Blood and Immunity — MCQs

A patient with mild congestive heart failure is treated with high-dose furosemide and diuresis of 3 liters of fluid. A complete blood count (CBC) taken before the diuresis shows an RBC count of 4 million/mm3; a CBC taken after diuresis shows an RBC count of 7 million/mm3. Which of the following is the most likely explanation?

Q358Easy

The need for vitamin B12 and folic acid in the formation of red blood cells is related primarily to their effects on which process?

Q359Easy

What is the normal range for prothrombin time?

Q360Easy

Prostacyclin is mainly produced by?

Blood and Immunity Indian Medical PG Practice Questions and MCQs

Question 351: Which of the following is likely to be increased in vitamin K deficiency?

A. PTT
B. PT (Correct Answer)
C. Platelet count
D. Fibrinogen time

Explanation: ### Explanation **Vitamin K** is a vital cofactor for the enzyme **gamma-glutamyl carboxylase**, which is responsible for the post-translational modification (gamma-carboxylation) of clotting factors **II, VII, IX, and X**, as well as proteins C and S. This process allows these factors to bind calcium and phospholipid membranes, making them functional. **Why PT is the correct answer:** Prothrombin Time (PT) measures the **extrinsic and common pathways**. Factor **VII** (extrinsic pathway) has the shortest half-life (approx. 6 hours) among all clotting factors. Consequently, when Vitamin K is deficient, Factor VII levels drop first, making **PT the most sensitive and earliest laboratory indicator** of Vitamin K deficiency or early warfarin therapy. **Analysis of Incorrect Options:** * **PTT (Partial Thromboplastin Time):** While PTT measures the intrinsic pathway (including Vitamin K-dependent factors IX, X, and II) and *can* be prolonged in severe or prolonged deficiency, it is not as sensitive or as early an indicator as PT. * **Platelet Count:** Vitamin K deficiency affects the coagulation cascade (secondary hemostasis), not platelet production or number (primary hemostasis). * **Fibrinogen Time (Thrombin Time):** This measures the conversion of fibrinogen to fibrin. Fibrinogen (Factor I) is not Vitamin K-dependent; therefore, this remains normal. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic:** Remember **"1972"** for Vitamin K-dependent factors (Factors **10, 9, 7, 2**). * **Warfarin:** Acts as a Vitamin K antagonist; PT/INR is used to monitor its therapeutic effect. * **Hemorrhagic Disease of the Newborn:** Neonates are Vitamin K deficient due to sterile guts and poor placental transfer; hence, prophylactic Vitamin K is given at birth. * **Absorption:** Vitamin K is fat-soluble; deficiency can occur in malabsorption syndromes (e.g., Celiac disease) or obstructive jaundice.

Question 352: Patients with hemophilia A have a bleeding disorder because of which of the following?

A. Lack of platelet count
B. Lack of platelet adhesion
C. Lack of factor VIII during activation of factor X in the coagulation cascade (Correct Answer)
D. Release of thromboxane A2

Explanation: **Explanation:** Hemophilia A is an X-linked recessive bleeding disorder caused by a deficiency or dysfunction of **Clotting Factor VIII**. **1. Why the Correct Answer is Right:** In the coagulation cascade, Factor VIII acts as a critical cofactor for Factor IXa. Together, they form the **"Intrinsic Tenase Complex"** on the surface of activated platelets. This complex is responsible for the proteolytic activation of **Factor X to Factor Xa**. Without Factor VIII, the intrinsic pathway is severely impaired, leading to inadequate thrombin generation and a failure to form a stable fibrin clot. This manifests clinically as deep tissue bleeding and hemarthrosis. **2. Why Incorrect Options are Wrong:** * **Option A:** Platelet count is typically **normal** in hemophilia. Low platelet count (thrombocytopenia) is seen in conditions like ITP or aplastic anemia. * **Option B:** Platelet adhesion involves von Willebrand Factor (vWF) and Glycoprotein Ib. While vWF carries Factor VIII in the blood, Hemophilia A specifically involves a deficiency of the clotting factor itself, not the adhesion process. * **Option C:** Thromboxane A2 is a product of the cyclooxygenase pathway in platelets that promotes aggregation and vasoconstriction. Its inhibition is the mechanism of action for Aspirin, not the cause of Hemophilia. **3. High-Yield Clinical Pearls for NEET-PG:** * **Lab Findings:** Prolonged **aPTT** (Intrinsic pathway) with a **Normal PT** and **Normal Bleeding Time**. * **Inheritance:** X-linked recessive (affects males; females are usually asymptomatic carriers). * **Treatment:** Recombinant Factor VIII concentrate or Desmopressin (for mild cases to release stored Factor VIII). * **Hemophilia B (Christmas Disease):** Deficiency of Factor IX. * **Hemophilia C:** Deficiency of Factor XI (Autosomal recessive).

Question 353: What is the Rh factor?

A. Antibody
B. Mucopolysaccharide
C. Protein (Correct Answer)
D. Fatty acid

Explanation: **Explanation:** The Rh factor (Rhesus factor) refers to a specific group of **antigens** found on the surface of red blood cells (RBCs). Chemically, these antigens are **transmembrane proteins** (specifically non-glycosylated polypeptides). The most clinically significant among them is the **D-antigen**. Individuals who possess this protein are classified as Rh-positive, while those lacking it are Rh-negative. **Why the other options are incorrect:** * **Antibody (A):** The Rh factor itself is an *antigen* (the target), not an antibody. However, Rh-negative individuals can produce anti-D antibodies (IgG) if exposed to Rh-positive blood. * **Mucopolysaccharide (B):** This describes the chemical nature of **ABO antigens**, which are oligosaccharide chains attached to a sphingolipid or protein backbone. Rh antigens differ because they are purely proteinaceous. * **Fatty acid (D):** Rh factors are structural components of the RBC membrane but are not composed of lipids or fatty acids. **Clinical Pearls for NEET-PG:** * **Inheritance:** Rh antigens are encoded by two genes, *RHD* and *RHCE*, located on **Chromosome 1**. * **Clinical Significance:** Unlike ABO antibodies, anti-Rh antibodies are not naturally occurring; they develop only after isoimmunization (e.g., mismatched transfusion or pregnancy). * **Erythroblastosis Fetalis:** This occurs when an Rh-negative mother carries an Rh-positive fetus. The resulting IgG antibodies can cross the placenta, causing hemolysis in the fetus. * **Prophylaxis:** Administering **Anti-D (RhoGAM)** to the mother at 28 weeks and within 72 hours of delivery prevents sensitization.

Question 354: Mast cells secrete all except:

A. Histamine
B. Heparin
C. MIP
D. Bradykinin (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. Bradykinin**. **Why Bradykinin is the correct answer:** Mast cells are specialized immune cells found in connective tissue that contain granules rich in inflammatory mediators. While mast cells release a wide array of substances, **Bradykinin** is not secreted directly by them. Instead, Bradykinin is a plasma-derived peptide formed through the **Kinin-Kallikrein system**. It is produced when the enzyme kallikrein acts on high-molecular-weight kininogen (HMWK) in the plasma, typically triggered by tissue injury or inflammation. **Analysis of incorrect options:** * **A. Histamine:** This is the primary pre-formed mediator stored in mast cell granules. It causes vasodilation and increased vascular permeability during allergic reactions (Type I Hypersensitivity). * **B. Heparin:** Mast cells are a major source of endogenous heparin. It acts as an anticoagulant and serves as a structural matrix for storing other mediators within the granules. * **C. MIP (Macrophage Inflammatory Protein):** Mast cells secrete various cytokines and chemokines, including MIP-1α and MIP-1β, which help recruit other immune cells to the site of inflammation. **High-Yield Clinical Pearls for NEET-PG:** * **Mast Cell Triggers:** They are activated by the cross-linking of **IgE antibodies** bound to **FcεRI receptors** on their surface. * **Markers:** **Tryptase** is a specific marker for mast cell activation and is used clinically to confirm a diagnosis of anaphylaxis. * **Cromolyn Sodium:** This drug acts as a "Mast Cell Stabilizer" by preventing degranulation, commonly used in the management of asthma and allergic rhinitis. * **Location:** Mast cells are most abundant in areas exposed to the external environment, such as the skin, lungs, and gastrointestinal tract.

Question 355: Cyanosis does not occur in severe anaemia because:

A. Hypoxia stimulates erythropoietin production
B. Oxygen carrying capacity of available haemoglobin is increased
C. The critical concentration of haemoglobin required to produce cyanosis is reduced (Correct Answer)
D. The oxygen-haemoglobin dissociation curve shifts to the right

Explanation: **Explanation:** **1. Why the Correct Answer is Right:** Cyanosis is a clinical sign characterized by a bluish discoloration of the skin and mucous membranes. It is not determined by the total amount of hemoglobin (Hb) or the degree of anemia, but specifically by the **absolute concentration of reduced (deoxygenated) hemoglobin** in the capillaries. The physiological threshold for central cyanosis to become visible is approximately **5 g/dL of reduced hemoglobin**. In severe anemia (e.g., Hb < 5 g/dL), even if all the hemoglobin were deoxygenated, the total amount would barely reach the threshold required to manifest as a blue tint. Therefore, a patient with severe anemia can be dangerously hypoxic without ever appearing cyanotic. **2. Why the Other Options are Wrong:** * **Option A:** While hypoxia does stimulate erythropoietin, this is a compensatory mechanism to increase RBC production over time; it does not explain the immediate absence of cyanosis. * **Option B:** The oxygen-carrying capacity per gram of Hb remains constant (1.34 ml O₂/g). Anemia reduces the *total* carrying capacity of the blood, not the efficiency of individual Hb molecules. * **Option D:** A rightward shift of the O₂-Hb dissociation curve (due to increased 2,3-BPG in anemia) facilitates oxygen unloading to tissues. While this helps combat hypoxia, it actually *increases* the amount of reduced hemoglobin, which would theoretically favor cyanosis, not prevent it. **3. NEET-PG High-Yield Pearls:** * **The "5 g/dL Rule":** Cyanosis depends on the *absolute* amount of reduced Hb, not the *ratio* of reduced to oxygenated Hb. * **Polycythemia:** Patients with polycythemia develop cyanosis more easily (at higher SaO₂ levels) because they have an abundance of Hb. * **Methemoglobinemia:** Cyanosis appears when methemoglobin levels reach **1.5 g/dL** (a much lower threshold than deoxy-Hb). * **Clinical Tip:** In anemic patients, look for **pallor** rather than cyanosis to assess clinical status.

Question 356: Cyanosis does not occur in severe anaemia because:

A. Hypoxia stimulates erythropoietin production
B. Oxygen carrying capacity of available haemoglobin is increased
C. The critical concentration of haemoglobin required to produce cyanosis is reduced (Correct Answer)
D. The oxygen-haemoglobin dissociation curve shifts to the right

Explanation: **Explanation:** **1. Why the Correct Answer is Right:** Cyanosis is a clinical sign characterized by a bluish discoloration of the skin and mucous membranes. It is not determined by the total amount of hemoglobin (Hb), but specifically by the **absolute concentration of reduced (deoxygenated) hemoglobin** in the capillary blood. The physiological threshold for central cyanosis to become visible is approximately **5 g/dL of reduced hemoglobin**. In severe anemia (e.g., Hb < 7 g/dL), even if a significant portion of the hemoglobin is deoxygenated, it is mathematically difficult to reach the absolute value of 5 g/dL. For instance, if a patient has a total Hb of 6 g/dL, they would need to be in a state of extreme, life-threatening hypoxia (nearly 85% desaturation) just to reach the 5 g/dL threshold. Therefore, anemic patients often die from hypoxia before they ever manifest cyanosis. **2. Why the Other Options are Wrong:** * **Option A:** While hypoxia does stimulate erythropoietin, this is a compensatory mechanism to increase RBC production over weeks; it does not explain the immediate absence of cyanosis. * **Option B:** The oxygen-carrying capacity per gram of Hb remains constant (1.34 ml O₂/g). Anemia reduces the *total* carrying capacity of the blood, not the efficiency of individual Hb molecules. * **Option D:** A rightward shift (due to increased 2,3-BPG in anemia) helps in oxygen unloading to tissues but does not change the absolute amount of reduced Hb required to visualize cyanosis. **3. High-Yield Clinical Pearls for NEET-PG:** * **Polycythemia:** Patients with polycythemia develop cyanosis very easily because they have a high total Hb, making it easy to reach the 5 g/dL reduced Hb threshold. * **Methemoglobinemia:** Cyanosis appears when methemoglobin levels reach **1.5 g/dL** (a much lower threshold than deoxy-Hb). * **Site of Observation:** Central cyanosis is best seen on the **tongue and soft palate** (highly vascular, not affected by cold).

Question 357: A patient with mild congestive heart failure is treated with high-dose furosemide and diuresis of 3 liters of fluid. A complete blood count (CBC) taken before the diuresis shows an RBC count of 4 million/mm3; a CBC taken after diuresis shows an RBC count of 7 million/mm3. Which of the following is the most likely explanation?

A. Cyanotic heart disease
B. Increased erythropoietin
C. Polycythemia vera
D. Relative polycythemia (Correct Answer)

Explanation: **Explanation:** The correct answer is **Relative polycythemia**. **1. Why it is correct:** Polycythemia is defined as an increase in the concentration of red blood cells (RBCs). It is classified into two types: **Absolute** (increase in total RBC mass) and **Relative** (decrease in plasma volume). In this clinical scenario, the patient underwent aggressive diuresis (3 liters of fluid loss). This rapid loss of intravascular fluid leads to **hemoconcentration**. Since the plasma volume decreases while the total number of RBCs remains constant, the *measured concentration* of RBCs per mm³ appears elevated (from 4 million to 7 million). This is a classic example of relative polycythemia (also known as Gaisböck syndrome in chronic cases). **2. Why the other options are incorrect:** * **A & B (Cyanotic heart disease / Increased EPO):** These conditions cause **Secondary Absolute Polycythemia**. Chronic hypoxia triggers the kidneys to release Erythropoietin (EPO), stimulating the bone marrow to produce *more* RBCs. This process takes weeks; it cannot happen acutely within the timeframe of a diuretic treatment. * **C (Polycythemia vera):** This is a **Primary Absolute Polycythemia**, a myeloproliferative neoplasm where the bone marrow produces excess RBCs independent of EPO levels. It is a chronic condition and would not be triggered by fluid loss. **3. High-Yield Clinical Pearls for NEET-PG:** * **Formula:** Hematocrit ≈ (RBC Mass) / (Plasma Volume). If Plasma Volume ↓, Hematocrit ↑ (Relative Polycythemia). * **Common causes of Relative Polycythemia:** Dehydration, severe vomiting/diarrhea, burns, and excessive use of diuretics. * **Key Distinguisher:** In relative polycythemia, the **Total RBC Mass is normal**, whereas in absolute polycythemia, the **Total RBC Mass is increased**.

Question 358: The need for vitamin B12 and folic acid in the formation of red blood cells is related primarily to their effects on which process?

A. Synthesis and release of erythropoietin from the kidney
B. Absorption of iron from the gut
C. DNA synthesis in bone marrow (Correct Answer)
D. Hemoglobin formation in the red blood cell

Explanation: **Explanation:** **Why DNA synthesis in bone marrow is correct:** Vitamin B12 (Cobalamin) and Folic acid are essential co-factors for the synthesis of **thymidine triphosphate**, one of the four building blocks of DNA. Specifically, Vitamin B12 is required for the conversion of homocysteine to methionine, a reaction that "unwraps" folate from its storage form (methyl-tetrahydrofolate) so it can participate in DNA synthesis. Without these vitamins, DNA replication in rapidly dividing cells like erythroid precursors in the bone marrow is impaired. This leads to **nuclear-cytoplasmic dyssynchrony**, where the nucleus matures slowly while the cytoplasm grows normally, resulting in large, fragile **megaloblasts**. **Why the other options are incorrect:** * **Option A:** Erythropoietin synthesis is primarily regulated by renal tissue oxygenation (hypoxia-inducible factor), not by vitamin levels. * **Option B:** Iron absorption is influenced by gastric acidity, Vitamin C, and hepcidin levels. B12 and Folate do not play a direct role in the mucosal transport of iron. * **Option D:** Hemoglobin formation is primarily dependent on iron availability (for heme) and globin chain synthesis. While B12/Folate deficiency affects the *number* of cells, the hemoglobin concentration within the megaloblasts is usually normal or elevated. **NEET-PG High-Yield Pearls:** * **Megaloblastic Anemia:** Characterized by MCV >100 fL and hypersegmented neutrophils (>5 lobes). * **Pernicious Anemia:** A specific type of B12 deficiency caused by a lack of **Intrinsic Factor** (secreted by gastric parietal cells). * **Folate Trap:** In B12 deficiency, folate is "trapped" in the N5-methyl THF form, leading to a functional folate deficiency. * **Neurological Symptoms:** B12 deficiency causes Subacute Combined Degeneration (SCD) of the spinal cord due to defective myelin synthesis; **Folic acid deficiency does NOT cause neurological symptoms.**

Question 359: What is the normal range for prothrombin time?

A. 5-7 seconds
B. 10-20 seconds (Correct Answer)
C. 30 seconds
D. 1 minute

Explanation: **Explanation:** **Prothrombin Time (PT)** is a screening test used to evaluate the **Extrinsic and Common pathways** of the coagulation cascade. It specifically measures the time taken for plasma to clot after the addition of Tissue Factor (Thromboplastin) and Calcium. 1. **Why Option B is correct:** The standard normal range for PT is typically **10 to 14 seconds** (extending up to 20 seconds depending on the laboratory reagents used). It reflects the activity of clotting factors **I (Fibrinogen), II (Prothrombin), V, VII, and X**. Since Factor VII has the shortest half-life, PT is the most sensitive indicator of Vitamin K deficiency and early liver dysfunction. 2. **Why other options are incorrect:** * **Option A (5-7 seconds):** This is too rapid; blood requires a sequence of enzymatic activations that take longer than 7 seconds. * **Option C (30 seconds):** This is significantly prolonged. A PT of 30 seconds suggests severe coagulopathy, such as advanced cirrhosis or warfarin overdose. Note: 25–40 seconds is the normal range for **aPTT** (Activated Partial Thromboplastin Time). * **Option D (1 minute):** This represents a critical clinical value indicating a high risk of spontaneous hemorrhage. **High-Yield Clinical Pearls for NEET-PG:** * **INR (International Normalized Ratio):** Since PT varies by lab, INR is used to standardize results, especially for monitoring **Warfarin** therapy. (Normal INR ≈ 1.0). * **Vitamin K Dependency:** PT monitors factors II, VII, IX, and X. However, it does *not* measure Factor IX (Intrinsic pathway). * **Mnemonic:** **PeT** (PT) has 2 letters = Extrinsic pathway; **aPTT** has 4 letters = Intrinsic pathway. * **Prolonged PT only:** Suggests Factor VII deficiency. * **Prolonged PT and aPTT:** Suggests Common pathway deficiency (Factors X, V, II, I) or severe liver disease.

Question 360: Prostacyclin is mainly produced by?

A. Platelet
B. Vascular endothelium (Correct Answer)
C. Prostate
D. Testis

Explanation: **Explanation:** **1. Why Vascular Endothelium is Correct:** Prostacyclin (also known as **PGI2**) is a member of the eicosanoid family of lipid mediators. It is synthesized primarily by the **vascular endothelial cells** through the action of the enzyme cyclooxygenase (COX) and prostacyclin synthase. Its primary physiological roles are **potent vasodilation** and **inhibition of platelet aggregation**. By preventing platelets from adhering to healthy vessel walls, PGI2 maintains blood fluidity and prevents intravascular clot formation. **2. Why Other Options are Incorrect:** * **Platelets:** These cells primarily produce **Thromboxane A2 (TXA2)**. TXA2 is the functional antagonist to PGI2; it promotes platelet aggregation and causes vasoconstriction. The balance between endothelial PGI2 and platelet TXA2 is crucial for hemostasis. * **Prostate:** Despite the name "prostaglandin" (originally discovered in seminal fluid), the prostate is not the primary source of PGI2. It secretes other prostaglandins (like PGE2) and enzymes like PSA. * **Testis:** While the testes produce various steroid hormones (testosterone) and local signaling molecules, they are not a significant source of systemic prostacyclin. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Mechanism of Action:** PGI2 acts by increasing intracellular **cAMP** levels in platelets, which inhibits their activation. * **Aspirin Paradox:** Low-dose aspirin irreversibly inhibits COX-1 in platelets (reducing TXA2). Since platelets lack a nucleus, they cannot regenerate the enzyme. Endothelial cells, however, can synthesize new COX, allowing PGI2 production to recover, leading to a net antithrombotic effect. * **Pharmacology:** **Epoprostenol** is a synthetic analog of PGI2 used clinically to treat Pulmonary Arterial Hypertension (PAH). * **Opposing Effects:** Remember the mnemonic: **P**GI2 **P**revents aggregation; **T**XA2 **T**riggers aggregation.

Practice by Chapter

Composition and Functions of Blood

Practice Questions

Erythrocytes and Hemoglobin

Practice Questions

Leukocytes and Immune Function

Practice Questions

Platelets and Hemostasis

Practice Questions

Blood Groups and Transfusion

Practice Questions

Coagulation and Fibrinolysis

Practice Questions

Hematopoiesis

Practice Questions

Innate Immunity

Practice Questions

Adaptive Immunity

Practice Questions

Immunological Memory and Tolerance

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free