness and warmth) and increasing vascular permeability in postcapillary venules (leading to swelling). IL-1 and TNF-α are slower-acting cytokines that mediate fever and systemic effects. Bradykinin also increases vascular permeability but is more involved in pain sensation.
2. During acute inflammation, neutrophils migrate from blood to tissue. Which adhesion molecule on endothelial cells allows neutrophil integrins to bind and achieve firm adhesion?
A. P-selectin
B. E-selectin
C. ICAM-1
D. PECAM-1
Answer: C. ICAM-1
Explanation: Neutrophils adhere to vascular endothelium through interactions between integrins (e.g., LFA-1 on neutrophils) and ICAM-1 (Intercellular Adhesion Molecule-1) on activated endothelial cells. This step, known as "firm adhesion," follows the rolling stage mediated by selectins and precedes transmigration, which involves PECAM-1 (CD31).
3. A 50-year-old man with tuberculosis has granulomas in his lungs. Which cytokine is most essential for macrophage activation and granuloma maintenance?
A. IL-10
B. IFN-γ
C. TNF-α
D. IL-4
Answer: B. IFN-γ
Explanation: Interferon-gamma is secreted by Th1 cells and is critical for classical activation of macrophages. Activated macrophages enhance intracellular killing of pathogens like Mycobacterium tuberculosis and secrete factors promoting granuloma formation. TNF-α assists in granuloma maintenance, while IL-10 and IL-4 inhibit macrophage activation and promote Th2 responses.
4. Which chemokine is primarily responsible for the recruitment of neutrophils to the site of acute inflammation?
A. IL-8
B. IL-10
C. IL-4
D. TGF-β
Answer: A. IL-8
Explanation: IL-8, also called CXCL8, is secreted by macrophages and endothelial cells and is a potent chemotactic factor specifically for neutrophils. It helps direct neutrophils to the site of infection or injury. IL-10 and TGF-β are anti-inflammatory, while IL-4 promotes eosinophil recruitment.
5. A patient with poor wound healing is found to have a deficiency that impairs hydroxylation of collagen. Which vitamin is most likely deficient?
A. Vitamin A
B. Vitamin D
C. Vitamin C
D. Vitamin K
Answer: C. Vitamin C
Explanation: Vitamin C (ascorbic acid) is essential for hydroxylation of proline and lysine residues on procollagen. This post-translational modification is necessary for proper triple-helix formation, which gives collagen its tensile strength. Deficiency results in fragile connective tissues and delayed wound healing (as seen in scurvy).
6. A 4-year-old boy has recurrent infections and a negative nitroblue tetrazolium test. What is the underlying defect?
A. Myeloperoxidase deficiency
B. Defective lysosomal fusion
C. NADPH oxidase deficiency
D. Defective integrins
Answer: C. NADPH oxidase deficiency
Explanation: Chronic granulomatous disease (CGD) results from a defect in NADPH oxidase, leading to impaired oxidative burst in neutrophils. These patients are especially vulnerable to catalase-positive organisms. The nitroblue tetrazolium (NBT) test or DHR flow cytometry confirms the diagnosis by assessing ROS production.
7. What type of immune cell is most characteristic of chronic inflammation?
A. Neutrophil
B. Mast cell
C. Eosinophil
D. Macrophage
Answer: D. Macrophage
Explanation: Macrophages are the dominant cells in chronic inflammation. They derive from circulating monocytes and have phagocytic and cytokine-secreting functions. They also present antigens and activate T cells, sustaining the inflammatory response.
8. A patient develops a granulomatous lesion in response to a persistent foreign body. Which hypersensitivity mechanism is primarily responsible?
A. Type I
B. Type II
C. Type III
D. Type IV
Answer: D. Type IV
Explanation: Type IV (delayed-type) hypersensitivity involves Th1 cells and macrophage activation. It is cell-mediated (not antibody-mediated) and underlies granuloma formation, including reactions to tuberculosis and foreign bodies.
9. Which enzyme converts arachidonic acid into prostaglandins and thromboxanes?
A. Lipoxygenase
B. Cyclooxygenase
C. Phospholipase A2
D. Peroxidase
Answer: B. Cyclooxygenase
Explanation: Cyclooxygenases (COX-1 and COX-2) catalyze the conversion of arachidonic acid into prostaglandin precursors. These mediators play roles in inflammation, vasodilation, pain, and fever. Lipoxygenase produces leukotrienes, while phospholipase A2 releases arachidonic acid from membrane phospholipids.
10. What is the function of fibrin in acute inflammation?
A. Traps pathogens
B. Enhances T cell activation
C. Prevents fever
D. Activates eosinophils
Answer: A. Traps pathogens
Explanation: Fibrin forms a meshwork during acute inflammation that helps localize infection and provides a scaffold for inflammatory cells. This limits the spread of pathogens and aids in tissue repair.
Neoplasia
11. A 6-year-old child develops bilateral retinoblastomas. Which gene is most likely mutated in this condition?
A. BCL2
B. Rb
C. KRAS
D. p53
Answer: B. Rb
Explanation: The Rb tumor suppressor gene regulates the G1→S checkpoint of the cell cycle by inhibiting E2F. Loss-of-function mutations allow uncontrolled cell proliferation. Bilateral disease indicates a germline mutation (familial form).
12. A lung tumor biopsy reveals intercellular bridges and keratin pearls. What is the most likely diagnosis?
A. Small cell carcinoma
B. Adenocarcinoma
C. Squamous cell carcinoma
D. Large cell carcinoma
Answer: C. Squamous cell carcinoma
Explanation: Squamous cell carcinoma of the lung typically shows features like keratin pearls and intercellular bridges under microscopy. It's strongly associated with smoking and often arises centrally.
13. Which feature best distinguishes a benign from a malignant tumor?
A. Rapid growth
B. High mitotic activity
C. Local invasion
D. Encapsulation
Answer: C. Local invasion
Explanation: Malignant tumors invade surrounding tissues and may metastasize. Benign tumors are usually well-circumscribed or encapsulated and do not invade or metastasize, despite possibly growing large.
14. A woman has a mutation in BRCA1. Which type of cancer is she at increased risk for?
A. Colon cancer
B. Renal cell carcinoma
C. Breast and ovarian cancer
D. Lung adenocarcinoma
Answer: C. Breast and ovarian cancer
Explanation: BRCA1 and BRCA2 are tumor suppressor genes involved in DNA repair. Mutations are inherited in an autosomal dominant fashion and greatly increase the risk for breast and ovarian cancers.
15. A patient has hepatocellular carcinoma. Which exposure is most strongly linked to its development?
A. Alcohol use
B. High-fat diet
C. Asbestos
D. Aflatoxin B1
Answer: D. Aflatoxin B1
Explanation: Aflatoxin B1, produced by Aspergillus species, contaminates improperly stored grains and peanuts. It is a potent hepatocarcinogen and synergizes with HBV to increase the risk of hepatocellular carcinoma.
16. Which oncogene encodes a receptor tyrosine kinase overexpressed in breast cancer?
A. KRAS
B. HER2/neu
C. MYC
D. APC
Answer: B. HER2/neu
Explanation: HER2/neu (ERBB2) encodes a growth factor receptor that is overexpressed in 20-30% of breast cancers. It is associated with a more aggressive tumor phenotype but can be targeted with trastuzumab.
17. Which of the following is the most common route of metastasis for carcinomas?
A. Lymphatic spread
B. Hematogenous spread
C. Direct seeding
D. Transcoelomic spread
Answer: A. Lymphatic spread
Explanation: Carcinomas typically spread via lymphatics to regional lymph nodes. Sarcomas, in contrast, tend to spread hematogenously.
18. A 60-year-old man presents with fatigue and pallor. Bone marrow biopsy shows immature myeloid cells. Which marker is most useful in confirming acute myeloid leukemia (AML)?
A. CD3
B. CD19
C. CD34
D. CD33
Answer: D. CD33
Explanation: CD33 is a myeloid marker used to identify AML. CD34 is a stem cell marker; CD3 is T-cell; CD19 is B-cell.
19. A tumor suppressor gene that induces cell cycle arrest or apoptosis in response to DNA damage is:
A. RAS
B. BCL2
C. p53
D. Cyclin D
Answer: C. p53
Explanation: p53 halts the cell cycle at the G1/S checkpoint in response to DNA damage, promoting repair or apoptosis. Loss-of-function mutations in p53 are found in many human cancers.
20. A colon polyp is removed and histology reveals invasive glands breaching the muscularis mucosa. What is the best classification?
A. Hyperplastic polyp
B. Tubular adenoma
C. Villous adenoma
D. Adenocarcinoma
Answer: D. Adenocarcinoma
Explanation: Once dysplastic glands invade beyond the muscularis mucosa into the submucosa, the lesion is no longer a polyp or adenoma but a true carcinoma.
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