Blood and Immunity — MCQs

Blood and Immunity Indian Medical PG Practice Questions and MCQs

Question 61: Erythropoiesis in the fetal liver begins during which period?

A. 2-4 weeks
B. 4-6 weeks
C. 6-8 weeks (Correct Answer)
D. 8-10 weeks

Explanation: ### Explanation The correct answer is **6-8 weeks**. Erythropoiesis (the production of red blood cells) in the fetus occurs in distinct stages, transitioning through different anatomical sites as development progresses. **1. Why 6-8 weeks is correct:** Fetal erythropoiesis is divided into three stages: * **Mesoblastic Stage:** Starts at ~3 weeks in the yolk sac. * **Hepatic Stage:** The liver becomes the primary site of hematopoiesis starting around **6-8 weeks** of gestation. It reaches its peak activity at 3-4 months and continues until shortly before birth. * **Myeloid Stage:** The bone marrow takes over as the primary site starting from the 5th month (20 weeks). **2. Analysis of Incorrect Options:** * **2-4 weeks:** This corresponds to the **Mesoblastic stage**, where erythropoiesis occurs in the yolk sac (specifically the blood islands). The liver has not yet developed hematopoietic function. * **4-6 weeks:** This is a transitional period. While the liver primordium is forming, active erythropoiesis typically establishes firmly between the 6th and 8th week. * **8-10 weeks:** By this time, hepatic erythropoiesis is already well-established. This option is too late for the *onset* of the hepatic stage. **3. NEET-PG High-Yield Facts (Clinical Pearls):** * **Mnemonic for sites:** **"Young Liver Synthesizes Blood"** (Yolk sac → Liver → Spleen → Bone marrow). * **Spleen involvement:** The spleen contributes to erythropoiesis between the 10th and 28th weeks. * **Fetal Hemoglobin (HbF):** The hepatic stage is primarily associated with the production of HbF ($\alpha_2\gamma_2$), which has a higher affinity for oxygen than adult hemoglobin (HbA). * **Post-natal site:** In adults, the liver only resumes erythropoiesis in pathological states (Extramedullary Hematopoiesis), such as Myelofibrosis or Thalassemia.

Question 62: Coagulation process starts with the help of all except?

A. Kalleikrein
B. Hageman factor
C. Phospholipids (Correct Answer)
D. HMW kininogen

Explanation: ### Explanation The coagulation cascade is initiated via two pathways: the **Extrinsic pathway** (triggered by Tissue Factor) and the **Intrinsic pathway** (triggered by contact activation). **1. Why Phospholipids is the Correct Answer:** While phospholipids (specifically Platelet Factor 3) are **essential co-factors** required for the formation of the Tenase and Prothrombinase complexes later in the cascade, they do not **start** (initiate) the process. Coagulation is initiated by the activation of Factor XII (in the intrinsic pathway) or Factor VII (in the extrinsic pathway). Phospholipids provide the surface upon which these activated factors interact, but they are not the primary triggers. **2. Analysis of Incorrect Options:** * **Hageman Factor (Factor XII):** This is the primary initiator of the **Intrinsic Pathway**. When it comes into contact with negatively charged surfaces (like collagen or glass), it undergoes a conformational change to become XIIa. * **Kallikrein & HMW Kininogen (HMWK):** These are part of the **"Contact Activation System."** HMWK acts as a cofactor that anchors Factor XII and Prekallikrein to the subendothelial surface. Kallikrein further activates Factor XII via a positive feedback loop. Together with Factor XII, they are the starting components of the intrinsic cascade. ### Clinical Pearls for NEET-PG: * **Contact Activation:** The trio of Factor XII, HMWK, and Prekallikrein initiates the intrinsic pathway *in vitro* (e.g., in a test tube). * **In Vivo Initiation:** In the human body, the **Extrinsic Pathway** (Factor VII + Tissue Factor) is the most important initiator of coagulation. * **Factor XII Deficiency:** Interestingly, patients with Factor XII deficiency show a prolonged aPTT in the lab but **do not** have clinical bleeding tendencies. * **Vitamin K Dependent Factors:** II, VII, IX, X, Protein C, and Protein S.

Question 63: In the coagulation cascade, the clot is initiated by negatively charged particles on a glass bead. How is it initiated in vivo?

A. Tissue factor (Correct Answer)
B. Thrombin
C. Endothelin
D. von Willebrand factor

Explanation: **Explanation:** The coagulation cascade is divided into two pathways that converge into a common pathway. 1. **The Correct Answer (A):** In an *in vitro* setting (like a glass tube), the **Intrinsic Pathway** is triggered by contact with negatively charged surfaces (Factor XII). However, **in vivo**, the primary initiator of coagulation is the **Extrinsic Pathway**. This is triggered by **Tissue Factor (Factor III/Thromboplastin)**, which is released from damaged subendothelial cells. Tissue Factor binds with Factor VIIa to form a complex that activates Factor X, leading to the "thrombin burst" necessary for stable clot formation. 2. **Why other options are incorrect:** * **B. Thrombin (Factor IIa):** Thrombin is the *product* of the coagulation cascade, not the initiator. While it provides positive feedback to amplify the cascade, it is not the trigger for the initial clot. * **C. Endothelin:** This is a potent vasoconstrictor released by damaged endothelium. It helps reduce blood flow to the site of injury but does not initiate the chemical coagulation cascade. * **D. von Willebrand factor (vWF):** vWF is crucial for **primary hemostasis** (platelet adhesion to subendothelial collagen). It does not initiate the secondary hemostasis (coagulation cascade), though it does stabilize Factor VIII in the blood. **High-Yield NEET-PG Pearls:** * **Rate-limiting step:** The activation of Factor X (where intrinsic and extrinsic pathways meet). * **Vitamin K dependent factors:** II, VII, IX, X, Protein C, and Protein S. * **Shortest half-life:** Factor VII (this is why PT/INR is used to monitor early liver failure or warfarin therapy). * **Calcium (Factor IV):** Required for almost all steps of the cascade except the initial steps of the intrinsic pathway.

Question 64: What is the function common to neutrophils, monocytes, and macrophages?

A. Immune response
B. Phagocytosis (Correct Answer)
C. Liberation of histamine
D. Destruction of old erythrocytes

Explanation: **Explanation:** The core physiological function shared by neutrophils, monocytes, and macrophages is **phagocytosis**—the process of engulfing and digesting cellular debris and pathogens. 1. **Why Phagocytosis is Correct:** * **Neutrophils:** These are the "first responders" to acute inflammation. They utilize chemotaxis to reach the site of infection and use phagocytosis to destroy bacteria. * **Monocytes:** These are agranulocytes present in the blood. Once they migrate into tissues, they mature into macrophages. * **Macrophages:** Part of the Reticuloendothelial System (RES), they are professional phagocytes that clear larger pathogens and apoptotic cells. 2. **Analysis of Incorrect Options:** * **A. Immune Response:** While all three are involved in the immune response, this is a broad category. Neutrophils are primarily involved in innate immunity, whereas macrophages bridge innate and adaptive immunity (via antigen presentation). Phagocytosis is the specific *mechanism* they all share. * **C. Liberation of Histamine:** This is the primary function of **Basophils** and **Mast cells** during allergic reactions and type I hypersensitivity. * **D. Destruction of old erythrocytes:** This is a specialized function of the **Splenic Macrophages** (in the cords of Billroth). Neutrophils do not participate in the physiological recycling of red blood cells. **High-Yield Clinical Pearls for NEET-PG:** * **Neutrophils** contain NADPH oxidase; a deficiency leads to **Chronic Granulomatous Disease (CGD)**, where phagocytosis occurs but "oxidative burst" fails. * **Monocytes** are the largest cells in a normal peripheral blood smear. * **Fixed Macrophages:** Know their names for various organs: Kupffer cells (Liver), Microglia (CNS), Mesangial cells (Kidney), and Osteoclasts (Bone).

Question 65: Which of the following is not a platelet-associated coagulation factor?

A. von Willebrand factor (vWF)
B. Factor IX (Correct Answer)
C. Factor XI
D. Factor XIII

Explanation: **Explanation:** Platelets play a dual role in hemostasis: they form the primary platelet plug and serve as a catalytic surface for secondary hemostasis (coagulation). While many coagulation factors are stored within platelet granules or adsorbed onto their surface, **Factor IX** is not considered a "platelet-associated" factor in the context of storage or synthesis. **Why Factor IX is the correct answer:** Factor IX (Christmas factor) is a vitamin K-dependent serine protease synthesized exclusively in the liver. It circulates in the plasma in its zymogen form. Unlike the other options, it is neither synthesized by megakaryocytes nor stored in platelet alpha-granules. While it binds to the platelet surface during the "propagation" phase of coagulation to form the intrinsic tenase complex, it is not inherently "associated" with the platelet structure or storage. **Analysis of Incorrect Options:** * **von Willebrand factor (vWF):** Synthesized by endothelial cells (Weibel-Palade bodies) and megakaryocytes. It is stored in the **alpha-granules** of platelets and is crucial for platelet adhesion to subendothelial collagen. * **Factor XI:** Recent studies and standard physiology texts (like Ganong) confirm that platelets contain Factor XI on their surface and it can be activated there, contributing to the "amplification" phase of the cell-based model of coagulation. * **Factor XIII:** Platelets contain the **a-subunit** of Factor XIII (Fibrin Stabilizing Factor) in high concentrations within their cytoplasm. It is released during activation to help cross-link fibrin strands. **High-Yield NEET-PG Pearls:** * **Alpha-granules contain:** vWF, Factor V, Factor XI, Factor XIII, Platelet Factor 4 (PF4), and PDGF. * **Dense granules contain:** ADP, ATP, Calcium (Factor IV), and Serotonin (SAC: Serotonin, Adenosine, Calcium). * **Factor V** is the most significant coagulation factor stored in platelets; approximately 20% of the body's Factor V is found within platelet alpha-granules.

Question 66: Which of the following types of white blood cells are most numerous in human blood?

A. Neutrophils (Correct Answer)
B. Eosinophils
C. Basophils
D. Monocytes

Explanation: **Explanation:** In human physiology, white blood cells (leukocytes) are categorized based on their prevalence and morphology. **Neutrophils** are the most abundant type of leukocyte, typically accounting for **40% to 70%** of the total white blood cell count in a healthy adult. They serve as the primary "first responders" of the innate immune system, migrating rapidly to sites of acute bacterial infection to perform phagocytosis. **Analysis of Options:** * **Neutrophils (Correct):** As the most numerous cell type, they are essential for acute inflammatory responses. Their count increases significantly during bacterial infections (Neutrophilia). * **Eosinophils (Incorrect):** These make up only **1% to 4%** of total WBCs. They are primarily involved in combating parasitic infections and mediating allergic reactions. * **Basophils (Incorrect):** These are the least common leukocytes, comprising **0.5% to 1%** of the total count. They contain histamine and heparin, playing a role in immediate hypersensitivity reactions. * **Monocytes (Incorrect):** These constitute **2% to 8%** of WBCs. They are the largest leukocytes and eventually migrate into tissues to become macrophages. **High-Yield NEET-PG Pearls:** 1. **Mnemonic for WBC Prevalence:** **N**ever **L**et **M**onkeys **E**at **B**ananas (**N**eutrophils > **L**ymphocytes > **M**onocytes > **E**osinophils > **B**asophils). 2. **Absolute Neutrophil Count (ANC):** A value below 1,500 cells/mm³ is defined as Neutropenia, which significantly increases the risk of life-threatening infections. 3. **Shift to the Left:** This clinical term refers to an increase in immature neutrophils (band cells) in the blood, usually indicating an active acute infection.

Question 67: Which of the following is not present in azurophil granules of neutrophils?

A. Defensins
B. Myeloperoxidase
C. Acid hydrolases
D. Lactoferrin (Correct Answer)

Explanation: Neutrophils contain two main types of granules: **Primary (Azurophilic)** and **Secondary (Specific)** granules. Understanding the distribution of enzymes between these granules is a high-yield topic for NEET-PG. ### **Explanation of the Correct Answer** **D. Lactoferrin** is the correct answer because it is a major constituent of **Secondary (Specific) granules**, not azurophilic granules. Lactoferrin acts as a bacteriostatic agent by sequestering iron, which is essential for bacterial growth. Specific granules also contain Alkaline Phosphatase, Collagenase, and Lysozyme. ### **Analysis of Incorrect Options** * **A. Defensins:** These are small cationic proteins found in **Azurophilic granules** that create pores in bacterial membranes, leading to cell lysis. * **B. Myeloperoxidase (MPO):** This is the hallmark enzyme of **Azurophilic granules**. It plays a critical role in the respiratory burst by converting hydrogen peroxide and chloride ions into hypochlorous acid (HOCl), a potent bactericidal agent. * **C. Acid Hydrolases:** These are typical lysosomal enzymes (e.g., glucuronidase, elastase, cathepsin G) found in **Azurophilic granules** that function to digest engulfed pathogens at an acidic pH. ### **High-Yield Clinical Pearls for NEET-PG** * **Mnemonic for Azurophilic (Primary) Granules:** Remember **"DAMN"** — **D**efensins, **A**cid hydrolases, **M**yeloperoxidase, **N**eutral proteases (Elastase). * **Neutrophil Alkaline Phosphatase (NAP/LAP):** Found in **Specific granules**. Its levels are **decreased** in Chronic Myeloid Leukemia (CML) and **increased** in Leukemoid reactions. * **MPO Deficiency:** The most common inherited defect of phagocytes, though often asymptomatic because other killing mechanisms remain intact. * **Tertiary Granules:** Contain Gelatinase and Cathepsins, which help in tissue migration.

Question 68: Alpha granules of platelets contain all of the following except?

A. Fibrinogen
B. TGF-beta
C. PDGF
D. ADP (Correct Answer)

Explanation: **Explanation:** Platelets contain two main types of secretory granules: **Alpha ($\alpha$) granules** and **Dense ($\delta$) granules**. Distinguishing between their contents is a high-yield topic for NEET-PG. **Why ADP is the correct answer:** **ADP (Adenosine Diphosphate)** is stored in the **Dense granules**, not alpha granules. Dense granules are smaller and contain non-protein substances essential for platelet activation and vasoconstriction, often remembered by the mnemonic **SAC** (Serotonin, ADP/ATP, and Calcium). ADP specifically plays a crucial role in recruiting more platelets to the site of injury by binding to P2Y1 and P2Y12 receptors. **Analysis of incorrect options:** * **A. Fibrinogen:** This is a major protein component of **Alpha granules**. It is essential for platelet aggregation as it forms bridges between GP IIb/IIIa receptors. * **B & C. TGF-beta and PDGF:** Alpha granules are the primary storage site for various growth factors, including **Transforming Growth Factor-beta (TGF-$\beta$)**, **Platelet-Derived Growth Factor (PDGF)**, and Vascular Endothelial Growth Factor (VEGF). These are vital for wound healing and tissue repair. **High-Yield Clinical Pearls:** * **Alpha Granules (Most numerous):** Contain high-molecular-weight proteins like vWF, Factor V, Fibrinogen, Fibronectin, and Platelet Factor 4 (PF4). * **Dense Granules (Fewer):** Contain "Small molecules" – ADP, ATP, Serotonin (5-HT), Calcium, and Pyrophosphate. * **Gray Platelet Syndrome:** A rare bleeding disorder caused by a congenital deficiency of **Alpha granules**. * **Hermansky-Pudlak Syndrome:** Associated with a deficiency of **Dense granules** (presents with albinism and bleeding diathesis).

Question 69: Plasma is the fluid portion of the blood which aids in the transport of other substances in the body. Total plasma volume in relation to body weight is:

A. 5% (Correct Answer)
B. 10%
C. 20%
D. 25%

Explanation: ### Explanation The correct answer is **A. 5%**. **1. Understanding the Medical Concept:** Total Body Water (TBW) constitutes approximately **60%** of the total body weight in an average adult male. This water is distributed into two main compartments: * **Intracellular Fluid (ICF):** 40% of body weight (2/3 of TBW). * **Extracellular Fluid (ECF):** 20% of body weight (1/3 of TBW). The ECF is further divided into **Interstitial Fluid (15%)** and **Plasma (5%)**. Therefore, plasma volume—the liquid component of blood—represents approximately 5% of the total body weight (e.g., in a 70 kg man, plasma volume is ~3.5 liters). **2. Analysis of Incorrect Options:** * **B. 10%:** This value does not correspond to a major fluid compartment. However, total blood volume (plasma + cells) is roughly 7–8% of body weight. * **C. 20%:** This represents the **Total Extracellular Fluid (ECF)** volume, which includes both plasma and the fluid bathing the cells (interstitial fluid). * **D. 25%:** This value is higher than the total ECF and does not align with standard physiological fluid distribution. **3. NEET-PG High-Yield Pearls:** * **Blood Volume vs. Plasma Volume:** Remember that Blood Volume = Plasma Volume / (1 – Hematocrit). Total blood volume is ~8% of body weight. * **Measurement:** Plasma volume is most commonly measured using **Evans Blue dye (T-1824)** or **Radioiodinated Albumin (I-131)** because these substances bind to albumin and remain within the vascular compartment. * **Indicator Dilution Principle:** The formula used for these calculations is $Volume = \frac{Amount\ of\ Tracer}{Concentration}$. * **Hematocrit (Hct):** The percentage of blood volume occupied by RBCs, normally ~45%.

Question 70: The Bombay blood group contains which of the following antibodies?

A. Anti H
B. Anti A and Anti B
C. Anti A, Anti B, and Anti H (Correct Answer)
D. H antibody along with H antigen

Explanation: ### Explanation **Concept Overview:** The Bombay phenotype ($O_h$) is a rare blood group characterized by the absence of the **H antigen** on red blood cells. In the normal ABO biosynthetic pathway, the *H gene* codes for fucosyltransferase, which adds L-fucose to a precursor substance to form the H antigen. This H antigen is the mandatory substrate upon which A or B sugars are attached. Individuals with the Bombay phenotype are homozygous recessive ($hh$); they cannot produce the H antigen. Consequently, even if they possess A or B enzymes, these enzymes have no substrate to act upon. Therefore, their RBCs lack A, B, and H antigens. **Why Option C is Correct:** Because the immune system recognizes any absent antigen as "foreign," individuals with the Bombay phenotype develop naturally occurring, potent, IgM antibodies against all antigens they lack. Since they lack A, B, and H antigens, their serum contains **Anti-A, Anti-B, and Anti-H**. **Analysis of Incorrect Options:** * **Option A:** While they do have Anti-H, this is incomplete as they also possess Anti-A and Anti-B. * **Option B:** This describes a typical Blood Group O individual. Group O individuals possess the H antigen, so they *do not* produce Anti-H. * **Option C:** Incorrect because Bombay phenotype individuals **lack the H antigen** entirely. The presence of the H antibody would cause immediate hemolysis if the H antigen were present. **High-Yield Clinical Pearls for NEET-PG:** * **Discovery:** First described by **Dr. Y.M. Bhende** in 1952 in Bombay (Mumbai). * **Cross-matching Paradox:** In routine forward grouping, Bombay blood group mimics **Group O** (no agglutination with Anti-A or Anti-B). However, in cross-matching, it shows vigorous incompatibility with Group O donor blood due to the presence of **Anti-H**. * **Transfusion:** They can **only** receive blood from another Bombay phenotype individual. * **Secretor Status:** They are always non-secretors (lack H substance in saliva).

Practice by Chapter

Composition and Functions of Blood

Practice Questions

Erythrocytes and Hemoglobin

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Leukocytes and Immune Function

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Platelets and Hemostasis

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Blood Groups and Transfusion

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Coagulation and Fibrinolysis

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Hematopoiesis

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Innate Immunity

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Adaptive Immunity

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Immunological Memory and Tolerance

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