Blood and Immunity — MCQs

Blood and Immunity Indian Medical PG Practice Questions and MCQs

Question 241: Which clotting factor is common to both the extrinsic and intrinsic pathways?

A. Factor II
B. Factor III
C. Factor V (Correct Answer)
D. Factor VII

Explanation: ### Explanation The coagulation cascade is divided into the **Intrinsic**, **Extrinsic**, and **Common pathways**. The correct answer is **Factor V** because it is a critical cofactor in the Common Pathway, where the intrinsic and extrinsic pathways converge. #### Why Factor V is Correct: The **Common Pathway** begins with the activation of **Factor X** (into Xa). Factor Xa, along with its cofactor **Factor V**, calcium ions, and phospholipids, forms the **Prothrombinase Complex**. This complex converts Prothrombin (II) into Thrombin (IIa). Since both the intrinsic and extrinsic pathways aim to activate Factor X, Factor V is essential for the subsequent steps shared by both. #### Why Other Options are Incorrect: * **Factor II (Prothrombin):** While it is part of the common pathway, it is a substrate (proenzyme) that is converted into thrombin, not a factor that bridges the two pathways in the same functional manner as the cofactors. * **Factor III (Tissue Factor):** This is the primary initiator of the **Extrinsic Pathway** only. It is released upon tissue injury. * **Factor VII (Stable Factor):** This factor is unique to the **Extrinsic Pathway**. It binds with Factor III to activate Factor X. #### High-Yield Clinical Pearls for NEET-PG: * **Factor V Leiden:** The most common inherited cause of hypercoagulability (thrombophilia). It involves a mutation that makes Factor V resistant to inactivation by Protein C. * **Lab Monitoring:** The Extrinsic pathway is monitored by **Prothrombin Time (PT)**, while the Intrinsic pathway is monitored by **Activated Partial Thromboplastin Time (aPTT)**. * **Vitamin K Dependent Factors:** II, VII, IX, and X (and Proteins C and S). * **Shortest Half-life:** Factor VII (reason why PT rises first in liver disease or Warfarin therapy).

Question 242: What is the half-life of prothrombin?

A. 24 hours
B. 60 hours (Correct Answer)
C. 5 days
D. 10 days

Explanation: **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 243: Plasma cells are derived from which of the following cell types?

A. B lymphocytes (Correct Answer)
B. T lymphocytes
C. NK cells
D. Monocytes

Explanation: **Explanation:** **1. Why B lymphocytes is correct:** Plasma cells are the final functional stage of B cell differentiation. When a **B lymphocyte** encounters a specific antigen and receives signals from helper T cells, it undergoes activation, proliferation, and differentiation. This process transforms the B cell into a **plasma cell**, which acts as an "antibody factory." These cells possess an extensive rough endoplasmic reticulum (RER) to synthesize and secrete large quantities of immunoglobulins (antibodies) into the blood and lymph. **2. Why other options are incorrect:** * **T lymphocytes:** These are responsible for cell-mediated immunity. They differentiate into Helper T cells (CD4+), Cytotoxic T cells (CD8+), or Regulatory T cells, but they never produce antibodies or transform into plasma cells. * **NK cells:** These are large granular lymphocytes that form part of the innate immune system. They kill virally infected or tumor cells directly without prior sensitization and do not differentiate into plasma cells. * **Monocytes:** These are myeloid lineage cells that circulate in the blood and migrate into tissues to differentiate into **macrophages** or dendritic cells, primarily functioning in phagocytosis and antigen presentation. **3. High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** Plasma cells have a characteristic **"Cartwheel" or "Clock-face" appearance** of chromatin in the nucleus and a prominent perinuclear halo (Golgi apparatus). * **Multiple Myeloma:** A plasma cell dyscrasia (malignancy) characterized by the "M-spike" on protein electrophoresis and **Bence-Jones proteins** in urine. * **Russell Bodies:** These are eosinophilic inclusions found in plasma cells representing overloaded immunoglobulin secretions. * **Surface Markers:** While B cells express CD19 and CD20, mature plasma cells typically lose these and express **CD138** (Syndecan-1).

Question 244: What is the major in vivo pathway of coagulation?

A. Contact pathway
B. Intrinsic pathway
C. Extrinsic pathway (Correct Answer)
D. None of the above

Explanation: ### Explanation **Why the Extrinsic Pathway is Correct:** In the body (**in vivo**), the coagulation cascade is primarily initiated by the **Extrinsic Pathway**. This pathway is triggered when blood comes into contact with **Tissue Factor (Factor III)**, which is expressed on the surface of subendothelial cells following vascular injury. Tissue Factor binds to Factor VIIa, forming a complex that directly activates Factor X. This process is the fastest and most physiologically significant way to generate the initial "thrombin spark" required for clot formation. **Why Other Options are Incorrect:** * **Intrinsic Pathway (Option B):** While essential for the amplification of the coagulation process, the intrinsic pathway is not the primary initiator in vivo. It involves Factors XII, XI, IX, and VIII. In the body, it is mainly activated by thrombin (produced by the extrinsic pathway) rather than spontaneous contact. * **Contact Pathway (Option A):** This is another name for the initial phase of the intrinsic pathway (involving Factor XII/Hageman factor). While it is the major pathway for coagulation **in vitro** (e.g., when blood touches a glass test tube), it is clinically less significant for hemostasis. Notably, individuals with Factor XII deficiency do not suffer from abnormal bleeding, proving it is not the major in vivo pathway. **High-Yield Clinical Pearls for NEET-PG:** * **The "Spark" and the "Burst":** Think of the Extrinsic pathway as the **spark** (initiation) and the Intrinsic pathway as the **amplifier** (propagation) that leads to the "Thrombin Burst." * **Monitoring:** The Extrinsic pathway is monitored by **Prothrombin Time (PT/INR)**, while the Intrinsic pathway is monitored by **Activated Partial Thromboplastin Time (aPTT)**. * **Vitamin K:** Factors II, VII, IX, and X are Vitamin K-dependent. **Factor VII** has the shortest half-life, making PT the first lab value to prolong in Vitamin K deficiency or liver disease.

Question 245: Glucocorticoids lead to an increase in blood levels of which of the following?

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

Explanation: **Explanation:** Glucocorticoids (like cortisol) have a profound effect on the distribution and count of white blood cells in the peripheral blood. **Why Neutrophils increase (Correct Answer):** Glucocorticoids cause **Neutrophilia** primarily through a process called **demargination**. Normally, a significant portion of neutrophils is "marginated" (adhered to the endothelial walls of blood vessels). Glucocorticoids decrease the expression of adhesion molecules (like L-selectin), causing these cells to detach into the main bloodstream. Additionally, they stimulate the release of mature neutrophils from the bone marrow and inhibit their migration into tissues, leading to an overall rise in the peripheral neutrophil count. **Why other options are incorrect:** Glucocorticoids are generally **immunosuppressive and lympholytic**. They cause a decrease in the peripheral levels of: * **Eosinophils (Eosinopenia):** They sequester eosinophils in the spleen and bone marrow and induce apoptosis. * **Basophils (Basopenia):** Similar to eosinophils, their circulating numbers are reduced. * **Lymphocytes (Lymphocytopenia):** Glucocorticoids cause the redistribution of T and B cells from the blood into other lymphoid compartments (like the bone marrow and lymph nodes) and can induce apoptosis in certain lymphocyte subsets. * **Monocytes (Monocytopenia):** Circulating levels also decrease. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic:** Glucocorticoids "drop" the **B-E-L-M** (Basophils, Eosinophils, Lymphocytes, Monocytes) and "raise" the **Neutrophils**. * **Clinical Correlation:** A patient on long-term steroid therapy will often show a high Total Leukocyte Count (TLC) on a CBC, but this is usually a physiological effect (demargination) rather than an active infection. * **Eosinopenia** is a very sensitive marker for hypercortisolism (Cushing’s syndrome).

Question 246: The Ivy technique is a test used to measure which of the following?

A. Clotting time
B. Bleeding time (Correct Answer)
C. Both clotting time and bleeding time
D. Neither clotting time nor bleeding time

Explanation: **Explanation:** The **Ivy technique** is the standardized clinical method used to measure **Bleeding Time (BT)**. Bleeding time is a functional test of **primary hemostasis**, which depends on two main factors: the integrity of the vascular wall and, most importantly, **platelet function** (both number and quality). 1. **Why Option B is correct:** In the Ivy method, a blood pressure cuff is inflated to 40 mmHg on the upper arm to maintain constant capillary pressure. A standardized incision is made on the volar aspect of the forearm, and the time taken for the bleeding to stop (via the formation of a temporary platelet plug) is recorded. The normal range is typically 2–9 minutes. 2. **Why Option A is incorrect:** **Clotting Time (CT)** measures secondary hemostasis (the coagulation cascade and fibrin formation). It is typically measured using the **Lee-White method** or Capillary Tube method. 3. **Why Options C & D are incorrect:** BT and CT assess different phases of the clotting process. While they are often ordered together, the Ivy technique is specific only to the assessment of platelet plug formation. **High-Yield Clinical Pearls for NEET-PG:** * **Duke’s Method:** An older, less standardized method for BT involving an earlobe prick. * **Prolonged BT:** Seen in **Thrombocytopenia** (low count), **Glanzmann Thrombasthenia** (defective aggregation), **Bernard-Soulier Syndrome** (defective adhesion), and **von Willebrand Disease** (vWD). * **Note:** In vWD, both BT and aPTT may be prolonged, but BT is the primary screening tool for platelet-related dysfunction. * **Aspirin:** Irreversibly inhibits COX-1, prolonging Bleeding Time for the life of the platelet (approx. 7–10 days).

Question 247: Erythropoiesis during gestation takes place in which of the following structures?

A. Yolk sac (Correct Answer)
B. Placenta
C. Amniotic sac
D. Chorion

Explanation: ### Explanation Erythropoiesis (the production of red blood cells) during intrauterine life occurs in distinct chronological stages, often referred to as the **Mesoblastic, Hepatic, and Myeloid phases**. **1. Why Yolk Sac is Correct:** The **Yolk sac** is the primary site of hematopoiesis during the **Mesoblastic phase** (the earliest stage). It begins around the 3rd week of gestation. Mesenchymal cells in the yolk sac aggregate into "blood islands," where peripheral cells form the endothelium and central cells become primitive erythroblasts. This remains the dominant site until approximately the 2nd month of gestation. **2. Why Other Options are Incorrect:** * **Placenta:** While the placenta is vital for nutrient and gas exchange between mother and fetus, it does not serve as a site for the production of fetal blood cells. * **Amniotic sac:** This is the fluid-filled sac surrounding the fetus; it provides protection and allows for movement but has no hematopoietic function. * **Chorion:** This is the outermost fetal membrane that contributes to the formation of the placenta; like the placenta, it does not produce red blood cells. **3. High-Yield Facts for NEET-PG:** To master questions on fetal erythropoiesis, remember this timeline: * **0–2 Months (Mesoblastic Phase):** Yolk sac (Primitive nucleated RBCs). * **2–7 Months (Hepatic Phase):** **Liver** is the primary site (starts at 6 weeks, peaks at 4 months). The **Spleen** also contributes between the 3rd and 6th months. * **7 Months–Birth (Myeloid Phase):** **Bone marrow** becomes the definitive site. * **Post-natal:** Bone marrow of almost all bones (until age 5); thereafter, primarily membranous bones (vertebrae, sternum, ribs, ilium). * **Fetal Hemoglobin (HbF):** Composed of two alpha and two **gamma** chains ($\alpha_2\gamma_2$), giving it a higher affinity for oxygen than adult hemoglobin (HbA).

Question 248: Which of the following defines hematocrit?

A. Number of erythrocytes in blood
B. Percentage of the blood, by volume, occupied by erythrocytes (Correct Answer)
C. Ratio of erythrocytes to leucocytes
D. Ratio of erythrocytes to all blood cells

Explanation: ### Explanation **Hematocrit (Hct)**, also known as **Packed Cell Volume (PCV)**, is defined as the percentage of total blood volume occupied by erythrocytes (red blood cells) after centrifugation. When blood is centrifuged, it separates into three layers: plasma (top), the "buffy coat" (leucocytes and platelets), and the packed red cells at the bottom. Since RBCs constitute over 99% of all formed elements, the PCV is a direct reflection of the erythrocyte volume. #### Analysis of Options: * **Option B (Correct):** This is the standard physiological definition. It measures the **volume** occupied by cells, not the absolute count. * **Option A:** This refers to the **Total RBC Count** (expressed in millions/mm³), which is a numerical value, not a percentage of volume. * **Option C & D:** These are incorrect because hematocrit is a ratio of cell volume to **total plasma volume**, not a ratio between different cell types. #### High-Yield Clinical Pearls for NEET-PG: * **Normal Values:** Males: 40–54%; Females: 36–46%. * **Wintrobe’s Tube:** The traditional instrument used to measure PCV (100 mm long). * **Clinical Significance:** * **Increased Hct:** Seen in Polycythemia and **Dehydration** (due to decreased plasma volume, causing hemoconcentration). * **Decreased Hct:** A hallmark of Anemia or hemodilution (e.g., pregnancy). * **Rule of Three:** In a healthy individual, Hemoglobin (Hb) × 3 ≈ Hematocrit. * **Buffy Coat:** Occupies approximately 1% of the volume and contains WBCs and Platelets.

Question 249: What percentage of total lymphocytes are formed by null cells?

A. 0-1%
B. 2-3%
C. 5-10% (Correct Answer)
D. 10-15%

Explanation: **Explanation:** Lymphocytes are the primary cells of the adaptive immune system, categorized based on their surface markers and functions. The majority are **T-lymphocytes (70-80%)** and **B-lymphocytes (10-15%)**. **Why 5-10% is correct:** **Null cells** are a small population of lymphocytes that lack the characteristic surface markers of either T-cells (CD3) or B-cells (surface immunoglobulins). They primarily consist of **Natural Killer (NK) cells** and some Killer (K) cells. In healthy individuals, these cells consistently constitute approximately **5-10%** of the total circulating lymphocyte pool. They play a vital role in innate immunity by identifying and destroying virally infected cells and tumor cells without prior sensitization. **Analysis of Incorrect Options:** * **A (0-1%) & B (2-3%):** These values are too low. While null cells are a minority, they are present in significant enough numbers to provide a rapid first line of defense before the adaptive response kicks in. * **D (10-15%):** This range typically represents the percentage of **B-lymphocytes** in the peripheral blood. Null cells are slightly less abundant than B-cells. **High-Yield NEET-PG Pearls:** * **NK Cells:** These are the largest of the lymphocytes (Large Granular Lymphocytes). * **Markers:** NK cells are identified by the presence of **CD56** and **CD16** markers. * **Mechanism:** They kill target cells via the release of **perforins and granzymes**, leading to apoptosis. * **MHC Independence:** Unlike T-cells, NK cells do not require MHC-restricted antigen presentation to function; they are inhibited by the presence of MHC-I on healthy self-cells.

Question 250: Which of the following white blood cells act as scavengers when they engulf and digest pathogens?

A. Macrophages (Correct Answer)
B. T cells
C. B cells
D. Lymphocytes

Explanation: **Explanation:** **1. Why Macrophages are Correct:** Macrophages are the primary "scavengers" of the immune system. Derived from circulating **monocytes**, they migrate into tissues where they perform **phagocytosis**. Their primary role is to engulf and digest cellular debris, foreign pathogens, and apoptotic cells. They contain specialized lysosomes filled with hydrolytic enzymes that break down ingested material. Beyond scavenging, they act as professional **Antigen-Presenting Cells (APCs)**, bridging the gap between innate and adaptive immunity. **2. Why Other Options are Incorrect:** * **B. T cells:** These are mediators of **cell-mediated immunity**. They do not engulf pathogens; instead, they kill infected cells directly (CD8+ Cytotoxic T cells) or coordinate the immune response (CD4+ Helper T cells). * **C. B cells:** These are responsible for **humoral immunity**. Their primary function is to differentiate into plasma cells and produce **antibodies**. While they can internalize antigens via receptor-mediated endocytosis to present them to T cells, they are not professional scavengers. * **D. Lymphocytes:** This is a broad category that includes T cells, B cells, and Natural Killer (NK) cells. While essential for the immune response, the group as a whole is characterized by specific recognition rather than the non-specific scavenging/phagocytic activity seen in macrophages. **3. NEET-PG High-Yield Pearls:** * **Tissue-Specific Macrophages:** Remember these names for matching questions: **Kupffer cells** (Liver), **Microglia** (CNS), **Mesangial cells** (Kidney), **Osteoclasts** (Bone), and **Dust cells** (Alveoli). * **Life Span:** Unlike Neutrophils (which are "short-lived" phagocytes), Macrophages are long-lived and can survive for months in tissues. * **Cytokine Production:** Macrophages are the major source of **IL-1, IL-6, and TNF-α**, which are key mediators of the acute phase response (fever).

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

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