Blood and Immunity Practice Questions

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

0.48%. ### 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.

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

Factor IX & X. **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**.

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

Polychromatic erythroblast. ### 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).

Q: Serotonin is mainly secreted by which of the following?

Platelets. **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**.

Q: Which test measures the extrinsic pathway of blood clotting?

Prothrombin time. **Explanation:** The coagulation cascade is divided into the intrinsic, extrinsic, and common pathways. The **Prothrombin Time (PT)** specifically measures the **Extrinsic Pathway** (Factor VII) and the **Common Pathway** (Factors X, V, II, and I). It is performed by adding thromboplastin (tissue factor) and calcium to the patient’s plasma. **Analysis of Options:** * **A. Prothrombin Time (PT):** Correct. It is the most sensitive test for the extrinsic pathway. It is also used to monitor **Warfarin** therapy and assess liver synthetic function. * **B. Activated Partial Thromboplastin Time (aPTT):** Incorrect. This measures the **Intrinsic Pathway** (Factors XII, XI, IX, VIII) and the common pathway. It is used to monitor **Unfractionated Heparin**. * **C. Bleeding Time (BT):** Incorrect. This measures **platelet function** and vascular integrity, not the coagulation cascade. It is prolonged in conditions like Von Willebrand Disease or thrombocytopenia. * **D. Clotting Time (CT):** Incorrect. This is a non-specific, bedside test (e.g., Lee-White method) that reflects the overall time taken for blood to clot, primarily influenced by the intrinsic pathway, but it lacks the sensitivity of PT/aPTT. **High-Yield Clinical Pearls for NEET-PG:** * **INR (International Normalized Ratio):** A standardized version of PT used to monitor oral anticoagulants (Warfarin). * **Vitamin K Dependent Factors:** II, VII, IX, and X. Since Factor VII has the shortest half-life, PT is the first to be prolonged in Vitamin K deficiency or early liver disease. * **Mnemonic:** **PeT** (PT = Extrinsic) and **PiTT** (aPTT = Intrinsic).

Q: The process whereby white blood cells can squeeze through pores in capillary walls is called what?

Diapedesis. ### Explanation **Correct Answer: B. Diapedesis** **Mechanism:** Diapedesis (also known as **leukocyte extravasation**) is the process by which white blood cells (WBCs), particularly neutrophils and monocytes, squeeze through the narrow intercellular junctions of the capillary endothelium to reach the site of inflammation or tissue injury. This is a highly regulated process involving: 1. **Margination and Rolling:** Mediated by **selectins**. 2. **Adhesion and Activation:** Mediated by **integrins** (ICAM-1/VCAM-1). 3. **Transmigration (Diapedesis):** Mediated by **PECAM-1** (CD31). Once outside the vessel, the cells move toward the injury site via **chemotaxis**. **Why Incorrect Options are Wrong:** * **A. Diffusion:** This is the passive movement of solutes (like O₂ or CO₂) from an area of high concentration to low concentration. It does not involve the active squeezing of whole cells. * **C. Osmosis:** This refers specifically to the movement of water molecules across a semi-permeable membrane. * **D. Pinocytosis:** Also known as "cell drinking," this is a form of endocytosis where the cell membrane folds inward to ingest extracellular fluid and small molecules. **High-Yield Clinical Pearls for NEET-PG:** * **Neutrophils** are the first cells to undergo diapedesis in acute inflammation, followed by **monocytes/macrophages**. * **Leukocyte Adhesion Deficiency (LAD):** A clinical condition where a defect in integrins (LAD-1) or selectin ligands (LAD-2) prevents diapedesis, leading to recurrent bacterial infections and delayed umbilical cord separation. * **CD31 (PECAM-1)** is the specific molecule found at endothelial junctions that facilitates the "squeezing" process.

Q: Delay in blood coagulation results from which of the following?

Heparin. **Explanation:** The correct answer is **Heparin**. Blood coagulation is a complex cascade of enzymatic reactions that leads to the formation of a fibrin clot. Delaying or preventing this process requires the inhibition of key clotting factors. **Why Heparin is correct:** Heparin is a potent **anticoagulant** produced naturally by mast cells and basophils. It works by binding to and activating **Antithrombin III**. This complex then inactivates several serine proteases in the coagulation cascade, most notably **Thrombin (Factor IIa)** and **Factor Xa**. By neutralizing these factors, heparin effectively prevents the conversion of fibrinogen to fibrin, thereby delaying or preventing clot formation. **Why the other options are incorrect:** * **Human Thrombin:** This is an active clotting factor (Factor IIa) that converts fibrinogen into fibrin. Adding thrombin would **accelerate** coagulation, not delay it. * **Ferric Chloride:** This is a **styptic agent**. It acts as a local hemostatic by causing rapid protein precipitation and vessel occlusion, which promotes clot formation to stop bleeding. * **Vitamin K:** This is an essential cofactor for the **gamma-carboxylation** of Factors II, VII, IX, and X. A deficiency in Vitamin K delays clotting, but its presence is necessary for the synthesis of functional procoagulants. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Heparin acts primarily on the **Intrinsic and Common pathways**. * **Monitoring:** The efficacy of Unfractionated Heparin (UFH) is monitored using **aPTT** (activated Partial Thromboplastin Time). * **Antidote:** The specific antagonist for heparin overdose is **Protamine Sulfate**. * **LMWH:** Low Molecular Weight Heparin (e.g., Enoxaparin) mainly inhibits Factor Xa and does not require routine aPTT monitoring.

Q: Which cell type lacks Human Leukocyte Antigen (HLA)?

Red blood cell. **Explanation:** The **Human Leukocyte Antigen (HLA)** system, also known as the Major Histocompatibility Complex (MHC), is a set of surface proteins found on almost all **nucleated cells** in the human body. These antigens are essential for the immune system to distinguish "self" from "non-self." **Why Red Blood Cells (RBCs) are the correct answer:** Mature Red Blood Cells are unique because they **lack a nucleus** and most organelles. Since HLA/MHC Class I molecules are synthesized and expressed based on nuclear genetic coding, RBCs do not express HLA on their surface. Instead, RBCs express their own specific surface antigens, primarily the ABO and Rh systems. **Analysis of Incorrect Options:** * **A. Monocyte:** These are nucleated white blood cells that function as professional antigen-presenting cells (APCs). They express both **MHC Class I** (found on all nucleated cells) and **MHC Class II** (found on APCs). * **B. Thrombocyte (Platelet):** Although platelets are fragments of megakaryocytes and lack a nucleus, they **do express HLA Class I** antigens on their surface. This is a high-yield distinction; HLA expression on platelets is clinically significant in cases of "platelet refractoriness" following multiple transfusions. * **C. Neutrophil:** As nucleated granulocytes, neutrophils express HLA Class I molecules. **High-Yield Clinical Pearls for NEET-PG:** * **MHC Class I:** Found on all nucleated cells + Platelets. (HLA-A, B, C). * **MHC Class II:** Found only on Antigen Presenting Cells (Macrophages, B-cells, Dendritic cells). (HLA-DP, DQ, DR). * **Exception:** The **Trophoblast** is a notable nucleated cell type that lacks classical HLA-A and B to prevent maternal immune rejection of the fetus. * **RBCs and Transfusion:** Because RBCs lack HLA, HLA-matching is not required for simple red cell transfusions; however, it is critical for organ transplants and platelet transfusions.

Q: Plasma is considered a Newtonian fluid because:

Viscosity is independent of shear stress.. ### Explanation **Core Concept: Newtonian vs. Non-Newtonian Fluids** A **Newtonian fluid** is defined as a fluid whose viscosity remains constant regardless of the forces applied to it. In mathematical terms, the shear stress is linearly proportional to the shear rate, meaning the ratio between them (**viscosity**) is a constant value. **Plasma** is considered a Newtonian fluid because it is essentially a solution of water, electrolytes, and proteins. Unlike whole blood, it does not contain suspended cellular elements (like RBCs) that can aggregate or deform. Therefore, its **viscosity is independent of shear stress** (Option D). **Analysis of Incorrect Options:** * **Option A & C:** In Newtonian fluids, viscosity is a constant property of the fluid itself (at a given temperature). It does not increase or decrease based on the flow velocity or pressure (shear stress). * **Option B:** Viscosity is the *ratio* of shear stress to shear rate ($\eta = \tau / \gamma$), not equal to the shear rate itself. **High-Yield NEET-PG Pearls:** 1. **Whole Blood is Non-Newtonian:** Unlike plasma, whole blood is **pseudoplastic (shear-thinning)**. At low shear rates (slow flow), RBCs form "Rouleaux" stacks, increasing viscosity. At high shear rates (fast flow), RBCs disperse and deform, decreasing viscosity. 2. **Fahraeus-Lindqvist Effect:** This refers to the decrease in apparent viscosity of blood as it flows through very small capillaries (radii < 1.5 mm) due to the "cell-free marginal layer." 3. **Key Determinants:** The primary determinant of **plasma** viscosity is the concentration of plasma proteins (especially **Fibrinogen**). The primary determinant of **whole blood** viscosity is the **Hematocrit**.

Question 1

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

Accepted Answer

0.48%

Answer

0.33%

Answer

0.90%

Answer

1.20%

Question 2

Which of the following are Vitamin K dependent clotting factors?

Accepted Answer

Factor IX & X

Answer

Factor III & XI

Answer

Factor V & VIII

Answer

Factor XI & XIII

Question 3

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

Accepted Answer

Polychromatic erythroblast

Answer

Basophilic erythroblast

Answer

Orthochromatic erythroblast

Answer

Reticulocyte

Question 4

Serotonin is mainly secreted by which of the following?

Accepted Answer

Platelets

Answer

Mast cells

Answer

Neutrophils

Answer

Macrophages

Question 5

Which test measures the extrinsic pathway of blood clotting?

Accepted Answer

Prothrombin time

Answer

Activated partial thromboplastin time

Answer

Bleeding time

Answer

Clotting time

Question 6

The process whereby white blood cells can squeeze through pores in capillary walls is called what?

Accepted Answer

Diapedesis

Answer

Diffusion

Answer

Osmosis

Answer

Pinocytosis

Question 7

Delay in blood coagulation results from which of the following?

Accepted Answer

Heparin

Answer

Human thrombin

Answer

Ferric chloride

Answer

Vitamin K

Question 8

Why does albumin provide the maximum contribution to oncotic pressure generation?

Accepted Answer

Low molecular weight, high concentration

Answer

High molecular weight, low concentration

Answer

High molecular weight, high concentration

Answer

Low molecular weight, low concentration

Question 9

Which cell type lacks Human Leukocyte Antigen (HLA)?

Accepted Answer

Red blood cell

Answer

Monocyte

Answer

Thrombocyte

Answer

Neutrophil

Question 10

Plasma is considered a Newtonian fluid because:

Accepted Answer

Viscosity is independent of shear stress.

Answer

Viscosity is directly proportional to shear stress.

Answer

Viscosity is equal to shear rate.

Answer

Viscosity is inversely related to shear stress.

Blood and Immunity — MCQs

Blood and Immunity — MCQs

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