Blood and Immunity — MCQs
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Maturation failure due to poor absorption of vitamin B12 causes which of the following?
A 40-year-old female patient complains of excessive bleeding. She has a history of a road traffic accident 5 hours ago with a lacerated wound on the lower back region. Blood grouping reveals the presence of antigen A and antigen B. This system for blood grouping consists of 3 major allelic genes which are located on which chromosome?
Which of the following is NOT a function of plasmin?
Erythropoietin production is inhibited by:
Heme is converted to bilirubin mainly in which of the following locations?
What is the approximate percentage of lymphocytes in the blood of a normal adult person?
Which white blood cell is considered the "second line of defense"?
Which of the following organs is a primary lymphoid organ?
Which of the following cells is responsible for destroying bacterial foreign bodies in liver sinusoids?
Which of the following clotting factor participates in the extrinsic pathway of coagulation?
Blood and Immunity Indian Medical PG Practice Questions and MCQs
Question 381: Maturation failure due to poor absorption of vitamin B12 causes which of the following?
- A. Microcytic hypochromic anemia
- B. Sickle cell anemia
- C. Megaloblastic anemia (manifesting in 3-4 months after absorption failure) (Correct Answer)
- D. Polycythemia
Explanation: **Explanation:** **Why Option C is Correct:** Vitamin B12 (Cobalamin) and Folic acid are essential for **DNA synthesis**, specifically for the formation of thymidine triphosphate. When B12 is deficient due to poor absorption (often caused by a lack of Intrinsic Factor), DNA replication slows down while cytoplasmic growth continues. This results in **nuclear-cytoplasmic asynchrony**, leading to the production of large, immature, and fragile red blood cells called **megaloblasts**. The parenthetical note in the option is a high-yield distinction: while folate stores last only a few months, the liver stores enough Vitamin B12 to last **3 to 4 years**. However, the physiological manifestation of megaloblastic changes in the bone marrow begins once stores are depleted. **Why Other Options are Incorrect:** * **Option A:** Microcytic hypochromic anemia is characteristic of **Iron Deficiency Anemia**, where there is a failure of hemoglobin synthesis, not DNA maturation. * **Option B:** Sickle cell anemia is a **qualitative hemoglobinopathy** caused by a point mutation (valine replacing glutamic acid) in the beta-globin chain. * **Option D:** Polycythemia refers to an **increase** in the total red cell mass, often due to chronic hypoxia or myeloproliferative disorders, which is the opposite of the cytopenia seen in B12 deficiency. **High-Yield NEET-PG Pearls:** * **Pernicious Anemia:** An autoimmune destruction of gastric parietal cells leading to B12 deficiency. * **Schilling Test:** Historically used to determine the cause of B12 malabsorption. * **Peripheral Smear:** Look for **Hypersegmented Neutrophils** (early sign) and **Macro-ovalocytes**. * **Neurological Symptoms:** B12 deficiency (unlike Folate) causes **Subacute Combined Degeneration (SCD)** of the spinal cord due to defective myelin synthesis.
Question 382: A 40-year-old female patient complains of excessive bleeding. She has a history of a road traffic accident 5 hours ago with a lacerated wound on the lower back region. Blood grouping reveals the presence of antigen A and antigen B. This system for blood grouping consists of 3 major allelic genes which are located on which chromosome?
- A. Chromosome 8
- B. Chromosome 9 (Correct Answer)
- C. Chromosome 10
- D. Chromosome 7
Explanation: ### Explanation **1. Why Chromosome 9 is Correct:** The patient’s blood group is **AB**, as indicated by the presence of both Antigen A and Antigen B on the red cell surface. This is determined by the **ABO blood group system**, which is governed by a single gene locus (the *ABO* gene) located on the **long arm of Chromosome 9 (9q34.2)**. The system follows the principle of **multiple allelism** (three alleles: $I^A$, $I^B$, and $i$) and **codominance** (where $I^A$ and $I^B$ are both expressed). These alleles encode specific glycosyltransferases that add sugar molecules to the H-substance to form A or B antigens. **2. Why Other Options are Incorrect:** * **Chromosome 8:** Does not harbor major blood group genes. It is clinically significant in hematology for the *c-myc* proto-oncogene (associated with Burkitt lymphoma). * **Chromosome 10:** Not associated with the ABO system. It contains genes like *RET* (associated with MEN 2) and *PTEN*. * **Chromosome 7:** While it carries the gene for the **Kell blood group system**, it is not responsible for the ABO system. **3. High-Yield Clinical Pearls for NEET-PG:** * **Rh Blood Group:** The genes for the Rh system (*RHD* and *RHCE*) are located on **Chromosome 1**. * **H-Substance:** The *H* gene (FUT1), which is the precursor for A and B antigens, is located on **Chromosome 19**. A deficiency in this leads to the rare **Bombay Blood Group**. * **Inheritance:** ABO inheritance is a classic example of **Mendelian genetics** involving codominance ($I^A$ and $I^B$) and complete dominance over the recessive allele ($i$). * **Universal Recipient:** AB positive; **Universal Donor:** O negative.
Question 383: Which of the following is NOT a function of plasmin?
- A. Fibrinolysis
- B. Activation of collagenase
- C. Destruction of von Willebrand Factor (vWF)
- D. Stabilization of fibrin (Correct Answer)
Explanation: **Explanation:** The core concept tested here is the distinction between the **Fibrinolytic System** (which breaks down clots) and the **Coagulation Cascade** (which forms clots). **Why Option D is the Correct Answer:** **Stabilization of fibrin** is a function of **Factor XIII (Fibrin Stabilizing Factor)**, not plasmin. Factor XIII is a transglutaminase that creates covalent cross-links between fibrin strands to form a stable, insoluble mesh. **Plasmin**, conversely, is the primary enzyme of the fibrinolytic system; its role is to dissolve clots, not stabilize them. **Analysis of Other Options:** * **A. Fibrinolysis:** This is the primary function of plasmin. It proteolytically cleaves fibrin and fibrinogen into soluble Fibrin Degradation Products (FDPs), such as D-dimers. * **B. Activation of collagenase:** Plasmin plays a role in tissue remodeling and wound healing by activating latent matrix metalloproteinases, specifically **pro-collagenase**, into active collagenase. * **C. Destruction of vWF:** Plasmin is a relatively non-specific serine protease. In addition to fibrin, it can degrade several clotting factors, including **Factors V, VIII, XII, and von Willebrand Factor (vWF)**, thereby exerting an anticoagulant effect. **High-Yield NEET-PG Pearls:** * **Plasminogen Activation:** Plasminogen is converted to active Plasmin by **tPA** (Tissue Plasminogen Activator) and **Urokinase**. * **Inhibitor:** The primary physiological inhibitor of plasmin is **$\alpha$2-antiplasmin**. * **Clinical Link:** Tranexamic acid (an antifibrinolytic) works by inhibiting the binding of plasminogen/plasmin to fibrin, preventing clot breakdown. * **D-Dimer:** A specific marker of fibrinolysis; it indicates that both thrombin (to form the clot) and plasmin (to break it) have been active.
Question 384: Erythropoietin production is inhibited by:
- A. Estrogen (Correct Answer)
- B. Progesterone
- C. Thyroxine
- D. Testosterone
Explanation: **Explanation:** The production of **Erythropoietin (EPO)**, the primary hormone regulating red blood cell production, is stimulated by tissue hypoxia. However, several hormones modulate this response. **1. Why Estrogen is the Correct Answer:** Estrogen is a known **inhibitor** of erythropoiesis. It acts by suppressing the production of erythropoietin in the kidneys and potentially decreasing the bone marrow's responsiveness to EPO. This inhibitory effect is one of the primary reasons why females of reproductive age typically have lower hemoglobin levels and hematocrit values compared to males. **2. Analysis of Incorrect Options:** * **Testosterone (Option D):** Testosterone **stimulates** EPO production and enhances the sensitivity of erythroid progenitor cells. This explains why men have higher hemoglobin levels than women. * **Thyroxine (Option C):** Thyroid hormones **stimulate** erythropoiesis by increasing the metabolic rate and oxygen consumption of tissues, which creates a state of relative hypoxia, triggering EPO release. * **Progesterone (Option B):** Unlike estrogen, progesterone does not have a significant inhibitory effect on erythropoietin production; in some contexts, it may even act as a mild respiratory stimulant. **3. Clinical Pearls for NEET-PG:** * **Site of EPO Production:** 85% in the **Peritubular interstitial cells** of the renal cortex; 15% in the liver (primary source in the fetus). * **Stimulus:** The primary stimulus for EPO is **hypoxia** (detected by HIF-1α), not the number of RBCs. * **Cobalt salts** are potent pharmacological stimulators of EPO production. * **Chronic Kidney Disease (CKD):** The most common cause of EPO deficiency, leading to normocytic normochromic anemia.
Question 385: Heme is converted to bilirubin mainly in which of the following locations?
- A. Kidney
- B. Liver
- C. Spleen (Correct Answer)
- D. Bone marrow
Explanation: **Explanation:** The conversion of heme to bilirubin is a key step in the catabolism of hemoglobin. This process occurs primarily within the **Reticuloendothelial System (RES)**, also known as the Mononuclear Phagocyte System. **1. Why Spleen is Correct:** The spleen is often referred to as the "graveyard of RBCs." Senescent (old) erythrocytes are trapped in the splenic sinusoids and phagocytosed by splenic macrophages. Inside these macrophages, **Heme Oxygenase** breaks down heme into biliverdin, which is then reduced to **unconjugated bilirubin** by Biliverdin Reductase. While this process also occurs in the liver and bone marrow, the **spleen** is the primary anatomical site for the initial breakdown of red cells. **2. Analysis of Incorrect Options:** * **Liver (B):** While the liver contains RES cells (Kupffer cells) that produce some bilirubin, its primary role is the **conjugation** of bilirubin (via UDP-glucuronosyltransferase) and its subsequent excretion into bile, rather than the initial production from heme. * **Bone Marrow (D):** This is a site of "ineffective erythropoiesis" where some heme is converted to bilirubin, but it is not the *main* location under physiological conditions. * **Kidney (A):** The kidneys do not play a significant role in the conversion of heme to bilirubin. They are primarily involved in the excretion of urobilinogen (which gives urine its yellow color). **Clinical Pearls for NEET-PG:** * **Rate-limiting enzyme:** Heme Oxygenase is the rate-limiting enzyme in bilirubin synthesis. * **By-product:** Carbon Monoxide (CO) is produced during the conversion of heme to biliverdin; it is the only endogenous source of CO in the body. * **Van den Bergh Reaction:** Unconjugated bilirubin (produced in the spleen) gives an **indirect** reaction, while conjugated bilirubin (produced in the liver) gives a **direct** reaction.
Question 386: What is the approximate percentage of lymphocytes in the blood of a normal adult person?
- A. 40%
- B. 30% (Correct Answer)
- C. 20%
- D. 10%
Explanation: ### Explanation **Correct Answer: B. 30%** In a healthy adult, White Blood Cells (WBCs) or Leucocytes are categorized into granulocytes and agranulocytes. Lymphocytes are the second most numerous type of leucocyte. The standard reference range for a Differential Leucocyte Count (DLC) is: * **Neutrophils:** 40–75% * **Lymphocytes:** 20–40% (Average: **30%**) * **Monocytes:** 2–8% * **Eosinophils:** 1–4% * **Basophils:** 0–0.5% Option B is the most accurate representation of the mean value within the physiological range. **Analysis of Incorrect Options:** * **Option A (40%):** This represents the upper limit of the normal range. While possible, it is less representative of the "average" adult than 30%. * **Option C (20%):** This is the lower limit of the normal range. * **Option D (10%):** This value is significantly below normal (Lymphocytopenia), often seen in immunodeficiency states or acute stress. **High-Yield Clinical Pearls for NEET-PG:** 1. **Mnemonic for DLC:** "Never Let Monkeys Eat Bananas" (Neutrophils > Lymphocytes > Monocytes > Eosinophils > Basophils). 2. **Pediatric Variation:** In children (up to 4–5 years), lymphocytes are the predominant WBC type, often exceeding neutrophils. 3. **Lymphocytosis:** An increase in lymphocyte count is classically associated with **viral infections** (e.g., Infectious Mononucleosis, where "atypical lymphocytes" or Downey cells are seen) and Chronic Lymphocytic Leukemia (CLL). 4. **Small vs. Large:** Most circulating lymphocytes (90%) are small lymphocytes; they are the only leucocytes that can recirculate between blood and lymph.
Question 387: Which white blood cell is considered the "second line of defense"?
- A. Neutrophil
- B. Eosinophil
- C. Basophil
- D. Monocyte (Correct Answer)
Explanation: **Explanation:** In the context of the cellular response to infection, white blood cells are categorized based on their arrival time and function at the site of injury or inflammation. **Why Monocytes are the "Second Line of Defense":** While **Neutrophils** are the first to arrive, they are short-lived and often die after phagocytosing a few bacteria. **Monocytes** (which circulate in the blood) migrate into the tissues and transform into **Macrophages**. These macrophages are larger, more powerful, and longer-lived than neutrophils. They arrive slightly later but are capable of engulfing much larger quantities of debris and pathogens, effectively taking over the defense once neutrophils are exhausted. Thus, the Monocyte-Macrophage system is termed the "second line of defense." **Analysis of Incorrect Options:** * **A. Neutrophils:** These are the **"first line of defense"** among WBCs. They are the most numerous and the first to reach the site of acute inflammation via chemotaxis. * **B. Eosinophils:** These are primarily involved in allergic reactions and defense against **parasitic infections** (e.g., helminths) by releasing major basic protein. * **C. Basophils:** These play a role in immediate hypersensitivity reactions. They contain histamine and heparin and are functionally similar to mast cells. **NEET-PG High-Yield Pearls:** * **First Line of Defense (General):** Physical and chemical barriers (Skin, Mucus, Gastric acid). * **First Line of Defense (Cellular):** Neutrophils. * **Second Line of Defense (Cellular):** Monocytes/Macrophages. * **Third Line of Defense:** Specific immunity involving **Lymphocytes** (T-cells and B-cells). * **Kupffer cells** (Liver) and **Microglia** (CNS) are specialized tissue macrophages derived from monocytes.
Question 388: Which of the following organs is a primary lymphoid organ?
- A. Lymph node
- B. MALT
- C. Thymus (Correct Answer)
- D. Spleen
Explanation: ***Thymus***- **Primary lymphoid organs** are the sites where lymphocytes are generated and mature into immunocompetent cells.- The **thymus** is essential for the maturation, selection, and central tolerance of **T lymphocytes**.*Lymph node*- Lymph nodes are classified as **secondary lymphoid organs** where matured lymphocytes activate and proliferate upon encountering specific antigens.- They serve as critical filters for **lymph**, organizing immune responses against pathogens draining from local tissues.*Spleen*- The spleen is a major **secondary lymphoid organ** responsible for filtering **blood** and mounting immune responses to systemic infections.- The **white pulp** contains T and B cell zones that are crucial for activating adaptive immunity against blood-borne pathogens.*MALT*- MALT (Mucosa-Associated Lymphoid Tissue) represents **secondary lymphoid tissues** found beneath epithelial surfaces.- It is responsible for initiating local immune responses at mucosal sites (e.g., **Peyer's patches** in the intestine).
Question 389: Which of the following cells is responsible for destroying bacterial foreign bodies in liver sinusoids?
- A. Hepatocytes
- B. Sinusoidal endothelial cells
- C. Kupffer cells (Correct Answer)
- D. Ito cells
Explanation: ***Kupffer cells***- These are resident **macrophages** specifically located within the **liver sinusoids**.- Their primary role is **phagocytosis**, enabling them to clear the blood of **bacteria**, old red blood cells, and other foreign particulate matter entering the liver via the portal vein.*Hepatocytes*- These are the main parenchymal cells of the liver, primarily responsible for metabolic functions such as **bile production**, **protein synthesis**, and **detoxification**.- They lack the specialized migratory and high-volume **phagocytic capacity** needed to clear circulating bacteria.*Ito cells*- Also known as **hepatic stellate cells**, they reside in the **Space of Dissé** and are specialized for storing **Vitamin A**.- Upon activation (e.g., due to injury), they differentiate into myofibroblasts and are central to **liver fibrosis**.*Sinusoidal endothelial cells*- These cells line the vascular space of the sinusoid and are characterized by numerous **fenestrations** (pores) that allow fluid exchange with the Space of Dissé.- Although they form the barrier, they are generally less active in high-capacity microbial clearance compared to the dedicated **Kupffer cell macrophages**.
Question 390: Which of the following clotting factor participates in the extrinsic pathway of coagulation?
- A. Factor VIII
- B. Factor VII (Correct Answer)
- C. Factor XI
- D. Factor IX
Explanation: ***Factor VII***- This factor is the key component initiating the **extrinsic pathway** when complexed with **Tissue Factor (TF)**.- The TF-Factor VIIa complex activates Factor X, linking the extrinsic pathway to the **common pathway**.*Factor VIII*- Factor VIII is a crucial component of the **intrinsic pathway**, where it acts as a cofactor for Factor IXa to activate Factor X.- Deficiency of Factor VIII causes **Hemophilia A**, a common inherited bleeding disorder.*Factor XI*- Factor XI is involved in the initial steps of the **intrinsic pathway**, typically activated by Factor XIIa.- Its main function is to activate Factor IX, continuing the cascade in the intrinsic pathway.*Factor IX*- Factor IX is part of the **intrinsic pathway**; when activated (IXa), it forms the tenase complex with Factor VIIIa to activate Factor X.- Deficiency of Factor IX leads to **Hemophilia B** (Christmas disease).
Practice by Chapter
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