Blood and Immunity Practice Questions

Q: What is the predominant site of erythropoiesis during the sixth month of gestation?

Liver. The process of erythropoiesis during fetal development occurs in distinct overlapping stages, often remembered by the mnemonic **"Young Liver Synthesizes Blood."** ### **1. Why Liver is the Correct Answer** The **hepatic stage** of erythropoiesis begins around the 6th week of gestation and reaches its peak activity during the **second trimester (3rd to 6th month)**. During the sixth month, the liver remains the primary erythropoietic organ, although the bone marrow is just beginning to take over this function. By the end of the second trimester, the liver is the predominant site for producing red blood cells. ### **2. Analysis of Incorrect Options** * **A. Yolk sac:** This is the site of the **Mesoblastic stage**. It is the first site of hematopoiesis, starting at the 3rd week, but it ceases to be active by the end of the first trimester (around 10–12 weeks). * **C. Bone marrow:** The **Myeloid stage** begins in the bone marrow around the 4th to 5th month. However, it only becomes the *predominant* site after the 7th month of gestation and remains the primary site for the rest of postnatal life. * **D. Thymus:** While the thymus is involved in T-lymphocyte maturation, it is never a primary site for erythropoiesis (RBC production). ### **3. High-Yield Clinical Pearls for NEET-PG** * **Chronology:** Yolk sac (3rd week) → Liver (6th week; peak at 3–6 months) → Spleen (3rd to 7th month) → Bone Marrow (starts at 4th month; dominant from 7th month onwards). * **Spleen's Role:** The spleen contributes to erythropoiesis primarily between the 3rd and 6th months but is always secondary to the liver. * **Post-natal site:** In adults, hematopoiesis is restricted to the **axial skeleton** (vertebrae, sternum, ribs, and pelvis). * **Extramedullary Hematopoiesis:** In certain pathological states (e.g., Thalassemia, Myelofibrosis), the liver and spleen can resume their fetal erythropoietic function.

Q: A person with anti-A and anti-B isoagglutinins in their serum belongs to which blood group?

O. ### Explanation The correct answer is **D. O**. This question is based on **Landsteiner’s Law**, which states that if an agglutinogen (antigen) is present on the red blood cell (RBC) membrane, the corresponding agglutinin (antibody) must be absent from the serum, and vice versa. **Why Option D is Correct:** Individuals with **Blood Group O** have neither Antigen A nor Antigen B on their RBC surfaces. According to Landsteiner’s Law, because these antigens are absent, the body produces both **anti-A and anti-B isoagglutinins** (antibodies) in the serum. These antibodies are typically IgM in nature and develop within the first few months of life. **Why Other Options are Incorrect:** * **Option A (Blood Group A):** These individuals have Antigen A on RBCs and only **anti-B** antibodies in the serum. * **Option B (Blood Group B):** These individuals have Antigen B on RBCs and only **anti-A** antibodies in the serum. * **Option C (Blood Group AB):** These individuals have both Antigen A and B on RBCs; therefore, they have **no isoagglutinins** in their serum (making them the "Universal Recipient"). **High-Yield Clinical Pearls for NEET-PG:** * **Universal Donor:** Group O (specifically O negative) is the universal donor because it lacks A and B antigens. * **Bombay Blood Group:** A rare phenotype where the H-antigen is absent. These individuals have anti-A, anti-B, and **anti-H** antibodies, meaning they can only receive blood from another Bombay phenotype individual. * **Antibody Type:** Naturally occurring ABO antibodies are primarily **IgM** (cannot cross the placenta), whereas Rh antibodies are **IgG** (can cross the placenta, leading to Erythroblastosis Fetalis). * **Secretors:** About 80% of the population secretes ABO antigens in body fluids like saliva and semen.

Q: Which of the following is not a component of secondary hemostasis?

Platelet degranulation. Hemostasis is the physiological process that stops bleeding at the site of vascular injury. It occurs in two distinct but overlapping phases: **1. Why "Platelet degranulation" is the correct answer:** Platelet degranulation is a hallmark of **Primary Hemostasis**. When blood vessels are injured, platelets adhere to the subendothelial collagen (via von Willebrand factor). This triggers activation and degranulation, where platelets release ADP and Thromboxane A2 to recruit more platelets and form a fragile **platelet plug**. Since the question asks for a component that is *not* part of secondary hemostasis, this is the correct choice. **2. Why the other options are incorrect:** Secondary hemostasis involves the **coagulation cascade**, which aims to stabilize the initial platelet plug by forming a cross-linked fibrin mesh. * **Formation of coagulation factor complexes (Option C):** This is the core of the cascade (e.g., the Tenase and Prothrombinase complexes). * **Thrombin activation (Option A):** This is the "explosive" step where prothrombin is converted to thrombin (Factor IIa). * **Fibrin polymerization (Option B):** Thrombin converts soluble fibrinogen into insoluble fibrin monomers, which then polymerize to form the stable clot. **Clinical Pearls for NEET-PG:** * **Primary Hemostasis defects:** Present with mucosal bleeding, petechiae, and prolonged **Bleeding Time (BT)** (e.g., von Willebrand Disease, ITP). * **Secondary Hemostasis defects:** Present with deep tissue hematomas and hemarthrosis (joint bleeding) and prolonged **PT/aPTT** (e.g., Hemophilia). * **Vitamin K-dependent factors:** II, VII, IX, X, and Proteins C and S. * **Rate-limiting step:** The activation of Factor X is the convergence point of the intrinsic and extrinsic pathways.

Q: Which coagulation pathway is activated upon contact with a glass test tube?

Intrinsic pathway. ### Explanation **Correct Option: A. Intrinsic pathway** The **Intrinsic pathway** is initiated when blood comes into contact with a **negatively charged surface**, such as the silica in a glass test tube, collagen in a damaged vessel wall, or basement membranes. This process is known as **contact activation**. * **Mechanism:** Contact with glass activates **Factor XII (Hageman factor)**. Once activated (XIIa), it triggers a cascade involving Factor XI, Factor IX, and Factor VIII, eventually leading to the activation of Factor X in the common pathway. * **Key Fact:** This pathway is called "intrinsic" because all the components required for it to function are found within the circulating blood itself. **Why other options are wrong:** * **B. Extrinsic pathway:** This pathway is triggered by **Tissue Factor (Factor III/Thromboplastin)**, which is released from damaged tissues *outside* the blood vessels. It is not activated by simple contact with glass. * **C & D:** Since the activation mechanism (surface contact) specifically targets Factor XII, only the intrinsic pathway is initially triggered. --- ### High-Yield Clinical Pearls for NEET-PG * **Laboratory Test:** The **aPTT (activated Partial Thromboplastin Time)** measures the integrity of the Intrinsic and Common pathways. * **Factor XII Deficiency:** Interestingly, patients with a deficiency in Factor XII (Hageman factor) show a prolonged aPTT in the lab but **do not have clinical bleeding disorders** in vivo. * **The "Glass" Connection:** In modern labs, plastic tubes are often coated with silica (glass particles) specifically to activate the intrinsic pathway and speed up clot formation for serum collection. * **Sequence of Activation:** Remember the "Countdown" for the Intrinsic pathway: **12 → 11 → 9 → 8** (skipping 10, which is the start of the Common pathway).

Q: Which of the following facilitates the entry of iron?

DMT-1. **Explanation:** Iron absorption is a tightly regulated process occurring primarily in the duodenum and proximal jejunum. The correct answer is **DMT-1 (Divalent Metal Transporter 1)**. 1. **Why DMT-1 is correct:** Iron in the diet exists as ferric ($Fe^{3+}$) or ferrous ($Fe^{2+}$) iron. After ferric iron is reduced to the ferrous state by duodenal cytochrome B (DcytB), **DMT-1** acts as the primary apical transporter that facilitates the entry of $Fe^{2+}$ from the intestinal lumen into the enterocyte. It is a symporter that transports iron along with protons ($H^+$). 2. **Why other options are incorrect:** * **Hepcidin:** This is the master regulator of iron homeostasis produced by the liver. It **inhibits** iron entry into the plasma by causing the degradation of ferroportin. High hepcidin levels decrease iron absorption. * **DMT-2:** This is a distractor; it is not a recognized major transporter in human iron metabolism. * **Ferroportin:** While it facilitates iron movement, it is the **basolateral** exporter that moves iron *out* of the enterocyte into the blood, rather than facilitating its initial entry into the cell. **High-Yield Clinical Pearls for NEET-PG:** * **Heme Iron:** Absorbed more efficiently than non-heme iron via the **HCP-1** (Heme Carrier Protein 1). * **Ferroportin:** The only known iron exporter in mammals; its deficiency or inhibition leads to iron-restricted erythropoiesis. * **Hepcidin Regulation:** Levels increase during inflammation (via IL-6), leading to "Anemia of Chronic Disease" due to iron sequestration. * **Vitamin C:** Enhances iron absorption by maintaining iron in the soluble ferrous ($Fe^{2+}$) state.

Q: Up to 6 weeks of gestation, in which structure does erythropoiesis primarily occur?

Yolk sac. **Explanation:** Erythropoiesis (the formation of red blood cells) occurs in distinct stages during intrauterine life, transitioning through three specific phases: **Mesoblastic, Hepatic, and Myeloid.** **1. Why A is Correct:** The **Mesoblastic stage** is the earliest phase of erythropoiesis. It begins around the 3rd week of gestation within the **yolk sac** (specifically in the blood islands). This remains the primary site of RBC production until approximately the **6th week** of gestation. These early cells are large, nucleated macroblasts. **2. Why the other options are incorrect:** * **D. Liver:** This marks the **Hepatic stage**. The liver takes over as the primary site of erythropoiesis from the 6th week until the mid-trimester (peak at 3–5 months). While it starts at 6 weeks, the yolk sac is the answer for the period *up to* 6 weeks. * **C. Spleen:** The spleen contributes to erythropoiesis during the second trimester (months 3 to 6) but is never the primary site compared to the liver. * **B. Bone Marrow:** This is the **Myeloid stage**. The bone marrow begins producing blood cells around the 4th to 5th month and becomes the dominant site from the 7th month onwards and throughout postnatal life. **NEET-PG High-Yield Pearls:** * **Sequence of sites:** Yolk Sac → Liver → Spleen → Bone Marrow. * **Hemoglobin types:** Yolk sac produces embryonic hemoglobins (Gower I, Gower II, and Portland). Fetal hemoglobin (HbF) is primarily produced in the liver. * **Post-birth:** In adults, erythropoiesis is restricted to the membranous bones (vertebrae, sternum, ribs, and ilia) after age 20, as the shafts of long bones undergo fat replacement.

Q: Which of the following is NOT true regarding fetal red blood cells?

Elevated 2,3-DPG. **Explanation:** The correct answer is **A (Elevated 2,3-DPG)** because fetal red blood cells (RBCs) actually have a **lower affinity for 2,3-DPG** compared to adult RBCs. **1. Why Option A is the correct (False) statement:** Fetal hemoglobin (HbF) consists of two alpha and two **gamma (γ)** chains. Unlike the beta chains in adult hemoglobin (HbA), the gamma chains lack certain positively charged amino acids, reducing their ability to bind to the negatively charged 2,3-DPG. Because 2,3-DPG normally functions to stabilize the "T-state" (deoxygenated state) and promote oxygen unloading, its inability to bind HbF results in a **higher oxygen affinity**. This shift to the left on the oxygen-dissociation curve is crucial for the fetus to extract oxygen from maternal blood across the placenta. **2. Analysis of Incorrect Options (True statements):** * **B. Decreased carbonic anhydrase activity:** Fetal RBCs have significantly lower levels of carbonic anhydrase compared to adults. This is a high-yield physiological characteristic of neonatal blood. * **C. Decreased life span:** Fetal RBCs have a shorter lifespan (approximately **60–90 days**) compared to the 120-day lifespan of adult RBCs. This contributes to physiological jaundice in neonates. * **D. High RBC volume:** Fetal RBCs are **macrocytic** (larger Mean Corpuscular Volume) and the fetus maintains a higher hematocrit/hemoglobin level to compensate for the relatively low pO2 in utero. **High-Yield Clinical Pearls for NEET-PG:** * **P50 Value:** The P50 (partial pressure of O2 at which Hb is 50% saturated) is **lower** in the fetus (~19 mmHg) than in adults (~27 mmHg), reflecting higher affinity. * **HbF Structure:** $\alpha_2\gamma_2$. * **Switchover:** HbF is gradually replaced by HbA after birth; by 6 months of age, HbA becomes the predominant type.

Q: What is the physiological result of storage of packed red blood cells?

Decrease in 2,3-diphosphoglycerate (2,3-DPG). ### Explanation The storage of Packed Red Blood Cells (PRBCs) leads to a series of biochemical and structural changes collectively known as the **"Storage Lesion."** **Why Option B is Correct:** During storage, RBCs continue to undergo anaerobic glycolysis, but at a reduced rate. Over time, there is a progressive **decrease in 2,3-diphosphoglycerate (2,3-DPG)** levels. Since 2,3-DPG normally facilitates oxygen unloading by stabilizing the T-state (deoxy-form) of hemoglobin, its depletion causes hemoglobin to bind oxygen more tightly. **Analysis of Incorrect Options:** * **Option A:** Because 2,3-DPG levels fall, the **Oxy-hemoglobin dissociation curve shifts to the LEFT**, not the right. This indicates an increased affinity of hemoglobin for oxygen and decreased delivery to tissues. * **Option C:** The pH actually **decreases (becomes more acidic)**. This is due to the accumulation of lactic acid and pyruvic acid from ongoing anaerobic metabolism within the storage bag. * **Option D:** There is an **increase in lactate** levels as a byproduct of anaerobic glycolysis during the storage period. **High-Yield Clinical Pearls for NEET-PG:** * **The Storage Lesion Summary:** ↓ 2,3-DPG, ↓ pH (Acidosis), ↓ ATP, ↑ Potassium (due to Na+/K+ pump failure), and ↑ Lactate. * **Shift to the Left:** Remember the mnemonic **"Left is Low"**—Low 2,3-DPG, Low Temp, Low H+ (High pH), and Low CO2 all shift the curve to the left. * **Clinical Impact:** Massive transfusion of stored blood can lead to **hyperkalemia** and **hypocalcemia** (due to citrate anticoagulant). * **Recovery:** Once transfused, 2,3-DPG levels typically begin to regenerate within 6–24 hours in the recipient’s circulation.

Question 1

What is the predominant site of erythropoiesis during the sixth month of gestation?

Accepted Answer

Liver

Answer

Yolk sac

Answer

Bone marrow

Answer

Thymus

Question 2

A person with anti-A and anti-B isoagglutinins in their serum belongs to which blood group?

Accepted Answer

O

Answer

A

Answer

B

Answer

AB

Question 3

Which of the following is not a component of secondary hemostasis?

Accepted Answer

Platelet degranulation

Answer

Thrombin activation

Answer

Fibrin polymerization

Answer

Formation of coagulation factor complexes

Question 4

2,3-Diphosphoglycerate (2,3-DPG) in red blood cells does not increase upon stimulation by which of the following conditions?

Accepted Answer

Chronic anemia

Answer

Hypoxia

Answer

Hypoxia

Answer

None of the above

Question 5

Which coagulation pathway is activated upon contact with a glass test tube?

Accepted Answer

Intrinsic pathway

Answer

Extrinsic pathway

Answer

Both pathways

Answer

Neither pathway

Question 6

Which of the following facilitates the entry of iron?

Accepted Answer

DMT-1

Answer

Hepcidin

Answer

DMT-2

Answer

Ferroportin

Question 7

Up to 6 weeks of gestation, in which structure does erythropoiesis primarily occur?

Accepted Answer

Yolk sac

Answer

Bone marrow

Answer

Spleen

Answer

Liver

Question 8

Which of the following is NOT true regarding fetal red blood cells?

Accepted Answer

Elevated 2,3-DPG

Answer

Decreased carbonic anhydrase activity

Answer

Decreased life span

Answer

High RBC volume

Question 9

What is the physiological result of storage of packed red blood cells?

Accepted Answer

Decrease in 2,3-diphosphoglycerate (2,3-DPG)

Answer

Oxy-hemoglobin curve shifts to the right

Answer

Increase in pH

Answer

Decrease in lactate

Question 10

Which one of the following is a potent stimulus for the production of erythropoietin?

Accepted Answer

Hypoxia

Answer

Alpha interferon

Answer

Interleukin-3

Answer

Hypercarbia

Blood and Immunity — MCQs

Blood and Immunity — MCQs

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