Blood and Immunity — MCQs

Blood and Immunity Indian Medical PG Practice Questions and MCQs

Question 171: What is the lifespan of neutrophils?

A. 6 hours (Correct Answer)
B. 6 days
C. 10 days
D. 15 days

Explanation: **Explanation:** **Correct Answer: A. 6 hours** Neutrophils (Polymorphonuclear leukocytes) have the shortest lifespan among the white blood cells once they enter the circulation. The physiological lifespan of a neutrophil in the peripheral blood is approximately **6 to 10 hours**. After this brief period, they migrate into the tissues (diapedesis), where they survive for another 2 to 5 days before undergoing apoptosis or being consumed during phagocytosis. In the context of NEET-PG, "6 hours" is the standard textbook value for their half-life in the bloodstream. **Analysis of Incorrect Options:** * **B. 6 days:** This duration more closely reflects the total lifespan of a neutrophil including its time spent in the tissues, but it does not represent its circulating time in the blood. * **C. 10 days:** This is the approximate lifespan of **Platelets** (8–12 days). * **D. 15 days:** This does not correspond to any specific leukocyte lifespan; however, it is worth noting that the maturation process of a neutrophil in the bone marrow takes about 10–14 days. **High-Yield Clinical Pearls for NEET-PG:** * **Granulopoiesis:** The bone marrow maintains a large "storage pool" of neutrophils, containing about 5–10 times more cells than the circulating pool. * **Left Shift:** An increase in immature neutrophils (band cells) in the blood indicates an acute bacterial infection. * **Hypersegmented Neutrophils:** Seen in Megaloblastic anemia (Vitamin B12/Folate deficiency); defined as presence of neutrophils with >5 lobes. * **Lifespan Comparison:** * **Lymphocytes:** Can live for months to years (memory cells). * **Erythrocytes (RBCs):** 120 days. * **Monocytes:** 10–20 hours in blood (before becoming tissue macrophages).

Question 172: In erythropoiesis, which of the following statements is true?

A. The size of the cells increases in subsequent stages.
B. Hemoglobin appears at the early normoblast stage.
C. Mitosis occurs in the late normoblast at the fastest rate.
D. Folic acid acts as a maturation factor. (Correct Answer)

Explanation: ### Explanation **1. Why Option D is Correct:** Erythropoiesis requires specific nutrients for the maturation of red blood cells. **Folic acid and Vitamin B12** are essential cofactors for DNA synthesis (specifically the synthesis of thymidine triphosphate). A deficiency in these "maturation factors" leads to impaired cell division while cytoplasmic growth continues, resulting in **Megaloblastic anemia** (large, immature nucleated cells). **2. Why the Other Options are Incorrect:** * **Option A:** In erythropoiesis, the **cell size decreases** as the cell matures (from Proerythroblast to Mature RBC). This is accompanied by a decrease in the nuclear-cytoplasmic ratio. * **Option B:** Hemoglobin first begins to appear at the **Intermediate Normoblast** (Polychromatic erythroblast) stage. It is not visible at the Early Normoblast stage. * **Option C:** The **Late Normoblast** (Orthochromatic erythroblast) is characterized by a pyknotic (condensed) nucleus. At this stage, **mitosis stops** completely, and the nucleus is eventually extruded to form a reticulocyte. **3. High-Yield Clinical Pearls for NEET-PG:** * **First stage of Hemoglobin synthesis:** Proerythroblast (though not visible until later). * **Stage of Nucleus Extrusion:** Late Normoblast. * **Reticulocyte:** The last immature stage; it contains remnants of Golgi apparatus and RNA (ribosomes), which gives it a "reticular" appearance with supravital stains like **New Methylene Blue**. * **Erythropoietin (EPO):** The primary regulator, produced by the **peritubular interstitial cells** of the kidney in response to hypoxia.

Question 173: Which of the following substances causes platelet aggregation?

A. Nitrous oxide
B. Thromboxane A2 (Correct Answer)
C. Aspirin
D. Prostacyclin (PGI2)

Explanation: **Explanation:** The formation of a platelet plug is a critical step in primary hemostasis. This process involves platelet adhesion, activation, and aggregation. **1. Why Thromboxane A2 (TXA2) is correct:** TXA2 is a potent eicosanoid synthesized from arachidonic acid by the enzyme cyclooxygenase (COX-1) within activated platelets. It acts as a powerful **platelet agonist** and **vasoconstrictor**. When released, it binds to G-protein coupled receptors on the surface of nearby platelets, leading to a conformational change in the GPIIb/IIIa receptors, which allows them to bind fibrinogen and cross-link platelets together (aggregation). **2. Why the other options are incorrect:** * **Nitric Oxide (NO):** Produced by healthy endothelial cells, NO increases cGMP levels in platelets, which inhibits their activation and promotes vasodilation. * **Prostacyclin (PGI2):** Also produced by healthy endothelium, PGI2 increases cAMP levels, acting as a potent **inhibitor** of platelet aggregation and a vasodilator. It serves as a natural antagonist to TXA2 to prevent unwanted clot formation. * **Aspirin:** This is an antiplatelet drug. It works by **irreversibly inhibiting the COX-1 enzyme**, thereby blocking the synthesis of Thromboxane A2. This prevents aggregation rather than causing it. **High-Yield Clinical Pearls for NEET-PG:** * **The Balance:** Hemostasis is maintained by the balance between **TXA2** (Pro-aggregatory/Vasoconstrictor) and **PGI2** (Anti-aggregatory/Vasodilator). * **ADP:** Another major platelet aggregator; it binds to P2Y1 and P2Y12 receptors. * **Aspirin Effect:** Since platelets lack a nucleus, they cannot synthesize new COX-1 enzymes. Thus, a single dose of aspirin inhibits platelet function for the remainder of the platelet's lifespan (approx. 7–10 days).

Question 174: Which of the following cells is not involved in leucopoiesis?

A. Myeloblast
B. Normoblast (Correct Answer)
C. Myelocyte
D. Metamyelocyte

Explanation: **Explanation:** The process of blood cell formation is collectively called **Hemopoiesis**. This is further divided into **Leucopoiesis** (formation of White Blood Cells) and **Erythropoiesis** (formation of Red Blood Cells). **Why Normoblast is the correct answer:** A **Normoblast** (also known as an erythroblast) is a nucleated precursor cell in the **Erythropoietic** lineage. It represents the stages of RBC development (Proerythroblast → Early/Intermediate/Late Normoblast → Reticulocyte → Erythrocyte). Since it specifically leads to the production of Red Blood Cells, it is not involved in Leucopoiesis. **Analysis of incorrect options (Leucopoietic lineage):** The options A, C, and D are all stages in **Granulopoiesis** (a subtype of leucopoiesis that forms Neutrophils, Eosinophils, and Basophils): * **Myeloblast:** The first identifiable committed precursor in the granulocytic series. * **Myelocyte:** The stage where specific (secondary) granules first appear, allowing for the differentiation between neutrophil, eosinophil, and basophil lines. It is the last stage capable of mitosis. * **Metamyelocyte:** A post-mitotic stage characterized by a kidney-shaped (indented) nucleus, leading eventually to the "Band" form and then the mature segmented leucocyte. **High-Yield Clinical Pearls for NEET-PG:** * **Shift to the left:** The presence of increased immature leucocytes (like metamyelocytes and band cells) in the peripheral blood, usually indicating acute infection or inflammation. * **Myelocyte:** Remember this as the "stage of differentiation" because specific granules appear here. * **Reticulocyte count:** The most reliable index of effective erythropoiesis (normal range: 0.5–2.5%). * **Site of Hemopoiesis:** In adults, it occurs primarily in the red bone marrow of membranous bones (vertebrae, sternum, ribs, and iliac crest).

Question 175: Platelets contain which of the following organelles?

A. Both mitochondria and nucleus
B. Both mitochondria and lysozymes (Correct Answer)
C. Both nucleus and lysozymes
D. Only mitochondria

Explanation: **Explanation:** Platelets (thrombocytes) are small, disc-shaped, **anucleated** cell fragments derived from the fragmentation of megakaryocytes in the bone marrow. **1. Why Option B is Correct:** Although platelets lack a nucleus, they are metabolically active and contain several specialized organelles and structures: * **Mitochondria:** Platelets require energy (ATP) for processes like shape change, granule secretion, and clot retraction. They possess a small number of mitochondria to perform aerobic respiration. * **Lysozymes:** These are found within the **lambda (λ) granules** of platelets. They contain hydrolytic enzymes that aid in the dissolution of blood clots and phagocytic activities during the inflammatory response. **2. Analysis of Incorrect Options:** * **Options A & C (Nucleus):** These are incorrect because platelets are **anucleated**. They cannot undergo mitosis or de novo protein synthesis (though they carry residual mRNA from megakaryocytes). * **Option D (Only mitochondria):** This is incorrect because it ignores the presence of other vital organelles. In addition to mitochondria and lysozymes, platelets contain **Alpha granules** (containing clotting factors like Fibrinogen and vWF) and **Dense granules** (containing ADP, ATP, Serotonin, and Calcium). **Clinical Pearls for NEET-PG:** * **Life Span:** 7–10 days. * **Storage:** Approximately 1/3rd of the total platelet pool is sequestered in the **Spleen**. * **Granule Deficiency:** * *Gray Platelet Syndrome:* Deficiency of Alpha granules. * *Hermansky-Pudlak Syndrome:* Deficiency of Dense granules. * **Key Surface Receptor:** **GpIIb/IIIa** is the most abundant receptor, essential for platelet aggregation via fibrinogen binding.

Question 176: Which test is used to evaluate platelet function?

A. Bleeding time (Correct Answer)
B. Prothrombin time
C. Clot retraction test
D. Thrombin time

Explanation: **Explanation:** The evaluation of hemostasis is divided into primary and secondary hemostasis. **Bleeding Time (BT)** is the standard clinical test used to evaluate **primary hemostasis**, which depends on the number and functional integrity of platelets and the vessel wall. * **Why A is Correct:** When a small incision is made, platelets must adhere to the subendothelium, undergo activation, and aggregate to form a "platelet plug." If platelets are deficient in number (thrombocytopenia) or function (thrombocytopathy, e.g., Glanzmann’s thrombasthenia), the bleeding time is prolonged. * **Why B is Incorrect:** Prothrombin Time (PT) evaluates the **Extrinsic and Common pathways** of the coagulation cascade (Factors VII, X, V, II, and I). It is used to monitor Warfarin therapy. * **Why C is Incorrect:** While the Clot Retraction Test depends on platelet contractile proteins (thrombosthenin), it is a qualitative assessment of the final stage of clotting rather than a primary screening test for platelet function. * **Why D is Incorrect:** Thrombin Time (TT) measures the time taken for fibrinogen to convert to fibrin. It is prolonged in hypofibrinogenemia or in the presence of inhibitors like Heparin. **High-Yield Clinical Pearls for NEET-PG:** * **Normal Bleeding Time:** 2–7 minutes (Ivy’s method). * **Isolated Prolonged BT:** Seen in Von Willebrand Disease (vWD) and Bernard-Soulier Syndrome. Note: In vWD, aPTT may also be prolonged due to Factor VIII deficiency. * **Platelet Function Analyzer (PFA-100):** Now considered a more sensitive and reproducible "in vitro" replacement for the traditional Bleeding Time. * **Aspirin:** Irreversibly inhibits COX-1, prolonging BT for the lifespan of the platelet (approx. 7–10 days).

Question 177: Bleeding time assesses which of the following?

A. Extrinsic clotting pathway
B. Intrinsic clotting pathway
C. Fibrinogen level
D. Function of platelets (Correct Answer)

Explanation: **Explanation:** **Bleeding Time (BT)** is a clinical test that measures the time taken for a standardized skin wound to stop bleeding. It primarily assesses the **primary hemostatic mechanism**, which involves the interaction between the vascular wall and platelets. 1. **Why Option D is Correct:** The cessation of bleeding in a small superficial wound depends on the formation of a **temporary platelet plug**. Therefore, BT is a direct reflection of both **platelet count** (quantity) and **platelet function** (quality). If platelets are low (thrombocytopenia) or dysfunctional (e.g., Glanzmann thrombasthenia, Bernard-Soulier syndrome, or aspirin use), the BT will be prolonged. 2. **Why Other Options are Incorrect:** * **Options A & B:** The Extrinsic and Intrinsic pathways refer to the **secondary hemostatic mechanism** (clotting cascade). These are assessed by **Prothrombin Time (PT)** and **Activated Partial Thromboplastin Time (aPTT)**, respectively. * **Option C:** Fibrinogen levels are part of the common pathway of coagulation. Deficiencies are typically assessed using **Thrombin Time (TT)** or specific fibrinogen assays. **High-Yield Clinical Pearls for NEET-PG:** * **Normal Range:** 2–7 minutes (Ivy’s method). * **Von Willebrand Disease (vWD):** This is a classic condition where **BT is prolonged** because vWF is essential for platelet adhesion, even though it is a "clotting" disorder. (Note: aPTT may also be prolonged in vWD due to low Factor VIII). * **Pure Coagulation Disorders:** In Hemophilia A or B, the **BT is normal**, but the Clotting Time (CT) is prolonged. * **Drug Alert:** Aspirin prolongs BT by irreversibly inhibiting COX-1, preventing Thromboxane A2 synthesis.

Question 178: All of the following factors are produced by hepatocytes except?

A. Fibrinogen
B. Prothrombin
C. Von Willebrand factor (Correct Answer)
D. Factor VIII

Explanation: **Explanation:** The liver is the primary site for the synthesis of almost all coagulation factors. However, **Von Willebrand factor (vWF)** is a notable exception. **1. Why Von Willebrand Factor (vWF) is the correct answer:** Unlike most clotting factors, vWF is synthesized and secreted by **vascular endothelial cells** and **megakaryocytes**. Within endothelial cells, it is stored in specialized organelles called **Weibel-Palade bodies**, and in platelets, it is stored in **alpha-granules**. Its primary role is to mediate platelet adhesion to the subendothelial matrix at sites of vascular injury and to act as a carrier protein for Factor VIII. **2. Analysis of incorrect options:** * **Fibrinogen (Factor I) & Prothrombin (Factor II):** These are classic plasma proteins synthesized exclusively by **hepatocytes**. * **Factor VIII:** This is a high-yield "trap" for students. While Factor VIII was historically thought to be produced elsewhere, modern research confirms that the primary source of Factor VIII is the **sinusoidal endothelial cells** of the liver (and to a lesser extent, hepatocytes). Therefore, it is still considered a liver-derived factor. **3. High-Yield Clinical Pearls for NEET-PG:** * **Vitamin K Dependent Factors:** Factors II, VII, IX, and X, as well as Protein C and S, are synthesized in the liver and require Vitamin K for gamma-carboxylation. * **Factor VII:** Has the shortest half-life among all clotting factors; hence, the Prothrombin Time (PT) is the first to be prolonged in acute liver failure. * **The "Exception" Rule:** Remember that **vWF** and **Factor VIII (partially)** are produced by endothelial cells, but only vWF is completely independent of the liver's synthetic function. * **vWF Function:** It stabilizes Factor VIII in circulation; without vWF, Factor VIII is rapidly degraded.

Question 179: What is the primary function of von Willebrand factor (vWF)?

A. Platelet adhesion (Correct Answer)
B. Platelet aggregation
C. Clot formation
D. Fibrinolysis

Explanation: **Explanation:** The primary function of **von Willebrand factor (vWF)** is to facilitate **platelet adhesion** to the subendothelial collagen at the site of vascular injury. It acts as a molecular bridge between the exposed collagen and the **GP Ib-IX-V receptor** complex on the platelet surface. This is the crucial first step in primary hemostasis. **Analysis of Options:** * **A. Platelet Adhesion (Correct):** vWF is essential for tethering platelets to the damaged vessel wall, especially under conditions of high shear stress (e.g., in small arteries). * **B. Platelet Aggregation:** This refers to platelets sticking to *each other*. While vWF can assist, the primary mediator of aggregation is **Fibrinogen**, which binds to the **GP IIb/IIIa** receptors on activated platelets. * **C. Clot Formation:** This is the end result of the coagulation cascade (secondary hemostasis). While vWF stabilizes Factor VIII, it is not the "primary" mechanism of the fibrin clot itself. * **D. Fibrinolysis:** This is the process of breaking down a clot (mediated by Plasmin). vWF is a pro-coagulant factor and does not participate in fibrinolysis. **High-Yield Clinical Pearls for NEET-PG:** * **Synthesis:** vWF is synthesized in **endothelial cells** (stored in **Weibel-Palade bodies**) and **megakaryocytes** (stored in **α-granules** of platelets). * **Factor VIII Carrier:** vWF serves as a carrier protein for Factor VIII, protecting it from rapid degradation. Therefore, von Willebrand Disease (vWD) often presents with a secondary deficiency of Factor VIII. * **Diagnostic Test:** The **Ristocetin cofactor assay** is used to measure vWF activity; Ristocetin induces vWF-mediated platelet agglutination. * **Treatment:** **Desmopressin (DDAVP)** stimulates the release of vWF from endothelial stores.

Question 180: What substance is released by mast cells?

A. IFN-g
B. IL-5
C. Histamine (Correct Answer)
D. Lysozyme

Explanation: **Explanation:** **Correct Answer: C. Histamine** Mast cells are key effector cells of the innate immune system, primarily located in mucosal and cutaneous tissues. They contain numerous basophilic granules rich in pre-formed inflammatory mediators. Upon activation (typically via IgE cross-linking on the FceRI receptor), mast cells undergo **degranulation**, releasing **Histamine**. Histamine acts on H1 receptors to cause vasodilation, increased vascular permeability, and bronchial smooth muscle contraction, mediating Type I hypersensitivity reactions. **Analysis of Incorrect Options:** * **A. IFN-γ (Interferon-gamma):** This is a pro-inflammatory cytokine primarily secreted by **Th1 cells, CD8+ cytotoxic T cells, and Natural Killer (NK) cells**. Its main role is macrophage activation. * **B. IL-5 (Interleukin-5):** This cytokine is primarily produced by **Th2 cells**. Its specific function is the recruitment, activation, and survival of **eosinophils**. * **D. Lysozyme:** This is an antibacterial enzyme found in secretions like tears, saliva, and mucus, and is also present in the cytoplasmic granules of **neutrophils and macrophages**. It works by cleaving the peptidoglycan layer of bacterial cell walls. **High-Yield Clinical Pearls for NEET-PG:** * **Markers:** **Tryptase** is the most specific marker for mast cell activation (useful in diagnosing anaphylaxis). * **Origin:** Mast cells originate from CD34+ hematopoietic stem cells in the bone marrow but mature only after reaching peripheral tissues. * **Mediators:** Besides histamine, mast cells release **Heparin** (anticoagulant), **ECF-A** (Eosinophil Chemotactic Factor of Anaphylaxis), and newly synthesized mediators like **Leukotrienes (C4, D4, E4)** and **Prostaglandin D2**.

Practice by Chapter

Composition and Functions of Blood

Practice Questions

Erythrocytes and Hemoglobin

Practice Questions

Leukocytes and Immune Function

Practice Questions

Platelets and Hemostasis

Practice Questions

Blood Groups and Transfusion

Practice Questions

Coagulation and Fibrinolysis

Practice Questions

Hematopoiesis

Practice Questions

Innate Immunity

Practice Questions

Adaptive Immunity

Practice Questions

Immunological Memory and Tolerance

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free