Blood and Immunity Practice Questions

Q: Which of the following statements about erythropoietin is FALSE?

It results in a decrease in reticulocyte count. **Explanation:** Erythropoietin (EPO) is a glycoprotein hormone produced primarily by the peritubular interstitial cells of the kidney in response to hypoxia [1]. Its primary function is to stimulate the proliferation and differentiation of erythroid progenitor cells in the bone marrow. **Why Option B is the Correct (False) Statement:** Erythropoietin stimulates the bone marrow to produce more red blood cells. As erythropoiesis increases, there is an accelerated release of immature red blood cells, known as **reticulocytes**, into the peripheral circulation. Therefore, EPO administration results in an **increase** (not a decrease) in the reticulocyte count. This "reticulocytosis" is a hallmark of the bone marrow's response to EPO. **Analysis of Incorrect Options:** * **Option A:** EPO is the standard treatment for anemia associated with **chronic renal failure**, where the kidneys fail to produce sufficient endogenous hormone [1]. * **Option C:** By stimulating the body’s own production of RBCs, exogenous EPO effectively raises hemoglobin levels, thereby **decreasing the clinical requirement for blood transfusions** [1]. * **Option D:** **Hypertension** is a well-documented side effect of EPO therapy, thought to be caused by an increase in total peripheral resistance due to rising hematocrit and direct endothelin-mediated vasoconstriction. **NEET-PG High-Yield Pearls:** * **Site of Production:** 85% Kidney (Peritubular interstitial cells), 15% Liver (Kupffer cells/Hepatocytes) [1]. * **Mechanism:** Binds to JAK2-STAT receptors on erythroid precursors (CFU-E). * **Side Effects:** Hypertension, increased risk of thromboembolism (stroke/MI), and rarely, Pure Red Cell Aplasia (PRCA). * **Trigger:** Hypoxia-Inducible Factor (HIF-1ʹ) is the transcription factor that upregulates EPO gene expression during low oxygen states.

Q: Which of the following cells is not involved in leucopoiesis?

Normoblast. **Explanation:** The process of blood cell formation is collectively called **Hemopoiesis**. This is further divided into **Leucopoiesis** (formation of White Blood Cells) and **Erythropoiesis** (formation of Red Blood Cells). **Why Normoblast is the correct answer:** A **Normoblast** (also known as an erythroblast) is a nucleated precursor cell in the **Erythropoietic** lineage. It represents the stages of RBC development (Proerythroblast → Early/Intermediate/Late Normoblast → Reticulocyte → Erythrocyte). Since it specifically leads to the production of Red Blood Cells, it is not involved in Leucopoiesis. **Analysis of incorrect options (Leucopoietic lineage):** The options A, C, and D are all stages in **Granulopoiesis** (a subtype of leucopoiesis that forms Neutrophils, Eosinophils, and Basophils): * **Myeloblast:** The first identifiable committed precursor in the granulocytic series. * **Myelocyte:** The stage where specific (secondary) granules first appear, allowing for the differentiation between neutrophil, eosinophil, and basophil lines. It is the last stage capable of mitosis. * **Metamyelocyte:** A post-mitotic stage characterized by a kidney-shaped (indented) nucleus, leading eventually to the "Band" form and then the mature segmented leucocyte. **High-Yield Clinical Pearls for NEET-PG:** * **Shift to the left:** The presence of increased immature leucocytes (like metamyelocytes and band cells) in the peripheral blood, usually indicating acute infection or inflammation. * **Myelocyte:** Remember this as the "stage of differentiation" because specific granules appear here. * **Reticulocyte count:** The most reliable index of effective erythropoiesis (normal range: 0.5–2.5%). * **Site of Hemopoiesis:** In adults, it occurs primarily in the red bone marrow of membranous bones (vertebrae, sternum, ribs, and iliac crest).

Q: Platelets contain which of the following organelles?

Both mitochondria and lysozymes. **Explanation:** Platelets (thrombocytes) are small, disc-shaped, **anucleated** cell fragments derived from the fragmentation of megakaryocytes in the bone marrow. **1. Why Option B is Correct:** Although platelets lack a nucleus, they are metabolically active and contain several specialized organelles and structures: * **Mitochondria:** Platelets require energy (ATP) for processes like shape change, granule secretion, and clot retraction. They possess a small number of mitochondria to perform aerobic respiration. * **Lysozymes:** These are found within the **lambda (λ) granules** of platelets. They contain hydrolytic enzymes that aid in the dissolution of blood clots and phagocytic activities during the inflammatory response. **2. Analysis of Incorrect Options:** * **Options A & C (Nucleus):** These are incorrect because platelets are **anucleated**. They cannot undergo mitosis or de novo protein synthesis (though they carry residual mRNA from megakaryocytes). * **Option D (Only mitochondria):** This is incorrect because it ignores the presence of other vital organelles. In addition to mitochondria and lysozymes, platelets contain **Alpha granules** (containing clotting factors like Fibrinogen and vWF) and **Dense granules** (containing ADP, ATP, Serotonin, and Calcium). **Clinical Pearls for NEET-PG:** * **Life Span:** 7–10 days. * **Storage:** Approximately 1/3rd of the total platelet pool is sequestered in the **Spleen**. * **Granule Deficiency:** * *Gray Platelet Syndrome:* Deficiency of Alpha granules. * *Hermansky-Pudlak Syndrome:* Deficiency of Dense granules. * **Key Surface Receptor:** **GpIIb/IIIa** is the most abundant receptor, essential for platelet aggregation via fibrinogen binding.

Q: Which test is used to evaluate platelet function?

Bleeding time. **Explanation:** The evaluation of hemostasis is divided into primary and secondary hemostasis. **Bleeding Time (BT)** is the standard clinical test used to evaluate **primary hemostasis**, which depends on the number and functional integrity of platelets and the vessel wall. * **Why A is Correct:** When a small incision is made, platelets must adhere to the subendothelium, undergo activation, and aggregate to form a "platelet plug." If platelets are deficient in number (thrombocytopenia) or function (thrombocytopathy, e.g., Glanzmann’s thrombasthenia), the bleeding time is prolonged. * **Why B is Incorrect:** Prothrombin Time (PT) evaluates the **Extrinsic and Common pathways** of the coagulation cascade (Factors VII, X, V, II, and I). It is used to monitor Warfarin therapy. * **Why C is Incorrect:** While the Clot Retraction Test depends on platelet contractile proteins (thrombosthenin), it is a qualitative assessment of the final stage of clotting rather than a primary screening test for platelet function. * **Why D is Incorrect:** Thrombin Time (TT) measures the time taken for fibrinogen to convert to fibrin. It is prolonged in hypofibrinogenemia or in the presence of inhibitors like Heparin. **High-Yield Clinical Pearls for NEET-PG:** * **Normal Bleeding Time:** 2–7 minutes (Ivy’s method). * **Isolated Prolonged BT:** Seen in Von Willebrand Disease (vWD) and Bernard-Soulier Syndrome. Note: In vWD, aPTT may also be prolonged due to Factor VIII deficiency. * **Platelet Function Analyzer (PFA-100):** Now considered a more sensitive and reproducible "in vitro" replacement for the traditional Bleeding Time. * **Aspirin:** Irreversibly inhibits COX-1, prolonging BT for the lifespan of the platelet (approx. 7–10 days).

Q: All of the following factors are produced by hepatocytes except?

Von Willebrand factor. **Explanation:** The liver is the primary site for the synthesis of almost all coagulation factors. However, **Von Willebrand factor (vWF)** is a notable exception. **1. Why Von Willebrand Factor (vWF) is the correct answer:** Unlike most clotting factors, vWF is synthesized and secreted by **vascular endothelial cells** and **megakaryocytes**. Within endothelial cells, it is stored in specialized organelles called **Weibel-Palade bodies**, and in platelets, it is stored in **alpha-granules**. Its primary role is to mediate platelet adhesion to the subendothelial matrix at sites of vascular injury and to act as a carrier protein for Factor VIII. **2. Analysis of incorrect options:** * **Fibrinogen (Factor I) & Prothrombin (Factor II):** These are classic plasma proteins synthesized exclusively by **hepatocytes**. * **Factor VIII:** This is a high-yield "trap" for students. While Factor VIII was historically thought to be produced elsewhere, modern research confirms that the primary source of Factor VIII is the **sinusoidal endothelial cells** of the liver (and to a lesser extent, hepatocytes). Therefore, it is still considered a liver-derived factor. **3. High-Yield Clinical Pearls for NEET-PG:** * **Vitamin K Dependent Factors:** Factors II, VII, IX, and X, as well as Protein C and S, are synthesized in the liver and require Vitamin K for gamma-carboxylation. * **Factor VII:** Has the shortest half-life among all clotting factors; hence, the Prothrombin Time (PT) is the first to be prolonged in acute liver failure. * **The "Exception" Rule:** Remember that **vWF** and **Factor VIII (partially)** are produced by endothelial cells, but only vWF is completely independent of the liver's synthetic function. * **vWF Function:** It stabilizes Factor VIII in circulation; without vWF, Factor VIII is rapidly degraded.

Q: What is the primary function of von Willebrand factor (vWF)?

Platelet adhesion. **Explanation:** The primary function of **von Willebrand factor (vWF)** is to facilitate **platelet adhesion** to the subendothelial collagen at the site of vascular injury. It acts as a molecular bridge between the exposed collagen and the **GP Ib-IX-V receptor** complex on the platelet surface. This is the crucial first step in primary hemostasis. **Analysis of Options:** * **A. Platelet Adhesion (Correct):** vWF is essential for tethering platelets to the damaged vessel wall, especially under conditions of high shear stress (e.g., in small arteries). * **B. Platelet Aggregation:** This refers to platelets sticking to *each other*. While vWF can assist, the primary mediator of aggregation is **Fibrinogen**, which binds to the **GP IIb/IIIa** receptors on activated platelets. * **C. Clot Formation:** This is the end result of the coagulation cascade (secondary hemostasis). While vWF stabilizes Factor VIII, it is not the "primary" mechanism of the fibrin clot itself. * **D. Fibrinolysis:** This is the process of breaking down a clot (mediated by Plasmin). vWF is a pro-coagulant factor and does not participate in fibrinolysis. **High-Yield Clinical Pearls for NEET-PG:** * **Synthesis:** vWF is synthesized in **endothelial cells** (stored in **Weibel-Palade bodies**) and **megakaryocytes** (stored in **α-granules** of platelets). * **Factor VIII Carrier:** vWF serves as a carrier protein for Factor VIII, protecting it from rapid degradation. Therefore, von Willebrand Disease (vWD) often presents with a secondary deficiency of Factor VIII. * **Diagnostic Test:** The **Ristocetin cofactor assay** is used to measure vWF activity; Ristocetin induces vWF-mediated platelet agglutination. * **Treatment:** **Desmopressin (DDAVP)** stimulates the release of vWF from endothelial stores.

Q: Erythropoietin is secreted mainly by:

Kidney. **Explanation:** **1. Why the Kidney is Correct:** Erythropoietin (EPO) is a glycoprotein hormone essential for erythropoiesis. In adults, approximately **85–90%** of EPO is synthesized and secreted by the **peritubular interstitial fibroblasts** (specifically the extraglomerular mesangial cells and cells in the renal cortex/outer medulla). These cells act as oxygen sensors; when renal tissue hypoxia occurs (detected via HIF-1α), EPO production increases to stimulate the bone marrow to produce more red blood cells. **2. Why Other Options are Incorrect:** * **Liver:** The liver is the primary source of EPO during **fetal life**. In adults, it contributes only about **10–15%** of total EPO production (primarily via hepatocytes and Ito cells). It cannot compensate sufficiently if the kidneys fail. * **Brain:** While small amounts of EPO are produced in the brain (astrocytes) to act as a neuroprotective agent, it does not contribute to systemic erythropoiesis. * **RBC:** Red blood cells are the *target* of EPO action (specifically the erythroid progenitor cells in the bone marrow), not the site of production. **3. Clinical Pearls for NEET-PG:** * **Chronic Kidney Disease (CKD):** The most common cause of anemia in CKD is the deficiency of EPO due to the destruction of peritubular interstitial cells. * **Stimulus:** The primary stimulus for EPO release is **hypoxia** (low $PO_2$), not anemia itself. * **Polycythemia:** Certain tumors, such as **Renal Cell Carcinoma (RCC)** and Hepatocellular Carcinoma, can secrete ectopic EPO, leading to secondary polycythemia. * **Recombinant EPO:** Used clinically to treat anemia in CKD patients and those undergoing chemotherapy.

Q: What substance is released by mast cells?

Histamine. **Explanation:** **Correct Answer: C. Histamine** Mast cells are key effector cells of the innate immune system, primarily located in mucosal and cutaneous tissues. They contain numerous basophilic granules rich in pre-formed inflammatory mediators. Upon activation (typically via IgE cross-linking on the FceRI receptor), mast cells undergo **degranulation**, releasing **Histamine**. Histamine acts on H1 receptors to cause vasodilation, increased vascular permeability, and bronchial smooth muscle contraction, mediating Type I hypersensitivity reactions. **Analysis of Incorrect Options:** * **A. IFN-γ (Interferon-gamma):** This is a pro-inflammatory cytokine primarily secreted by **Th1 cells, CD8+ cytotoxic T cells, and Natural Killer (NK) cells**. Its main role is macrophage activation. * **B. IL-5 (Interleukin-5):** This cytokine is primarily produced by **Th2 cells**. Its specific function is the recruitment, activation, and survival of **eosinophils**. * **D. Lysozyme:** This is an antibacterial enzyme found in secretions like tears, saliva, and mucus, and is also present in the cytoplasmic granules of **neutrophils and macrophages**. It works by cleaving the peptidoglycan layer of bacterial cell walls. **High-Yield Clinical Pearls for NEET-PG:** * **Markers:** **Tryptase** is the most specific marker for mast cell activation (useful in diagnosing anaphylaxis). * **Origin:** Mast cells originate from CD34+ hematopoietic stem cells in the bone marrow but mature only after reaching peripheral tissues. * **Mediators:** Besides histamine, mast cells release **Heparin** (anticoagulant), **ECF-A** (Eosinophil Chemotactic Factor of Anaphylaxis), and newly synthesized mediators like **Leukotrienes (C4, D4, E4)** and **Prostaglandin D2**.

Q: What does the CD4 count primarily refer to?

T helper cells. **Explanation:** **Correct Answer: A. T helper cells** The CD4 (Cluster of Differentiation 4) molecule is a glycoprotein found primarily on the surface of **Helper T lymphocytes**. These cells play a central role in the adaptive immune system by recognizing antigens presented by MHC class II molecules on antigen-presenting cells (APCs). Once activated, they secrete cytokines that coordinate the activity of other immune cells. **Analysis of Incorrect Options:** * **B. B cells:** B cells are characterized by the presence of CD19, CD20, and CD21 markers. They do not express CD4; instead, they function in humoral immunity by producing antibodies. * **C. Cytotoxic cells:** These are T cells that express the **CD8** marker. They recognize antigens presented by MHC class I molecules and are responsible for directly killing virally infected or tumor cells. * **D. Both B and T cells:** CD4 is specific to a subset of T cells (Helper cells) and is not found on B cells. **High-Yield Clinical Pearls for NEET-PG:** * **HIV Pathogenesis:** The HIV virus specifically targets CD4+ cells by binding to the CD4 molecule via its **gp120** envelope protein. * **AIDS Definition:** A CD4 count below **200 cells/mm³** (or a CD4 percentage <14%) is a diagnostic criterion for AIDS. * **MHC Restriction Rule:** Remember the "Rule of 8": CD4 cells interact with MHC II (4 × 2 = 8), while CD8 cells interact with MHC I (8 × 1 = 8). * **Normal Range:** The typical adult CD4 count ranges from 500 to 1,500 cells/mm³.

Q: Which of the following has the greatest effect on the ability of blood to transport oxygen?

Amount of hemoglobin in the blood. **Explanation:** The transport of oxygen in the blood occurs in two forms: **dissolved in plasma** and **bound to hemoglobin (Hb)**. Under normal physiological conditions, approximately **98.5%** of oxygen is transported bound to hemoglobin, while only **1.5%** is dissolved in plasma. **Why Option B is Correct:** The oxygen-carrying capacity of blood is directly proportional to the hemoglobin concentration. Each gram of hemoglobin can bind approximately **1.34 ml of oxygen** (Hüfner's constant). Because the vast majority of oxygen is carried by Hb, any change in its concentration (e.g., anemia or polycythemia) has the most significant impact on the total oxygen content of the blood compared to other factors. **Why Other Options are Incorrect:** * **Option A:** The solubility of oxygen in plasma is extremely low (0.003 ml O2/100ml blood/mmHg). Even at a high PaO2 of 100 mmHg, only 0.3 ml of O2 is dissolved, which is insufficient to meet tissue demands. * **Option C:** The pH of plasma affects the **affinity** of hemoglobin for oxygen (Bohr Effect). While a decrease in pH shifts the dissociation curve to the right (facilitating unloading), it does not change the total carrying *capacity* as significantly as the amount of Hb itself. * **Option D:** CO2 content affects oxygen binding via the carbamino effect and pH changes, but like pH, it primarily influences the loading/unloading kinetics rather than the total transport capacity. **High-Yield Clinical Pearls for NEET-PG:** * **Oxygen Content Formula:** $CaO_2 = (1.34 \times Hb \times SaO_2) + (0.003 \times PaO_2)$. This formula highlights that Hb is the primary determinant. * **Anemic Hypoxia:** In anemia, PaO2 (dissolved O2) is normal, but the total oxygen content is low because of decreased Hb. * **Carbon Monoxide (CO) Poisoning:** CO does not reduce the amount of Hb, but it reduces the *functional* Hb available for O2 transport and shifts the curve to the left.

Question 1

Which of the following statements about erythropoietin is FALSE?

Accepted Answer

It results in a decrease in reticulocyte count

Answer

It is used for the treatment of anemia due to chronic renal failure

Answer

It decreases the requirement of blood transfusion

Answer

It can cause hypertension

Question 2

Which of the following cells is not involved in leucopoiesis?

Accepted Answer

Normoblast

Answer

Myeloblast

Answer

Myelocyte

Answer

Metamyelocyte

Question 3

Platelets contain which of the following organelles?

Accepted Answer

Both mitochondria and lysozymes

Answer

Both mitochondria and nucleus

Answer

Both nucleus and lysozymes

Answer

Only mitochondria

Question 4

Which test is used to evaluate platelet function?

Accepted Answer

Bleeding time

Answer

Prothrombin time

Answer

Clot retraction test

Answer

Thrombin time

Question 5

All of the following factors are produced by hepatocytes except?

Accepted Answer

Von Willebrand factor

Answer

Fibrinogen

Answer

Prothrombin

Answer

Factor VIII

Question 6

What is the primary function of von Willebrand factor (vWF)?

Accepted Answer

Platelet adhesion

Answer

Platelet aggregation

Answer

Clot formation

Answer

Fibrinolysis

Question 7

Erythropoietin is secreted mainly by:

Accepted Answer

Kidney

Answer

Liver

Answer

Brain

Answer

RBC

Question 8

What substance is released by mast cells?

Accepted Answer

Histamine

Answer

IFN-g

Answer

IL-5

Answer

Lysozyme

Question 9

What does the CD4 count primarily refer to?

Accepted Answer

T helper cells

Answer

B cells

Answer

Cytotoxic cells

Answer

Both B and T cells

Question 10

Which of the following has the greatest effect on the ability of blood to transport oxygen?

Accepted Answer

Amount of hemoglobin in the blood

Answer

Capacity of the blood to dissolve oxygen

Answer

pH of plasma

Answer

CO2 content of red blood cells

Blood and Immunity — MCQs

Blood and Immunity — MCQs

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