Blood and Immunity Indian Medical PG Practice Questions and MCQs
Practice Indian Medical PG questions for Blood and Immunity. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Blood and Immunity Indian Medical PG Question 1: What is the inheritance pattern of the ABO blood group system and the HLA system?
- A. Pseudodominance
- B. Autosomal dominant
- C. Autosomal recessive
- D. Codominant (Correct Answer)
Blood and Immunity Explanation: ### Explanation
**Correct Option: D (Codominant)**
The ABO blood group and the Human Leukocyte Antigen (HLA) system are classic examples of **codominance**. In codominance, both alleles in a heterozygous individual are fully expressed, and neither masks the other.
* **ABO System:** The $I^A$ and $I^B$ alleles are codominant. If an individual inherits $I^A$ from one parent and $I^B$ from the other, their phenotype is AB, expressing both A and B antigens on the RBC surface. (Note: Both $I^A$ and $I^B$ are dominant over the $i$ allele).
* **HLA System:** HLA genes (located on Chromosome 6) are the most polymorphic genes in humans. An individual expresses HLA antigens from both maternal and paternal haplotypes simultaneously on the cell surface. This is critical for immune recognition and organ transplant matching.
**Why other options are incorrect:**
* **A. Pseudodominance:** This occurs when a recessive allele is expressed because the dominant allele is missing (e.g., due to deletion), commonly seen in X-linked disorders in males.
* **B & C. Autosomal Dominant/Recessive:** These follow Mendelian patterns where one allele masks the other. In ABO, while A and B are dominant over O, they do not mask each other, making "Codominant" the more specific and accurate description.
**High-Yield Facts for NEET-PG:**
1. **Multiple Allelism:** The ABO system is also an example of multiple allelism (three alleles: A, B, and O).
2. **Bombay Phenotype:** A rare condition where the H-substance is missing; these individuals phenotypically appear as Type O regardless of their genotype.
3. **HLA Association:** HLA-B27 is strongly associated with Ankylosing Spondylitis; HLA-DR3/DR4 is associated with Type 1 Diabetes Mellitus.
4. **Chromosome 9:** The locus for the ABO gene is on the long arm of Chromosome 9.
Blood and Immunity Indian Medical PG Question 2: All of the following are functions of the spleen EXCEPT?
- A. Clearance of damaged or aged red blood cells (RBCs) from the blood.
- B. Extramedullary site for hematopoiesis and recycling iron.
- C. Initiation of adaptive immune response from filtration of lymph. (Correct Answer)
- D. Clearance of encapsulated bacteria from the bloodstream.
Blood and Immunity Explanation: ### Explanation
The correct answer is **C. Initiation of adaptive immune response from filtration of lymph.**
The spleen is often described as a "giant lymph node," but there is a critical anatomical difference: **the spleen filters blood, not lymph.** Lymph nodes are responsible for filtering interstitial fluid (lymph) via afferent lymphatic vessels. The spleen lacks afferent lymphatics; instead, it samples antigens directly from the systemic circulation via the splenic artery.
#### Analysis of Options:
* **Option A (Correct Function):** The splenic sinusoids and the "pitting" mechanism in the Red Pulp act as a biological filter, removing senescent, rigid, or damaged RBCs (Culling).
* **Option B (Correct Function):** During fetal development (months 3–7), the spleen is a primary hematopoietic organ. In adults, it can resume this role (extramedullary hematopoiesis) in conditions like myelofibrosis. It also recycles iron from hemoglobin via splenic macrophages.
* **Option D (Correct Function):** The White Pulp contains B-cells and T-cells. Splenic macrophages and antibodies are essential for opsonizing and clearing **encapsulated organisms** (e.g., *S. pneumoniae, H. influenzae, N. meningitidis*).
#### High-Yield Clinical Pearls for NEET-PG:
* **Asplenia/Splenectomy:** Patients are at high risk for **OPSI (Overwhelming Post-Splenectomy Infection)**. Vaccination against encapsulated bacteria is mandatory (ideally 2 weeks before elective surgery).
* **Howell-Jolly Bodies:** These are nuclear remnants in RBCs normally removed by the spleen; their presence on a peripheral smear is a hallmark of splenic dysfunction or asplenia.
* **Pitting:** The spleen’s ability to remove inclusions (like malaria parasites or Heinz bodies) from RBCs without destroying the cell itself.
Blood and Immunity Indian Medical PG Question 3: What is the first cell in the development of red blood cells?
- A. Proerythroblast (Correct Answer)
- B. Intermediate normoblast
- C. Reticulocyte
- D. Basophilic erythroblast
Blood and Immunity Explanation: **Explanation:**
The process of red blood cell formation, known as **erythropoiesis**, occurs in the bone marrow. It begins with a multipotent hematopoietic stem cell, which differentiates into a **Proerythroblast** (also called a Pronormoblast).
**Why Proerythroblast is correct:**
The Proerythroblast is the **first morphologically identifiable committed precursor** of the erythroid series. It is a large cell with a big nucleus, visible nucleoli, and a thin rim of basophilic cytoplasm. Once a stem cell differentiates into a proerythroblast, it is "committed" to becoming a mature erythrocyte.
**Analysis of Incorrect Options:**
* **Basophilic erythroblast (Early Normoblast):** This is the second stage. It is smaller than the proerythroblast and shows intense cytoplasmic basophilia due to an accumulation of RNA for hemoglobin synthesis.
* **Intermediate normoblast (Polychromatophilic erythroblast):** This is the third stage. It is characterized by a "checkered" nucleus and a cytoplasm that appears grayish/purple because it contains both basic RNA and acidic hemoglobin.
* **Reticulocyte:** This is the penultimate stage, occurring after the nucleus is extruded (at the orthochromatic stage). It is an immature RBC that stays in the marrow for 1–2 days before entering the peripheral circulation.
**NEET-PG High-Yield Pearls:**
1. **Hemoglobin synthesis** begins in the **Proerythroblast** stage, but becomes visible (morphologically detectable) in the **Intermediate Normoblast** stage.
2. The **nucleus is extruded** at the **Orthochromatic Normoblast** (Late Normoblast) stage.
3. **Reticulocyte count** is the best clinical indicator of effective erythropoiesis in the bone marrow.
4. **Erythropoietin (EPO)** primarily acts on the CFU-E (Colony Forming Unit-Erythroid) to stimulate the production of proerythroblasts.
Blood and Immunity Indian Medical PG Question 4: The biconcave shape of RBC is useful for all the following functions EXCEPT:
- A. Allows considerable alteration in cell volume
- B. Increasing surface area for diffusion (Correct Answer)
- C. Resisting hemolysis
- D. Passing easily through smaller capillaries
Blood and Immunity Explanation: The biconcave shape of the Red Blood Cell (RBC) is a specialized structural adaptation designed for flexibility and volume management rather than maximizing surface area.
### **Explanation of the Correct Answer**
**Option B (Increasing surface area for diffusion)** is the correct answer because it is a common misconception. Mathematically, a **sphere** has the minimum surface area for a given volume, while a **flat disc** or complex shape has more. However, the biconcave shape is *not* the most efficient shape for maximizing surface area; a thin, flat sheet or a highly folded membrane would provide more area for gas exchange. The primary evolutionary "goal" of the biconcave shape is to provide a high **surface-area-to-volume ratio**, which allows for significant cell deformation and volume changes without stretching the membrane.
### **Analysis of Other Options**
* **Option A & C:** The biconcave shape provides "excess" membrane. This allows the RBC to undergo **considerable alteration in cell volume** (swelling in hypotonic solutions) without rupturing. Because the membrane isn't under tension in its resting state, it can expand into a spherical shape before bursting, thereby **resisting hemolysis**.
* **Option D:** RBCs (7.5 µm) must pass through splenic sinusoids and capillaries as small as 3 µm. The biconcave shape allows the cell to fold and deform easily (**high deformability**), facilitating passage through narrow microvasculature.
### **High-Yield Clinical Pearls for NEET-PG**
* **Hereditary Spherocytosis:** A defect in membrane proteins (Ankyrin/Spectrin) causes RBCs to lose their biconcave shape and become spherical. These cells have the *lowest* surface-area-to-volume ratio, are fragile, and are easily destroyed in the spleen.
* **Average RBC Diameter:** 7.5 µm (Thickness: 2 µm at periphery, 1 µm at center).
* **Rouleaux Formation:** The biconcave shape facilitates the "stacking" of RBCs, seen in states of high ESR (e.g., chronic inflammation).
Blood and Immunity Indian Medical PG Question 5: Which of the following is responsible for the adhesion of platelets to the vessel wall?
- A. Von Willebrand factor (Correct Answer)
- B. Factor IX
- C. Fibrinogen
- D. Fibronectin
Blood and Immunity Explanation: **Explanation:**
The correct answer is **Von Willebrand factor (vWF)**. Platelet plug formation occurs in three distinct stages: Adhesion, Activation, and Aggregation.
1. **Why vWF is correct:** When a blood vessel is injured, the subendothelial collagen is exposed. Platelets cannot bind directly to collagen under high-shear stress (like in arteries). **vWF** acts as a molecular bridge; one end binds to the exposed **subendothelial collagen**, and the other end binds to the **Glycoprotein Ib (GpIb)** receptor on the platelet surface. This specific interaction is responsible for **platelet adhesion**.
2. **Why the other options are incorrect:**
* **Factor IX:** This is a component of the intrinsic pathway of the coagulation cascade. Its deficiency leads to Hemophilia B (Christmas disease). It is involved in secondary hemostasis (clotting), not primary platelet adhesion.
* **Fibrinogen:** This is responsible for **platelet aggregation**. Fibrinogen binds to the **GpIIb/IIIa** receptors on adjacent platelets, linking them together to form a plug.
* **Fibronectin:** While fibronectin is present in the extracellular matrix and plasma and plays a minor role in cell-matrix interactions, it is not the primary mediator of initial platelet adhesion to the vessel wall.
**High-Yield Clinical Pearls for NEET-PG:**
* **Bernard-Soulier Syndrome:** A deficiency of the **GpIb** receptor, leading to defective adhesion (characterized by giant platelets and thrombocytopenia).
* **Von Willebrand Disease (vWD):** The most common inherited bleeding disorder; it results in defective adhesion due to a deficiency or dysfunction of vWF.
* **Glanzmann Thrombasthenia:** A deficiency of the **GpIIb/IIIa** receptor, leading to defective **aggregation**.
* **vWF Source:** It is synthesized in endothelial cells (stored in **Weibel-Palade bodies**) and megakaryocytes (stored in **α-granules** of platelets).
More Blood and Immunity Indian Medical PG questions available in the OnCourse app. Practice MCQs, flashcards, and get detailed explanations.
