Blood and Immunity — MCQs

Blood and Immunity Indian Medical PG Practice Questions and MCQs

Question 431: What is the PRIMARY mechanism by which Interleukin-1 (IL-1) induces fever?

A. Stimulates antibody production
B. Inhibits inflammation
C. Endogenous pyrogen (Correct Answer)
D. Activates complement cascade

Explanation: ***Endogenous pyrogen*** - **IL-1** is a potent **endogenous pyrogen** that acts directly on the **hypothalamus**, the body's thermoregulatory center. - It stimulates the production of **prostaglandin E2 (PGE2)** in the hypothalamus, which then resets the body's thermoregulatory set point to a higher temperature, leading to fever. *Stimulates antibody production* - While IL-1 can have broader immune functions and can influence B cell activity, its **primary role in fever** production is not through antibody stimulation. - Antibody production is a function of **B lymphocytes** and is primarily driven by antigen presentation and T cell help. *Inhibits inflammation* - **IL-1** is a key **pro-inflammatory cytokine** that promotes inflammation, rather than inhibiting it. - It induces the expression of various adhesion molecules and inflammatory mediators, contributing to the inflammatory response. *Activates complement cascade* - The **complement cascade** is a part of the innate immune system, typically activated by **antigen-antibody complexes** (classical pathway) or **microbial surfaces** (alternative and lectin pathways). - While IL-1 plays a role in overall immune responses, its direct mechanism for inducing fever does not primarily involve activating the complement system.

Question 432: What is the lower limit of normal hemoglobin (Hb) value for a non-pregnant adult female in grams per deciliter (gm/dl)?

A. 10 gm/dl
B. 11 gm/dl
C. 12 gm/dl (Correct Answer)
D. 15.8 gm/dl

Explanation: ***12 gm/dl*** - The **World Health Organization (WHO)** defines anemia in non-pregnant adult females as a hemoglobin level below **12 gm/dl** - This threshold represents the **lower limit of normal** for this population - Below this value indicates clinically significant anemia requiring evaluation and potential treatment *10 gm/dl* - A hemoglobin level of **10 gm/dl** is **below the normal range** and indicates **moderate anemia** in a non-pregnant adult female - This is **2 gm/dl below the lower limit** and would require investigation for causes such as iron deficiency, chronic disease, or blood loss - Not the lower limit of normal, but a pathological value *11 gm/dl* - A hemoglobin level of **11 gm/dl** indicates **mild anemia** in a non-pregnant adult female - This is **1 gm/dl below the WHO cutoff** for defining anemia in this population - Note: This value (11 gm/dl) is the lower limit for **pregnant females**, not non-pregnant females *15.8 gm/dl* - A hemoglobin level of **15.8 gm/dl** is **well within the normal range** for a non-pregnant adult female - This value is toward the **upper end of normal** (typical range: 12-16 gm/dl for females) - This cannot be a lower limit as it exceeds the normal range minimum by nearly 4 gm/dl

Question 433: Which test is used for both intrinsic and common clotting pathways?

A. Thrombin time
B. Partial thromboplastin time (Correct Answer)
C. Ristocetin agglutination test
D. FDPs

Explanation: ***Partial thromboplastin time*** - The **partial thromboplastin time (PTT)** assay evaluates both the **intrinsic** and **common pathways** of coagulation [1], crucial for diagnosing bleeding disorders. - It is used to monitor patients on **heparin therapy**, assessing factors including **VIII, IX, XI, and XII**. *Ristocetin agglutination test* - This test specifically assesses **von Willebrand factor** function, reflecting defects in platelet adhesion rather than a comprehensive assessment of clotting pathways. - It does not evaluate intrinsic or common pathways effectively, focusing primarily on **primary hemostasis**. *FDPs* - Fibrin degradation products (FDPs) are markers of clot breakdown rather than direct tests of the intrinsic or common pathways of coagulation. - Elevated FDPs indicate **disease states** like disseminated intravascular coagulation (DIC), not functioning coagulation pathways. *Thrombin time* - Thrombin time measures the conversion of **fibrinogen to fibrin**, assessing the **final step** in the coagulation cascade, primarily related to the **common pathway**. - It does not evaluate the intrinsic pathway, making it unsuitable for assessing both pathways comprehensively. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Hemodynamic Disorders, Thromboembolic Disease, and Shock, pp. 128-130.

Question 434: Which type of white blood cell is responsible for 'remembering' previous encounters with pathogens?

A. Basophils
B. Eosinophils
C. Lymphocytes (Correct Answer)
D. Neutrophils

Explanation: ***Correct: Lymphocytes*** - **B-lymphocytes** and **T-lymphocytes** are central to adaptive immunity, which includes immunological memory. - Upon primary exposure to a pathogen, some lymphocytes differentiate into **memory cells** that can quickly respond to subsequent encounters. *Incorrect: Basophils* - **Basophils** are involved in allergic reactions and inflammatory responses, releasing histamine and other mediators. - They do not possess the ability to "remember" pathogens. *Incorrect: Eosinophils* - **Eosinophils** are primarily involved in defense against parasites and in allergic reactions. - They do not play a role in immunological memory. *Incorrect: Neutrophils* - **Neutrophils** are phagocytic cells that are part of the innate immune system, acting as the first responders to infection. - While crucial for immediate defense, they do not retain memory of past pathogen encounters.

Question 435: What is the primary function of the peroxidase enzyme found in neutrophils?

A. Macrophage activation
B. Chemotactic agent
C. Microbial killing (Correct Answer)
D. Vasodilatation

Explanation: ***Microbial killing*** - **Myeloperoxidase (MPO)**, found in neutrophil azurophilic granules, catalyzes the formation of **hypochlorous acid (HOCl)** from hydrogen peroxide (H2O2) and chloride ions (Cl-). - **HOCl** is a potent oxidant that effectively destroys ingested microbes within the phagolysosome. *Macrophage activation* - While neutrophils interact with macrophages, the primary function of their peroxidase enzyme is not to activate macrophages. - Macrophage activation is typically driven by cytokines and recognition of pathogen-associated molecular patterns (PAMPs). *Chemotactic agent* - Peroxidase itself is not a primary chemotactic agent that attracts other immune cells. - Chemotaxis is mainly mediated by chemokines and complement components. *Vasodilatation* - Vasodilatation is primarily controlled by mediators like **histamine**, **nitric oxide**, and **prostaglandins**, which are not directly produced by the peroxidase action. - Peroxidase's role is specifically within the neutrophil for microbial destruction.

Question 436: Which endothelial molecule is primarily involved in the rolling of leukocytes?

A. ICAM-1
B. VCAM-1
C. CD31
D. P-selectin (Correct Answer)

Explanation: ***CD 34*** - CD 34 is a key **endothelial molecule** that facilitates leukocyte **rolling** during the initial stages of inflammation [1]. - It acts as a cell adhesion **molecule**, allowing immune cells to transiently adhere and roll along the vascular endothelium [1][2]. *VCAM 1* - VCAM 1 is mainly involved in the **adherence** and **firm adhesion** of leukocytes, rather than rolling [1][2]. - It primarily binds to **VLA-4** on activated lymphocytes, a step that occurs after rolling [2]. *CD 31* - CD 31 (also known as **PECAM-1**) plays a role in **transmigration** of leukocytes through the endothelium, not in rolling [3]. - Its primary function is in cell-to-cell interactions and **diapedesis** rather than initial adhesion [3]. *ICAM 1* - ICAM 1 is important for **firm attachment** and is involved later in the process after rolling [1][2]. - It interacts with the integrin **LFA-1** on leukocytes, which aids in strong adhesion following rolling [2]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, p. 87. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Migration in the tissues toward a chemotactic stimulus, pp. 86-87. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 87-89.

Question 437: Which pathway is primarily initiated by tissue factor in the coagulation process?

A. Extrinsic pathway (Correct Answer)
B. Contact pathway
C. Intrinsic pathway
D. Common pathway

Explanation: ***In vivo pathway*** - Tissue factor is primarily involved in the **extrinsic pathway** of coagulation, which activates **thrombin** and leads to the formation of fibrin in response to tissue injury [1]. - It is expressed on the surface of **vascular cells**, interacting with factor VII to initiate the clotting cascade during **hemostasis** [1]. *In vitro pathway* - This refers to coagulation processes studied in a **controlled laboratory** environment, not involving tissue factor as it predominantly relates to the **extrinsic pathway**. - In vitro conditions may not mimic the complex physiological responses seen in vivo. *Intrinsic pathway* - This pathway is activated by contact with negatively charged surfaces and does not require **tissue factor**, instead involving factors like **XII, XI, IX, and VIII**. - It primarily takes place in the **test tube** setting rather than in a physiological context. *Contact pathway* - This term generally refers to the activation of the intrinsic pathway via the **contact with an artificial surface**, which again does not involve **tissue factor**. - It is not a primary pathway for activating coagulation in normal **physiological** processes. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Hemodynamic Disorders, Thromboembolic Disease, and Shock, pp. 126-128.

Question 438: What does tissue factor activate?

A. Prothrombin
B. Hageman factor
C. Labile factor
D. Proconvertin (Correct Answer)

Explanation: ***Preaccelerin*** - Tissue factor is known to activate **factor VII**, which is also referred to as **preaccelerin**, leading to the initiation of the extrinsic pathway of the coagulation cascade [1]. - This activation is crucial for the conversion of **prothrombin to thrombin**, facilitating clot formation [1]. *Labile factor* - Labile factor is another name for **factor V**, which is not directly activated by tissue factor but is involved in later stages of the coagulation pathway. - It is more relevant in the **prothrombinase complex**, which is formed after tissue factor activation. *Prothrombin* - Prothrombin is the **substrate** that tissue factor helps to convert, not an immediate product of tissue factor activation. - The activation of prothrombin requires **thrombin**, which is generated as a downstream effect of tissue factor activation [1]. *Hageman factor* - Hageman factor, also known as **factor XII**, plays a role in the intrinsic pathway and is activated by contact with collagen or glass, not directly by tissue factor. - Tissue factor primarily activates **factor VII**, which does not involve Hageman factor in the coagulation cascade [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Hemodynamic Disorders, Thromboembolic Disease, and Shock, pp. 126-130.

Question 439: Which of the following statements about carboxyhemoglobin is true?

A. Causes a left shift of the Hb-O2 dissociation curve (Correct Answer)
B. None of the options
C. Takes up oxygen very quickly
D. Causes histotoxic hypoxia in tissues

Explanation: ***Correct: Causes a left shift of the Hb-O2 dissociation curve*** - Carbon monoxide (CO) binds to hemoglobin with an affinity **210-250 times greater** than oxygen, forming carboxyhemoglobin (COHb). - When CO occupies some heme sites, it causes **allosteric conformational changes** in the hemoglobin molecule, increasing the oxygen affinity of the remaining unoccupied heme sites. - This results in a **left shift of the oxygen-hemoglobin dissociation curve**, meaning hemoglobin holds oxygen more tightly and releases it less readily to tissues. - This combination of **reduced oxygen-carrying capacity** (functional anemia) and **impaired oxygen release** (left shift) makes CO poisoning particularly dangerous. *Incorrect: Takes up oxygen very quickly* - This is false; COHb does **not** take up oxygen. - CO occupies the heme binding sites, **preventing** oxygen from binding. - CO's high affinity for hemoglobin means it displaces and blocks oxygen binding, reducing the blood's oxygen-carrying capacity. *Incorrect: Causes histotoxic hypoxia in tissues* - This is incorrect; CO poisoning causes **hypoxic hypoxia** (inadequate oxygen delivery), not histotoxic hypoxia. - **Histotoxic hypoxia** is caused by agents like **cyanide**, which inhibit cellular enzymes (cytochrome oxidase) and prevent tissues from utilizing oxygen. - COHb reduces oxygen delivery but does not impair cellular oxygen utilization mechanisms. *Incorrect: None of the options* - This is incorrect because the statement about the left shift of the Hb-O2 dissociation curve is physiologically accurate and well-established in medical literature.

Question 440: How does myoglobin respond to the Bohr effect compared to hemoglobin?

A. Increased affinity for oxygen
B. Decreased affinity for oxygen
C. Same affinity for oxygen
D. No effect on oxygen affinity (Correct Answer)

Explanation: **No effect on oxygen affinity (Correct)** - Myoglobin has only one heme group, thus it **does not exhibit cooperativity** or allosteric regulation, unlike hemoglobin - The **Bohr effect**, which describes the pH and CO2-dependent changes in oxygen affinity, primarily applies to **hemoglobin's tetrameric structure** - Myoglobin's oxygen affinity **remains constant** regardless of pH or CO2 levels *Increased affinity for oxygen (Incorrect)* - This statement is incorrect because myoglobin's oxygen affinity is **already very high** and largely unaffected by the conditions that trigger the Bohr effect - The Bohr effect causes hemoglobin's affinity to *decrease* in acidic or high CO2 environments, facilitating oxygen release - Myoglobin does not exhibit this pH-dependent shift *Decreased affinity for oxygen (Incorrect)* - This would imply that myoglobin is sensitive to pH and CO2 levels in a way that promotes oxygen release, which is **not the case** - Myoglobin functions to **store oxygen** in muscles and release it only at very low partial pressures, independent of pH changes - Only hemoglobin shows decreased affinity under Bohr effect conditions *Same affinity for oxygen (Incorrect)* - This is incorrect because it suggests both molecules maintain the same affinity under varying conditions, which misunderstands the question - Hemoglobin's oxygen affinity **changes significantly** due to the Bohr effect (decreases with lower pH), whereas myoglobin's remains constant - The key distinction is that myoglobin has **no response** to Bohr effect conditions, not that it maintains the "same" affinity as hemoglobin

Practice by Chapter

Composition and Functions of Blood

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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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