Blood and Immunity Practice Questions

Q: The Arneth count is used to quantify which of the following?

Lobes in neutrophils. **Explanation:** The **Arneth count** (or Arneth index) is a hematological method used to evaluate the maturity of **neutrophils** by counting the number of **lobes in their nuclei**. Under normal conditions, a mature neutrophil typically has 2 to 5 lobes. As a neutrophil ages, the number of nuclear lobes increases. The Arneth count categorizes 100 neutrophils into five classes based on lobe count: * **Class I:** 1 lobe (immature/band forms) * **Class II:** 2 lobes * **Class III:** 3 lobes * **Class IV:** 4 lobes * **Class V:** 5 or more lobes (mature/older forms) **Analysis of Options:** * **Option A & C:** The Arneth count specifically assesses nuclear morphology, not the presence of granules (eosinophils) or the cell type (lymphocytes). * **Option D:** While bone marrow activity influences the count, the Arneth count is performed on a peripheral blood smear, not the marrow itself. **Clinical Pearls for NEET-PG:** 1. **Shift to the Left:** An increase in immature neutrophils (Class I & II). This occurs in **acute pyogenic infections**, where the bone marrow releases young cells rapidly to fight infection. 2. **Shift to the Right:** An increase in older neutrophils (Class IV & V). This is a classic finding in **Megaloblastic Anemia** (Vitamin B12 or Folate deficiency), characterized by **hypersegmented neutrophils** (more than 5 lobes). 3. **Cooke’s Criterion:** A similar classification used to identify hypersegmentation; if >5% of neutrophils have 5 lobes or any have 6 lobes, it is clinically significant.

Q: Prothrombin Time (PT) detects deficiency of all the following clotting factors EXCEPT?

VIII. **Explanation:** The **Prothrombin Time (PT)** is a laboratory test used to evaluate the integrity of the **Extrinsic** and **Common pathways** of the coagulation cascade. **1. Why Option D (Factor VIII) is the correct answer:** Factor VIII is a critical component of the **Intrinsic pathway**. Deficiencies in Factor VIII (as seen in Hemophilia A) or other intrinsic factors (XII, XI, IX) will prolong the **Activated Partial Thromboplastin Time (aPTT)**, but will leave the PT unaffected. Therefore, PT cannot detect a deficiency in Factor VIII. **2. Why the other options are incorrect:** The PT test specifically measures the activity of factors involved in the extrinsic and common pathways: * **Factor VII (Option C):** This is the key factor of the **Extrinsic pathway**. PT is the most sensitive test for Factor VII deficiency. * **Factors II, V, and X (Options A & B):** These factors belong to the **Common pathway**. Since the PT test monitors the progression from the extrinsic pathway through the common pathway to fibrin clot formation, deficiencies in Factor II (Prothrombin), Factor V, or Factor X will result in a prolonged PT. **Clinical Pearls for NEET-PG:** * **Reagent used for PT:** Tissue Thromboplastin (Tissue Factor) and Calcium. * **INR (International Normalized Ratio):** A standardized version of PT used primarily to monitor **Warfarin (Oral Anticoagulant)** therapy. * **Vitamin K Dependent Factors:** II, VII, IX, and X. Since Factor VII has the shortest half-life, PT is the first test to become prolonged in Vitamin K deficiency or early liver disease. * **Mnemonic for PT (Extrinsic):** "PET" — **P**T measures **E**xtrinsic pathway and involves Factor **T**en (X) and Seven (VII).

Q: What is a major source of Von Willebrand factor (vWF)?

Endothelial cells. **Explanation:** **Von Willebrand factor (vWF)** is a large multimeric glycoprotein essential for primary hemostasis. It acts as a molecular bridge between the subendothelial collagen and platelets (via the GpIb receptor) and serves as a carrier protein for Factor VIII. **Why Endothelial Cells are the Correct Answer:** The primary sources of vWF are **vascular endothelial cells** and **megakaryocytes**. Within endothelial cells, vWF is synthesized and stored in specialized cigar-shaped organelles called **Weibel-Palade bodies**. When the endothelium is injured, these bodies release vWF into the subendothelium and plasma to initiate platelet adhesion. (Note: In megakaryocytes/platelets, vWF is stored in **alpha-granules**). **Analysis of Incorrect Options:** * **A. Erythrocytes:** Red blood cells are primarily involved in oxygen transport and do not synthesize or store clotting factors. * **B. Neutrophils:** These are granulocytes involved in innate immunity and phagocytosis; they do not produce vWF. * **D. Monocytes:** While they play a role in inflammation and can express Tissue Factor, they are not a source of vWF. **High-Yield Clinical Pearls for NEET-PG:** * **vWF Function:** It stabilizes **Factor VIII**; in Von Willebrand Disease (vWD), Factor VIII levels may be low, leading to a prolonged aPTT. * **Diagnostic Marker:** vWF is used as an immunohistochemical marker for vascular tumors (e.g., angiosarcoma). * **Desmopressin (DDAVP):** This drug is used in treatment as it stimulates the release of vWF from Weibel-Palade bodies. * **ADAMTS13:** This enzyme cleaves large vWF multimers; its deficiency leads to Thrombotic Thrombocytopenic Purpura (TTP).

Q: What is true of fetal hematopoiesis in the course of pregnancy?

Rise in Hemoglobin content. ### Explanation **Correct Option: C. Rise in Hemoglobin content** During fetal development, there is a progressive and significant increase in hemoglobin (Hb) concentration to meet the rising oxygen demands of the growing fetus. At 10 weeks of gestation, Hb is approximately 8–10 g/dL; by term, it rises to **14–20 g/dL**. This increase is driven by the high levels of **Erythropoietin (EPO)** produced by the fetal liver (and later the kidneys) in response to the relatively low oxygen tension ($PaO_2$) of the intrauterine environment. **Analysis of Incorrect Options:** * **A. Rise in MCV:** This is incorrect. Fetal red blood cells (RBCs) are initially **macrocytic**. As gestation progresses, the Mean Corpuscular Volume (MCV) actually **decreases**. It starts at >130 fL in the first trimester and drops to approximately 100–110 fL at birth. * **B. Rise in reticulocyte count:** The reticulocyte count is very high in early pregnancy (up to 40% at 12 weeks) due to rapid erythropoiesis but **decreases** as the fetus approaches term (dropping to 3–5% at birth). * **C. Decrease in blood volume:** This is incorrect. Fetal blood volume **increases** linearly with fetal weight throughout pregnancy to support the expanding vascular bed and placental circulation. **High-Yield Facts for NEET-PG:** 1. **Sites of Hematopoiesis:** * **Mesoblastic Stage (3–8 weeks):** Yolk sac (specifically "blood islands"). * **Hepatic Stage (6 weeks – Birth):** Liver is the chief site (peaks at 3–4 months). The spleen also contributes (12–28 weeks). * **Myeloid Stage (18 weeks onwards):** Bone marrow becomes the primary site. 2. **Fetal Hemoglobin (HbF):** Composed of $\alpha_2\gamma_2$ chains. It has a higher affinity for oxygen than adult Hb (HbA) because it binds poorly to 2,3-BPG. 3. **Nucleated RBCs:** These are commonly seen in fetal peripheral blood early on but disappear as the bone marrow matures.

Q: A father's blood group is 'A' and a mother's blood group is 'AB'. Which of the following blood groups is not possible in any of their child?

O. ### Explanation The inheritance of ABO blood groups is determined by the **ABO gene**, which follows the principles of **Co-dominance** and **Multiple Allelism**. The alleles involved are $I^A$, $I^B$ (both dominant), and $i$ (recessive). **1. Why 'O' is the Correct Answer:** To have blood group **O**, a child must have the genotype **$ii$**, receiving one recessive '$i$' allele from each parent. * The **Mother (AB)** has the genotype **$I^A I^B$**. She can only pass on either an $A$ or a $B$ allele. She does not possess the '$i$' allele. * The **Father (A)** can be either homozygous ($I^A I^A$) or heterozygous ($I^A i$). Since the mother cannot contribute an '$i$' allele, a child with genotype $ii$ (Group O) is **genetically impossible**. **2. Analysis of Incorrect Options:** * **Option A (Group A):** Possible if the child inherits $I^A$ from the mother and either $I^A$ or $i$ from the father (Genotypes: $I^A I^A$ or $I^A i$). * **Option B (Group B):** Possible if the child inherits $I^B$ from the mother and $i$ from the father (Genotype: $I^B i$). * **Option C (Group AB):** Possible if the child inherits $I^B$ from the mother and $I^A$ from the father (Genotype: $I^A I^B$). **3. High-Yield Clinical Pearls for NEET-PG:** * **Bombay Blood Group:** A rare phenotype where individuals lack the **H-antigen**. They phenotypically test as Group O, regardless of their ABO genotype. This can lead to "impossible" inheritance patterns. * **Universal Donor/Recipient:** O negative is the universal donor (lacks A, B, and Rh antigens); AB positive is the universal recipient (lacks anti-A, anti-B, and anti-Rh antibodies). * **Inheritance Rule:** An AB parent can never have an O child, and an O parent can never have an AB child (excluding the Bombay phenotype).

Q: Approximately what percentage of clot retraction is completed within 1 hour?

1 hour. **Explanation:** **Clot retraction** (also known as syneresis) is the process by which a blood clot shrinks and expresses serum. This process is primarily mediated by **platelets**. 1. **Why 1 hour is correct:** Clot retraction begins within a few minutes of clot formation (typically 20–30 minutes). However, the process is dynamic and reaches its maximum extent—where approximately **100% of the retraction is completed—within 1 hour**. This contraction is driven by the activation of **thrombosthenin** (a contractile protein complex of actin and myosin) within the platelets, which pulls the fibrin threads together, squeezing out the serum and closing the vascular breach. 2. **Why the other options are incorrect:** * **15 minutes:** At this stage, the process has only just begun. The clot is still soft and has not yet achieved significant shrinkage. * **2 hours:** While the clot remains stable at this time, the active phase of retraction is already finished by the 60-minute mark. * **24 hours:** This is the timeframe associated with **fibrinolysis** (clot dissolution) rather than retraction. By 24 hours, the clot is being broken down by plasmin. **High-Yield Clinical Pearls for NEET-PG:** * **Platelet Requirement:** Clot retraction requires a normal platelet count. In **Thrombocytopenia**, the clot is "friable" and retraction is poor. * **Glanzmann Thrombasthenia:** This is a qualitative platelet disorder caused by a deficiency of **GP IIb/IIIa**. In this condition, platelets cannot bind fibrinogen, leading to **absent or defective clot retraction** despite a normal platelet count. * **Serum vs. Plasma:** Serum is essentially plasma minus fibrinogen and clotting factors II, V, VIII, and XIII, which are consumed during the retraction process.

Q: Which factor activates prekallikrein?

Factor XII. **Explanation:** The correct answer is **Factor XII (Hageman Factor)**. This question tests the understanding of the **Contact Activation Pathway** (Intrinsic Pathway) of blood coagulation. **Why Factor XII is correct:** When blood comes into contact with a negatively charged surface (like collagen, glass, or kaolin), Factor XII is activated to **Factor XIIa**. Factor XIIa then acts as a protease to convert the zymogen **prekallikrein** into its active form, **kallikrein**. This process is part of a reciprocal activation loop: while XIIa activates prekallikrein, the resulting kallikrein further accelerates the activation of Factor XII, creating a potent amplification cycle. High-molecular-weight kininogen (HMWK) acts as a cofactor in this reaction. **Why the other options are incorrect:** * **Factor VIII (Anti-hemophilic Factor):** Acts as a cofactor for Factor IXa in the "tenase" complex to activate Factor X. It has no role in the initial contact phase. * **Factor II (Prothrombin):** This is a downstream factor. It is converted to Thrombin (IIa) by the prothrombinase complex (Xa, Va, Ca²⁺, and phospholipids). * **Factor X (Stuart-Prower Factor):** This is the start of the Common Pathway. It is activated by either the intrinsic or extrinsic pathways but does not activate prekallikrein. **Clinical Pearls for NEET-PG:** * **The Kallikrein-Kinin System:** Kallikrein not only aids coagulation but also converts HMWK into **Bradykinin**, a potent vasodilator that increases vascular permeability and causes pain. * **Deficiency Paradox:** Patients with Factor XII, Prekallikrein, or HMWK deficiency show a **markedly prolonged aPTT** in vitro, but clinically, they **do not have a bleeding tendency**. In fact, Factor XII deficiency may be associated with an increased risk of thrombosis. * **Fibrinolysis:** Kallikrein also helps convert plasminogen to plasmin, linking the clotting cascade to fibrinolysis.

Q: At what gestational age does the switchover from fetal to adult hemoglobin synthesis begin?

36 weeks. ### Explanation **Underlying Medical Concept** Hemoglobin synthesis in humans undergoes a programmed "switching" process. Fetal hemoglobin (HbF, $\alpha_2\gamma_2$) is the predominant type during intrauterine life due to its high oxygen affinity. The transition from the synthesis of $\gamma$-globin (fetal) to $\beta$-globin (adult) is a developmentally regulated process that is **not** triggered by birth, but rather by the gestational age of the fetus. This switchover begins at approximately **36 weeks of gestation**. By birth, adult hemoglobin (HbA, $\alpha_2\beta_2$) accounts for about 20–30% of total hemoglobin, and the process continues postnatally until HbF levels drop to <1% by 6–12 months of age. **Analysis of Options** * **Option A (30 weeks):** At this stage, the fetus is still almost entirely dependent on HbF for efficient oxygen extraction from maternal blood. * **Option B (36 weeks):** **Correct.** This is the physiological timing when the $\beta$-globin gene expression significantly increases, marking the start of the transition to HbA. * **Option C & D (Postnatal):** These are incorrect because the switch is a pre-programmed genetic event that begins **in utero**. While the *predominance* of HbA occurs postnatally, the *switchover* starts before birth. **NEET-PG High-Yield Pearls** * **HbF Structure:** $\alpha_2\gamma_2$. It does not bind 2,3-BPG effectively, leading to a leftward shift in the oxygen dissociation curve (higher affinity). * **Site of Erythropoiesis:** Yolk sac (3–8 weeks) $\rightarrow$ Liver (6–30 weeks, primary site) $\rightarrow$ Bone Marrow (begins at 18–20 weeks; becomes primary site by 30 weeks). * **Clinical Correlation:** Conditions like $\beta$-Thalassemia major do not manifest at birth because HbF levels are still high; symptoms appear only after 6 months when the switch to HbA is nearly complete.

Q: Which of the following constitutes the prothrombin activator complex?

Factor Xa, Va, Platelet Phospholipids. ### Explanation The **Prothrombin Activator Complex** represents the final common pathway of the coagulation cascade, where the intrinsic and extrinsic pathways converge to convert Prothrombin (Factor II) into Thrombin (Factor IIa). **1. Why Option D is Correct:** The formation of the prothrombin activator complex requires four essential components: * **Factor Xa:** The active enzyme (protease) that cleaves prothrombin. * **Factor Va:** The essential cofactor that accelerates the reaction rate by several thousand-fold. * **Platelet Phospholipids (PF3):** Provides the surface for the assembly of the complex. * **Calcium Ions (Ca²⁺):** Acts as a bridge between the clotting factors and the phospholipid surface. Without any of these components, the rate of thrombin formation is insufficient for effective hemostasis. **2. Why Other Options are Incorrect:** * **Option A:** Includes **Factor VIIIa**, which is a cofactor for the "Tenase complex" (Intrinsic pathway), not the prothrombin activator complex. * **Option B:** Includes **Factor VIIa**, which is the primary initiator of the Extrinsic pathway and does not directly form the prothrombin activator. * **Option C:** While tissue phospholipids can initiate the extrinsic pathway, the physiological prothrombin activator complex specifically utilizes **Factor Va** as a cofactor, which is missing here. **3. NEET-PG High-Yield Pearls:** * **Rate-Limiting Step:** The formation of the prothrombin activator is generally considered the rate-limiting step in blood coagulation. * **Factor V Activation:** Factor V is activated to Va by a positive feedback loop initiated by small amounts of Thrombin. * **Parahemophilia:** A rare bleeding disorder caused by a deficiency in Factor V. * **Vitamin K Dependency:** Factors II, VII, IX, and X are Vitamin K dependent, but their cofactors (V and VIII) are not.

Question 1

All of the following statements about Hepcidin are true EXCEPT:

Accepted Answer

Mice with enhanced hepcidin expression have elevated body iron stores.

Answer

It is a 25-amino acid peptide secreted by Kupffer cells.

Answer

It decreases duodenal absorption of iron.

Answer

It regulates the activity of transporters DMT-1 and ferroportin-1.

Question 2

The Arneth count is used to quantify which of the following?

Accepted Answer

Lobes in neutrophils

Answer

Lymphocytes

Answer

Granules in eosinophils

Answer

White blood cells in bone marrow

Question 3

Prothrombin Time (PT) detects deficiency of all the following clotting factors EXCEPT?

Accepted Answer

VIII

Answer

II

Answer

V

Answer

VII

Question 4

What is a major source of Von Willebrand factor (vWF)?

Accepted Answer

Endothelial cells

Answer

Erythrocytes

Answer

Neutrophils

Answer

Monocytes

Question 5

What is true of fetal hematopoiesis in the course of pregnancy?

Accepted Answer

Rise in Hemoglobin content

Answer

Rise in MCV

Answer

Rise in reticulocyte count

Answer

Decrease in blood volume

Question 6

A father's blood group is 'A' and a mother's blood group is 'AB'. Which of the following blood groups is not possible in any of their child?

Accepted Answer

O

Answer

A

Answer

B

Answer

AB

Question 7

Approximately what percentage of clot retraction is completed within 1 hour?

Accepted Answer

1 hour

Answer

24 hours

Answer

2 hours

Answer

15 minutes

Question 8

Which factor activates prekallikrein?

Accepted Answer

Factor XII

Answer

Factor VIII

Answer

Factor II

Answer

Factor X

Question 9

At what gestational age does the switchover from fetal to adult hemoglobin synthesis begin?

Accepted Answer

36 weeks

Answer

30 weeks

Answer

7 days postnatal

Answer

3 weeks postnatal

Question 10

Which of the following constitutes the prothrombin activator complex?

Accepted Answer

Factor Xa, Va, Platelet Phospholipids

Answer

Factor Xa, Va, VIIIa

Answer

Factor Va, VIIa, Platelet Phospholipids

Answer

Factor Xa, VIIIa, Tissue Phospholipids

Blood and Immunity — MCQs

Blood and Immunity — MCQs

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