Blood and Immunity — MCQs

Blood and Immunity Indian Medical PG Practice Questions and MCQs

Question 271: All statements about lactoferrin are true, except?

A. It is present in the secondary granules of neutrophils.
B. It is present in exocrine secretions of the body.
C. It has a great affinity for iron.
D. It transports iron for erythropoiesis. (Correct Answer)

Explanation: ### Explanation Lactoferrin is a multifunctional iron-binding glycoprotein belonging to the transferrin family. Its primary role is **bacteriostatic**—it sequesters free iron, making it unavailable for bacterial growth. **Why Option D is the Correct Answer (The False Statement):** While lactoferrin has a high affinity for iron, it **does not** transport iron for erythropoiesis. That function is exclusively performed by **Transferrin**. Lactoferrin actually competes with bacteria for iron and helps in the sequestration of iron into the Reticuloendothelial System (RES) during inflammation, which is a contributing factor to the "Anemia of Chronic Disease." **Analysis of Other Options:** * **Option A:** Lactoferrin is a major constituent of the **secondary (specific) granules** of neutrophils. It is released into the phagosome and extracellular space during degranulation to inhibit microbial proliferation. * **Option B:** It is found in high concentrations in **exocrine secretions** such as breast milk (highest in colostrum), tears, nasal secretions, saliva, and gastrointestinal mucus, serving as a first-line innate immune defense. * **Option C:** Lactoferrin has an iron-binding affinity approximately **250 times higher** than that of serum transferrin, allowing it to retain iron even at the low pH levels typical of infection sites. ### High-Yield NEET-PG Pearls * **Marker of Inflammation:** Fecal lactoferrin is a sensitive marker used to differentiate Inflammatory Bowel Disease (IBD) from Irritable Bowel Syndrome (IBS). * **Bacteriostatic vs. Bactericidal:** It is bacteriostatic by iron deprivation, but can be bactericidal by directly binding to bacterial lipopolysaccharides (LPS) and disrupting cell membranes. * **Neutrophil Granules:** Remember: Primary granules contain **Myeloperoxidase (MPO)**; Secondary granules contain **Lactoferrin** and **Alkaline Phosphatase**.

Question 272: Pre-B cells and B cells are produced in which location?

A. Bone marrow (Correct Answer)
B. Thymus
C. Tonsils
D. Gut associated lymphoid tissue

Explanation: **Explanation:** The correct answer is **Bone marrow**. In humans, the bone marrow serves as the primary lymphoid organ where B-cell lymphopoiesis occurs throughout life. **Why Bone Marrow is Correct:** The development of B cells is a multi-step process that begins with hematopoietic stem cells. These differentiate into **Pro-B cells**, then **Pre-B cells** (characterized by the presence of cytoplasmic $\mu$ heavy chains), and finally into **immature B cells** (expressing surface IgM). All these stages occur within the microenvironment of the **bone marrow**. Once they express surface IgM and IgD, they become mature (but naive) B cells and migrate to peripheral lymphoid organs. **Why Other Options are Incorrect:** * **Thymus:** This is the primary lymphoid organ for **T-cell** maturation. While T-cell precursors originate in the bone marrow, they must migrate to the thymus to undergo TCR rearrangement and selection. * **Tonsils & GALT:** These are **secondary lymphoid organs**. They are sites where mature B cells encounter antigens, undergo clonal expansion, and perform effector functions (like isotype switching). They do not produce B cells from precursors. **High-Yield NEET-PG Pearls:** * **B-cell maturation site:** Bone marrow (Mnemonic: **B**-cell = **B**one marrow). * **T-cell maturation site:** Thymus (Mnemonic: **T**-cell = **T**hymus). * **Bursa of Fabricius:** In birds, B cells mature in this specialized organ; in humans, the bone marrow is the functional equivalent. * **Negative Selection:** Immature B cells that recognize "self" antigens in the bone marrow are eliminated via apoptosis or undergo **receptor editing** to prevent autoimmunity.

Question 273: Platelet activation includes:

A. Adhesion
B. Secretion
C. Aggregation
D. All of the above (Correct Answer)

Explanation: **Explanation:** Platelet activation is a complex, multi-step process essential for **primary hemostasis**. When a blood vessel is injured, platelets undergo a series of rapid functional changes to form a temporary hemostatic plug. 1. **Adhesion (Option A):** This is the initial step. Platelets adhere to the exposed subendothelial collagen. This process is primarily mediated by **von Willebrand Factor (vWF)**, which acts as a bridge between the subendothelial collagen and the platelet surface receptor **Glycoprotein Ib/IX/V (GpIb/IX/V)**. 2. **Secretion/Release Reaction (Option B):** Once adhered, platelets become activated and change shape. They release the contents of their granules: * **Alpha granules:** Contain Fibrinogen, vWF, and Platelet-Derived Growth Factor (PDGF). * **Dense granules:** Contain **ADP**, Calcium, and Serotonin (mnemonic: **SAC**). ADP and Thromboxane A2 (TxA2) further recruit and activate more platelets. 3. **Aggregation (Option C):** This is the final step of activation where platelets stick to each other. ADP and TxA2 cause a conformational change in the **GpIIb/IIIa** receptors, allowing them to bind to **Fibrinogen**, which links multiple platelets together to form the plug. Since all three processes—Adhesion, Secretion, and Aggregation—are integral components of the platelet activation sequence, **Option D** is the correct answer. **High-Yield Clinical Pearls for NEET-PG:** * **Bernard-Soulier Syndrome:** Deficiency of **GpIb** (Defect in Adhesion). * **Glanzmann Thrombasthenia:** Deficiency of **GpIIb/IIIa** (Defect in Aggregation). * **Aspirin:** Irreversibly inhibits Cyclooxygenase-1 (COX-1), preventing the synthesis of **Thromboxane A2**, thereby inhibiting platelet aggregation. * **vWF:** Synthesized in endothelial cells (stored in **Weibel-Palade bodies**) and megakaryocytes.

Question 274: In a person weighing 100 Kgs, what is the estimated blood volume?

A. 5 L
B. 6 L
C. 8 L (Correct Answer)
D. 10 L

Explanation: **Explanation:** The correct answer is **8 L**. The total blood volume (TBV) in a healthy adult is approximately **7% to 8% of the total body weight**. For a person weighing 100 kg, the calculation is: $100\text{ kg} \times 0.08 (8\%) = 8\text{ Liters}$. **Why other options are incorrect:** * **A (5 L):** This is the average blood volume for a standard **70 kg male** ($70 \times 0.07 = 4.9\text{ L}$). It is the most common "textbook" value but does not apply to a 100 kg individual. * **B (6 L):** This represents roughly 6% of the body weight for a 100 kg person, which is slightly below the physiological norm for an average adult. * **D (10 L):** This would represent 10% of the body weight. While blood volume can increase in certain states (like pregnancy), 10% is significantly higher than the normal physiological range for a healthy adult. **High-Yield Clinical Pearls for NEET-PG:** 1. **Volume Distribution:** Roughly 55% of blood is Plasma, and 45% is Formed Elements (Hematocrit). 2. **Gender Variation:** Females typically have a slightly lower blood volume per kg (~65-70 ml/kg) compared to males (~70-75 ml/kg) due to a higher percentage of body fat. 3. **Measurement:** The "Gold Standard" for measuring plasma volume is **Evans Blue dye (T-1824)** or **Radio-iodinated albumin**, while RBC volume is measured using **Chromium-51 ($^{51}\text{Cr}$)** labeled RBCs. 4. **Blood Reservoir:** The **systemic veins and venules** contain the largest portion of blood volume (~64%) at any given time, acting as the body's blood reservoir.

Question 275: Which coagulation factor is not freely circulating in the blood?

A. Factor 9
B. Factor 10
C. Factor 12
D. Factor 3 (Correct Answer)

Explanation: **Explanation:** The correct answer is **Factor 3 (Tissue Factor/Thromboplastin)**. **Why Factor 3 is the correct answer:** Unlike most clotting factors, which are proenzymes synthesized by the liver and secreted into the plasma to circulate freely, **Factor 3 (Tissue Factor)** is a cell-surface glycoprotein. It is constitutively expressed on the adventitia of blood vessels and in the membranes of extravascular cells (like fibroblasts). It only comes into contact with blood following **vascular injury**. Once exposed, it binds to Factor VIIa to initiate the **Extrinsic Pathway** of coagulation. Because it is structurally bound to cell membranes, it does not circulate freely in the blood under physiological conditions. **Why the other options are incorrect:** * **Factor 9 (Christmas Factor):** A vitamin K-dependent serine protease that circulates freely in the plasma. It is a key component of the intrinsic pathway. * **Factor 10 (Stuart-Prower Factor):** A vitamin K-dependent factor that circulates freely. It is the first factor of the **Common Pathway**, where it is activated to Xa. * **Factor 12 (Hageman Factor):** A plasma protein that circulates freely. it is activated upon contact with negatively charged surfaces (like collagen or glass), initiating the intrinsic pathway. **High-Yield Clinical Pearls for NEET-PG:** * **Factor 4:** Refers to **Calcium ions (Ca²⁺)**, which are essential for almost all steps of the coagulation cascade except the initial stages of the intrinsic pathway. * **Labile Factor:** Factor 5 (activity decreases quickly in stored blood). * **Stable Factor:** Factor 7 (has the shortest half-life among all factors). * **Hageman Factor (F12) Deficiency:** Unique because it causes a prolonged aPTT in vitro but does **not** cause clinical bleeding in vivo.

Question 276: When osmotic fragility is normal, RBCs begin to hemolyse when suspended in saline at what concentration?

A. 0.33%
B. 0.48% (Correct Answer)
C. 0.90%
D. 1.20%

Explanation: ### Explanation **Concept Overview:** Osmotic fragility refers to the susceptibility of Red Blood Cells (RBCs) to hemolysis when exposed to increasingly hypotonic solutions. In a hypotonic environment, water enters the RBC via osmosis, causing it to swell from a biconcave disc into a sphere. Since the spherical shape has the minimum surface-area-to-volume ratio, any further water intake causes the cell membrane to rupture (hemolysis). **Why 0.48% is Correct:** In a healthy individual with normal RBC morphology: * **Initial Hemolysis:** RBCs begin to lyse at a saline concentration of approximately **0.48% to 0.50%**. * **Complete Hemolysis:** All RBCs are typically lysed when the concentration drops to **0.33% to 0.35%**. **Analysis of Incorrect Options:** * **A. 0.33%:** This represents the point of **complete hemolysis**, not the beginning. * **C. 0.90%:** This is **Isotonic Saline** (Normal Saline). At this concentration, there is no net movement of water; RBCs remain stable and do not hemolyse. * **D. 1.20%:** This is a **hypertonic solution**. In this environment, water leaves the RBC, causing it to shrink or "crenate" rather than burst. **High-Yield Clinical Pearls for NEET-PG:** 1. **Increased Fragility (Shifts to the Right):** Seen in **Hereditary Spherocytosis**. Because spherocytes already have a decreased surface-area-to-volume ratio, they burst at higher saline concentrations (e.g., 0.6%). 2. **Decreased Fragility (Shifts to the Left):** Seen in **Thalassemia, Sickle Cell Anemia, and Iron Deficiency Anemia**. These conditions often feature "target cells" or microcytes with a high surface-area-to-volume ratio, making them more resistant to osmotic lysis. 3. **Incubation:** The test is more sensitive if the blood is incubated at 37°C for 24 hours before testing.

Question 277: Which of the following are Vitamin K dependent clotting factors?

A. Factor III & XI
B. Factor IX & X (Correct Answer)
C. Factor V & VIII
D. Factor XI & XIII

Explanation: **Explanation:** Vitamin K is an essential cofactor for the enzyme **gamma-glutamyl carboxylase**, which catalyzes the post-translational carboxylation of glutamic acid residues on specific clotting factors. This process allows these factors to bind calcium ions ($Ca^{2+}$) and attach to phospholipid membranes, a crucial step in the coagulation cascade. The **Vitamin K-dependent factors** include: * **Pro-coagulants:** Factors **II (Prothrombin), VII, IX, and X**. * **Anti-coagulants:** **Protein C and Protein S**. **Analysis of Options:** * **Option B (Correct):** Factors IX (Christmas factor) and X (Stuart-Prower factor) are both Vitamin K-dependent. * **Option A:** Factor III (Tissue Factor) is a cell surface glycoprotein, and Factor XI is part of the intrinsic pathway but does not require Vitamin K for synthesis. * **Option C:** Factor V (Labile factor) and Factor VIII (Anti-hemophilic factor) are cofactors that do not undergo gamma-carboxylation. * **Option D:** Factor XIII (Fibrin stabilizing factor) is a transglutaminase that cross-links fibrin; it is not Vitamin K-dependent. **High-Yield Clinical Pearls for NEET-PG:** 1. **Warfarin Mechanism:** Warfarin acts as a Vitamin K antagonist by inhibiting **Vitamin K Epoxide Reductase (VKOR)**, preventing the recycling of Vitamin K. 2. **Half-life:** Factor VII has the shortest half-life (~6 hours), making the **Prothrombin Time (PT)** the first lab value to prolong during Vitamin K deficiency or early Warfarin therapy. 3. **Newborns:** Neonates are Vitamin K deficient due to a sterile gut and poor placental transfer; hence, prophylactic Vitamin K is given at birth to prevent **Hemorrhagic Disease of the Newborn**.

Question 278: Higher hematocrit in venous blood than in arterial blood is due to which of the following?

A. High chloride in RBC (Correct Answer)
B. High Na+ in plasma
C. High HCO3- in plasma
D. High K+ in RBC

Explanation: ### Explanation The phenomenon of higher hematocrit in venous blood compared to arterial blood is primarily due to the **Chloride Shift (Hamburger Phenomenon)**. **1. Why Option A is Correct:** In venous blood, the partial pressure of $CO_2$ is high. $CO_2$ diffuses into Red Blood Cells (RBCs) and reacts with water to form carbonic acid ($H_2CO_3$), which dissociates into $H^+$ and $HCO_3^-$. To maintain electrical neutrality, as $HCO_3^-$ diffuses out of the RBC into the plasma, **Chloride ions ($Cl^-$) shift from the plasma into the RBC** via the Anion Exchanger 1 (Band 3 protein). The influx of $Cl^-$ increases the intracellular osmotic pressure, causing water to enter the RBC by osmosis. This results in **slight swelling of the RBCs**, thereby increasing the Mean Corpuscular Volume (MCV) and the overall hematocrit (Hct) in venous blood. **2. Why Other Options are Incorrect:** * **Option B & C:** While $Na^+$ and $HCO_3^-$ are high in the plasma of venous blood, they do not cause the RBC swelling. In fact, the movement of $HCO_3^-$ *out* of the cell is what triggers the $Cl^-$ shift. * **Option D:** $K^+$ is the primary intracellular cation, but its concentration does not change significantly between arterial and venous blood to affect hematocrit. **High-Yield Clinical Pearls for NEET-PG:** * **Reverse Chloride Shift:** Occurs in the lungs (arterial blood) where $Cl^-$ moves out of the RBC, causing them to shrink slightly. * **MCV Difference:** Venous RBCs have an MCV approximately 3% higher than arterial RBCs. * **Band 3 Protein:** The specific membrane transporter responsible for the $Cl^-/HCO_3^-$ exchange. * **Hematocrit Variation:** Because of this shift, hematocrit measured from peripheral venous samples is slightly higher than the actual systemic arterial hematocrit.

Question 279: In RBC development, in which stage does haemoglobin first appear?

A. Basophilic erythroblast
B. Polychromatic erythroblast (Correct Answer)
C. Orthochromatic erythroblast
D. Reticulocyte

Explanation: ### Explanation The correct answer is **Polychromatic erythroblast** (Intermediate Normoblast). #### 1. Why Polychromatic Erythroblast is Correct Hemoglobin synthesis begins early in the Proerythroblast stage, but it is **first visible** under a light microscope during the **Polychromatic erythroblast** stage. At this stage, the cytoplasm exhibits a "muddy" or "polychromatic" appearance. This is due to the dual presence of: * **Basophilia:** From the remaining ribosomes and RNA. * **Acidophilia:** From the newly synthesized hemoglobin. The mix of pink (hemoglobin) and blue (RNA) gives the cell its characteristic greyish-purple hue. #### 2. Why Other Options are Incorrect * **Basophilic Erythroblast (Early Normoblast):** While the cell is actively synthesizing the machinery for hemoglobin, the cytoplasm is intensely basophilic due to a high concentration of RNA and ribosomes. Hemoglobin is not yet visible. * **Orthochromatic Erythroblast (Late Normoblast):** In this stage, hemoglobin is present in high concentrations, giving the cytoplasm a purely eosinophilic (pink) appearance similar to a mature RBC. However, it is not the *first* stage of appearance. This is also the stage where the nucleus is extruded. * **Reticulocyte:** This is a post-nuclear stage. While it contains 80% of the total hemoglobin of a mature RBC, it represents a later stage of development. #### 3. NEET-PG High-Yield Pearls * **Nucleolus Disappears:** In the Basophilic erythroblast stage. * **Nucleus Extrusion:** Occurs at the Orthochromatic erythroblast stage. * **Reticulocyte Count:** An index of effective erythropoiesis (Normal: 0.5–2%). They contain "reticulum" which is actually remnants of RNA/ribosomes, best seen with **Supravital stains** (e.g., New Methylene Blue). * **Total Time for Erythropoiesis:** Approximately 7 days (5 days to reach reticulocyte stage + 2 days to mature into RBC).

Question 280: Serotonin is mainly secreted by which of the following?

A. Mast cells
B. Platelets (Correct Answer)
C. Neutrophils
D. Macrophages

Explanation: **Explanation:** **Correct Answer: B. Platelets** Serotonin (5-hydroxytryptamine) is a potent vasoconstrictor and neurotransmitter. In the blood, it is **not synthesized** by platelets but is actively taken up from the plasma (produced by enterochromaffin cells of the gut) and stored in the **Dense Granules (delta granules)** of platelets. When a blood vessel is injured, platelets aggregate and release serotonin, which causes local vasoconstriction to minimize blood loss. **Why other options are incorrect:** * **A. Mast cells:** These primarily secrete **Histamine**, heparin, and proteases. While mast cells in rodents contain serotonin, human mast cells do not typically store or secrete significant amounts of it. * **C. Neutrophils:** These are phagocytic cells primarily involved in acute inflammation. They secrete lysosomal enzymes and reactive oxygen species (ROS), not serotonin. * **D. Macrophages:** These are involved in phagocytosis and cytokine production (like TNF-alpha and IL-1). They do not serve as a primary source of serotonin. **High-Yield Clinical Pearls for NEET-PG:** * **Platelet Granules:** * **Dense Granules:** Contain **S**erotonin, **A**DP/ATP, and **C**alcium (**SAC**). * **Alpha Granules:** Contain vWF, Fibrinogen, and Platelet-Derived Growth Factor (PDGF). * **Synthesis:** 90% of the body's serotonin is synthesized by the **Enterochromaffin (Kulchitsky) cells** of the gastrointestinal tract. * **Precursor:** Serotonin is derived from the amino acid **Tryptophan**. * **Clinical Correlation:** In **Carcinoid Syndrome**, excessive serotonin production leads to flushing, diarrhea, and right-sided heart valve lesions. The diagnostic marker is elevated urinary **5-HIAA**.

Practice by Chapter

Composition and Functions of Blood

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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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