Blood and Immunity — MCQs

Blood and Immunity Indian Medical PG Practice Questions and MCQs

Question 151: What is the Fahraeus Lindquist effect?

A. Increase in viscosity in vessels less than 0.5-1 mm in diameter (Correct Answer)
B. Decrease in viscosity in vessels less than 0.5-1 mm in diameter
C. Increase in viscosity in vessels more than 0.5-1 mm in diameter
D. Decrease in viscosity in vessels more than 0.5-1 mm in diameter

Explanation: **Explanation:** The **Fahraeus-Lindqvist effect** describes the phenomenon where the **apparent viscosity of blood changes depending on the diameter of the vessel** through which it flows. **Why Option A is Correct:** In larger vessels, blood behaves as a non-Newtonian fluid. However, as blood enters smaller vessels (specifically those with a diameter less than **0.5 mm to 1 mm**, down to the capillary level), the apparent viscosity **decreases**. This occurs because of **axial accumulation**: red blood cells (RBCs) migrate to the center of the vessel (the high-velocity zone), leaving a cell-free layer of plasma (marginal plasma zone) near the vessel walls. Since plasma has lower viscosity than whole blood and is located at the area of maximum shear stress (the walls), the overall resistance to flow decreases. **Why Other Options are Incorrect:** * **Option B:** This is the opposite of the effect. Viscosity decreases, it does not increase in these small vessels. * **Options C & D:** The effect is specifically observed in microcirculation (vessels <1 mm). In larger vessels (diameters >1 mm), the hematocrit is uniform across the vessel width, and the viscosity remains relatively constant and high. **High-Yield NEET-PG Pearls:** 1. **Critical Diameter:** The effect is most prominent in vessels between 15 μm and 500 μm. 2. **Inversion Phenomenon:** Below a vessel diameter of **5–7 μm** (the size of an RBC), the viscosity suddenly **increases** again because the RBCs must deform to squeeze through the capillaries (Bolus flow). 3. **Physiological Significance:** This effect reduces the workload on the heart by lowering the peripheral resistance in the microvasculature. 4. **Fahraeus Effect:** Closely related; it states that the **tube hematocrit** (average hematocrit in a small vessel) is lower than the **discharge hematocrit** (hematocrit in the reservoir feeding it).

Question 152: An individual with AB blood group has which of the following agglutinins?

A. Anti-A and anti-B
B. Neither anti-A nor anti-B (Correct Answer)
C. Anti-A
D. Anti-B

Explanation: ### Explanation **Concept:** The ABO blood grouping system is based on **Landsteiner’s Law**, which states that if an antigen (agglutinogen) is present on the Red Blood Cell (RBC) membrane, the corresponding antibody (agglutinin) must be absent from the plasma. Conversely, if an antigen is absent on the RBC, the corresponding antibody must be present in the plasma. In an individual with **AB blood group**, both **Antigen A and Antigen B** are present on the surface of the RBCs. To prevent auto-agglutination (destruction of one's own cells), the body does not produce antibodies against these antigens. Therefore, the plasma contains **neither anti-A nor anti-B antibodies**. **Analysis of Options:** * **Option B (Correct):** As explained, the presence of both A and B antigens necessitates the absence of both antibodies in the plasma. * **Option A:** This is characteristic of **Blood Group O**, where neither antigen is present on the RBC, leading to the production of both anti-A and anti-B antibodies. * **Option C:** Anti-A antibodies are found in individuals with **Blood Group B**. * **Option D:** Anti-B antibodies are found in individuals with **Blood Group A**. **High-Yield Facts for NEET-PG:** * **Universal Recipient:** AB positive is the universal recipient because it lacks anti-A and anti-B antibodies, meaning it won't react against transfused RBCs. * **Universal Donor:** O negative is the universal donor because it lacks A, B, and Rh antigens. * **Agglutinins:** These are typically **IgM** antibodies that do not cross the placenta (unlike Rh antibodies, which are IgG). * **Bombay Blood Group:** Lacks the H-antigen; these individuals have anti-A, anti-B, and anti-H antibodies.

Question 153: What is the lifespan of platelets and neutrophils, respectively?

A. 8-9 days and 5 days (Correct Answer)
B. 120 days and 5 days
C. 5 days and 120 days
D. 5 days and 8-9 days

Explanation: ### Explanation The correct answer is **Option A: 8-9 days and 5 days.** **1. Understanding the Lifespan (Kinetics):** * **Platelets (Thrombocytes):** These are anuclear fragments derived from megakaryocytes in the bone marrow. Their average lifespan in the peripheral blood is approximately **8 to 11 days** (commonly cited as 8–9 days in standard textbooks like Guyton and Ganong). After this period, they are sequestered and destroyed primarily by the splenic macrophages. * **Neutrophils (PMNs):** These are the most abundant leukocytes but have a relatively short half-life. Once released from the bone marrow, they circulate in the blood for about **6 to 10 hours** before migrating into tissues, where they survive for **2 to 5 days**. In the context of NEET-PG, "5 days" is the standard representative figure for their total functional lifespan. **2. Analysis of Incorrect Options:** * **Option B & C:** Mention **120 days**, which is the classic lifespan of a mature **Red Blood Cell (RBC)**. RBCs have a longer lifespan because they lack a nucleus and mitochondria, focusing entirely on hemoglobin transport. * **Option D:** Reverses the order. While both numbers are used, platelets live longer than the tissue-resident lifespan of neutrophils. **3. NEET-PG High-Yield Clinical Pearls:** * **Storage:** 1/3rd of the body's platelets are stored in the **spleen** at any given time (Splenic Pool). In splenomegaly, platelet counts may drop due to increased sequestration. * **Transfusion:** Because of their short lifespan and the risk of bacterial growth, pooled platelets are stored at room temperature and have a shelf life of only **5 days**. * **Neutrophil Kinetics:** In acute infections, the "Left Shift" refers to the premature release of immature neutrophils (band cells) because the 5-day supply is rapidly exhausted.

Question 154: Rh antibodies are:

A. IgM (Correct Answer)
B. IgA
C. IgE
D. IgD

Explanation: **Explanation:** The correct answer is **A. IgM**. **Medical Concept:** Rh antibodies are primarily produced following exposure to Rh-positive red blood cells in an Rh-negative individual (isoimmunization). The **initial immune response** (primary response) to the D-antigen results in the production of **IgM** antibodies. These are pentameric, large molecules that do not cross the placenta. However, upon subsequent exposure or as the immune response matures (secondary response), the body undergoes class switching to produce **IgG** antibodies. While clinical complications like Hemolytic Disease of the Newborn (HDN) are caused by IgG (which crosses the placenta), the fundamental physiological classification of the initial Rh antibody formed is IgM. **Analysis of Incorrect Options:** * **B. IgA:** Found primarily in secretions (colostrum, saliva, tears) and mucosal surfaces; it is not involved in Rh incompatibility. * **C. IgE:** Mediates Type I hypersensitivity reactions (allergies) and defense against helminthic parasites. * **D. IgD:** Primarily acts as an antigen receptor on the surface of B-lymphocytes; its role in serum is minimal and unrelated to blood group antigens. **High-Yield NEET-PG Pearls:** * **ABO Antibodies:** Naturally occurring, predominantly **IgM** (cannot cross placenta). * **Rh Antibodies:** Immune-mediated, initially **IgM**, then predominantly **IgG** (can cross placenta). * **Anti-D (RhoGAM):** Given to Rh-negative mothers to prevent sensitization; it is an IgG preparation that destroys fetal Rh+ cells before the mother's immune system can react. * **Direct Coombs Test:** Detects antibodies already bound to the surface of RBCs (used to diagnose HDN).

Question 155: Blood cells arise in bone marrow and are subject to what type of renewal process?

A. Irregular renewal
B. Regular renewal (Correct Answer)
C. Infrequent renewal
D. None of the above

Explanation: **Explanation:** The correct answer is **Regular renewal**. Hematopoiesis is a continuous and highly regulated process. Blood cells (erythrocytes, leukocytes, and platelets) have finite lifespans—ranging from a few hours (neutrophils) to 120 days (RBCs). To maintain physiological homeostasis, the bone marrow must produce billions of new cells daily to replace those that are aged or destroyed. This constant turnover is termed **regular renewal**. It ensures that the peripheral blood count remains within a narrow therapeutic range despite the continuous loss of cells. **Analysis of Options:** * **Irregular renewal:** This is incorrect because hematopoiesis is not haphazard. It follows a strict circadian and feedback-driven rhythm (mediated by erythropoietin, G-CSF, etc.) to match production with demand. * **Infrequent renewal:** This is incorrect as blood cells are among the most rapidly dividing and replaced cell populations in the body. "Infrequent renewal" would apply to tissues like the myocardium or neurons, which have limited regenerative capacity. **High-Yield NEET-PG Pearls:** * **Site of Hematopoiesis:** In adults, it occurs in the **red bone marrow** (primarily membranous bones like the pelvis, sternum, and vertebrae). In the fetus, the **liver** is the chief site during the second trimester. * **Pluripotent Stem Cells:** All blood cells originate from **CD34+** hematopoietic stem cells. * **Kinetics:** The bone marrow produces approximately $10^{11}$ to $10^{12}$ new blood cells daily under steady-state conditions. * **Clinical Correlation:** A failure in this regular renewal process leads to **Aplastic Anemia** (pancytopenia).

Question 156: All of the following stem cell populations are found within the bone marrow, except?

A. Endothelial Progenitor cells
B. Myoblast Progenitor cells (Correct Answer)
C. Mesenchymal stem cells
D. Hematopoietic stem cells

Explanation: ### Explanation The bone marrow is a complex microenvironment (niche) that serves as the primary site for hematopoiesis and houses various multipotent stem cell populations. **Why Myoblast Progenitor Cells are the Correct Answer:** **Myoblast progenitor cells** (satellite cells) are the precursors to skeletal muscle fibers. They are found located between the sarcolemma and the basal lamina of **muscle fibers**, not in the bone marrow. Their primary role is the repair and regeneration of muscle tissue following injury. **Analysis of Incorrect Options:** * **Hematopoietic Stem Cells (HSCs):** These are the most well-known residents of the bone marrow. They are multipotent cells responsible for the constant production of all blood cell lineages (RBCs, WBCs, and platelets). * **Mesenchymal Stem Cells (MSCs):** Also known as marrow stromal cells, these are multipotent cells that can differentiate into non-hematopoietic lineages, including **osteoblasts** (bone), **chondrocytes** (cartilage), and **adipocytes** (fat). * **Endothelial Progenitor Cells (EPCs):** These cells reside in the bone marrow and can be mobilized into the circulation to participate in angiogenesis and the repair of blood vessel linings. **High-Yield Clinical Pearls for NEET-PG:** * **Niche Concept:** The bone marrow "niche" consists of cellular components (osteoblasts, endothelial cells) and humoral factors (CXCL12/SDF-1) that regulate stem cell quiescence and proliferation. * **CD Markers:** HSCs are typically identified by the presence of **CD34+** and **CD117+ (c-kit)**, and the absence of lineage-specific markers (Lin-). * **Transdifferentiation:** While MSCs primarily form bone/cartilage/fat, they are a major focus of regenerative medicine due to their potential to differentiate into various tissues under specific experimental conditions.

Question 157: Which of the following cell types are classified as large granular lymphocytes?

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

Explanation: **Explanation:** **Natural Killer (NK) cells** are the correct answer because they are morphologically defined as **Large Granular Lymphocytes (LGLs)**. Unlike small lymphocytes (B and T cells), NK cells possess a more abundant cytoplasm containing prominent azurophilic granules. These granules house cytotoxic proteins like **perforins and granzymes**, which are essential for the innate immune response against virally infected cells and tumor cells. **Analysis of Incorrect Options:** * **B cells and T cells (Options A & C):** These are typically classified as **small, non-granular lymphocytes**. They have a high nuclear-to-cytoplasmic ratio with very little cytoplasm and generally lack visible granules under light microscopy. While a small subset of T cells (specifically activated CD8+ T cells) can exhibit an LGL morphology, the classic and primary definition of an LGL refers to NK cells. * **Plasma cells (Option D):** These are terminally differentiated B cells. Morphologically, they are characterized by an eccentric "cartwheel" nucleus and a prominent perinuclear clear zone (Golgi apparatus), but they are not classified as large granular lymphocytes. **High-Yield Pearls for NEET-PG:** * **Surface Markers:** NK cells are identified by the presence of **CD56 and CD16**, and the absence of CD3 (T-cell marker). * **Function:** They provide the first line of defense and do not require prior sensitization (MHC-independent killing). * **Clinical Correlation:** **LGL Leukemia** is a rare lymphoproliferative disorder that can arise from either NK cells or T cells, often presenting with neutropenia and splenomegaly. * **Chediak-Higashi Syndrome:** A condition where NK cell function is impaired due to defective granule formation/trafficking.

Question 158: A patient with blood group O can safely receive plasma from which blood group donor?

A. Group A only
B. Group B only
C. Group AB only
D. Group A, B, and AB (Correct Answer)

Explanation: ### Explanation The core concept in transfusion medicine is understanding the difference between **Whole Blood/Packed Red Blood Cell (PRBC)** transfusion and **Plasma** transfusion. **1. The Underlying Medical Concept:** * **PRBC Transfusion:** We worry about the **antigens** on the donor's RBCs and the **antibodies** in the recipient's plasma. * **Plasma Transfusion:** We worry about the **antibodies** present in the donor's plasma and how they will react with the **antigens** on the recipient's RBCs. A patient with **Blood Group O** has **no A or B antigens** on their red blood cells. Because there are no antigens for antibodies to attack, they can safely receive plasma containing Anti-A antibodies (from Group B), Anti-B antibodies (from Group A), or both. Therefore, plasma from A, B, or AB donors will not cause hemolysis in a Group O recipient. **2. Analysis of Options:** * **Options A & B:** While Group O can receive plasma from A or B, these options are "incomplete." Since Group O RBCs lack antigens, they are compatible with plasma from any group. * **Option C:** Group AB plasma is the "Universal Donor" for plasma because it contains **no antibodies**. While safe, it is not the *only* safe option for a Group O recipient. * **Option D (Correct):** Since Group O RBCs are "antigen-neutral," they are compatible with any plasma regardless of the antibody content. **3. NEET-PG High-Yield Pearls:** * **Universal Donor (RBCs):** Group O Negative (No antigens). * **Universal Recipient (RBCs):** Group AB Positive (No antibodies). * **Universal Donor (Plasma):** Group AB (No antibodies in plasma). * **Universal Recipient (Plasma):** Group O (No antigens on RBCs to be attacked). * **Landsteiner’s Law:** States that if an antigen is present on RBCs, the corresponding antibody must be absent in the plasma (and vice versa). This law does not apply to Group AB (no antibodies) or Group O (no antigens).

Question 159: What is the normal leukocyte count per cubic millimeter of blood?

A. 8,000-15,000
B. 4,000-11,000 (Correct Answer)
C. 5,000-8,000
D. 7,000-14,000

Explanation: **Explanation:** The Total Leukocyte Count (TLC) represents the number of white blood cells (WBCs) circulating in the peripheral blood. In a healthy adult, the physiological range is **4,000 to 11,000 cells per cubic millimeter (mm³)**. These cells are essential components of the immune system, categorized into granulocytes (neutrophils, eosinophils, basophils) and agranulocytes (lymphocytes, monocytes). * **Why Option B is correct:** This range is the globally accepted clinical standard. Variations slightly below or above this range are termed leukopenia and leukocytosis, respectively. * **Why Options A, C, and D are incorrect:** These ranges do not align with standard physiological data. While a count of 8,000 (Option C) or 14,000 (Option D) might occur in specific individuals or during mild inflammation, they do not represent the established "normal" baseline range for the general population. **High-Yield Clinical Pearls for NEET-PG:** 1. **Leukocytosis:** A TLC >11,000/mm³. Common causes include acute bacterial infections (neutrophilia), viral infections (lymphocytosis), or physiological stress (exercise, pregnancy). 2. **Leukopenia:** A TLC <4,000/mm³. Seen in bone marrow suppression, typhoid fever, aplastic anemia, and certain viral infections like HIV. 3. **Leukemoid Reaction:** An extreme elevation of TLC (>50,000/mm³) mimicking leukemia, usually due to severe infection or inflammation, but characterized by a high **LAP (Leukocyte Alkaline Phosphatase) score**, unlike Chronic Myeloid Leukemia (CML). 4. **Newborns:** It is important to remember that newborns have a much higher normal TLC, often ranging from 10,000 to 25,000/mm³.

Question 160: What is the longest lifespan among the following blood cells?

A. Red Blood Cells (RBC)
B. Platelets
C. Neutrophils
D. Macrophages (Correct Answer)

Explanation: ### Explanation The lifespan of blood cells varies significantly based on their function and environment. Among the options provided, **Macrophages** possess the longest lifespan. **1. Why Macrophages are the Correct Answer:** Monocytes circulate in the blood for about 10–20 hours before migrating into tissues, where they differentiate into **Macrophages**. Once in the tissues (e.g., Kupffer cells in the liver, Alveolar macrophages in the lungs), they can survive for **several months to even years**. Their longevity is essential for their role in chronic inflammation, antigen presentation, and tissue remodeling. **2. Why the Other Options are Incorrect:** * **Red Blood Cells (RBCs):** These have a fixed average lifespan of **120 days** in adults. While longer than most white blood cells, they are eventually sequestered and destroyed by the splenic sinusoids. * **Platelets (Thrombocytes):** These are cell fragments with a short lifespan of approximately **7 to 10 days**. They are primarily involved in hemostasis and are rapidly consumed or cleared by the spleen. * **Neutrophils:** These are the "first responders" of the immune system but have a very short half-life. They circulate for about **6–12 hours** and survive in tissues for only **2–5 days** before undergoing apoptosis. **3. NEET-PG High-Yield Clinical Pearls:** * **Memory Cells:** If "Memory B or T cells" were an option, they would be the correct answer, as they can persist for **decades**. * **RBC Lifespan:** It is shorter in neonates (approx. 60–90 days) and decreased in conditions like Hereditary Spherocytosis or Sickle Cell Anemia. * **Platelet Storage:** Because of their short 7–10 day lifespan, donated platelets can only be stored for **5 days** at room temperature, unlike RBCs which can be stored for 35–42 days.

Practice by Chapter

Composition and Functions of Blood

Practice Questions

Erythrocytes and Hemoglobin

Practice Questions

Leukocytes and Immune Function

Practice Questions

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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