Blood and Immunity Practice Questions

Q: The anemia in chronic renal failure (CRF) is primarily due to which pathophysiological mechanism?

Decreased erythropoiesis. **Explanation:** The primary cause of anemia in Chronic Renal Failure (CRF) is a deficiency in **Erythropoietin (EPO)** production. Erythropoietin is a glycoprotein hormone synthesized by the **peritubular interstitial cells** of the renal cortex in response to hypoxia. In CRF, the progressive destruction of renal parenchyma leads to a significant decline in EPO levels, resulting in **decreased erythropoiesis** (reduced red blood cell production) in the bone marrow. This typically manifests as a normocytic, normochromic anemia. **Analysis of Options:** * **Option A (Correct):** As explained, the loss of functional renal tissue directly impairs the synthesis of EPO, the primary stimulator of the bone marrow to produce RBCs. This is the hallmark pathophysiological mechanism. * **Option B (Incorrect):** While the uremic environment in advanced CRF can slightly shorten the lifespan of RBCs (mild hemolysis), it is a secondary factor and not the *primary* cause of the anemia. * **Option C (Incorrect):** Although both factors can exist, "decreased erythropoiesis" is the definitive primary mechanism. In the context of NEET-PG, when asked for the "primary" or "most important" cause, EPO deficiency (decreased production) is the prioritized answer. **High-Yield Clinical Pearls for NEET-PG:** * **Target Hb:** In CRF patients on EPO therapy, the target Hemoglobin is usually **10–11 g/dL**. Higher levels (above 13 g/dL) are avoided due to increased risk of cardiovascular events and stroke. * **Iron Stores:** Before starting EPO, always check iron stores (Ferritin/TSAT), as EPO therapy is ineffective in the presence of iron deficiency. * **Other contributing factors in CRF:** Chronic blood loss (due to platelet dysfunction/uremic gastropathy) and secondary hyperparathyroidism (causing marrow fibrosis).

Q: Which of the following is secreted by neutrophils?

Myeloperoxidase. **Explanation:** **Neutrophils** are the primary effector cells of the innate immune system, specialized for the destruction of invading pathogens through phagocytosis and the respiratory burst. **Why Myeloperoxidase (MPO) is Correct:** Myeloperoxidase is a heme-containing enzyme stored in the **primary (azurophilic) granules** of neutrophils. During the respiratory burst, NADPH oxidase produces superoxide radicals, which are converted to hydrogen peroxide ($H_2O_2$). MPO then catalyzes the reaction between $H_2O_2$ and chloride ions ($Cl^-$) to produce **hypochlorous acid (HOCl)**—the active ingredient in household bleach and a potent bactericidal agent. This MPO-halide system is the most efficient bactericidal mechanism in neutrophils. **Analysis of Incorrect Options:** * **Superoxide dismutase (SOD) & Catalase:** These are **antioxidant enzymes** found within the cytoplasm of various cells. Their primary role is to neutralize reactive oxygen species (ROS) to protect the cell from oxidative damage, rather than being "secreted" for pathogen destruction. * **Lysosomal enzymes:** While neutrophils do contain lysosomes (acid hydrolases), the term is too broad. Myeloperoxidase is the specific, hallmark enzyme secreted during the degranulation process of the respiratory burst that defines neutrophil function. **High-Yield Clinical Pearls for NEET-PG:** * **MPO Deficiency:** The most common inherited neutrophil primary granule deficiency; patients are usually asymptomatic except for a predisposition to *Candida* infections. * **Markers:** MPO is a key histochemical marker used to differentiate **Acute Myeloid Leukemia (AML)** from Acute Lymphoblastic Leukemia (ALL). * **P-ANCA:** Perinuclear Anti-Neutrophil Cytoplasmic Antibodies (found in Microscopic Polyangiitis and Churg-Strauss) are specifically directed against myeloperoxidase.

Q: At what age do children typically acquire antibodies against ABO antigens?

6 Months. **Explanation:** The development of ABO antibodies (isoagglutinins) is a classic high-yield concept in hematology. Unlike most antibodies, ABO antibodies are not present at birth; they are "naturally occurring" but require environmental exposure to develop. **Why 6 Months is Correct:** At birth, a newborn’s serum lacks its own ABO antibodies. These antibodies (primarily IgM) begin to appear around **3 to 6 months of age**. They are produced in response to exposure to A-like and B-like polysaccharides found in common intestinal bacteria and food. Antibody titers continue to rise throughout childhood, reaching peak levels between 5 and 10 years of age. **Analysis of Incorrect Options:** * **A. At Birth:** Newborns do not produce their own ABO antibodies. Any ABO antibodies detected in a neonate are typically maternal IgG that crossed the placenta (relevant in ABO hemolytic disease of the newborn). * **C & D. 2 Years and 5 Years:** While antibody titers are higher at these ages, the *initial acquisition* occurs much earlier. By age 2, a child already has a well-established repertoire of isoagglutinins. **Clinical Pearls for NEET-PG:** * **Antibody Type:** ABO antibodies are predominantly **IgM** (which do not cross the placenta), whereas Rh antibodies are **IgG** (which do cross the placenta). * **Landsteiner’s Law:** States that if an agglutinogen (antigen) is present on RBCs, the corresponding agglutinin (antibody) must be absent; conversely, if an antigen is absent, the antibody must be present. This law applies to the ABO system but **not** the Rh system. * **Reverse Grouping:** Because infants lack these antibodies, "reverse grouping" (testing serum against known RBCs) is unreliable until the child is at least 4–6 months old.

Q: Which of the following is not a naturally occurring anticoagulant in the body?

Von Willebrand factor. **Explanation:** The correct answer is **Von Willebrand factor (vWF)** because it is a **pro-coagulant** protein, not an anticoagulant. Its primary roles in hemostasis are: 1. **Platelet Adhesion:** It acts as a molecular bridge between platelet glycoprotein Ib (GpIb) receptors and exposed subendothelial collagen at the site of vascular injury. 2. **Stabilization of Factor VIII:** It binds to and protects Factor VIII from rapid degradation in the plasma. **Analysis of Incorrect Options:** * **Protein C and Protein S:** These are Vitamin K-dependent natural anticoagulants. Activated Protein C (with Protein S as a cofactor) proteolytically inactivates **Factors Va and VIIIa**, thereby limiting the coagulation cascade. * **Antithrombin III (AT-III):** This is the most potent circulating anticoagulant. It inactivates **Thrombin (IIa)** and **Factor Xa** (as well as IXa, XIa, and XIIa). Its activity is increased several thousand-fold in the presence of Heparin. **High-Yield Clinical Pearls for NEET-PG:** * **vWF Deficiency:** The most common inherited bleeding disorder (Von Willebrand Disease), characterized by mucosal bleeding and prolonged Bleeding Time (BT). * **Virchow’s Triad:** Deficiency of Protein C, Protein S, or Antithrombin III leads to a hypercoagulable state (thrombophilia), increasing the risk of Deep Vein Thrombosis (DVT). * **Factor V Leiden:** The most common cause of inherited thrombophilia, where Factor Va is resistant to inactivation by Protein C. * **Site of Synthesis:** Most clotting factors and anticoagulants are synthesized in the liver; however, vWF is synthesized in **endothelial cells (Weibel-Palade bodies)** and megakaryocytes.

Q: 2,3-DPG levels are decreased in which of the following conditions?

Acidosis. **Explanation:** The level of **2,3-Bisphosphoglycerate (2,3-DPG)** in red blood cells is a critical regulator of hemoglobin's affinity for oxygen. 2,3-DPG binds to the beta chains of deoxyhemoglobin, stabilizing the "T" (Tense) state and shifting the oxygen-dissociation curve to the **right**, facilitating oxygen unloading to tissues. **Why Acidosis is the Correct Answer:** The synthesis of 2,3-DPG is catalyzed by the enzyme **phosphoglycerate mutase**. This enzyme is highly sensitive to pH; it is **inhibited by a decrease in pH (acidosis)**. Therefore, in states of acidosis, the glycolytic pathway in RBCs is slowed, leading to decreased production of 2,3-DPG. This serves as a compensatory mechanism: while acidosis itself shifts the curve to the right (Bohr effect), the resulting decrease in 2,3-DPG shifts it back to the left, helping maintain equilibrium. **Analysis of Incorrect Options:** * **Anemia:** In anemia, there is a functional hypoxia. The body compensates by **increasing** 2,3-DPG levels to enhance oxygen delivery to tissues. * **High Altitude:** Low partial pressure of oxygen triggers an **increase** in 2,3-DPG to facilitate better peripheral unloading of oxygen. * **Exercise:** Strenuous exercise leads to increased metabolism and temporary hypoxia, which stimulates an **increase** in 2,3-DPG levels. **NEET-PG High-Yield Pearls:** * **Stored Blood:** 2,3-DPG levels **decrease** in stored blood (bank blood). Transfusing large amounts of old blood can impair oxygen delivery to tissues due to a leftward shift of the curve. * **Fetal Hemoglobin (HbF):** HbF has a **lower affinity** for 2,3-DPG because its gamma chains lack the specific binding sites found in beta chains. This results in HbF having a higher affinity for oxygen than adult hemoglobin (HbA). * **Mnemonic:** Factors that shift the curve to the **Right** (increase 2,3-DPG): **CADET**, face Right! (**C**O2, **A**cid, **D**PG, **E**xercise, **T**emperature).

Q: Erythropoietin secretion decreases in which of the following conditions?

Severe renal disease. ### Explanation **Correct Option: B. Severe renal disease** **Underlying Medical Concept:** Erythropoietin (EPO) is a glycoprotein hormone essential for erythropoiesis. In adults, approximately **85–90% of EPO is produced by the peritubular interstitial cells (fibroblasts)** in the renal cortex, while the remaining 10–15% is produced by the liver. The primary stimulus for EPO secretion is **hypoxia** (detected via Hypoxia-Inducible Factor, HIF-1α). In **severe renal disease** (such as Chronic Kidney Disease), the functional parenchyma and peritubular cells are destroyed or replaced by fibrosis. Consequently, the kidneys lose their ability to synthesize EPO, leading to the classic "normocytic normochromic anemia of chronic renal failure." **Analysis of Incorrect Options:** * **A. High altitude:** Decreased atmospheric pressure leads to a lower partial pressure of oxygen ($PO_2$). This systemic hypoxia stimulates the kidneys to **increase** EPO production to enhance oxygen-carrying capacity. * **C. Congestive heart failure:** Reduced cardiac output leads to decreased tissue perfusion and stagnant hypoxia. This triggers a compensatory **increase** in EPO secretion. * **D. Lung disease:** Conditions like COPD or interstitial lung disease impair gas exchange, causing arterial hypoxemia. This is a potent stimulus that **increases** EPO, often resulting in secondary polycythemia. **High-Yield Clinical Pearls for NEET-PG:** * **Site of Action:** EPO acts on the **CFU-E** (Colony Forming Unit-Erythroid) receptors in the bone marrow. * **Recombinant EPO:** Used clinically to treat anemia in CKD patients; however, it can cause **hypertension** as a side effect. * **Non-Renal EPO:** In the fetus, the **liver** is the primary source of EPO. * **Tumor Association:** Certain tumors (e.g., Renal Cell Carcinoma, Hemangioblastoma, Hepatocellular Carcinoma) can cause **ectopic EPO production**, leading to paraneoplastic polycythemia.

Q: What concentration of methemoglobin in the blood is typically required to cause cyanosis?

1.5 gm/dL. **Explanation:** Cyanosis is the bluish discoloration of the skin and mucous membranes, typically occurring when a specific threshold of deoxygenated or abnormal hemoglobin is reached in the capillary blood. **1. Why 1.5 gm/dL is Correct:** While central cyanosis traditionally requires **5 gm/dL of reduced (deoxygenated) hemoglobin**, methemoglobin has a much more profound effect on skin color. Because methemoglobin is dark, chocolate-colored, and has a high molar extinction coefficient, it produces visible cyanosis at much lower concentrations. Specifically, only **1.5 gm/dL of methemoglobin** is required to produce clinical cyanosis. This is why patients with methemoglobinemia often appear "cyanotic" despite having a normal PaO2 on arterial blood gas. **2. Analysis of Incorrect Options:** * **5 gm/dL (Option A):** This is the threshold for **reduced hemoglobin** (deoxy-Hb) to cause cyanosis. It is a classic "distractor" for students who confuse general cyanosis with methemoglobin-specific cyanosis. * **2 gm/dL (Option B):** This value is sometimes cited as the threshold for sulfhemoglobinemia to cause cyanosis, but it is not the standard for methemoglobin. * **12 gm/dL (Option D):** This is a dangerously high level associated with severe hypoxia and neurological symptoms, far exceeding the initial threshold for visible cyanosis. **High-Yield Clinical Pearls for NEET-PG:** * **The "Saturation Gap":** A hallmark of methemoglobinemia is a discrepancy between low SpO2 (pulse oximetry, often hovering around 85%) and a normal PaO2 (on ABG). * **Blood Appearance:** Blood in these patients appears **chocolate-brown** and does not change color when exposed to 100% oxygen. * **Treatment:** The drug of choice is **Intravenous Methylene Blue**, which acts as an exogenous electron acceptor to reduce Fe3+ back to Fe2+. * **Common Triggers:** Nitrites, benzocaine, dapsone, and sulfonamides.

Q: What is the typical volume of blood per kilogram of body weight in a child?

60-70 ml. **Explanation:** The total blood volume (TBV) in humans varies significantly based on age, body composition, and physiological state. The correct answer is **60-70 ml/kg**, which represents the standard physiological range for an older child or adolescent. **1. Why Option A is Correct:** As a child grows, their body composition changes. While neonates have a very high proportion of water and blood relative to their weight, this ratio decreases as they mature. In children and adolescents, the blood volume stabilizes to approximately **70 ml/kg** (ranging between 60-80 ml/kg depending on the specific age and lean body mass), which is slightly higher than the adult average of 65-70 ml/kg. **2. Why Other Options are Incorrect:** * **Option B (100-150 ml):** This is excessively high for a child. However, a **preterm neonate** can have a blood volume of approximately **90-100 ml/kg**. * **Options C & D (150-250 ml):** These values are physiologically impossible under normal conditions. Such high volumes would lead to circulatory overload and heart failure. **High-Yield Clinical Pearls for NEET-PG:** * **Age-wise TBV Distribution:** * **Preterm Neonate:** ~90-100 ml/kg * **Term Neonate:** ~80-90 ml/kg * **Infant:** ~75-80 ml/kg * **Child:** ~70-75 ml/kg * **Adult Male:** ~70 ml/kg * **Adult Female:** ~65 ml/kg (lower due to higher body fat percentage). * **Clinical Application:** Calculating TBV is critical in pediatrics for managing fluid resuscitation, estimating allowable blood loss during surgery, and determining dosages for blood component therapy (e.g., 10 ml/kg of packed RBCs typically raises hemoglobin by 2-3 g/dL).

Q: In an adult man, what is the approximate total amount of hemoglobin in the circulating blood in grams?

900. To determine the total amount of hemoglobin (Hb) in the circulating blood, we must apply the standard physiological values for an average adult male (approx. 70 kg). ### **The Calculation** 1. **Total Blood Volume:** The average blood volume in an adult male is approximately **5 liters** (or 70 ml/kg). 2. **Hemoglobin Concentration:** The normal average Hb concentration is **14–16 g/dL** (deciliter = 100 ml). 3. **The Formula:** Total Hb = (Hb concentration per 100 ml) × (Total blood volume in ml / 100). * Calculation: $15\text{ g/dL} \times 50\text{ dL} = \mathbf{750\text{--}900\text{ grams}}$. Among the given options, **900 grams** (Option C) is the most accurate representation of the upper limit for a healthy adult male. ### **Analysis of Incorrect Options** * **A (350g) & B (500g):** These values are too low. 350g would imply a blood volume of only 2.3L or severe anemia. * **D (1000g):** This value is slightly higher than the physiological average, typically seen only in cases of polycythemia or in very large individuals with high muscle mass. ### **High-Yield NEET-PG Pearls** * **Iron Content:** Each gram of Hb contains **3.34 mg of iron**. Therefore, the total body iron stored in Hb is approximately 2.5–3 grams. * **Oxygen Carrying Capacity:** 1 gram of Hb carries **1.34 ml of oxygen** (Hufner's constant). * **Life Span:** The average lifespan of an RBC is **120 days**, after which Hb is broken down into heme and globin in the Reticuloendothelial system (Spleen). * **Fetal Hb (HbF):** Has a higher affinity for oxygen than adult Hb (HbA) due to poor binding with 2,3-BPG.

Question 1

The anemia in chronic renal failure (CRF) is primarily due to which pathophysiological mechanism?

Accepted Answer

Decreased erythropoiesis

Answer

Increased hemolysis

Answer

Both decreased erythropoiesis and increased hemolysis

Answer

None of the above

Question 2

Which of the following is secreted by neutrophils?

Accepted Answer

Myeloperoxidase

Answer

Superoxide dismutase

Answer

Lysosomal enzyme

Answer

Catalase

Question 3

At what age do children typically acquire antibodies against ABO antigens?

Accepted Answer

6 Months

Answer

At birth

Answer

2 Years

Answer

5 Years

Question 4

Which of the following is not a naturally occurring anticoagulant in the body?

Accepted Answer

Von Willebrand factor

Answer

Protein C

Answer

Protein S

Answer

Antithrombin III

Question 5

In which of the following conditions is the synthesis of hepcidin not reduced?

Accepted Answer

Hemosiderosis

Answer

Hypoxia

Answer

Anemia

Answer

Hemorrhage

Question 6

2,3-DPG levels are decreased in which of the following conditions?

Accepted Answer

Acidosis

Answer

Anemia

Answer

High altitude

Answer

Exercise

Question 7

Erythropoietin secretion decreases in which of the following conditions?

Accepted Answer

Severe renal disease

Answer

High altitude

Answer

Congestive heart failure

Answer

Lung disease

Question 8

What concentration of methemoglobin in the blood is typically required to cause cyanosis?

Accepted Answer

1.5 gm/dL

Answer

5 gm/dL

Answer

2 gm/dL

Answer

12 gm/dL

Question 9

What is the typical volume of blood per kilogram of body weight in a child?

Accepted Answer

60-70 ml

Answer

100-150 ml

Answer

150-200 ml

Answer

200-250 ml

Question 10

In an adult man, what is the approximate total amount of hemoglobin in the circulating blood in grams?

Accepted Answer

900

Answer

350

Answer

500

Answer

1000

Blood and Immunity — MCQs

Blood and Immunity — MCQs

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