General Pathology Practice Questions

Q: Which factor is present in the final common terminal complement pathway?

C5. ### Explanation The complement system consists of three activation pathways—**Classical, Lectin, and Alternative**—all of which converge at the level of C3 and lead to the formation of the **Terminal Pathway (Membrane Attack Complex - MAC).** [1] **Why C5 is Correct:** The terminal pathway begins with the cleavage of **C5** by C5 convertase. [1] This generates C5a (a potent anaphylatoxin) and **C5b**. C5b then serves as the anchor for the assembly of the remaining components: **C6, C7, C8, and C9**. Together, these form the **C5b-9 complex (MAC)**, which creates pores in the target cell membrane, leading to osmotic lysis. [1] Therefore, C5 is the first component of the final common terminal sequence. **Analysis of Incorrect Options:** * **A. C3:** This is the most abundant complement protein and the point where all three pathways converge. [1] However, it is considered part of the **early steps** or the "amplification loop" rather than the terminal MAC assembly. * **B. C4:** This is unique to the **Classical and Lectin pathways**. [1] It is not involved in the Alternative pathway or the final terminal sequence. * **D. Factor B:** This is a specific component of the **Alternative pathway** (forming the C3bBb convertase). It is not part of the common terminal pathway. **High-Yield Clinical Pearls for NEET-PG:** * **MAC Components:** C5b, C6, C7, C8, C9. * **Deficiency of C5-C9:** Increases susceptibility to recurrent **Neisseria** infections (meningitis and gonorrhea). * **Paroxysmal Nocturnal Hemoglobinuria (PNH):** Caused by a deficiency of DAF (CD55) and MIRL (CD59), which normally protect host cells from MAC-mediated lysis. * **Eculizumab:** A monoclonal antibody against **C5** used to treat PNH and atypical HUS. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 99-100.

Q: Which CD marker represents the leucocyte common antigen?

CD 45. ### Explanation **Correct Option: D (CD 45)** CD 45 is known as the **Leucocyte Common Antigen (LCA)**. It is a transmembrane protein tyrosine phosphatase expressed on the surface of **all hematopoietic cells**, except for mature erythrocytes and platelets. In diagnostic pathology, CD 45 is the primary immunohistochemical (IHC) marker used to differentiate **lymphomas/leukemias** from non-hematopoietic tumors like carcinomas or sarcomas. **Analysis of Incorrect Options:** * **A. CD 14:** This is a specific marker for **monocytes and macrophages**. It acts as a co-receptor for bacterial lipopolysaccharide (LPS). * **B. CD 15:** This marker is expressed on **Reed-Sternberg cells** (in classical Hodgkin Lymphoma, along with CD 30) and is also found on mature **granulocytes**. * **C. CD 23:** This is a low-affinity IgE receptor [1]. It is a key marker for **B-cell Chronic Lymphocytic Leukemia (CLL)** and is used to differentiate it from Mantle Cell Lymphoma (which is CD 23 negative) [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Pan-B cell markers:** CD 19, CD 20 [1]. * **Pan-T cell markers:** CD 3 (most specific), CD 2, CD 5, CD 7 [1]. * **NK cell markers:** CD 16, CD 56. * **Hairy Cell Leukemia:** Characterized by CD 11c, CD 25, and CD 103 [1]. * **Stem cell marker:** CD 34 (used to identify blasts in acute leukemia). * **Memory Tip:** If a tumor is "LCA positive," think Lymphoma; if "Cytokeratin positive," think Carcinoma. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of White Blood Cells, Lymph Nodes, Spleen, and Thymus, p. 598.

Question 1

A 31-year-old man presents with infertility and aspermia. He reports chronic diarrhea with elevated quantitative stool fat, and has a history of recurrent, severe respiratory tract infections since early childhood. As a neonate, he experienced bowel obstruction due to meconium ileus. Which gene is most likely to harbor a mutation causing these symptoms?

Accepted Answer

CFTR

Answer

FGFR

Answer

G6PD

Answer

HFE

Question 2

Which factor is present in the final common terminal complement pathway?

Accepted Answer

C5

Answer

C3

Answer

C4

Answer

Factor B

Question 3

Increased capillary permeability is caused by all of the following except?

Accepted Answer

Renin

Answer

Anaphylatoxin

Answer

5-hydroxytryptamine

Answer

Histamine

Question 4

Which of the following is false regarding Noonan syndrome?

Accepted Answer

It is autosomal recessive.

Answer

It involves mutations in chromosome 12.

Answer

Both males and females are affected.

Answer

Low levels of clotting factors XI and XII are present.

Question 5

In which of the following types of pathologic calcification is normal calcium metabolism observed?

Accepted Answer

Dystrophic calcification

Answer

Metastatic calcification

Answer

Ionotropic calcification

Answer

Radiation calcification

Question 6

Which of the following is referred to as the "gatekeeper of colonic neoplasia"?

Accepted Answer

APC

Answer

SMAD2

Answer

PTEN

Answer

STK11

Question 7

What is the most common type of cell death resulting from sudden occlusion of blood supply?

Accepted Answer

Coagulation necrosis

Answer

Caseation necrosis

Answer

Liquefactive necrosis

Answer

Gangrene

Question 8

Which of the following findings is characteristic of Marfan's syndrome?

Accepted Answer

All of the above

Answer

Mutation of the fibrillin-1 gene

Answer

Flat cornea

Answer

Aortic aneurysm

Question 9

Which CD marker represents the leucocyte common antigen?

Accepted Answer

CD 45

Answer

CD 14

Answer

CD 15

Answer

CD 23

Question 10

Who discovered the process of phagocytosis?

Accepted Answer

Metchnikoff

Answer

Virchow

Answer

Koch

Answer

None of the above

General Pathology — MCQs

General Pathology — MCQs

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