Blood and Immunity Practice Questions

Q: Factor Xa is necessary for the conversion of prothrombin to thrombin in which pathway?

As part of both extrinsic and intrinsic pathways. ### Explanation The coagulation cascade is divided into the **Intrinsic**, **Extrinsic**, and **Common pathways**. The correct answer is **C** because Factor Xa is the central protease of the **Common Pathway**, where both the intrinsic and extrinsic pathways converge. **1. Why Option C is Correct:** The conversion of prothrombin (Factor II) to thrombin (Factor IIa) is the hallmark of the Common Pathway. This process is catalyzed by the **Prothrombinase Complex**, which consists of **Factor Xa** (the enzyme), Factor Va (the cofactor), Calcium ions, and phospholipids. Since both the Intrinsic pathway (via the Tenase complex) and the Extrinsic pathway (via Tissue Factor-VIIa) aim to activate Factor X into Factor Xa, Factor Xa is essential for thrombin formation regardless of how the cascade was initiated. **2. Why Other Options are Wrong:** * **Options A & B:** These are incorrect because they are too restrictive. While the pathways start differently (Intrinsic via Factor XII; Extrinsic via Tissue Factor), they are not independent silos. They both terminate by activating Factor X. * **Option D:** This is factually incorrect. Factor Xa is a physiological requirement for normal hemostasis, not a compensatory mechanism for inhibition. **3. NEET-PG Clinical Pearls & High-Yield Facts:** * **The Prothrombinase Complex:** Remember the mnemonic **"5, 10, 2, 1"** (Factors V, X, II, I) to represent the sequence of the Common Pathway. * **Rate-Limiting Step:** The activation of Factor X is often considered the rate-limiting step of coagulation. * **Pharmacology Link:** **Rivaroxaban** and **Apixaban** are Direct Factor Xa inhibitors (DOACs) that block the common pathway, preventing thrombin generation. * **Lab Correlation:** The **PT (Prothrombin Time)** measures the Extrinsic and Common pathways, while **aPTT** measures the Intrinsic and Common pathways. Both will be prolonged if Factor X is deficient.

Q: All of the following increase the 2,3-DPG concentration of red blood cells except?

Acidosis. **Explanation:** The concentration of **2,3-Bisphosphoglycerate (2,3-DPG)** in red blood cells is a critical regulator of hemoglobin’s affinity for oxygen. 2,3-DPG is produced via the **Rapoport-Luebering shunt**, a side pathway of glycolysis. **Why Acidosis is the Correct Answer:** The rate-limiting enzyme for 2,3-DPG production is **phosphofructokinase (PFK)**. Acidosis (low pH) inhibits PFK activity, thereby decreasing glycolysis and the subsequent production of 2,3-DPG. Conversely, **alkalosis** stimulates 2,3-DPG production. This is a physiological compensatory mechanism: while acidosis itself shifts the oxygen-dissociation curve (ODC) to the right (Bohr effect), the resulting decrease in 2,3-DPG helps shift it back toward the left, stabilizing oxygen delivery. **Why the other options are incorrect:** * **Thyroid Hormones:** These increase the metabolic rate and stimulate red cell glycolysis, leading to an increase in 2,3-DPG. * **Growth Hormone:** This exerts an anabolic effect and stimulates erythropoiesis and RBC metabolism, increasing 2,3-DPG levels. * **Androgens:** Testosterone and other androgens stimulate the production of erythropoietin and directly enhance RBC glycolysis, raising 2,3-DPG concentrations. **High-Yield Clinical Pearls for NEET-PG:** * **ODC Shift:** Increased 2,3-DPG shifts the ODC to the **Right** (decreasing O2 affinity, favoring unloading to tissues). * **Mnemonic (CADET, face Right!):** Factors shifting the curve to the **Right** are **C**O2 increase, **A**cidosis, **D**PG increase, **E**xercise, and **T**emperature increase. * **Stored Blood:** 2,3-DPG levels drop in stored blood. Massive transfusions of old blood can cause a "Left Shift," impairing oxygen delivery to tissues. * **Fetal Hemoglobin (HbF):** HbF has a low affinity for 2,3-DPG, which is why its ODC is shifted to the **Left** compared to adult HbA.

Q: Which factor activates preaccelerin to Vila?

Tissue factor. **Explanation:** The question refers to the activation of **Factor VII** (proconvertin) into **Factor VIIa**. Note: There is a slight nomenclature nuance in the question; **Preaccelerin** is technically the name for **Factor V**, while **Factor VII** is Proconvertin. However, in the context of the extrinsic pathway initiation, the factor activated by **Tissue Factor (TF)** is Factor VII. 1. **Why Tissue Factor is correct:** The **Extrinsic Pathway** of coagulation is initiated when subendothelial **Tissue Factor (Factor III)** is exposed to the blood due to vascular injury. Tissue Factor acts as a high-affinity receptor and a mandatory cofactor for Factor VII. Upon binding to TF in the presence of calcium ions, Factor VII is rapidly converted into its active form, **Factor VIIa**. This TF-VIIa complex then activates Factors X and IX. 2. **Analysis of Incorrect Options:** * **Christmas Factor (Factor IX):** This is a component of the Intrinsic Pathway. It is activated by Factor XIa and, in turn, activates Factor X (with Factor VIIIa). * **Fibrinogen (Factor I):** This is the soluble precursor that is converted into insoluble **Fibrin** by Thrombin at the final stage of the common pathway. * **Prothrombin (Factor II):** This is the precursor to **Thrombin**. It is activated by the prothrombinase complex (Xa, Va, Ca²⁺, and phospholipids). **High-Yield Clinical Pearls for NEET-PG:** * **Factor VII** has the **shortest half-life** (approx. 4–6 hours) among all clotting factors. Therefore, it is the first factor to decrease in Vitamin K deficiency or liver disease, making **Prothrombin Time (PT)** the earliest indicator of liver dysfunction. * **Factor V (Preaccelerin)** is a cofactor for Factor Xa; its deficiency or mutation (Factor V Leiden) is a common cause of inherited thrombophilia. * The **Extrinsic Pathway** is monitored by **PT/INR**, while the **Intrinsic Pathway** is monitored by **aPTT**.

Q: Which of the following cells forms Major Basic Protein?

Eosinophil. **Explanation:** **Correct Option: D (Eosinophil)** Eosinophils are specialized granulocytes primarily involved in defending the body against parasitic infections and modulating allergic reactions. The characteristic acidophilic (pink) granules of eosinophils contain several cytotoxic proteins, the most abundant being **Major Basic Protein (MBP)**. MBP is highly toxic to helminths (parasites) as it disrupts their cell membranes. It also triggers the release of histamine from mast cells and basophils, contributing to the inflammatory response in conditions like bronchial asthma. **Why other options are incorrect:** * **A. Lymphocytes:** These are agranulocytes involved in adaptive immunity (B-cells and T-cells). They produce antibodies or cytokines, not MBP. * **B. Basophils:** While they share some functional similarities with eosinophils in allergies, their granules primarily contain **histamine, heparin, and serotonin**. * **C. Neutrophils:** These are the primary cells for acute bacterial defense. Their granules contain enzymes like **myeloperoxidase (MPO)**, lysozyme, and alkaline phosphatase, but not MBP. **High-Yield Clinical Pearls for NEET-PG:** * **Eosinophil Granule Contents:** Besides MBP, they contain Eosinophil Cationic Protein (ECP), Eosinophil Peroxidase (EPO), and Eosinophil-Derived Neurotoxin (EDN). * **Charcot-Leyden Crystals:** Found in the sputum of asthmatics (Curschmann spirals), these crystals are formed from the breakdown of eosinophil membrane proteins (**Galectin-10**). * **Eosinophilia:** Classically seen in **NAACP**: **N**eoplasia, **A**llergy/Asthma, **A**ddison’s disease, **C**onnective tissue disorders, and **P**arasitic infections.

Q: What is the normal CD4 cell count?

1000 cells/cu.mm. **Explanation:** The CD4+ T-lymphocyte count is a primary indicator of immune system health. In a healthy adult, the normal range for CD4 cells is typically between **500 and 1,500 cells/cu.mm**. Among the given options, **1,000 cells/cu.mm** (Option B) represents the most accurate median value for a healthy individual. These cells are "helper" T-cells that coordinate the immune response by releasing cytokines and activating other immune cells. **Analysis of Options:** * **Option A (500 cells/cu.mm):** While this is the lower limit of the normal range, it is not the standard "average" used in clinical definitions. * **Option C (200 cells/cu.mm):** This is a critical clinical threshold. A count below 200 cells/cu.mm is the diagnostic criterion for **AIDS** in HIV-positive individuals, indicating severe immunodeficiency and high risk for opportunistic infections. * **Option D (700 cells/cu.mm):** This falls within the normal range but is less representative of the standard physiological mean (1,000) taught in core physiology and pathology textbooks. **High-Yield Clinical Pearls for NEET-PG:** * **CD4:CD8 Ratio:** In healthy individuals, the normal ratio is approximately **2:1**. In HIV/AIDS, this ratio is inverted (<1:1). * **Prognostic Marker:** The CD4 count is the best predictor of immediate risk for opportunistic infections (e.g., *Pneumocystis jirovecii* occurs when CD4 < 200). * **Physiological Variation:** CD4 counts can fluctuate based on diurnal rhythm (lowest in the morning, highest in the evening), stress, and acute infections.

Q: What is embryonic hemoglobin?

Gower hemoglobin. ### Explanation **Correct Answer: C. Gower hemoglobin** **Why it is correct:** Embryonic hemoglobin refers to the hemoglobin variants synthesized during the first trimester of intrauterine life (specifically from the 3rd to the 10th week of gestation). These are produced in the **yolk sac** before the liver and bone marrow take over erythropoiesis. There are three primary types of embryonic hemoglobin: 1. **Gower 1:** ($\zeta_2\epsilon_2$) 2. **Gower 2:** ($\alpha_2\epsilon_2$) 3. **Portland:** ($\zeta_2\gamma_2$) Since Gower hemoglobin is the classic representative of this stage, it is the correct choice. **Why other options are incorrect:** * **A. Adult hemoglobin (HbA):** This consists of two alpha ($\alpha$) and two beta ($\beta$) chains ($\alpha_2\beta_2$). It begins to appear at around 30 weeks of gestation but only becomes the predominant form after birth (around 6 months of age). * **B. Fetal hemoglobin (HbF):** This consists of two alpha ($\alpha$) and two gamma ($\gamma$) chains ($\alpha_2\gamma_2$). It is the primary hemoglobin from the late first trimester until birth. It has a higher affinity for oxygen than HbA to facilitate oxygen transfer across the placenta. **High-Yield Clinical Pearls for NEET-PG:** * **Site of Erythropoiesis:** Yolk sac (3–10 weeks) $\rightarrow$ Liver (6 weeks–birth; peak at 4 months) $\rightarrow$ Spleen (10–28 weeks) $\rightarrow$ Bone Marrow (from 18 weeks onwards). * **Chain Transition:** The $\zeta$ (zeta) and $\epsilon$ (epsilon) chains are replaced by $\alpha$ (alpha) and $\gamma$ (gamma) chains as the fetus develops. * **P50 Value:** HbF has a lower P50 (approx. 19 mmHg) compared to HbA (approx. 27 mmHg), reflecting its higher oxygen affinity. * **HbA2:** A minor adult hemoglobin ($\alpha_2\delta_2$) normally comprising <3% of total hemoglobin.

Q: Which plasma protein is NOT normally synthesized in the liver?

Angiotensin-converting enzyme. **Explanation** The liver is the primary factory for plasma proteins, synthesizing nearly all of them except for immunoglobulins (produced by plasma cells) and specific enzymes produced by vascular endothelium. **1. Why Angiotensin-converting enzyme (ACE) is the correct answer:** ACE is a glycoprotein primarily synthesized and located on the **luminal surface of vascular endothelial cells**, particularly within the **pulmonary capillaries**. While it is found in various tissues (kidneys, heart), the lungs are the major site of conversion for Angiotensin I to Angiotensin II. Because it is an endothelial product rather than a hepatic one, it is the correct exception. **2. Analysis of Incorrect Options:** * **Angiotensin (Angiotensinogen):** Angiotensinogen is the precursor protein of the RAAS pathway. It is synthesized and secreted constitutively into the plasma exclusively by the **liver**. * **C-reactive protein (CRP):** This is a classic "Acute Phase Reactant." Its synthesis is induced in the **hepatocytes** in response to inflammatory cytokines like IL-6. * **Albumin:** This is the most abundant plasma protein and is synthesized solely by the **liver**. It serves as a marker of hepatic synthetic function. **High-Yield Clinical Pearls for NEET-PG:** * **Site of Synthesis:** All plasma proteins are synthesized in the liver EXCEPT Gamma-globulins (Plasma cells), ACE (Endothelium), and von Willebrand Factor (Endothelium/Megakaryocytes). * **ACE Inhibitors:** Drugs like Enalapril and Ramipril target this enzyme to treat hypertension and heart failure. * **Negative Acute Phase Reactants:** Remember that while CRP goes up during inflammation, **Albumin and Transferrin** levels decrease (Negative APRs).

Q: Thromboxane is produced by which of the following cells?

Platelets. **Explanation:** **Correct Answer: A. Platelets** Thromboxane A2 (TXA2) is a potent vasoconstrictor and a key mediator of platelet aggregation. It is synthesized from arachidonic acid via the **Cyclooxygenase (COX-1) pathway**. Platelets contain the enzyme **thromboxane synthase**, which converts Prostaglandin H2 (PGH2) into Thromboxane A2. Once released, TXA2 acts on G-protein coupled receptors to increase intracellular calcium, leading to platelet shape change and degranulation, facilitating the formation of a primary hemostatic plug. **Why other options are incorrect:** * **B. Leukocytes:** These cells primarily produce **Leukotrienes** (via the Lipoxygenase/LOX pathway) and various cytokines involved in the inflammatory response rather than thromboxane. * **C. Vessel wall:** Endothelial cells of the vessel wall primarily produce **Prostacyclin (PGI2)**. PGI2 acts as a physiological antagonist to TXA2; it causes vasodilation and inhibits platelet aggregation, maintaining blood fluidity under normal conditions. * **D. RBCs:** Red blood cells lack the enzymatic machinery (like COX-1 and thromboxane synthase) required for the synthesis of eicosanoids like thromboxane. **High-Yield Clinical Pearls for NEET-PG:** * **Aspirin Mechanism:** Low-dose aspirin irreversibly inhibits COX-1 in platelets. Since platelets are anucleated and cannot synthesize new enzymes, the inhibition of TXA2 lasts for the entire lifespan of the platelet (approx. 7–10 days). * **TXA2 vs. PGI2 Balance:** Hemostasis depends on the balance between TXA2 (pro-thrombotic, from platelets) and PGI2 (anti-thrombotic, from endothelium). * **Vasoactive properties:** TXA2 is a potent **vasoconstrictor**, whereas PGI2 is a potent **vasodilator**.

Question 1

Factor Xa is necessary for the conversion of prothrombin to thrombin in which pathway?

Accepted Answer

As part of both extrinsic and intrinsic pathways

Answer

Only in the extrinsic pathway

Answer

Only in the intrinsic pathway

Answer

Only if the normal blood clotting cascade is inhibited

Question 2

All of the following increase the 2,3-DPG concentration of red blood cells except?

Accepted Answer

Acidosis

Answer

Thyroid hormones

Answer

Growth hormone

Answer

Androgen

Question 3

Which factor activates preaccelerin to Vila?

Accepted Answer

Tissue factor

Answer

Christmas factor

Answer

Fibrinogen

Answer

Prothrombin

Question 4

Which of the following cells forms Major Basic Protein?

Accepted Answer

Eosinophil

Answer

Lymphocyte

Answer

Basophil

Answer

Neutrophil

Question 5

Thrombosthenin is a:

Accepted Answer

Coagulation factor

Answer

Contractile protein

Answer

A thrombosis promoting protein

Answer

A protein regulating platelet production

Question 6

What is the normal CD4 cell count?

Accepted Answer

1000 cells/cu.mm

Answer

500 cells/cu.mm

Answer

200 cells/cu.mm

Answer

700 cells/cu.mm

Question 7

All of the following occur when the blood flows through the capillaries except:

Accepted Answer

Hb curve shift to the left

Answer

Increase in hematocrit

Answer

Decreased protein content

Answer

Decrease in pH

Question 8

What is embryonic hemoglobin?

Accepted Answer

Gower hemoglobin

Answer

Adult hemoglobin

Answer

Fetal hemoglobin

Answer

None of the above

Question 9

Which plasma protein is NOT normally synthesized in the liver?

Accepted Answer

Angiotensin-converting enzyme

Answer

Angiotensin

Answer

C-reactive protein

Answer

Albumin

Question 10

Thromboxane is produced by which of the following cells?

Accepted Answer

Platelets

Answer

Leukocytes

Answer

Vessel wall

Answer

RBCs

Blood and Immunity — MCQs

Blood and Immunity — MCQs

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