Blood and Immunity — MCQs
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Nude mice are not resistant to xenografts due to absence of
Interleukin responsible for Pyrexia is:
The major role of 2,3-bisphosphoglycerate in RBCs is -
Which of the following statements is TRUE regarding the Bohr effect?
What is Proaccelerin?
What is the average size of platelets in micrometers?
Increase in plasma viscosity is maximally caused by which plasma protein?
Chemotaxis is mediated by-
Which protein primarily contributes to oncotic pressure in the blood?
Which immunoglobulin is primarily secreted by the intestine?
Blood and Immunity Indian Medical PG Practice Questions and MCQs
Question 451: Nude mice are not resistant to xenografts due to absence of
- A. B cell
- B. T cell (Correct Answer)
- C. Absence of both B and T cells
- D. Presence of both B and T cells
Explanation: ***T cell*** - Nude mice have a **congenital athymia**, meaning they lack a functional **thymus**. - The thymus is essential for the maturation and development of **T lymphocytes**, making these mice severely **T-cell deficient**. - Without functional T cells, nude mice cannot reject **xenografts** (tissue transplanted from a different species). *B cell* - While nude mice have impaired T-cell function, their **B-cell development and function remain largely intact**. - B cells develop in the **bone marrow** and do not require the thymus for maturation. - B cells alone are insufficient to reject xenografts, as this requires cell-mediated immunity. *Absence of both B and T cells* - This statement is incorrect because nude mice **do possess B cells**, even if their T-cell immunity is severely compromised. - The primary defect is in the **thymus**, affecting T-cell maturation, not B cells. - Complete absence of both would describe **SCID mice**, not nude mice. *Presence of both B and T cells* - This is incorrect as nude mice clearly have a **severe deficiency in T cells** due to athymia. - Their inability to reject xenografts is directly linked to this lack of functional T-cell immunity. - If both were present and functional, the mice would reject xenografts normally.
Question 452: Interleukin responsible for Pyrexia is:
- A. IL1 (Correct Answer)
- B. IL4
- C. IL3
- D. IL8
Explanation: ***IL1*** - **Interleukin-1 (IL-1)** is a primary **endogenous pyrogen**, directly acting on the thermoregulatory center in the hypothalamus to induce fever. - It stimulates the production of **prostaglandin E2 (PGE2)**, which then alters the hypothalamic set point, leading to increased body temperature. *IL3* - **Interleukin-3 (IL-3)** is a **hematopoietic growth factor** that primarily stimulates the proliferation and differentiation of hematopoietic stem cells. - Its main role is in the development of various blood cell lineages, not directly in inducing fever. *IL4* - **Interleukin-4 (IL-4)** is a key cytokine in **allergic reactions** and **Th2 immune responses**, promoting B cell activation and IgE production. - It does not directly cause pyrexia; its primary functions are related to humoral immunity and immune regulation. *IL8* - **Interleukin-8 (IL-8)**, also known as **CXCL8**, is a potent **chemotactic factor** for neutrophils and other immune cells. - Its main function is to recruit inflammatory cells to sites of infection or injury, not to induce fever directly.
Question 453: The major role of 2,3-bisphosphoglycerate in RBCs is -
- A. Acid-base balance
- B. Reversal of glycolysis
- C. Release of oxygen (Correct Answer)
- D. Binding of oxygen
Explanation: ***Release of oxygen*** - **2,3-bisphosphoglycerate (2,3-BPG)** binds allosterically to **deoxyhemoglobin**, stabilizing its T (tense) state. - This binding reduces hemoglobin's affinity for oxygen, promoting the **release of oxygen** to tissues. *Acid-base balance* - While red blood cells play a role in **acid-base balance** through the bicarbonate buffer system, 2,3-BPG's primary role is not buffering. - The **chloride shift** and **carbonic anhydrase** are more directly involved in RBC acid-base regulation. *Reversal of glycolysis* - 2,3-BPG is an intermediate of the **Rapoport-Luebering shunt**, a side pathway of glycolysis. - It does not reverse glycolysis but rather is produced during glycolysis to serve a specific function in oxygen transport. *Binding of oxygen* - 2,3-BPG **decreases** hemoglobin's affinity for oxygen, thus promoting its *release* from hemoglobin, not its binding. - Oxygen binding to hemoglobin occurs primarily at the **heme iron** without 2,3-BPG.
Question 454: Which of the following statements is TRUE regarding the Bohr effect?
- A. Decreased affinity of Hb to O2 is associated with increased pH & decreased CO2
- B. Decreased affinity of Hb to O2 is associated with increased pH & CO2
- C. Decreased affinity of Hb to O2 is associated with decreased pH & increased CO2 (Correct Answer)
- D. Decreased affinity of Hb to O2 is associated with decreased pH & decreased CO2
Explanation: ***Decreased affinity of Hb to O2 is associated with decreased pH & increased CO2*** - The **Bohr effect** describes how **hemoglobin's (Hb) affinity for oxygen (O2) decreases** in the presence of increased **acidity (decreased pH)** and higher **carbon dioxide (CO2)** concentrations. - This physiological adaptation ensures that O2 is **released more readily** to tissues that are actively metabolizing (e.g., muscle during exercise), as these tissues produce more CO2 and lactic acid, leading to a drop in pH. *Decreased affinity of Hb to O2 is associated with increased pH & decreased CO2* - An **increased pH** (more alkaline) and **decreased CO2** actually **increase Hb's affinity for O2**, shifting the oxygen dissociation curve to the left. - This scenario promotes **oxygen loading** onto hemoglobin, typically occurring in the lungs rather than O2 release in the tissues. *Decreased affinity of Hb to O2 is associated with increased pH & CO2* - This statement combines an **increased pH** (which increases Hb-O2 affinity) with **increased CO2** (which decreases Hb-O2 affinity), leading to a contradictory and incorrect physiological effect based on the Bohr principle. - The net effect of an increased pH would typically dominate in terms of O2 binding. *Decreased affinity of Hb to O2 is associated with decreased pH & decreased CO2* - While **decreased pH** does reduce Hb's affinity for O2, **decreased CO2** would tend to increase it. - Therefore, this combination does not accurately represent the primary conditions that lead to a significant decrease in Hb-O2 affinity as described by the Bohr effect in active tissues.
Question 455: What is Proaccelerin?
- A. Factor VII
- B. Factor II
- C. Factor V (Correct Answer)
- D. Factor X
Explanation: ***Factor V*** - **Factor V**, also known as **proaccelerin** or **labile factor**, is a **plasma protein** that plays a crucial role in the coagulation cascade. - It is activated by thrombin to **Factor Va**, which then combines with Factor Xa, calcium, and phospholipid to form the **prothrombinase complex**, significantly enhancing thrombin generation. *Factor II* - **Factor II** is **prothrombin**, a precursor to **thrombin**, which is central to coagulation. - It is not referred to as preaccelerin. *Factor VII* - **Factor VII** is primarily involved in the **extrinsic pathway** of coagulation, becoming activated to Factor VIIa upon contact with tissue factor. - It works to activate Factor IX and Factor X, but it is not preaccelerin. *Factor X* - **Factor X**, also known as **Stuart-Prower factor**, is a key enzyme in the **common pathway** of coagulation, converting prothrombin to thrombin. - It is distinct from Factor V, which acts as a cofactor.
Question 456: What is the average size of platelets in micrometers?
- A. 4-5 µm
- B. 3-4 µm
- C. 2-3 µm (Correct Answer)
- D. 1-2 µm
Explanation: ***2-3 µm*** - Platelets, also known as **thrombocytes**, are small, anucleated cell fragments crucial for **hemostasis**, and their average diameter generally falls within the range of 2-3 micrometers. - This **small size** allows them to easily navigate through capillaries and aggregate rapidly at sites of vascular injury. *3-4 µm* - While platelets can vary slightly in size, an average of 3-4 µm is generally considered a bit on the larger side and not the typical average diameter. - Larger platelets might be seen in certain conditions like **idiopathic thrombocytopenic purpura (ITP)**, but this is not the average normal size. *4-5 µm* - This range is significantly larger than the typical size of normal circulating platelets. - Platelets this large would be considered **macroplatelets** and could indicate specific pathological conditions or inherited platelet disorders. *1-2 µm* - This size range is generally considered smaller than the average normal platelet size. - Very small platelets might be seen in some specific conditions, but it's not the usual average for healthy individuals.
Question 457: Increase in plasma viscosity is maximally caused by which plasma protein?
- A. Albumin
- B. All have equal effect
- C. Globulin
- D. Fibrinogen (Correct Answer)
Explanation: ***Globulin*** - Increased levels of **globulin** proteins, particularly in inflammatory or proliferative conditions, have a significant impact on plasma viscosity due to their **high molecular weight** [1]. - **Globulins** contribute to **hyperviscosity syndrome**, which can lead to clinical symptoms like fatigue and visual disturbances [1]. *Albumin* - While **albumin** is the most abundant plasma protein, its primary role is in maintaining **oncotic pressure**, not significantly affecting plasma viscosity. - An increase in albumin does not correlate with plasma viscosity increases to the extent seen with globulins. *All have equal effect* - Different plasma proteins do not have **equal effects** on viscosity; **globulins** and **fibrinogen** particularly influence it more than **albumin**. - The impact on viscosity varies significantly with protein concentration and type, making this statement inaccurate. *Fibrinogen* - **Fibrinogen** does contribute to plasma viscosity but is typically less than that caused by globulins, especially when globulin levels are markedly elevated. - Its effect is more pronounced during **coagulation**, rather than in the general increase of plasma viscosity associated with inflammatory states. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 141-142.
Question 458: Chemotaxis is mediated by-
- A. Histamine
- B. Leukotriene C4 and C3a
- C. Bradykinin
- D. Leukotriene B4 and C5a (Correct Answer)
Explanation: ***Leukotriene B4 and C5a*** - Both **Leukotriene B4** [2] and **C5a** [1] are potent **chemoattractants** that guide the migration of neutrophils and other immune cells to sites of inflammation. - They are crucial in amplifying the **immune response**, particularly during acute inflammatory reactions. *Histamine* - Primarily involved in **vasodilation** and increased **vascular permeability**, rather than mediating chemotaxis. - Does not specifically attract immune cells to sites of injury or infection like leukotrienes do. *Bradykinin* - Mainly functions in **pain sensation** and promoting **vascular permeability**, not as a direct chemotactic agent. - It influences inflammation but does not effectively recruit immune cells to tissues. *Leukotriene C4 and C3a* - **Leukotriene C4** is involved in bronchoconstriction, while **C3a** [1] has roles in the complement system but is less potent than C5a in chemotaxis. - These mediators have different primary roles in inflammation, lacking the specificity of B4 and C5a for leukocyte attraction. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 99-100. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 95-96.
Question 459: Which protein primarily contributes to oncotic pressure in the blood?
- A. Albumin (Correct Answer)
- B. Globulins
- C. Fibrinogen
- D. Transferrin
Explanation: ***Albumin*** - **Albumin** is the most abundant plasma protein and its small size and high concentration make it the primary determinant of **oncotic pressure** in the blood. - Its presence in the capillaries draws water from the **interstitial space** back into the blood vessels, maintaining **fluid balance** and blood volume. *Fibrinogen* - **Fibrinogen** is a crucial protein involved in **blood clotting**, where it is converted into **fibrin** to form a clot. - While a plasma protein, its contribution to **oncotic pressure** is minor compared to albumin, as it's less abundant and larger in size. *Globulins* - **Globulins** are a diverse group of proteins involved in immune function (**immunoglobulins**), transport (e.g., **alpha** and **beta globulins**), and clotting. - While they contribute to total plasma protein concentration, their collective impact on **oncotic pressure** is secondary to that of albumin due to lower concentrations and varied molecular weights. *Transferrin* - **Transferrin** is a specific **beta-globulin** that plays a vital role in **iron transport** in the blood. - Its primary function is not related to **oncotic pressure**, and its concentration is significantly lower than albumin.
Question 460: Which immunoglobulin is primarily secreted by the intestine?
- A. IgG
- B. IgM
- C. IgA (Correct Answer)
- D. IgD
Explanation: **IgA** - **Secretory IgA** is the dominant immunoglobulin in mucosal secretions, including those of the intestine. - It plays a crucial role in providing **local immunity** by preventing microbial adherence and neutralizing toxins on mucosal surfaces. *IgG* - **IgG** is the most abundant immunoglobulin in serum and plays a major role in systemic immunity, including opsonization and complement activation. - While some IgG is found in secretions, it is not the primary immunoglobulin secreted by the intestine. *IgM* - **IgM** is a pentameric immunoglobulin, primarily found in blood and lymph, where it is very effective in activating the complement system and agglutinating antigens. - Although it can be found at mucosal surfaces in small amounts, it is not the principal secreted antibody in the intestine. *IgD* - **IgD** is primarily found on the surface of naive B lymphocytes, where it functions as a B cell receptor. - Its role in secreted form is minimal, and it is not significantly secreted into the intestine or other bodily fluids.
Practice by Chapter
Composition and Functions of Blood
Practice Questions
Erythrocytes and Hemoglobin
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Leukocytes and Immune Function
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Platelets and Hemostasis
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Blood Groups and Transfusion
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Coagulation and Fibrinolysis
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Hematopoiesis
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Innate Immunity
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Adaptive Immunity
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Immunological Memory and Tolerance
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