Blood and Immunity Practice Questions

Q: Which of the following anticoagulants prevent clotting of blood in the normal vascular system?

Antithrombin III. ### Explanation The maintenance of blood fluidity within the normal vascular system is achieved through a delicate balance between procoagulants and natural anticoagulants. **Why Antithrombin III is correct:** Antithrombin III (AT-III) is the most important **natural circulating anticoagulant**. It is a serine protease inhibitor (serpin) that irreversibly inactivates several factors in the clotting cascade, most notably **Thrombin (Factor IIa)** and **Factor Xa**. It also inhibits Factors IXa, XIa, and XIIa. While it works independently to prevent spontaneous clot formation in normal vessels, its activity is increased several thousand-fold in the presence of heparin or heparin-like molecules on the endothelial surface. **Analysis of Incorrect Options:** * **Plasminogen (B):** This is the inactive precursor of plasmin. It is involved in **fibrinolysis** (dissolving an existing clot) rather than preventing the initial formation of a clot in the normal vascular system. * **Fibrinogen (C):** This is **Factor I**, a procoagulant. It is converted into fibrin by thrombin to form the structural mesh of a blood clot. * **Heparin (D):** While heparin is a potent anticoagulant, it is primarily found in the granules of mast cells and basophils. Endogenous heparin levels in normal circulating plasma are **negligible**; therefore, it does not function as the primary systemic anticoagulant under physiological conditions. It acts as a cofactor that enhances Antithrombin III. **High-Yield NEET-PG Pearls:** * **Antithrombin III Deficiency:** Leads to a hypercoagulable state (thrombophilia) and "Heparin Resistance," where standard doses of heparin fail to prolong the PTT. * **Protein C and S:** Other key natural anticoagulants; they specifically inactivate Factors Va and VIIIa. * **Virchow’s Triad:** Endothelial injury, stasis, and hypercoagulability are the three factors leading to intravascular thrombosis.

Q: Which substance is present in both serum and plasma?

Factor VII. To answer this question, one must understand the fundamental difference between **plasma** and **serum**: * **Plasma:** The liquid, cell-free part of blood that has been treated with anti-coagulants. It contains all clotting factors. * **Serum:** The liquid remains after blood has clotted. Therefore, **Serum = Plasma – Clotting Factors (I, II, V, VIII, XIII).** ### Why Factor VII is the Correct Answer During the coagulation process, certain clotting factors are entirely consumed to form the fibrin clot, while others remain in the serum. * **Factor VII** (Proconvertin) is a stable factor. While it participates in the extrinsic pathway, it is **not consumed** during the clotting process. Therefore, it remains present in both plasma and serum. ### Why the Other Options are Incorrect * **A. Fibrinogen (Factor I):** This is the precursor to fibrin. During clotting, fibrinogen is converted into fibrin threads to form the meshwork of the clot. Thus, it is absent in serum. * **C. Factor V (Proaccelerin):** This is a "labile factor" that is consumed during the formation of the prothrombinase complex. It is absent in serum. * **D. Factor II (Prothrombin):** This is converted into thrombin during the coagulation cascade. As it is used up to activate fibrinogen, it is absent in serum. ### NEET-PG High-Yield Pearls * **Consumed Factors (Absent in Serum):** Factors I, II, V, VIII, and XIII. (Mnemonic: "1, 2, 5, 8, 13 are used up"). * **Factors present in Serum:** VII, IX, X, XI, and XII. * **Vitamin K Dependent Factors:** II, VII, IX, and X. * **Most Stable Factor:** Factor VII (also has the shortest half-life). * **Labile Factors:** Factor V and Factor VIII (activity decreases rapidly in stored blood).

Q: Increased Prothrombin time results from deficiency of which factor?

Fibrinogen. **Explanation:** Prothrombin Time (PT) measures the integrity of the **Extrinsic** and **Common pathways** of the coagulation cascade. It specifically assesses Factors **I (Fibrinogen)**, **II (Prothrombin)**, **V**, **VII**, and **X**. 1. **Why Fibrinogen is correct:** Fibrinogen (Factor I) is the final substrate of the common pathway. Since PT measures the time taken for a fibrin clot to form, a significant deficiency in Fibrinogen will lead to a prolonged PT. 2. **Why Factor IX and XI are incorrect:** These factors belong to the **Intrinsic pathway**. Deficiencies in Factors VIII, IX, XI, or XII result in a prolonged **Activated Partial Thromboplastin Time (aPTT)**, while the PT remains normal. 3. **Why Factor VI is incorrect:** There is no "Factor VI" in the modern coagulation cascade (it was previously thought to be activated Factor V but was later removed from the nomenclature). **Clinical Pearls for NEET-PG:** * **PT** is the most sensitive screening test for **Vitamin K deficiency** and **Liver disease** because it monitors Factor VII, which has the shortest half-life (approx. 6 hours). * **Warfarin** therapy is monitored using PT/INR (Extrinsic pathway). * **Heparin** therapy is monitored using aPTT (Intrinsic pathway). * **Isolated prolonged PT** usually indicates Factor VII deficiency. * **Prolongation of both PT and aPTT** suggests a deficiency in the common pathway (Factors I, II, V, or X).

Q: Although more than 400 blood groups have been identified, the ABO Rh blood group systems remain the most important in clinical medicine because?

A, B and Rh antigens are most immunogenic.. ### Explanation The clinical significance of a blood group system is determined by its **immunogenicity**—the ability of an antigen to provoke an immune response (antibody production). **1. Why Option C is Correct:** While hundreds of antigens exist on the erythrocyte surface, the **A, B, and D (Rh) antigens** are the most potent immunogens. In the ABO system, individuals naturally possess pre-formed "isoagglutinins" (antibodies) against the antigens they lack. In the Rh system, although antibodies are not naturally occurring, the D-antigen is so highly immunogenic that an Rh-negative individual exposed to even a small amount of Rh-positive blood has an 80% probability of developing anti-D antibodies. This leads to severe **Acute Hemolytic Transfusion Reactions** or **Hemolytic Disease of the Fetus and Newborn (HDFN)**. **2. Why Other Options are Incorrect:** * **Option A:** Being the first identified (by Landsteiner in 1900) is a historical fact, not a clinical reason for its importance. * **Option B:** The number of phenotypes (four in ABO) does not dictate clinical risk; many minor systems have multiple phenotypes but rarely cause reactions. * **Option D:** All blood group antigens (Kell, Duffy, Kidd, etc.) are inherited via Mendelian genetics; this is not a unique feature of the ABO/Rh systems. **3. High-Yield Clinical Pearls for NEET-PG:** * **Landsteiner’s Law:** States that if an agglutinogen (antigen) is present on RBCs, the corresponding agglutinin (antibody) must be absent from the plasma (applies strictly to the ABO system). * **Universal Donor:** O Negative (no A, B, or D antigens). * **Universal Recipient:** AB Positive (no anti-A, anti-B, or anti-D antibodies). * **Bombay Blood Group (Oh):** Lacks the H-antigen; these individuals produce anti-H antibodies and can only receive blood from another Bombay phenotype donor. * **Most Immunogenic Rh Antigen:** D > c > E > C > e.

Q: Which of the following factors is NOT derived from endothelial cells?

Thromboxane A2. **Explanation:** The correct answer is **Thromboxane A2 (TXA2)**. The vascular endothelium plays a dual role in hemostasis, primarily maintaining an anti-thrombotic surface under physiological conditions while facilitating coagulation upon injury. **1. Why Thromboxane A2 is the correct answer:** Thromboxane A2 is a potent vasoconstrictor and platelet aggregator. It is synthesized and released primarily by **activated platelets** (via the cyclooxygenase pathway), not by endothelial cells. Its primary function is to promote clot formation, opposing the effects of endothelial-derived factors. **2. Why the other options are incorrect:** * **Thrombomodulin:** This is a specific receptor expressed on the **luminal surface of endothelial cells**. It binds to thrombin, converting it from a procoagulant enzyme into an anticoagulant that activates Protein C. * **Protein S:** While primarily synthesized in the liver, Protein S is also synthesized and secreted by **vascular endothelial cells** and megakaryocytes. It acts as a non-enzymatic cofactor for activated Protein C (APC). * **Prostacyclin (PGI2):** This is the major prostaglandin synthesized by **endothelial cells**. It is a potent vasodilator and inhibitor of platelet aggregation, acting as a physiological antagonist to Thromboxane A2. **High-Yield Clinical Pearls for NEET-PG:** * **The PGI2:TXA2 Balance:** In health, the endothelium-derived PGI2 inhibits platelet aggregation. In endothelial injury, this balance shifts toward TXA2, favoring clot formation. * **Other Endothelial Products:** Nitric Oxide (vasodilator), von Willebrand Factor (vWF - stored in Weibel-Palade bodies), and Tissue Plasminogen Activator (t-PA). * **Aspirin Mechanism:** Low-dose aspirin irreversibly inhibits COX-1 in platelets, reducing TXA2 levels. Since platelets lack a nucleus, they cannot synthesize new enzymes, leading to a prolonged anti-platelet effect.

Q: Erythropoietin production is inhibited by?

Estrogen. **Explanation:** The production of **Erythropoietin (EPO)**, the primary hormone regulating red blood cell production, is stimulated by hypoxia and various hormones. Among the options provided, **Estrogen** is the only hormone that exerts an inhibitory effect on erythropoiesis. **1. Why Estrogen is Correct:** Estrogen inhibits erythropoietin production and also blunts the bone marrow's response to EPO. This hormonal influence is a primary reason why females of reproductive age typically have lower hemoglobin levels and red cell counts compared to males. **2. Analysis of Incorrect Options:** * **Testosterone (D):** Androgens are potent stimulators of EPO production in the kidneys and directly stimulate erythroid stem cells in the bone marrow. This explains the higher hematocrit levels seen in males. * **Thyroxine (C):** Thyroid hormones increase oxygen consumption and metabolic rate, leading to relative tissue hypoxia, which triggers an increase in EPO production. * **Progesterone (B):** Unlike estrogen, progesterone does not have a significant inhibitory effect on erythropoiesis; in some physiological contexts, it may even mildly stimulate ventilation, indirectly affecting oxygenation. **Clinical Pearls for NEET-PG:** * **Site of Production:** In adults, 85-90% of EPO is produced by **peritubular interstitial cells** of the renal cortex; the remainder comes from the liver. * **Stimulus:** The fundamental stimulus for EPO is **hypoxia** (sensed by HIF-1α), not the number of RBCs. * **Other Stimulants:** Catecholamines (via β-receptors), Alkalosis, and Cobalt salts also increase EPO production. * **Clinical Correlation:** Chronic Renal Failure (CRF) leads to normocytic normochromic anemia due to EPO deficiency.

Q: What is the half-life of prothrombin?

60 hours. **Explanation:** The correct answer is **60 hours (Option B)**. Prothrombin (Factor II) is a vitamin K-dependent glycoprotein synthesized in the liver. It serves as the precursor to thrombin, the central enzyme in the coagulation cascade that converts fibrinogen to fibrin. **Why 60 hours is correct:** In hematology, the half-lives of clotting factors are high-yield facts because they determine how quickly a deficiency (or its correction) manifests. Prothrombin has a relatively long half-life of approximately **60 to 72 hours**. This is significantly longer than other vitamin K-dependent factors like Factor VII, making prothrombin one of the last factors to decline during oral anticoagulant therapy (Warfarin). **Analysis of Incorrect Options:** * **A. 24 hours:** This is closer to the half-life of Factor IX (approx. 18–24 hours) or Factor X (approx. 25–40 hours). * **C. 5 days (120 hours):** This is too long for prothrombin. However, Fibrinogen (Factor I) has a half-life of about 4–5 days. * **D. 10 days:** No major coagulation factor has a half-life this long; most circulate for hours to a few days. **NEET-PG High-Yield Pearls:** 1. **Shortest Half-life:** Factor VII (~4–6 hours). This is why the Prothrombin Time (PT) is the first to prolong in liver disease or early Warfarin therapy. 2. **Longest Half-life:** Factor I (Fibrinogen) and Factor XIII (up to 5–10 days). 3. **Vitamin K-dependent Factors:** II, VII, IX, and X (mnemonic: 1972). 4. **Warfarin Monitoring:** Because of the long half-life of Factor II (60 hours), it takes roughly 3–5 days to reach a steady-state therapeutic anticoagulation level.

Question 1

Which of the following anticoagulants prevent clotting of blood in the normal vascular system?

Accepted Answer

Antithrombin III

Answer

Plasminogen

Answer

Fibrinogen

Answer

Heparin

Question 2

Which substance is present in both serum and plasma?

Accepted Answer

Factor VII

Answer

Fibrinogen

Answer

Factor V

Answer

Factor II

Question 3

A patient with mild congestive heart failure is treated with high-dose furosemide and diuresis of fluid. A complete blood count (CBC) taken before the diuresis shows an RBC count of 4 million/mm3; a CBC taken after diuresis shows a RBC count of 7 million/mm3. Which of the following is the most likely explanation?

Accepted Answer

Relative polycythemia

Answer

Cyanotic heart disease

Answer

Increased erythropoietin

Answer

Polycythemia vera

Question 4

Increased Prothrombin time results from deficiency of which factor?

Accepted Answer

Fibrinogen

Answer

Factor IX

Answer

Factor VI

Answer

Factor XI

Question 5

The biconcave shape of RBC is useful in all aspects except:

Accepted Answer

Helps in cellular metabolism

Answer

Helps in passing through capillaries

Answer

Increased surface area for gas diffusion

Answer

Prevents osmotic lysis

Question 6

Although more than 400 blood groups have been identified, the ABO Rh blood group systems remain the most important in clinical medicine because?

Accepted Answer

A, B and Rh antigens are most immunogenic.

Answer

It was first identified.

Answer

It has four different types of blood groups.

Answer

They are inherited.

Question 7

Which of the following factors is NOT derived from endothelial cells?

Accepted Answer

Thromboxane A2

Answer

Thrombomodulin

Answer

Protein S

Answer

Prostacyclin

Question 8

Vesicular transmission of antibody can occur in all of the following, EXCEPT?

Accepted Answer

Neonatal toxic erythema

Answer

Rh incompatibility

Answer

Isoimmune thrombocytopenia

Answer

Neonatal myasthenia gravis

Question 9

Erythropoietin production is inhibited by?

Accepted Answer

Estrogen

Answer

Progesterone

Answer

Thyroxine

Answer

Testosterone

Question 10

What is the half-life of prothrombin?

Accepted Answer

60 hours

Answer

24 hours

Answer

5 days

Answer

10 days

Blood and Immunity — MCQs

Blood and Immunity — MCQs

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