Blood and Immunity Practice Questions

Q: What is the approximate percentage of HbF in a 6-month-old infant?

10%. ### Explanation **1. Understanding the Concept (Why A is correct):** Fetal Hemoglobin (HbF, $\alpha_2\gamma_2$) has a higher affinity for oxygen than adult hemoglobin (HbA, $\alpha_2\beta_2$), which is essential for oxygen transfer across the placenta. However, shortly before birth, a "switch" from $\gamma$-globin to $\beta$-globin synthesis begins. At birth, HbF constitutes approximately **60–80%** of total hemoglobin. This level declines rapidly as HbA production takes over. By **6 months of age**, the concentration of HbF typically drops to about **5–10%**. By the end of the first year (12 months), it reaches near-adult levels of less than 1–2%. **2. Analysis of Incorrect Options:** * **Option B (30%):** This level is typically seen around the age of 2–3 months as the rapid decline from birth levels occurs. * **Option C (50%):** This is too high for a 6-month-old; such levels are usually seen within the first few weeks of life. * **Option D (60%):** This represents the physiological level at the time of birth (full-term neonate). **3. High-Yield Clinical Pearls for NEET-PG:** * **The Switch:** The transition from HbF to HbA is clinically significant in hemoglobinopathies. Symptoms of **Sickle Cell Anemia** and **$\beta$-Thalassemia Major** typically manifest at **6 months of age**, coinciding with the physiological decline of protective HbF. * **P50 Value:** HbF has a lower P50 (approx. 19 mmHg) compared to HbA (approx. 27 mmHg), reflecting its higher oxygen affinity. * **2,3-BPG:** HbF binds poorly to 2,3-BPG because the $\gamma$-chain lacks the positively charged binding sites found in the $\beta$-chain. * **HbA2:** Adult hemoglobin also contains a small fraction of HbA2 ($\alpha_2\delta_2$), normally <3%.

Q: Interleukin-1 (IL-1) helps in which of the following functions?

Stimulation of T-lymphocytes. **Explanation:** Interleukin-1 (IL-1) is a key pro-inflammatory cytokine primarily produced by activated macrophages and monocytes. It serves as a critical mediator of the innate and adaptive immune responses. **1. Why Option A is Correct:** IL-1 acts as a "co-stimulator" for T-cell activation. When an Antigen-Presenting Cell (APC) presents an antigen to a T-helper (CD4+) cell, it releases IL-1. This cytokine induces the T-cell to express receptors for **Interleukin-2 (IL-2)** and stimulates the secretion of IL-2 itself, leading to T-cell proliferation and clonal expansion. **2. Why Other Options are Incorrect:** * **Option B:** IL-1 actually **stimulates** B-lymphocytes, promoting their proliferation and differentiation into antibody-secreting plasma cells. * **Option C:** IL-1 is a potent **pro-inflammatory** mediator. It increases the expression of adhesion molecules (like E-selectin) on vascular endothelium, thereby **promoting** the chemotaxis and emigration of neutrophils and macrophages to the site of infection. * **Option D:** IL-1 **increases** fibroblast activity (leading to collagen synthesis/scarring) and stimulates osteoclasts, which **increases** bone resorption. **High-Yield Clinical Pearls for NEET-PG:** * **Endogenous Pyrogen:** IL-1 is a primary mediator of fever; it acts on the anterior hypothalamus to increase prostaglandin E2 (PGE2) production, raising the thermal set-point. * **Acute Phase Response:** Along with IL-6 and TNF-α, IL-1 stimulates the liver to produce acute-phase reactants (e.g., CRP, Fibrinogen). * **Anakinra:** This is a recombinant IL-1 receptor antagonist used clinically in the treatment of Rheumatoid Arthritis.

Q: Which of the following is involved in iron absorption, synthesized by the liver, and secreted through bile into the intestine?

Apotransferrin. ### Explanation The correct answer is **Apotransferrin**. **1. Why Apotransferrin is Correct:** Iron absorption in the small intestine involves a specific mechanism where the liver synthesizes **apotransferrin** and secretes it into the **bile**. This apotransferrin travels to the duodenum and jejunum, where it binds with free iron (forming transferrin) or iron compounds in the intestinal lumen. This complex then binds to receptors on the brush border of enterocytes and is internalized via pinocytosis. Once inside the cell, iron is released into the blood, and the apotransferrin is recycled back into the lumen to pick up more iron. **2. Why Other Options are Incorrect:** * **Apoferritin (A):** This is the protein shell that combines with iron *inside* cells (primarily in the liver and intestinal mucosa) to form **Ferritin**, the primary intracellular storage form of iron. It is not secreted into bile for absorption. * **Transferrin (B):** This is the plasma transport protein. While apotransferrin becomes transferrin once it binds iron, the specific substance *synthesized and secreted* by the liver into the bile to facilitate the initial uptake from the gut is apotransferrin. **3. NEET-PG High-Yield Clinical Pearls:** * **Hepcidin:** The "Master Regulator" of iron. It is a liver-derived peptide that inhibits iron absorption by causing the degradation of **Ferroportin** (the basal exporter). * **DMT-1 (Divalent Metal Transporter 1):** Responsible for the uptake of inorganic non-heme iron ($Fe^{2+}$) into the enterocyte. * **Ferroportin:** The only known cellular iron exporter; it moves iron from the enterocyte into the portal circulation. * **Ceruloplasmin/Hephaestin:** Ferrooxidases that convert $Fe^{2+}$ to $Fe^{3+}$ so it can bind to plasma transferrin.

Q: Which cell count is characteristically increased following splenectomy?

Platelets. **Explanation:** The spleen acts as a major reservoir for blood cells, particularly platelets. Under normal physiological conditions, approximately **one-third (30-33%) of the total body platelet pool** is sequestered within the splenic red pulp. Following a **splenectomy**, this sequestration site is removed, leading to a rapid redistribution of platelets into the systemic circulation. This results in **thrombocytosis** (increased platelet count), which typically peaks 1–2 weeks post-surgery. While the count often stabilizes over months, it may remain higher than the patient's baseline indefinitely. **Analysis of Options:** * **Platelets (Correct):** The immediate loss of the splenic reservoir causes a characteristic and significant rise in circulating platelets. * **Lymphocytes:** While the spleen is a lymphoid organ, peripheral lymphocyte counts do not show a characteristic or sustained increase post-splenectomy; rather, there is a loss of specific B-cell populations (marginal zone B-cells). * **Monocytes:** Monocyte counts are not significantly or characteristically altered by the absence of the spleen. * **Neutrophils:** A transient, mild neutrophilia may occur immediately post-operatively due to surgical stress and demargination, but it is not the hallmark hematological change associated with splenectomy. **Clinical Pearls for NEET-PG:** 1. **Howell-Jolly Bodies:** These are nuclear remnants in RBCs that are normally removed by the spleen; their presence on a peripheral smear is a classic sign of asplenia. 2. **OPSI (Overwhelming Post-Splenectomy Infection):** Patients are at high risk for infections by encapsulated organisms (*S. pneumoniae, H. influenzae, N. meningitidis*). 3. **Other Smear Findings:** Look for Pappenheimer bodies, Heinz bodies, and target cells post-splenectomy.

Q: Which of the following proteins is responsible for the flexibility of red blood cells?

All of the above. **Explanation:** The flexibility and biconcave shape of Red Blood Cells (RBCs) are maintained by a complex **cytoskeletal network** located just beneath the lipid bilayer. This network allows the RBC to undergo extreme deformation while passing through narrow capillaries (as small as 3 µm) and return to its original shape. * **Spectrin (Option A):** This is the primary structural protein of the RBC cytoskeleton. It consists of $\alpha$ and $\beta$ chains that form a long, flexible hexagonal lattice. It acts like a "spring," providing the membrane with its essential tensile strength and elasticity. * **Ankyrin (Option B):** This protein acts as the primary "bridge" or anchor. It attaches the spectrin lattice to the transmembrane protein, Band 3. Without ankyrin, the cytoskeleton would detach from the lipid bilayer. * **Band 3 (Option C):** This is a multipass transmembrane protein (anion exchanger). While its primary role is exchanging $Cl^-$ and $HCO_3^-$, it serves as a crucial anchoring point for the underlying cytoskeleton. **Why "All of the above" is correct:** The flexibility of the RBC is not dependent on a single protein but on the **vertical and horizontal interactions** between these proteins. A defect in any of these components disrupts the structural integrity of the membrane, leading to a loss of deformability. **Clinical Pearls for NEET-PG:** 1. **Hereditary Spherocytosis:** Most commonly caused by a deficiency in **Ankyrin** (followed by Spectrin or Band 3). This leads to a loss of membrane surface area, resulting in rigid, spherical cells that are destroyed in the spleen. 2. **Hereditary Elliptocytosis:** Primarily caused by defects in **Spectrin** (disruption of horizontal interactions). 3. **Band 3** is also known as the Anion Exchanger 1 (AE1) and is vital for the "Chloride Shift" (Hamburger phenomenon).

Q: Thrombin activity is inhibited by which of the following?

Heparin. ### Explanation **Correct Option: B (Heparin)** Thrombin (Factor IIa) is a central protease in the coagulation cascade. Its activity is primarily regulated by **Antithrombin III (AT-III)**, a naturally occurring plasma protein. Heparin acts as an indirect anticoagulant by binding to AT-III, inducing a conformational change that increases AT-III’s affinity for Thrombin by nearly **1,000-fold**. This complex rapidly inactivates Thrombin and other serine proteases (Factors IXa, Xa, XIa, and XIIa), effectively halting clot formation. **Analysis of Incorrect Options:** * **A. Chymotrypsin:** This is a digestive proteolytic enzyme produced in the pancreas. It functions in the small intestine to break down proteins into peptides and has no physiological role in inhibiting the blood coagulation cascade. * **C. Alpha 2 antitrypsin:** While it is a serine protease inhibitor (Serpin), its primary clinical role is inhibiting **neutrophil elastase** in the lungs. Deficiency leads to emphysema and liver cirrhosis, not coagulation disorders. * **D. Alpha 2 macroglobulin:** This is a broad-spectrum protease inhibitor that can neutralize various enzymes, including thrombin, but its role is minor compared to the potent AT-III/Heparin mechanism. It serves more as a secondary backup inhibitor. **High-Yield NEET-PG Pearls:** * **Mechanism of Action:** Heparin does not dissolve existing clots; it prevents the formation and extension of new clots. * **Monitoring:** The efficacy of Unfractionated Heparin (UFH) is monitored using **aPTT** (Intrinsic pathway). * **Antidote:** The specific antagonist for Heparin overdose is **Protamine Sulfate** (derived from salmon sperm). * **LMWH vs. UFH:** Low Molecular Weight Heparin (e.g., Enoxaparin) has a higher affinity for inhibiting **Factor Xa** than Thrombin (IIa).

Q: What parameter is used to measure the size of red blood cells?

MCV. ### Explanation **Correct Option: A. MCV (Mean Corpuscular Volume)** MCV is the parameter that directly measures the **average volume (size)** of a single red blood cell. It is calculated by dividing the Packed Cell Volume (PCV/Hematocrit) by the total RBC count. * **Formula:** $MCV = \frac{Hematocrit (\%) \times 10}{RBC\ count\ (millions/mm^3)}$ * **Normal Range:** 82–98 femtoliters (fL). * **Clinical Significance:** It is the primary index used to classify anemias into **Microcytic** (e.g., Iron Deficiency Anemia), **Normocytic**, or **Macrocytic** (e.g., Vitamin B12/Folate deficiency). **Incorrect Options:** * **B. MCHC (Mean Corpuscular Hemoglobin Concentration):** This measures the average concentration of hemoglobin in a given volume of packed red cells. It indicates the "intensity" of the red color (hypochromic vs. normochromic). * **C. ESR (Erythrocyte Sedimentation Rate):** This is a non-specific marker of inflammation. It measures how quickly RBCs sink to the bottom of a tube, influenced largely by plasma proteins like fibrinogen. * **D. MCH (Mean Corpuscular Hemoglobin):** This measures the average **weight** of hemoglobin in a single RBC. While it often correlates with size, it measures mass, not volume. **High-Yield Clinical Pearls for NEET-PG:** * **RDW (RBC Distribution Width):** While MCV measures average size, RDW measures the **variation** in size (Anisocytosis). A high RDW with low MCV is classic for early Iron Deficiency Anemia. * **Mentzer Index:** $MCV / RBC\ count$. If 13, it suggests Iron Deficiency Anemia. * **Macrocytosis without Anemia:** Often seen in chronic alcoholism or hypothyroidism.

Question 1

What is the approximate percentage of HbF in a 6-month-old infant?

Accepted Answer

10%

Answer

30%

Answer

50%

Answer

60%

Question 2

Interleukin-1 (IL-1) helps in which of the following functions?

Accepted Answer

Stimulation of T-lymphocytes

Answer

Inhibition of B-lymphocytes

Answer

Inhibition of chemotaxis of neutrophils and macrophages

Answer

Decreased fibroblast and bone resorption activity

Question 3

Which of the following are essential components of the intrinsic coagulation system?

Accepted Answer

Pre-kallikrein, High molecular weight kininogen, Factor VIII

Answer

High molecular weight kininogen, Factor VII, Tissue factor

Answer

Factor VII, Tissue factor, Factor X

Answer

Pre-kallikrein, Factor VII, Factor X

Question 4

Which of the following is involved in iron absorption, synthesized by the liver, and secreted through bile into the intestine?

Accepted Answer

Apotransferrin

Answer

Apoferritin

Answer

Transferrin

Answer

All of the above

Question 5

Which cell count is characteristically increased following splenectomy?

Accepted Answer

Platelets

Answer

Lymphocytes

Answer

Monocytes

Answer

Neutrophils

Question 6

Which of the following proteins is responsible for the flexibility of red blood cells?

Accepted Answer

All of the above

Answer

Spectrin

Answer

Ankyrin

Answer

Band 3

Question 7

Thrombin activity is inhibited by which of the following?

Accepted Answer

Heparin

Answer

Chymotrypsin

Answer

Alpha 2 antitrypsin

Answer

Alpha 2 macroglobulin

Question 8

What is the common function of neutrophils, monocytes, and macrophages?

Accepted Answer

Phagocytosis

Answer

Immune response

Answer

Liberation of histamine

Answer

Destruction of old erythrocytes

Question 9

What parameter is used to measure the size of red blood cells?

Accepted Answer

MCV

Answer

MCHC

Answer

ESR

Answer

MCH

Question 10

Thrombomodulin-thrombin complex prevents clotting because it:

Accepted Answer

Activates protein C, which inactivates activated factors V and VIII, and also removes thrombin

Answer

Inhibits prothrombin activator

Answer

Activates anti-thrombin III

Answer

Activates heparin

Blood and Immunity — MCQs

Blood and Immunity — MCQs

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