Blood and Immunity Practice Questions

Q: Which factor initiates in vitro coagulation?

Factor XII. **Explanation:** The process of blood coagulation occurs via two primary pathways: the **Intrinsic Pathway** and the **Extrinsic Pathway**. **Why Factor XII is correct:** In an *in vitro* (laboratory/test tube) environment, coagulation is initiated when blood comes into contact with a "foreign" negatively charged surface, such as glass or kaolin. This process is known as the **Contact Activation Pathway**. **Factor XII (Hageman factor)** is the specific plasma protein that binds to these surfaces, undergoing a conformational change to become activated (Factor XIIa). This triggers the intrinsic cascade (XII → XI → IX → VIII → X). **Analysis of Incorrect Options:** * **Factor XI:** While part of the intrinsic pathway, it is activated by Factor XIIa, not by the glass surface itself. * **Factor X:** This is the start of the **Common Pathway**. It is the point where both intrinsic and extrinsic pathways converge, but it does not initiate the process *in vitro*. * **Factor VII:** This factor initiates the **Extrinsic Pathway** *in vivo*. It requires **Tissue Factor (Factor III)**, which is released upon vascular injury, rather than contact with a glass surface. **High-Yield NEET-PG Pearls:** * **Factor XII Deficiency:** Interestingly, patients with Factor XII deficiency show a prolonged PTT (Partial Thromboplastin Time) in the lab but **do not** have a clinical bleeding tendency *in vivo*. * **In Vivo Initiation:** In the living body, the Extrinsic Pathway (Factor VII + Tissue Factor) is the primary initiator of coagulation. * **Vitamin K Dependent Factors:** II, VII, IX, and X. * **Lab Tests:** PT (Prothrombin Time) monitors the Extrinsic pathway; aPTT monitors the Intrinsic pathway.

Q: All of the following are macrophages except—

Lymphocyte. **Explanation:** The question tests the concept of the **Mononuclear Phagocyte System (MPS)**, formerly known as the Reticuloendothelial System. This system consists of monocytes and their tissue-specific derivatives, which are specialized for phagocytosis and antigen presentation. **Why Lymphocyte is the correct answer:** Lymphocytes (B-cells, T-cells, and NK cells) are part of the **adaptive immune system** (and innate in the case of NK cells), but they are **not phagocytic cells**. They function through antibody production or cell-mediated cytotoxicity rather than engulfing and digesting pathogens. Therefore, they do not belong to the macrophage lineage. **Analysis of Incorrect Options:** * **Monocyte:** These are the precursor cells found in the blood. Once they migrate into tissues, they differentiate into mature macrophages. * **Kupffer Cells:** These are specialized, resident macrophages located in the **liver** (sinusoids). They are essential for clearing bacteria and debris from the portal circulation. * **Microglia:** These are the resident macrophages of the **Central Nervous System (CNS)**. They act as the primary active immune defense in the brain and spinal cord. **High-Yield Clinical Pearls for NEET-PG:** * **Tissue-Specific Macrophages to Remember:** * **Lung:** Alveolar macrophages (Dust cells). * **Skin:** Langerhans cells. * **Bone:** Osteoclasts. * **Kidney:** Mesangial cells. * **Placenta:** Hofbauer cells. * **Key Marker:** CD14 is a common surface marker used to identify monocytes and macrophages. * **Function:** Macrophages are the primary source of **Interleukin-1 (IL-1)**, which induces fever.

Q: Which coagulation factor is not present in serum?

II. **Explanation:** The fundamental difference between **plasma** and **serum** lies in the presence of clotting factors. Serum is defined as plasma minus the clotting factors that are consumed during the coagulation process. **Why Option A is Correct:** Coagulation **Factor II (Prothrombin)** is a key component of the common pathway. During the clotting process, Prothrombin is converted into its active form, **Thrombin (IIa)**, which then converts fibrinogen into a fibrin mesh. Because Factor II is utilized and converted to form the clot, it is **absent in serum**. Other factors consumed during clotting (and thus absent in serum) include factors **I, V, VIII, and XIII**. **Why the other options are incorrect:** * **Option B (Factor IV):** This is Calcium. While it is essential for almost all steps of the coagulation cascade, it is an ion and remains present in the serum after the clot has formed. * **Option C & D (Factors X and VII):** These are part of the stable factors. While they are activated during the cascade (to Xa and VIIa), they are not entirely consumed in the same manner as Prothrombin or Fibrinogen and can still be detected in serum. **High-Yield NEET-PG Pearls:** * **Mnemonic for factors absent in serum:** "1, 2, 5, 8, 13" (The factors consumed during clotting). * **Serum vs. Plasma:** Plasma contains Fibrinogen; Serum does **not**. * **Vitamin K Dependent Factors:** II, VII, IX, and X (Note: Only II is consumed; VII, IX, and X are present in serum). * **Factor I (Fibrinogen)** is the most abundant clotting factor in plasma but is completely absent in serum as it becomes the fibrin clot.

Q: At what stage do neutrophils first appear in peripheral blood?

Band forms. **Explanation:** The correct answer is **Band forms**. This question tests the understanding of granulopoiesis and the transition of cells from the bone marrow to the systemic circulation. **Why Band forms are correct:** Granulopoiesis follows a specific maturation sequence: Myeloblast → Promyelocyte → Myelocyte → Metamyelocyte → Band form → Mature Neutrophil (Segmented). Under normal physiological conditions, the bone marrow acts as a barrier, releasing only mature neutrophils and a small percentage (3-5%) of **Band forms** (immature neutrophils with non-segmented, curved nuclei) into the peripheral blood. Band forms represent the final stage of maturation before full segmentation and are the earliest stage routinely seen in a normal peripheral smear. **Why other options are incorrect:** * **Myeloblast:** This is the first identifiable myeloid precursor. It is confined to the bone marrow. Its presence in peripheral blood is always pathological (e.g., Acute Myeloid Leukemia). * **Promyelocyte:** Characterized by primary (azurophilic) granules, these cells stay within the marrow. * **Myelocyte:** This is the last stage capable of mitosis and the stage where secondary (specific) granules first appear. Like the stages above, it is restricted to the bone marrow in healthy individuals. **High-Yield Clinical Pearls for NEET-PG:** * **Left Shift:** An increase in band forms (>10%) in the peripheral blood is termed a "shift to the left," typically indicating an acute bacterial infection or inflammation. * **Myelocyte Stage:** High-yield fact—this is the stage where **specific granules** (e.g., alkaline phosphatase, lactoferrin) first appear. * **Leukemoid Reaction:** The presence of early precursors like myelocytes or metamyelocytes in the blood, often seen in severe infections, mimicking leukemia but with a high LAP (Leukocyte Alkaline Phosphatase) score.

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.

Question 1

Which factor initiates in vitro coagulation?

Accepted Answer

Factor XII

Answer

Factor XI

Answer

Factor X

Answer

Factor VII

Question 2

Citrate is a useful anticoagulant because of its ability to

Accepted Answer

Chelate calcium

Answer

Buffer basic groups of coagulation factors

Answer

Bind factor XII

Answer

Bind vitamin K

Question 3

Adding glucose to stored blood causes what?

Accepted Answer

Nutrition to red blood cells

Answer

Prevention of hemolysis

Answer

Increased acidosis of stored blood

Answer

Prevention of hyperkalemia

Question 4

Which of the following is responsible for adhesion of platelets to the vessel wall?

Accepted Answer

Von Willebrand factor

Answer

Factor IX

Answer

Fibrinogen

Answer

Fibronectin

Question 5

All of the following are macrophages except—

Accepted Answer

Lymphocyte

Answer

Monocyte

Answer

Kupffer cell

Answer

Microglia

Question 6

Which coagulation factor is not present in serum?

Accepted Answer

II

Answer

IV

Answer

X

Answer

VII

Question 7

The biconcave shape of red blood cells is primarily maintained by which protein complex?

Accepted Answer

Spectrin

Answer

Ankyrin

Answer

Band 3 protein

Answer

Glycophorin-C

Question 8

At what stage do neutrophils first appear in peripheral blood?

Accepted Answer

Band forms

Answer

Myeloblast

Answer

Promyelocyte

Answer

Myelocyte

Question 9

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 10

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

Blood and Immunity — MCQs

Blood and Immunity — MCQs

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