Blood and Immunity Practice Questions

Q: All statements about lactoferrin are true, except?

It transports iron for erythropoiesis.. ### Explanation Lactoferrin is a multifunctional iron-binding glycoprotein belonging to the transferrin family. Its primary role is **bacteriostatic**—it sequesters free iron, making it unavailable for bacterial growth. **Why Option D is the Correct Answer (The False Statement):** While lactoferrin has a high affinity for iron, it **does not** transport iron for erythropoiesis. That function is exclusively performed by **Transferrin**. Lactoferrin actually competes with bacteria for iron and helps in the sequestration of iron into the Reticuloendothelial System (RES) during inflammation, which is a contributing factor to the "Anemia of Chronic Disease." **Analysis of Other Options:** * **Option A:** Lactoferrin is a major constituent of the **secondary (specific) granules** of neutrophils. It is released into the phagosome and extracellular space during degranulation to inhibit microbial proliferation. * **Option B:** It is found in high concentrations in **exocrine secretions** such as breast milk (highest in colostrum), tears, nasal secretions, saliva, and gastrointestinal mucus, serving as a first-line innate immune defense. * **Option C:** Lactoferrin has an iron-binding affinity approximately **250 times higher** than that of serum transferrin, allowing it to retain iron even at the low pH levels typical of infection sites. ### High-Yield NEET-PG Pearls * **Marker of Inflammation:** Fecal lactoferrin is a sensitive marker used to differentiate Inflammatory Bowel Disease (IBD) from Irritable Bowel Syndrome (IBS). * **Bacteriostatic vs. Bactericidal:** It is bacteriostatic by iron deprivation, but can be bactericidal by directly binding to bacterial lipopolysaccharides (LPS) and disrupting cell membranes. * **Neutrophil Granules:** Remember: Primary granules contain **Myeloperoxidase (MPO)**; Secondary granules contain **Lactoferrin** and **Alkaline Phosphatase**.

Q: Pre-B cells and B cells are produced in which location?

Bone marrow. **Explanation:** The correct answer is **Bone marrow**. In humans, the bone marrow serves as the primary lymphoid organ where B-cell lymphopoiesis occurs throughout life. **Why Bone Marrow is Correct:** The development of B cells is a multi-step process that begins with hematopoietic stem cells. These differentiate into **Pro-B cells**, then **Pre-B cells** (characterized by the presence of cytoplasmic $\mu$ heavy chains), and finally into **immature B cells** (expressing surface IgM). All these stages occur within the microenvironment of the **bone marrow**. Once they express surface IgM and IgD, they become mature (but naive) B cells and migrate to peripheral lymphoid organs. **Why Other Options are Incorrect:** * **Thymus:** This is the primary lymphoid organ for **T-cell** maturation. While T-cell precursors originate in the bone marrow, they must migrate to the thymus to undergo TCR rearrangement and selection. * **Tonsils & GALT:** These are **secondary lymphoid organs**. They are sites where mature B cells encounter antigens, undergo clonal expansion, and perform effector functions (like isotype switching). They do not produce B cells from precursors. **High-Yield NEET-PG Pearls:** * **B-cell maturation site:** Bone marrow (Mnemonic: **B**-cell = **B**one marrow). * **T-cell maturation site:** Thymus (Mnemonic: **T**-cell = **T**hymus). * **Bursa of Fabricius:** In birds, B cells mature in this specialized organ; in humans, the bone marrow is the functional equivalent. * **Negative Selection:** Immature B cells that recognize "self" antigens in the bone marrow are eliminated via apoptosis or undergo **receptor editing** to prevent autoimmunity.

Q: Platelet activation includes:

All of the above. **Explanation:** Platelet activation is a complex, multi-step process essential for **primary hemostasis**. When a blood vessel is injured, platelets undergo a series of rapid functional changes to form a temporary hemostatic plug. 1. **Adhesion (Option A):** This is the initial step. Platelets adhere to the exposed subendothelial collagen. This process is primarily mediated by **von Willebrand Factor (vWF)**, which acts as a bridge between the subendothelial collagen and the platelet surface receptor **Glycoprotein Ib/IX/V (GpIb/IX/V)**. 2. **Secretion/Release Reaction (Option B):** Once adhered, platelets become activated and change shape. They release the contents of their granules: * **Alpha granules:** Contain Fibrinogen, vWF, and Platelet-Derived Growth Factor (PDGF). * **Dense granules:** Contain **ADP**, Calcium, and Serotonin (mnemonic: **SAC**). ADP and Thromboxane A2 (TxA2) further recruit and activate more platelets. 3. **Aggregation (Option C):** This is the final step of activation where platelets stick to each other. ADP and TxA2 cause a conformational change in the **GpIIb/IIIa** receptors, allowing them to bind to **Fibrinogen**, which links multiple platelets together to form the plug. Since all three processes—Adhesion, Secretion, and Aggregation—are integral components of the platelet activation sequence, **Option D** is the correct answer. **High-Yield Clinical Pearls for NEET-PG:** * **Bernard-Soulier Syndrome:** Deficiency of **GpIb** (Defect in Adhesion). * **Glanzmann Thrombasthenia:** Deficiency of **GpIIb/IIIa** (Defect in Aggregation). * **Aspirin:** Irreversibly inhibits Cyclooxygenase-1 (COX-1), preventing the synthesis of **Thromboxane A2**, thereby inhibiting platelet aggregation. * **vWF:** Synthesized in endothelial cells (stored in **Weibel-Palade bodies**) and megakaryocytes.

Q: In a person weighing 100 Kgs, what is the estimated blood volume?

8 L. **Explanation:** The correct answer is **8 L**. The total blood volume (TBV) in a healthy adult is approximately **7% to 8% of the total body weight**. For a person weighing 100 kg, the calculation is: $100\text{ kg} \times 0.08 (8\%) = 8\text{ Liters}$. **Why other options are incorrect:** * **A (5 L):** This is the average blood volume for a standard **70 kg male** ($70 \times 0.07 = 4.9\text{ L}$). It is the most common "textbook" value but does not apply to a 100 kg individual. * **B (6 L):** This represents roughly 6% of the body weight for a 100 kg person, which is slightly below the physiological norm for an average adult. * **D (10 L):** This would represent 10% of the body weight. While blood volume can increase in certain states (like pregnancy), 10% is significantly higher than the normal physiological range for a healthy adult. **High-Yield Clinical Pearls for NEET-PG:** 1. **Volume Distribution:** Roughly 55% of blood is Plasma, and 45% is Formed Elements (Hematocrit). 2. **Gender Variation:** Females typically have a slightly lower blood volume per kg (~65-70 ml/kg) compared to males (~70-75 ml/kg) due to a higher percentage of body fat. 3. **Measurement:** The "Gold Standard" for measuring plasma volume is **Evans Blue dye (T-1824)** or **Radio-iodinated albumin**, while RBC volume is measured using **Chromium-51 ($^{51}\text{Cr}$)** labeled RBCs. 4. **Blood Reservoir:** The **systemic veins and venules** contain the largest portion of blood volume (~64%) at any given time, acting as the body's blood reservoir.

Q: Which coagulation factor is not freely circulating in the blood?

Factor 3. **Explanation:** The correct answer is **Factor 3 (Tissue Factor/Thromboplastin)**. **Why Factor 3 is the correct answer:** Unlike most clotting factors, which are proenzymes synthesized by the liver and secreted into the plasma to circulate freely, **Factor 3 (Tissue Factor)** is a cell-surface glycoprotein. It is constitutively expressed on the adventitia of blood vessels and in the membranes of extravascular cells (like fibroblasts). It only comes into contact with blood following **vascular injury**. Once exposed, it binds to Factor VIIa to initiate the **Extrinsic Pathway** of coagulation. Because it is structurally bound to cell membranes, it does not circulate freely in the blood under physiological conditions. **Why the other options are incorrect:** * **Factor 9 (Christmas Factor):** A vitamin K-dependent serine protease that circulates freely in the plasma. It is a key component of the intrinsic pathway. * **Factor 10 (Stuart-Prower Factor):** A vitamin K-dependent factor that circulates freely. It is the first factor of the **Common Pathway**, where it is activated to Xa. * **Factor 12 (Hageman Factor):** A plasma protein that circulates freely. it is activated upon contact with negatively charged surfaces (like collagen or glass), initiating the intrinsic pathway. **High-Yield Clinical Pearls for NEET-PG:** * **Factor 4:** Refers to **Calcium ions (Ca²⁺)**, which are essential for almost all steps of the coagulation cascade except the initial stages of the intrinsic pathway. * **Labile Factor:** Factor 5 (activity decreases quickly in stored blood). * **Stable Factor:** Factor 7 (has the shortest half-life among all factors). * **Hageman Factor (F12) Deficiency:** Unique because it causes a prolonged aPTT in vitro but does **not** cause clinical bleeding in vivo.

Q: When osmotic fragility is normal, RBCs begin to hemolyse when suspended in saline at what concentration?

0.48%. ### Explanation **Concept Overview:** Osmotic fragility refers to the susceptibility of Red Blood Cells (RBCs) to hemolysis when exposed to increasingly hypotonic solutions. In a hypotonic environment, water enters the RBC via osmosis, causing it to swell from a biconcave disc into a sphere. Since the spherical shape has the minimum surface-area-to-volume ratio, any further water intake causes the cell membrane to rupture (hemolysis). **Why 0.48% is Correct:** In a healthy individual with normal RBC morphology: * **Initial Hemolysis:** RBCs begin to lyse at a saline concentration of approximately **0.48% to 0.50%**. * **Complete Hemolysis:** All RBCs are typically lysed when the concentration drops to **0.33% to 0.35%**. **Analysis of Incorrect Options:** * **A. 0.33%:** This represents the point of **complete hemolysis**, not the beginning. * **C. 0.90%:** This is **Isotonic Saline** (Normal Saline). At this concentration, there is no net movement of water; RBCs remain stable and do not hemolyse. * **D. 1.20%:** This is a **hypertonic solution**. In this environment, water leaves the RBC, causing it to shrink or "crenate" rather than burst. **High-Yield Clinical Pearls for NEET-PG:** 1. **Increased Fragility (Shifts to the Right):** Seen in **Hereditary Spherocytosis**. Because spherocytes already have a decreased surface-area-to-volume ratio, they burst at higher saline concentrations (e.g., 0.6%). 2. **Decreased Fragility (Shifts to the Left):** Seen in **Thalassemia, Sickle Cell Anemia, and Iron Deficiency Anemia**. These conditions often feature "target cells" or microcytes with a high surface-area-to-volume ratio, making them more resistant to osmotic lysis. 3. **Incubation:** The test is more sensitive if the blood is incubated at 37°C for 24 hours before testing.

Q: Which of the following are Vitamin K dependent clotting factors?

Factor IX & X. **Explanation:** Vitamin K is an essential cofactor for the enzyme **gamma-glutamyl carboxylase**, which catalyzes the post-translational carboxylation of glutamic acid residues on specific clotting factors. This process allows these factors to bind calcium ions ($Ca^{2+}$) and attach to phospholipid membranes, a crucial step in the coagulation cascade. The **Vitamin K-dependent factors** include: * **Pro-coagulants:** Factors **II (Prothrombin), VII, IX, and X**. * **Anti-coagulants:** **Protein C and Protein S**. **Analysis of Options:** * **Option B (Correct):** Factors IX (Christmas factor) and X (Stuart-Prower factor) are both Vitamin K-dependent. * **Option A:** Factor III (Tissue Factor) is a cell surface glycoprotein, and Factor XI is part of the intrinsic pathway but does not require Vitamin K for synthesis. * **Option C:** Factor V (Labile factor) and Factor VIII (Anti-hemophilic factor) are cofactors that do not undergo gamma-carboxylation. * **Option D:** Factor XIII (Fibrin stabilizing factor) is a transglutaminase that cross-links fibrin; it is not Vitamin K-dependent. **High-Yield Clinical Pearls for NEET-PG:** 1. **Warfarin Mechanism:** Warfarin acts as a Vitamin K antagonist by inhibiting **Vitamin K Epoxide Reductase (VKOR)**, preventing the recycling of Vitamin K. 2. **Half-life:** Factor VII has the shortest half-life (~6 hours), making the **Prothrombin Time (PT)** the first lab value to prolong during Vitamin K deficiency or early Warfarin therapy. 3. **Newborns:** Neonates are Vitamin K deficient due to a sterile gut and poor placental transfer; hence, prophylactic Vitamin K is given at birth to prevent **Hemorrhagic Disease of the Newborn**.

Q: Higher hematocrit in venous blood than in arterial blood is due to which of the following?

High chloride in RBC. ### Explanation The phenomenon of higher hematocrit in venous blood compared to arterial blood is primarily due to the **Chloride Shift (Hamburger Phenomenon)**. **1. Why Option A is Correct:** In venous blood, the partial pressure of $CO_2$ is high. $CO_2$ diffuses into Red Blood Cells (RBCs) and reacts with water to form carbonic acid ($H_2CO_3$), which dissociates into $H^+$ and $HCO_3^-$. To maintain electrical neutrality, as $HCO_3^-$ diffuses out of the RBC into the plasma, **Chloride ions ($Cl^-$) shift from the plasma into the RBC** via the Anion Exchanger 1 (Band 3 protein). The influx of $Cl^-$ increases the intracellular osmotic pressure, causing water to enter the RBC by osmosis. This results in **slight swelling of the RBCs**, thereby increasing the Mean Corpuscular Volume (MCV) and the overall hematocrit (Hct) in venous blood. **2. Why Other Options are Incorrect:** * **Option B & C:** While $Na^+$ and $HCO_3^-$ are high in the plasma of venous blood, they do not cause the RBC swelling. In fact, the movement of $HCO_3^-$ *out* of the cell is what triggers the $Cl^-$ shift. * **Option D:** $K^+$ is the primary intracellular cation, but its concentration does not change significantly between arterial and venous blood to affect hematocrit. **High-Yield Clinical Pearls for NEET-PG:** * **Reverse Chloride Shift:** Occurs in the lungs (arterial blood) where $Cl^-$ moves out of the RBC, causing them to shrink slightly. * **MCV Difference:** Venous RBCs have an MCV approximately 3% higher than arterial RBCs. * **Band 3 Protein:** The specific membrane transporter responsible for the $Cl^-/HCO_3^-$ exchange. * **Hematocrit Variation:** Because of this shift, hematocrit measured from peripheral venous samples is slightly higher than the actual systemic arterial hematocrit.

Q: In RBC development, in which stage does haemoglobin first appear?

Polychromatic erythroblast. ### Explanation The correct answer is **Polychromatic erythroblast** (Intermediate Normoblast). #### 1. Why Polychromatic Erythroblast is Correct Hemoglobin synthesis begins early in the Proerythroblast stage, but it is **first visible** under a light microscope during the **Polychromatic erythroblast** stage. At this stage, the cytoplasm exhibits a "muddy" or "polychromatic" appearance. This is due to the dual presence of: * **Basophilia:** From the remaining ribosomes and RNA. * **Acidophilia:** From the newly synthesized hemoglobin. The mix of pink (hemoglobin) and blue (RNA) gives the cell its characteristic greyish-purple hue. #### 2. Why Other Options are Incorrect * **Basophilic Erythroblast (Early Normoblast):** While the cell is actively synthesizing the machinery for hemoglobin, the cytoplasm is intensely basophilic due to a high concentration of RNA and ribosomes. Hemoglobin is not yet visible. * **Orthochromatic Erythroblast (Late Normoblast):** In this stage, hemoglobin is present in high concentrations, giving the cytoplasm a purely eosinophilic (pink) appearance similar to a mature RBC. However, it is not the *first* stage of appearance. This is also the stage where the nucleus is extruded. * **Reticulocyte:** This is a post-nuclear stage. While it contains 80% of the total hemoglobin of a mature RBC, it represents a later stage of development. #### 3. NEET-PG High-Yield Pearls * **Nucleolus Disappears:** In the Basophilic erythroblast stage. * **Nucleus Extrusion:** Occurs at the Orthochromatic erythroblast stage. * **Reticulocyte Count:** An index of effective erythropoiesis (Normal: 0.5–2%). They contain "reticulum" which is actually remnants of RNA/ribosomes, best seen with **Supravital stains** (e.g., New Methylene Blue). * **Total Time for Erythropoiesis:** Approximately 7 days (5 days to reach reticulocyte stage + 2 days to mature into RBC).

Q: Serotonin is mainly secreted by which of the following?

Platelets. **Explanation:** **Correct Answer: B. Platelets** Serotonin (5-hydroxytryptamine) is a potent vasoconstrictor and neurotransmitter. In the blood, it is **not synthesized** by platelets but is actively taken up from the plasma (produced by enterochromaffin cells of the gut) and stored in the **Dense Granules (delta granules)** of platelets. When a blood vessel is injured, platelets aggregate and release serotonin, which causes local vasoconstriction to minimize blood loss. **Why other options are incorrect:** * **A. Mast cells:** These primarily secrete **Histamine**, heparin, and proteases. While mast cells in rodents contain serotonin, human mast cells do not typically store or secrete significant amounts of it. * **C. Neutrophils:** These are phagocytic cells primarily involved in acute inflammation. They secrete lysosomal enzymes and reactive oxygen species (ROS), not serotonin. * **D. Macrophages:** These are involved in phagocytosis and cytokine production (like TNF-alpha and IL-1). They do not serve as a primary source of serotonin. **High-Yield Clinical Pearls for NEET-PG:** * **Platelet Granules:** * **Dense Granules:** Contain **S**erotonin, **A**DP/ATP, and **C**alcium (**SAC**). * **Alpha Granules:** Contain vWF, Fibrinogen, and Platelet-Derived Growth Factor (PDGF). * **Synthesis:** 90% of the body's serotonin is synthesized by the **Enterochromaffin (Kulchitsky) cells** of the gastrointestinal tract. * **Precursor:** Serotonin is derived from the amino acid **Tryptophan**. * **Clinical Correlation:** In **Carcinoid Syndrome**, excessive serotonin production leads to flushing, diarrhea, and right-sided heart valve lesions. The diagnostic marker is elevated urinary **5-HIAA**.

Question 1

All statements about lactoferrin are true, except?

Accepted Answer

It transports iron for erythropoiesis.

Answer

It is present in the secondary granules of neutrophils.

Answer

It is present in exocrine secretions of the body.

Answer

It has a great affinity for iron.

Question 2

Pre-B cells and B cells are produced in which location?

Accepted Answer

Bone marrow

Answer

Thymus

Answer

Tonsils

Answer

Gut associated lymphoid tissue

Question 3

Platelet activation includes:

Accepted Answer

All of the above

Answer

Adhesion

Answer

Secretion

Answer

Aggregation

Question 4

In a person weighing 100 Kgs, what is the estimated blood volume?

Accepted Answer

8 L

Answer

5 L

Answer

6 L

Answer

10 L

Question 5

Which coagulation factor is not freely circulating in the blood?

Accepted Answer

Factor 3

Answer

Factor 9

Answer

Factor 10

Answer

Factor 12

Question 6

When osmotic fragility is normal, RBCs begin to hemolyse when suspended in saline at what concentration?

Accepted Answer

0.48%

Answer

0.33%

Answer

0.90%

Answer

1.20%

Question 7

Which of the following are Vitamin K dependent clotting factors?

Accepted Answer

Factor IX & X

Answer

Factor III & XI

Answer

Factor V & VIII

Answer

Factor XI & XIII

Question 8

Higher hematocrit in venous blood than in arterial blood is due to which of the following?

Accepted Answer

High chloride in RBC

Answer

High Na+ in plasma

Answer

High HCO3- in plasma

Answer

High K+ in RBC

Question 9

In RBC development, in which stage does haemoglobin first appear?

Accepted Answer

Polychromatic erythroblast

Answer

Basophilic erythroblast

Answer

Orthochromatic erythroblast

Answer

Reticulocyte

Question 10

Serotonin is mainly secreted by which of the following?

Accepted Answer

Platelets

Answer

Mast cells

Answer

Neutrophils

Answer

Macrophages

Blood and Immunity — MCQs

Blood and Immunity — MCQs

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