Blood and Immunity Practice Questions

Q: Which of the following is a common step in the coagulation pathway?

Activation of factor X. ### Explanation The coagulation cascade is divided into three pathways: the **Intrinsic**, **Extrinsic**, and **Common** pathways. **Why Option D is Correct:** The **Common Pathway** begins with the activation of **Factor X (Stuart-Prower factor)**. Both the intrinsic and extrinsic pathways converge at this point. Once Factor X is activated to **Xa** (by the Tenase complexes), it combines with Factor Va, calcium, and phospholipids to form the **Prothrombinase complex**. This complex converts Prothrombin (II) into Thrombin (IIa), which ultimately converts Fibrinogen (I) into a stable Fibrin clot (Ia). Therefore, Factor X activation is the definitive "common step." **Analysis of Incorrect Options:** * **Option A (Factor VII):** This is unique to the **Extrinsic pathway**. It is activated by Tissue Factor (Factor III) following vascular injury. * **Options B & C (Factors VIII & IX):** These are components of the **Intrinsic pathway**. Factor IXa, along with its cofactor VIIIa, forms the "Intrinsic Tenase complex" to activate Factor X. Deficiencies in these lead to Hemophilia A and B, respectively. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Common Pathway:** "1 × 2 × 5 = 10" (Factors I, II, V, and X are involved). * **Rate-limiting step:** The conversion of Prothrombin to Thrombin is the most critical rate-limiting step in thrombus formation. * **Monitoring:** The Extrinsic pathway is monitored by **PT/INR** (Warfarin), while the Intrinsic pathway is monitored by **aPTT** (Heparin). * **Vitamin K Dependent Factors:** II, VII, IX, and X (plus Protein C and S). Note that Factor VII has the shortest half-life.

Q: A middle-aged man's blood sample shows a hematocrit of 45% and biconcave red blood cells. The biconcavity of RBCs is a function of which of the following?

Spectrin. **Explanation:** The biconcave shape of the Red Blood Cell (RBC) is crucial for its function, providing a high surface-area-to-volume ratio for gas exchange and the flexibility needed to squeeze through narrow capillaries. **Why Spectrin is Correct:** **Spectrin** is the primary structural protein of the RBC cytoskeleton. It forms a hexagonal meshwork on the inner surface of the plasma membrane. It acts as a "molecular spring," providing the structural integrity and elasticity required to maintain the biconcave shape. While other proteins assist in anchoring, the actual scaffold that dictates the shape is the spectrin network. **Analysis of Incorrect Options:** * **Ankyrin:** This is an anchoring protein. Its primary role is to link the spectrin network to the transmembrane protein, Band 3. While a deficiency in ankyrin leads to shape changes (like Spherocytosis), it is not the structural framework itself. * **Band 3 Protein:** This is a major integral membrane protein that functions as an anion exchanger (Chloride-Bicarbonate shift). It serves as an attachment site for the cytoskeleton but does not determine the biconcave geometry. * **Glycophorin-C:** This is a sialoglycoprotein that provides the RBC with a negative surface charge (zeta potential) to prevent aggregation. It anchors the membrane to the cytoskeleton via Protein 4.1 but is not the primary determinant of shape. **NEET-PG High-Yield Pearls:** * **Hereditary Spherocytosis:** Most commonly caused by a deficiency in **Ankyrin** (most common) or **Spectrin**. * **Hereditary Elliptocytosis:** Most commonly due to a defect in **Spectrin** (specifically the inability of spectrin dimers to form tetramers). * **RBC Membrane:** It is a lipid bilayer with a "laminated" protein cytoskeleton. Remember: **Spectrin = Shape & Stability.**

Q: During the second trimester of pregnancy, in which organ does erythropoiesis primarily occur in the fetus?

Liver. ### Explanation The site of fetal erythropoiesis changes in a predictable chronological sequence, often remembered by the mnemonic **"Young Liver Synthesizes Blood."** **1. Why Liver is the Correct Answer:** During the **second trimester** (specifically from the 6th week to the 5th month), the **Liver** is the primary (dominant) site of erythropoiesis. While it begins around the 6th week of gestation, it reaches its peak activity during the second trimester before gradually declining as the bone marrow takes over. **2. Analysis of Incorrect Options:** * **B. Spleen:** The spleen acts as a secondary lymphoid and hematopoietic organ during the second trimester (roughly months 3 to 5), but its contribution is significantly less than that of the liver. * **C. Red bone marrow:** This becomes the primary site of erythropoiesis only during the **third trimester** (from the 7th month onwards) and remains the sole site after birth. * **D. Lymph nodes:** While lymph nodes can show minor hematopoietic activity during the fetal period, they are never the "primary" site for red blood cell production. **3. High-Yield Facts for NEET-PG:** * **Mesoblastic Stage (3–8 weeks):** Erythropoiesis begins in the **Yolk Sac** (specifically the blood islands). * **Hepatic Stage (6 weeks – Birth):** The Liver is the main site during the 2nd trimester. * **Myeloid Stage (18 weeks – Life):** Bone marrow starts at month 4-5 and becomes dominant by month 7. * **Fetal Hemoglobin (HbF):** It has a higher affinity for oxygen than adult hemoglobin (HbA) due to poor binding with 2,3-BPG, facilitating oxygen transfer across the placenta. * **Clinical Note:** If the bone marrow fails in adults (e.g., Myelofibrosis), the liver and spleen can resume blood cell production, a process called **Extramedullary Hematopoiesis**.

Q: What is the half-life of albumin?

20 days. **Explanation:** Albumin is the most abundant plasma protein, synthesized exclusively by the liver. The correct answer is **20 days** (Option D), which represents the average biological half-life of albumin in a healthy adult. **Why 20 days is correct:** Albumin is designed for long-term stability to maintain **plasma oncotic pressure** and serve as a carrier protein for hormones, drugs, and bilirubin. Its long half-life is primarily due to its interaction with the **neonatal Fc receptor (FcRn)**. This receptor protects albumin from lysosomal degradation by recycling it back into the circulation, a mechanism similar to how IgG antibodies are preserved. **Why other options are incorrect:** * **36-48 hours (Option A):** This is too short for albumin but is characteristic of proteins with rapid turnover, such as certain clotting factors (e.g., Factor VII). * **3-5 days (Option B):** This is the half-life of **Pre-albumin (Transthyretin)**. Because of its shorter half-life, pre-albumin is a more sensitive clinical indicator of acute nutritional status than albumin. * **5-10 days (Option C):** This range is incorrect for albumin; however, some globulins and specific transferrins fall within this window. **High-Yield Clinical Pearls for NEET-PG:** * **Nutritional Marker:** Due to its long half-life (20 days), serum albumin is a marker of **chronic** nutritional status or chronic liver disease, not acute changes. * **Oncotic Pressure:** Albumin provides approximately **70-80%** of the total plasma colloid osmotic pressure. * **Hypoalbuminemia:** Leads to a decrease in oncotic pressure, resulting in edema (e.g., in Nephrotic syndrome or Cirrhosis). * **Synthesis:** Approximately 10-15 grams of albumin are synthesized daily; synthesis is stimulated by thyroid hormone and inhibited by inflammatory cytokines (it is a **negative acute-phase reactant**).

Q: ABO antigens are not found in which of the following bodily fluids?

Cerebrospinal fluid (CSF). **Explanation:** The presence of ABO blood group antigens in body fluids is determined by the **Se (Secretor) gene**. Approximately 80% of the population are "secretors," meaning they possess the dominant Se allele, which allows for the expression of soluble A, B, and H antigens in various exocrine secretions. **1. Why CSF is the Correct Answer:** ABO antigens are primarily found in fluids produced by **exocrine glands**. The **Cerebrospinal Fluid (CSF)** is a specialized ultrafiltrate of plasma produced by the choroid plexus and is not an exocrine secretion. It lacks the soluble glycoproteins required to carry ABO antigens. Therefore, even in secretors, ABO antigens are **not found in the CSF**. **2. Analysis of Incorrect Options:** * **Saliva:** This is the most common fluid used to determine secretor status. Salivary glands (exocrine) secrete high concentrations of water-soluble ABO antigens. * **Semen and Sweat:** Both are products of exocrine glands (seminal vesicles/prostate and sweat glands, respectively). In secretors, these fluids contain detectable levels of ABO antigens. Other fluids include tears, breast milk, and amniotic fluid. **3. High-Yield Clinical Pearls for NEET-PG:** * **Secretor Status:** Controlled by the *FUT2* gene on chromosome 19. * **Non-secretors (20%):** These individuals have the genotype *sese* and do not have ABO antigens in their body fluids, though the antigens remain present on their red blood cells. * **Forensic Significance:** Detecting ABO antigens in stains (semen or saliva) at a crime scene can help in identifying or excluding suspects. * **Antigen Location:** Remember that ABO antigens are not just on RBCs; they are also found on vascular endothelium and most epithelial cells (hence their importance in solid organ transplants).

Q: What are the functions of cytoplasmic enzymes in Red Blood Cells?

Maintain pliability of the cell membrane. ### Explanation Mature Red Blood Cells (RBCs) lack a nucleus and mitochondria, making them entirely dependent on cytoplasmic enzymes for survival and function. These enzymes primarily drive **anaerobic glycolysis (Embden-Meyerhof pathway)** and the **Pentose Phosphate Pathway (PPP)**. **1. Why Option A is Correct:** The primary role of cytoplasmic enzymes is to generate **ATP** and **NADPH**. ATP is essential for fueling the Na⁺/K⁺-ATPase pumps, which regulate intracellular volume and osmotic pressure. By maintaining the correct ionic balance and preventing cell swelling, these enzymes ensure the RBC remains **pliable and deformable**. This flexibility is critical for the 8μm RBC to squeeze through 2-3μm splenic capillaries without undergoing hemolysis. **2. Analysis of Incorrect Options:** * **Option B:** Cytoplasmic enzymes do the opposite; they *facilitate* and power the transmembrane transport of ions (like Na⁺ and K⁺) to maintain homeostasis. * **Option C:** This is a conceptual reversal. Enzymes like **Methemoglobin Reductase** function to keep iron in the **Ferrous (Fe²⁺)** state. The Ferric (Fe³⁺) state (Methemoglobin) cannot bind oxygen. * **Option D:** Enzymes like **Glucose-6-Phosphate Dehydrogenase (G6PD)** produce NADPH to *prevent* the oxidation of proteins. Oxidation leads to the formation of Heinz bodies and membrane damage. **Clinical Pearls for NEET-PG:** * **G6PD Deficiency:** The most common enzyme deficiency; leads to oxidative stress, Heinz bodies, and "bite cells" in the peripheral smear. * **Pyruvate Kinase Deficiency:** The most common enzyme deficiency in the Embden-Meyerhof pathway, leading to decreased ATP and chronic hemolytic anemia. * **2,3-BPG:** A byproduct of RBC glycolysis (Rapoport-Luebering Shunt) that shifts the oxygen dissociation curve to the right, facilitating oxygen unloading to tissues.

Q: A patient with A-negative blood group can receive blood from which of the following donor blood groups?

A negative. ### Explanation The fundamental principle of blood transfusion is that the recipient must not have antibodies against the donor’s red cell antigens [1]. **1. Why A negative is correct:** A patient with **A-negative** blood has: * **Antigens:** A antigen on the RBC surface [2]. * **Antibodies:** Naturally occurring anti-B antibodies in the plasma [1]. * **Rh status:** Absence of the D antigen (Rh-negative). These individuals will develop anti-D antibodies if exposed to Rh-positive blood. Therefore, an A-negative patient can safely receive blood that lacks the B antigen and lacks the Rh (D) antigen. **A-negative** and **O-negative** are the only compatible groups [1]. **2. Why the other options are incorrect:** * **O positive:** While O is the "universal donor" for ABO, the **positive** Rh status means it contains the D antigen. This would trigger a transfusion reaction (isoimmunization) in an Rh-negative recipient. * **B negative:** This blood contains the B antigen. The recipient’s naturally occurring **anti-B antibodies** would cause immediate hemolytic transfusion reaction [1]. * **AB positive:** This blood contains both the B antigen and the Rh (D) antigen, both of which are incompatible with an A-negative recipient [1]. **3. Clinical Pearls for NEET-PG:** * **Universal Donor (RBCs):** O negative (lacks A, B, and D antigens) [1]. * **Universal Recipient (RBCs):** AB positive (lacks anti-A, anti-B, and anti-D antibodies). * **Universal Donor (Plasma):** AB (lacks anti-A and anti-B antibodies). * **Rh Incompatibility:** In emergencies, Rh-negative females of childbearing age **must** receive Rh-negative blood to prevent Rh isoimmunization and future Hemolytic Disease of the Newborn (HDN).

Q: Which of the following Interleukins is raised in fever?

TNF-α. ### Explanation **Correct Option: B (TNF-α)** **Concept:** Fever (pyrexia) is primarily mediated by **pyrogens**. When the body encounters pathogens or inflammation, phagocytic cells release **Endogenous Pyrogens**. The most potent endogenous pyrogens are **IL-1, IL-6, and TNF-α (Tumor Necrosis Factor-alpha)**. These cytokines travel via the bloodstream to the hypothalamus (specifically the Organum Vasculosum of the Lamina Terminalis - OVLT), where they stimulate the release of **Prostaglandin E2 (PGE2)**. PGE2 then resets the hypothalamic thermostat to a higher set point, resulting in fever. **Analysis of Options:** * **TNF-α (Correct):** Along with IL-1 and IL-6, it is a primary pro-inflammatory cytokine and a major mediator of the acute phase response and fever. * **IFN-γ (Option A):** Produced by Th1 cells and NK cells, its primary role is activating macrophages and stimulating MHC expression. While it aids the immune response, it is not a primary pyrogen. * **IL-10 (Option C):** This is an **anti-inflammatory cytokine**. It inhibits the synthesis of pro-inflammatory cytokines (like TNF-α and IL-1) and actually helps in resolving inflammation rather than inducing fever. * **IL-2 (Option D):** Primarily functions as a T-cell growth factor, promoting the proliferation and differentiation of T-lymphocytes. **NEET-PG High-Yield Pearls:** * **Master Pyrogens:** Remember the "Big Three" of fever: **IL-1, IL-6, and TNF-α**. * **The Mediator:** **PGE2** is the ultimate mediator of fever in the hypothalamus. This is why NSAIDs (COX inhibitors) are effective antipyretics—they block PGE2 synthesis. * **Cryogens:** Molecules like **IL-10 and Arginine Vasopressin (AVP)** act as endogenous antipyretics (cryogens) to prevent excessive temperature rise. * **IL-1** is often cited as the most potent endogenous pyrogen in many textbooks.

Q: Which of the following pathways does aPTT measure?

Extrinsic pathway. **Explanation:** The **Activated Partial Thromboplastin Time (aPTT)** is a screening test used to evaluate the efficiency of the **Intrinsic** and **Common pathways** of the coagulation cascade. *Note: There appears to be a discrepancy in the provided key. In standard medical physiology, **aPTT measures the Intrinsic pathway**, while **PT (Prothrombin Time) measures the Extrinsic pathway**.* ### Why the Options are Correct/Incorrect: * **A. Intrinsic Pathway (Correct Concept):** aPTT measures factors XII, XI, IX, and VIII (Intrinsic), as well as factors X, V, II (Prothrombin), and I (Fibrinogen) of the Common pathway. It is the gold standard for monitoring **Unfractionated Heparin** therapy. * **B. Extrinsic Pathway (Incorrect):** This pathway is measured by **Prothrombin Time (PT)**. The extrinsic pathway involves Factor VII and Tissue Factor. PT is used to monitor **Warfarin** therapy. * **C. Both Pathways:** While both tests share the "Common Pathway" (Factors X, V, II, I), they are clinically distinct tests used to isolate deficiencies in either the Intrinsic (aPTT) or Extrinsic (PT) arms. * **D. Complement Pathway:** This is part of the innate immune system (C1-C9) and is unrelated to the secondary hemostasis (clotting) measured by aPTT. ### High-Yield Clinical Pearls for NEET-PG: 1. **Mnemonic for PT:** "PET" – **P**T measures **E**xtrinsic pathway and involves Factor **7** (VII). 2. **Mnemonic for aPTT:** "PITT" – **P**TT measures **I**ntrinsic pathway and involves **T**welve, **T**en, etc. 3. **Hemophilia A (VIII) and B (IX):** These involve the intrinsic pathway, so they present with a **prolonged aPTT** but a normal PT. 4. **Vitamin K Deficiency:** Affects Factors II, VII, IX, and X. Since Factor VII has the shortest half-life, **PT is usually prolonged first**.

Question 1

Which of the following is a common step in the coagulation pathway?

Accepted Answer

Activation of factor X

Answer

Activation of factor VII

Answer

Activation of factor VIII

Answer

Activation of factor IX

Question 2

A middle-aged man's blood sample shows a hematocrit of 45% and biconcave red blood cells. The biconcavity of RBCs is a function of which of the following?

Accepted Answer

Spectrin

Answer

Ankyrin

Answer

Band protein

Answer

Glycophorin-C

Question 3

Which of the following is considered an immune privileged site?

Accepted Answer

Seminiferous tubules

Answer

Area postrema

Answer

Loop of Henle

Answer

Optic nerve

Question 4

During the second trimester of pregnancy, in which organ does erythropoiesis primarily occur in the fetus?

Accepted Answer

Liver

Answer

Spleen

Answer

Red bone marrow

Answer

Lymph nodes

Question 5

What is the half-life of albumin?

Accepted Answer

20 days

Answer

36-48 hours

Answer

3-5 days

Answer

5-10 days

Question 6

ABO antigens are not found in which of the following bodily fluids?

Accepted Answer

Cerebrospinal fluid (CSF)

Answer

Semen

Answer

Sweat

Answer

Saliva

Question 7

What are the functions of cytoplasmic enzymes in Red Blood Cells?

Accepted Answer

Maintain pliability of the cell membrane

Answer

Prevent transmembrane transport of ions

Answer

Keep the iron of hemoglobin in the ferric form rather than ferrous form

Answer

Cause oxidation of the proteins in the RBCs

Question 8

A patient with A-negative blood group can receive blood from which of the following donor blood groups?

Accepted Answer

A negative

Answer

O positive

Answer

B negative

Answer

AB positive

Question 9

Which of the following Interleukins is raised in fever?

Accepted Answer

TNF-α

Answer

IFN-γ

Answer

IL-10

Answer

IL-2

Question 10

Which of the following pathways does aPTT measure?

Accepted Answer

Extrinsic pathway

Answer

Intrinsic pathway

Answer

Both intrinsic and extrinsic pathways

Answer

Complement pathway

Blood and Immunity — MCQs

Blood and Immunity — MCQs

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