Blood and Immunity

Blood and Immunity Indian Medical PG Question 1: What is the inheritance pattern of the ABO blood group system and the HLA system?

• A. Pseudodominance
• B. Autosomal dominant
• C. Autosomal recessive
• D. Codominant (Correct Answer)

Blood and Immunity Explanation: ### Explanation **Correct Option: D (Codominant)** The ABO blood group and the Human Leukocyte Antigen (HLA) system are classic examples of **codominance**. In codominance, both alleles in a heterozygous individual are fully expressed, and neither masks the other. * **ABO System:** The $I^A$ and $I^B$ alleles are codominant. If an individual inherits $I^A$ from one parent and $I^B$ from the other, their phenotype is AB, expressing both A and B antigens on the RBC surface. (Note: Both $I^A$ and $I^B$ are dominant over the $i$ allele). * **HLA System:** HLA genes (located on Chromosome 6) are the most polymorphic genes in humans. An individual expresses HLA antigens from both maternal and paternal haplotypes simultaneously on the cell surface. This is critical for immune recognition and organ transplant matching. **Why other options are incorrect:** * **A. Pseudodominance:** This occurs when a recessive allele is expressed because the dominant allele is missing (e.g., due to deletion), commonly seen in X-linked disorders in males. * **B & C. Autosomal Dominant/Recessive:** These follow Mendelian patterns where one allele masks the other. In ABO, while A and B are dominant over O, they do not mask each other, making "Codominant" the more specific and accurate description. **High-Yield Facts for NEET-PG:** 1. **Multiple Allelism:** The ABO system is also an example of multiple allelism (three alleles: A, B, and O). 2. **Bombay Phenotype:** A rare condition where the H-substance is missing; these individuals phenotypically appear as Type O regardless of their genotype. 3. **HLA Association:** HLA-B27 is strongly associated with Ankylosing Spondylitis; HLA-DR3/DR4 is associated with Type 1 Diabetes Mellitus. 4. **Chromosome 9:** The locus for the ABO gene is on the long arm of Chromosome 9.

Blood and Immunity Indian Medical PG Question 2: All of the following are functions of the spleen EXCEPT?

• A. Clearance of damaged or aged red blood cells (RBCs) from the blood.
• B. Extramedullary site for hematopoiesis and recycling iron.
• C. Initiation of adaptive immune response from filtration of lymph. (Correct Answer)
• D. Clearance of encapsulated bacteria from the bloodstream.

Blood and Immunity Explanation: ### Explanation The correct answer is **C. Initiation of adaptive immune response from filtration of lymph.** The spleen is often described as a "giant lymph node," but there is a critical anatomical difference: **the spleen filters blood, not lymph.** Lymph nodes are responsible for filtering interstitial fluid (lymph) via afferent lymphatic vessels. The spleen lacks afferent lymphatics; instead, it samples antigens directly from the systemic circulation via the splenic artery. #### Analysis of Options: * **Option A (Correct Function):** The splenic sinusoids and the "pitting" mechanism in the Red Pulp act as a biological filter, removing senescent, rigid, or damaged RBCs (Culling). * **Option B (Correct Function):** During fetal development (months 3–7), the spleen is a primary hematopoietic organ. In adults, it can resume this role (extramedullary hematopoiesis) in conditions like myelofibrosis. It also recycles iron from hemoglobin via splenic macrophages. * **Option D (Correct Function):** The White Pulp contains B-cells and T-cells. Splenic macrophages and antibodies are essential for opsonizing and clearing **encapsulated organisms** (e.g., *S. pneumoniae, H. influenzae, N. meningitidis*). #### High-Yield Clinical Pearls for NEET-PG: * **Asplenia/Splenectomy:** Patients are at high risk for **OPSI (Overwhelming Post-Splenectomy Infection)**. Vaccination against encapsulated bacteria is mandatory (ideally 2 weeks before elective surgery). * **Howell-Jolly Bodies:** These are nuclear remnants in RBCs normally removed by the spleen; their presence on a peripheral smear is a hallmark of splenic dysfunction or asplenia. * **Pitting:** The spleen’s ability to remove inclusions (like malaria parasites or Heinz bodies) from RBCs without destroying the cell itself.

Blood and Immunity Indian Medical PG Question 3: What is the first cell in the development of red blood cells?

• A. Proerythroblast (Correct Answer)
• B. Intermediate normoblast
• C. Reticulocyte
• D. Basophilic erythroblast

Blood and Immunity Explanation: **Explanation:** The process of red blood cell formation, known as **erythropoiesis**, occurs in the bone marrow. It begins with a multipotent hematopoietic stem cell, which differentiates into a **Proerythroblast** (also called a Pronormoblast). **Why Proerythroblast is correct:** The Proerythroblast is the **first morphologically identifiable committed precursor** of the erythroid series. It is a large cell with a big nucleus, visible nucleoli, and a thin rim of basophilic cytoplasm. Once a stem cell differentiates into a proerythroblast, it is "committed" to becoming a mature erythrocyte. **Analysis of Incorrect Options:** * **Basophilic erythroblast (Early Normoblast):** This is the second stage. It is smaller than the proerythroblast and shows intense cytoplasmic basophilia due to an accumulation of RNA for hemoglobin synthesis. * **Intermediate normoblast (Polychromatophilic erythroblast):** This is the third stage. It is characterized by a "checkered" nucleus and a cytoplasm that appears grayish/purple because it contains both basic RNA and acidic hemoglobin. * **Reticulocyte:** This is the penultimate stage, occurring after the nucleus is extruded (at the orthochromatic stage). It is an immature RBC that stays in the marrow for 1–2 days before entering the peripheral circulation. **NEET-PG High-Yield Pearls:** 1. **Hemoglobin synthesis** begins in the **Proerythroblast** stage, but becomes visible (morphologically detectable) in the **Intermediate Normoblast** stage. 2. The **nucleus is extruded** at the **Orthochromatic Normoblast** (Late Normoblast) stage. 3. **Reticulocyte count** is the best clinical indicator of effective erythropoiesis in the bone marrow. 4. **Erythropoietin (EPO)** primarily acts on the CFU-E (Colony Forming Unit-Erythroid) to stimulate the production of proerythroblasts.

Blood and Immunity Indian Medical PG Question 4: The biconcave shape of RBC is useful for all the following functions EXCEPT:

• A. Allows considerable alteration in cell volume
• B. Increasing surface area for diffusion (Correct Answer)
• C. Resisting hemolysis
• D. Passing easily through smaller capillaries

Blood and Immunity Explanation: The biconcave shape of the Red Blood Cell (RBC) is a specialized structural adaptation designed for flexibility and volume management rather than maximizing surface area. ### **Explanation of the Correct Answer** **Option B (Increasing surface area for diffusion)** is the correct answer because it is a common misconception. Mathematically, a **sphere** has the minimum surface area for a given volume, while a **flat disc** or complex shape has more. However, the biconcave shape is *not* the most efficient shape for maximizing surface area; a thin, flat sheet or a highly folded membrane would provide more area for gas exchange. The primary evolutionary "goal" of the biconcave shape is to provide a high **surface-area-to-volume ratio**, which allows for significant cell deformation and volume changes without stretching the membrane. ### **Analysis of Other Options** * **Option A & C:** The biconcave shape provides "excess" membrane. This allows the RBC to undergo **considerable alteration in cell volume** (swelling in hypotonic solutions) without rupturing. Because the membrane isn't under tension in its resting state, it can expand into a spherical shape before bursting, thereby **resisting hemolysis**. * **Option D:** RBCs (7.5 µm) must pass through splenic sinusoids and capillaries as small as 3 µm. The biconcave shape allows the cell to fold and deform easily (**high deformability**), facilitating passage through narrow microvasculature. ### **High-Yield Clinical Pearls for NEET-PG** * **Hereditary Spherocytosis:** A defect in membrane proteins (Ankyrin/Spectrin) causes RBCs to lose their biconcave shape and become spherical. These cells have the *lowest* surface-area-to-volume ratio, are fragile, and are easily destroyed in the spleen. * **Average RBC Diameter:** 7.5 µm (Thickness: 2 µm at periphery, 1 µm at center). * **Rouleaux Formation:** The biconcave shape facilitates the "stacking" of RBCs, seen in states of high ESR (e.g., chronic inflammation).

Blood and Immunity Indian Medical PG Question 5: Which of the following is responsible for the adhesion of platelets to the vessel wall?

• A. Von Willebrand factor (Correct Answer)
• B. Factor IX
• C. Fibrinogen
• D. Fibronectin

Blood and Immunity Explanation: **Explanation:** The correct answer is **Von Willebrand factor (vWF)**. Platelet plug formation occurs in three distinct stages: Adhesion, Activation, and Aggregation. 1. **Why vWF is correct:** When a blood vessel is injured, the subendothelial collagen is exposed. Platelets cannot bind directly to collagen under high-shear stress (like in arteries). **vWF** acts as a molecular bridge; one end binds to the exposed **subendothelial collagen**, and the other end binds to the **Glycoprotein Ib (GpIb)** receptor on the platelet surface. This specific interaction is responsible for **platelet adhesion**. 2. **Why the other options are incorrect:** * **Factor IX:** This is a component of the intrinsic pathway of the coagulation cascade. Its deficiency leads to Hemophilia B (Christmas disease). It is involved in secondary hemostasis (clotting), not primary platelet adhesion. * **Fibrinogen:** This is responsible for **platelet aggregation**. Fibrinogen binds to the **GpIIb/IIIa** receptors on adjacent platelets, linking them together to form a plug. * **Fibronectin:** While fibronectin is present in the extracellular matrix and plasma and plays a minor role in cell-matrix interactions, it is not the primary mediator of initial platelet adhesion to the vessel wall. **High-Yield Clinical Pearls for NEET-PG:** * **Bernard-Soulier Syndrome:** A deficiency of the **GpIb** receptor, leading to defective adhesion (characterized by giant platelets and thrombocytopenia). * **Von Willebrand Disease (vWD):** The most common inherited bleeding disorder; it results in defective adhesion due to a deficiency or dysfunction of vWF. * **Glanzmann Thrombasthenia:** A deficiency of the **GpIIb/IIIa** receptor, leading to defective **aggregation**. * **vWF Source:** It is synthesized in endothelial cells (stored in **Weibel-Palade bodies**) and megakaryocytes (stored in **α-granules** of platelets).

Blood and Immunity Indian Medical PG Question 6: Deficiency of the intrinsic factor of Castle causes which of the following?

• A. Microcytic anemia
• B. Pernicious anemia (Correct Answer)
• C. Cooley's anemia
• D. Aplastic anemia

Blood and Immunity Explanation: **Explanation:** **1. Why Pernicious Anemia is Correct:** Intrinsic Factor (IF) of Castle is a glycoprotein secreted by the **parietal cells** of the gastric mucosa. Its primary role is to bind to Vitamin B12 (Cobalamin) in the duodenum, protecting it from digestion and facilitating its absorption in the **terminal ileum**. Pernicious anemia is an autoimmune condition where antibodies are directed against parietal cells or the IF itself. This leads to a failure of Vitamin B12 absorption, resulting in megaloblastic erythropoiesis because B12 is essential for DNA synthesis (specifically the conversion of homocysteine to methionine). **2. Why Other Options are Incorrect:** * **A. Microcytic anemia:** This is typically caused by iron deficiency, thalassemias, or lead poisoning. B12 deficiency causes **macrocytic** (megaloblastic) anemia. * **C. Cooley’s anemia:** This is another name for **Beta-thalassemia major**, a genetic defect in hemoglobin chain synthesis, not related to intrinsic factor. * **D. Aplastic anemia:** This involves bone marrow failure leading to pancytopenia (reduction in RBCs, WBCs, and platelets), usually due to toxins, drugs, or radiation. **3. High-Yield NEET-PG Pearls:** * **Site of Secretion:** Parietal cells (Body/Fundus of the stomach). * **Site of Absorption:** Terminal Ileum (requires Calcium and a pH > 5.6). * **Schilling Test:** Historically used to differentiate between B12 malabsorption causes (now largely replaced by antibody testing). * **Neurological Involvement:** Unlike folate deficiency, B12 deficiency (Pernicious anemia) causes **Subacute Combined Degeneration (SCD)** of the spinal cord due to methylmalonic acid accumulation. * **Morphology:** Look for **hypersegmented neutrophils** on a peripheral smear.

Blood and Immunity Indian Medical PG Question 7: What is the predominant immunoglobulin found in saliva?

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

Blood and Immunity Explanation: **Explanation:** **Correct Option: A (IgA)** Immunoglobulin A (IgA) is the predominant antibody found in seromucous secretions, including **saliva**, tears, colostrum, and gastrointestinal/respiratory secretions. In these fluids, it exists primarily as **Secretory IgA (sIgA)**, which is a dimer. It contains a **J-chain** (joining chain) and a **secretory component** that protects the antibody from degradation by proteolytic enzymes in the harsh environments of the gut and mouth. Its primary function is "immune exclusion," preventing the attachment of pathogens to mucosal surfaces. **Why other options are incorrect:** * **IgD:** Primarily found on the surface of B-lymphocytes where it acts as an antigen receptor. It is present in only trace amounts in serum and secretions. * **IgE:** Involved in type I hypersensitivity (allergic) reactions and defense against helminthic parasites. It is found in very low concentrations in the blood and is typically bound to mast cells and basophils. * **IgG:** The most abundant immunoglobulin in the **serum** (approx. 75-80%) and the only one that crosses the placenta. While it can be found in saliva via gingival crevicular fluid, it is not the predominant type. **High-Yield NEET-PG Pearls:** * **Structure:** IgA is a monomer in serum but a **dimer** in secretions. * **Selective IgA Deficiency:** The most common primary immunodeficiency; patients often present with recurrent sinopulmonary and GI infections. * **Breast Milk:** IgA is the most abundant antibody in colostrum, providing passive immunity to the neonate's gut. * **Half-life:** IgG has the longest half-life (approx. 23 days), making it the mainstay of secondary immune responses.

Blood and Immunity Indian Medical PG Question 8: Which of the following clotting factors helps in bridging fibrin in a clot and stabilizes the clot?

• A. Factor III
• B. Factor V
• C. Factor VIII
• D. Factor XIII (Correct Answer)

Blood and Immunity Explanation: ### Explanation **Correct Answer: D. Factor XIII (Fibrin Stabilizing Factor)** Factor XIII, also known as **Laki-Lorand factor**, is the final enzyme in the coagulation cascade. Once thrombin converts soluble fibrinogen into fibrin monomers, these monomers aggregate to form a "soft" or unstable clot. Factor XIII is activated by thrombin (in the presence of Calcium) to **Factor XIIIa**, which acts as a transglutaminase. It creates **covalent cross-links** between the glutamine and lysine residues of adjacent fibrin strands. This "bridging" transforms the weak fibrin polymer into a stable, insoluble meshwork resistant to premature lysis. **Analysis of Incorrect Options:** * **Factor III (Tissue Thromboplastin):** This is the initiator of the **Extrinsic Pathway**. It is released upon tissue injury and activates Factor VII; it does not stabilize the final clot. * **Factor V (Proaccelerin/Labile Factor):** This acts as a cofactor in the **Prothrombinase complex** (along with Factor Xa, Ca²⁺, and phospholipids) to convert prothrombin to thrombin. * **Factor VIII (Anti-hemophilic Factor A):** This is a cofactor for Factor IXa in the **Intrinsic Tenase complex**, which activates Factor X. Deficiency leads to Hemophilia A. **High-Yield Clinical Pearls for NEET-PG:** * **Inheritance:** Factor XIII deficiency is rare and typically follows an **Autosomal Recessive** pattern. * **Clinical Presentation:** Characterized by delayed bleeding (clot forms but breaks down), poor wound healing, and **umbilical cord stump bleeding** in neonates. * **Lab Diagnosis:** Standard PT, aPTT, and Thrombin Time (TT) are **normal** because Factor XIII acts *after* the formation of the initial fibrin clot. Diagnosis is made using the **Urea Solubility Test** (clot dissolves in 5M urea if Factor XIII is deficient).

Blood and Immunity Indian Medical PG Question 9: Which of the following does NOT occur during hemostasis?

• A. Vasospasm of the blood vessel
• B. Platelet plug formation
• C. Dissolution of the clot by plasmin
• D. None of the above (Correct Answer)

Blood and Immunity Explanation: ### Explanation The correct answer is **None of the above** because all the processes listed (Vasospasm, Platelet plug formation, and Clot dissolution) are integral components of the physiological process of **Hemostasis**. Hemostasis is the body's mechanism to stop bleeding and maintain blood in a fluid state within the vessels. It occurs in four distinct but overlapping stages: 1. **Vascular Spasm (Vasoconstriction):** Immediately after injury, smooth muscles in the vessel wall contract. This is mediated by local myogenic spasms, nervous reflexes, and humoral factors like **Thromboxane A2 (TXA2)** and **Serotonin** released from platelets. This reduces blood flow to the injured area. 2. **Primary Hemostasis (Platelet Plug Formation):** Platelets adhere to exposed sub-endothelial collagen (via von Willebrand factor), undergo activation, and aggregate to form a temporary, friable "primary platelet plug." 3. **Secondary Hemostasis (Blood Coagulation):** The coagulation cascade is activated, leading to the conversion of soluble fibrinogen into insoluble **fibrin** threads, which stabilize the platelet plug into a solid clot. 4. **Tertiary Hemostasis (Fibrinolysis):** Once the vessel wall is repaired, the clot must be removed to restore normal blood flow. **Plasmin** (derived from plasminogen) digests the fibrin meshwork, leading to clot dissolution. **Why other options are incorrect:** * **Option A & B:** These are the initial steps of hemostasis. * **Option C:** Fibrinolysis (clot dissolution) is considered the final stage of the hemostatic process to prevent permanent vessel occlusion. **High-Yield NEET-PG Pearls:** * **Rate-limiting step of coagulation:** The formation of **Prothrombin Activator**. * **Vitamin K-dependent factors:** II, VII, IX, X, Protein C, and Protein S. * **Antithrombin III:** The most important natural anticoagulant; its action is potentiated by Heparin. * **Fibrin Degradation Products (FDPs):** D-dimer is a specific marker for fibrinolysis, used clinically to rule out DVT or PE.

Blood and Immunity Indian Medical PG Question 10: What is the common function of neutrophils, monocytes, and macrophages?

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

Blood and Immunity Explanation: ### Explanation **Phagocytosis** is the primary shared function of neutrophils, monocytes, and macrophages. These cells are collectively known as **professional phagocytes**. They identify, engulf, and digest cellular debris, foreign particles, and microorganisms. * **Neutrophils:** These are the "first responders" to acute inflammation. They utilize granules and oxidative bursts to kill pathogens. * **Monocytes:** These are the circulating precursors that migrate into tissues to differentiate into macrophages. * **Macrophages:** These are tissue-resident phagocytes (e.g., Kupffer cells in the liver, Alveolar macrophages in the lungs) that provide long-term defense and bridge innate and adaptive immunity. #### Analysis of Incorrect Options: * **A. Immune response:** While these cells participate in the immune response, this is a broad category. Phagocytosis is the specific *mechanism* they all share. Note that lymphocytes (B and T cells) drive the specific immune response but are not primarily phagocytic. * **C. Liberation of histamine:** This is the characteristic function of **Basophils** and **Mast cells** during Type I hypersensitivity reactions. * **D. Destruction of old erythrocytes:** This is specifically the role of the **Reticuloendothelial system (RES)**, primarily macrophages in the spleen and liver. Neutrophils do not typically participate in the physiological destruction of RBCs. #### High-Yield Clinical Pearls for NEET-PG: * **Neutrophils** are the hallmark of **acute inflammation**, whereas **macrophages** are the hallmark of **chronic inflammation**. * **Opsonization:** The process of coating a pathogen with Opsonins (C3b, IgG) to enhance phagocytosis. * **Chediak-Higashi Syndrome:** A clinical condition where there is a defect in phagosome-lysosome fusion, leading to recurrent infections. * **Respiratory Burst:** The rapid release of reactive oxygen species (ROS) during phagocytosis, mediated by **NADPH oxidase**. Deficiency leads to Chronic Granulomatous Disease (CGD).

Blood and Immunity Flashcard 1 of 10

Question: Which blood type does not have any group antigens on RBC surfaces? _____

Answer:

Blood and Immunity Flashcard 2 of 10

Question: What unique antibodies in plasma do patients with the A blood type have? _____

Answer:

Blood and Immunity Flashcard 3 of 10

Question: What is the formula for calculating Blood volume from Plasma volume and hematocrit? _____

Answer:

Blood and Immunity Flashcard 4 of 10

Question: Patients with the B blood type cannot receive which blood types? _____

Answer:

Blood and Immunity Flashcard 5 of 10

Question: oral polio vaccine produces _____ immunity

Answer: humoral and local

Extra Information: 

Blood and Immunity Flashcard 6 of 10

Question: Differentiation of helper T cells to _____ is induced by IL-1, IL-6 and TGF-

Answer: Th17

Blood and Immunity Flashcard 7 of 10

Question: Endothelial cells prevent thrombosis by blocking exposure to underlying _____ and tissue thromboplastin

Answer: subendothelial collagen

Blood and Immunity Flashcard 8 of 10

Question: IgA is transported through the mucosa via binding between the _____ of IgA and the polymeric Ig receptor on epithelial cells

Answer: J chain

Blood and Immunity Flashcard 9 of 10

Question: The first step of primary hemostasis is _____ of the damaged vessel; which is mediated by reflex neural stimulation and endothelin-1 release from endothelial cells

Answer: transient vasoconstriction

Blood and Immunity Flashcard 10 of 10

Question: Activation of the coagulation cascade requires _____ ions derived from platelet dense granules

Answer: Ca2+