Blood and Immunity — MCQs

Blood and Immunity Indian Medical PG Practice Questions and MCQs

Question 491: Partial thromboplastin time (PTT) correlates with which pathway or function?

A. Intrinsic pathway (Correct Answer)
B. Extrinsic pathway
C. Fibrinogen function
D. Platelet function

Explanation: ***Function of platelets*** - The **partial thromboplastin time (PTT)** primarily assesses the **intrinsic and common pathways** of blood coagulation [1], indirectly reflecting platelet function through clotting factors. - Abnormal PTT can indicate issues with **platelet activation** and interactions in the clotting process, although it is not a direct measure of platelet count or function. *Intrinsic and common pathway* - While PTT is indeed related to the **intrinsic pathway** [1], it does not correlate directly with the **overall intrinsic pathway function** alone, as it primarily assesses clotting factor activity. - The **PTT** specifically examines factors like **factor VIII** and **IX** [1], rather than the broader aspect of the intrinsic mechanism itself. *Fibrinogen level* - Fibrinogen levels are assessed using the **prothrombin time (PT)** and not through PTT, as fibrinogen is involved in the **common pathway** but does not directly correlate with PTT. - Fibrinogen deficiency can affect clotting time, but the **PTT** primarily evaluates other factors independent of fibrinogen concentration. *Extrinsic and common pathway* - The **extrinsic pathway** is evaluated using **prothrombin time (PT)** [1], not PTT, which focuses on intrinsic factors' performance. - PTT measures factors involved mainly in the **intrinsic pathway**, including **factor XII**, **XI**, **IX**, and **VIII** [1], making this option incorrect. **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 492: Senescent RBCs are mainly attacked in:

A. Liver
B. Bone Marrow
C. Spleen (Correct Answer)
D. Lymph Nodes

Explanation: ***Spleen*** - The **spleen** is the primary organ responsible for filtering and removing **senescent (aged) red blood cells (RBCs)** from circulation. - Its unique **microcirculation** and **macrophage-rich red pulp** allow for the detection and destruction of old, rigid RBCs. *Liver* - While the **liver** plays a role in iron metabolism and can clear some damaged RBCs, it is not the primary site for the routine destruction of **senescent RBCs**. - Its main roles in RBC breakdown involve processing **hemoglobin** components after splenic destruction and removing severely damaged cells. *Bone Marrow* - The **bone marrow** is primarily responsible for **hematopoiesis**, the production of new blood cells, including RBCs. - It does not significantly participate in the destruction of **aged RBCs**. *Lymph Nodes* - **Lymph nodes** are key components of the **immune system**, filtering lymph and housing immune cells. - They are not involved in the routine clearance of **senescent RBCs**.

Question 493: What are the characteristics of polymorphonuclear leukocytes (PMNs) in the oral cavity?

A. PMNs function mainly as antigen-presenting cells in oral tissues.
B. Granulocytes found in the gingival connective tissue.
C. PMNs actively migrate to the gingival crevicular fluid as part of the immune response. (Correct Answer)
D. None of the options.

Explanation: **PMNs actively migrate to the gingival crevicular fluid as part of the immune response.** - **Polymorphonuclear leukocytes (PMNs)**, primarily neutrophils, are highly motile phagocytes that play a crucial role in the innate immune response to oral microbes. - Their active migration into the **gingival crevicular fluid (GCF)** is a hallmark of the body's defense against bacterial plaque, forming a crucial first line of defense against periodontal pathogens. *Granulocytes found in the gingival connective tissue.* - While PMNs are granulocytes that reside in the **gingival connective tissue**, this statement alone does not fully encompass their dynamic role and key characteristics in the oral cavity. - Their most significant characteristic in the context of oral health is their **active migration** to the epithelial surface and into the GCF, not just their presence in the connective tissue. *PMNs function mainly as antigen-presenting cells in oral tissues.* - **PMNs** are primarily involved in **phagocytosis** and intracellular destruction of pathogens, not as primary antigen-presenting cells (APCs). - **Dendritic cells** and **macrophages** are the main APCs that bridge innate and adaptive immunity by presenting antigens. *None of the options.* - This option is incorrect because the statement regarding **PMNs** actively migrating to the **gingival crevicular fluid** accurately describes a major characteristic and function of these cells in oral immunity.

Question 494: Which blood cell is most likely to be involved in phagocytosing bacteria at sites of infection?

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

Explanation: ***Correct Option: Neutrophils*** - **Neutrophils** are the **most abundant type of white blood cell** (50-70% of circulating leukocytes) and are the **primary phagocytes** responsible for engulfing and destroying bacteria at the site of infection. - They are rapidly recruited to inflammatory sites and are equipped with powerful antimicrobial mechanisms, including the release of **reactive oxygen species** (respiratory burst) and **lysosomal enzymes** from azurophilic and specific granules. - Neutrophils are the **first responders** to acute bacterial infections and form the main component of pus. *Incorrect Option: Basophils* - **Basophils** are involved in **allergic reactions** and the release of **histamine** and other inflammatory mediators, but their primary role is not direct bacterial phagocytosis. - They play a role in modulating immune responses rather than directly engulfing pathogens. *Incorrect Option: B lymphocytes* - **B lymphocytes** are a type of **adaptive immune cell** primarily responsible for producing **antibodies** in response to antigens. - While antibodies can opsonize bacteria (making them easier targets for phagocytes), B lymphocytes themselves are **not phagocytic cells**. *Incorrect Option: Eosinophils* - **Eosinophils** are primarily involved in the immune response against **parasitic infections** and in modulating **allergic reactions**. - Although they can perform some phagocytosis, it is generally limited and not their main function as compared to neutrophils, especially for bacterial infections.

Question 495: Transmigration of white blood cells across the endothelium is called?

A. Margination
B. Rolling
C. Pavementing
D. Diapedesis (Correct Answer)

Explanation: ***Diapedesis*** - Refers to the process where **white blood cells** squeeze through the endothelial cell junctions to exit the bloodstream and enter tissues [1,2]. - It is a critical step in the **inflammatory response**, allowing immune cells to reach sites of infection or injury [2]. *Rolling* - This is an earlier step in leukocyte adhesion, where white blood cells adhere loosely to the endothelium, allowing them to **roll** along the blood vessel wall [3]. - It does not involve the actual **transmigration** through the endothelium, which distinguishes it from diapedesis [4]. *Pavementing* - This term generally describes the process of leukocytes forming a **monolayer** on the endothelium but does not specifically refer to their movement through it. - Pavementing precedes diapedesis but does not involve the **transmigration** itself. *Margination* - Refers to the localization of white blood cells towards the **peripheral margins** of the bloodstream, facilitating their access to the endothelium [4]. - It is a preliminary step and does not denote the **actual entry** of cells into the tissues, distinguishing it from diapedesis. **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. 188-189. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 87-89. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, p. 87. [4] 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.

Question 496: Following injury to a blood vessel, immediate hemostasis is achieved by:

A. Fibrin deposition
B. Vasoconstriction (Correct Answer)
C. Platelet adhesion
D. Thrombosis

Explanation: ***Vasoconstriction*** - Following blood vessel injury, **vasoconstriction** occurs immediately, reducing blood flow and minimizing blood loss. - It is a **reflex response** mediated by local factors and neural mechanisms aiming to maintain hemostasis. *Fibrin deposition* - **Fibrin deposition** occurs later in the hemostatic process, primarily during the **coagulation phase** after initial vascular responses. - It is not an immediate response; rather, it's part of the **clot stabilization** process, requiring activation of the clotting cascade. *Thrombosis* - Thrombosis refers to the formation of a **blood clot** within a vessel, which happens after initial hemostatic mechanisms are activated. - It is not the **immediate** response post-injury; there is a sequence of events that lead to thrombosis after vasoconstriction and platelet activation. *Platelet adhesion* - Although platelet adhesion is crucial in hemostasis, it occurs following **vasoconstriction** and is not an immediate response to vessel injury [1][2]. - This process is part of the **primary hemostasis** phase, which cannot occur efficiently without prior initial vasoconstriction. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Blood And Bone Marrow Disease, pp. 581-582. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Hemodynamic Disorders, Thromboembolic Disease, and Shock, p. 128.

Question 497: Which substance enhances the multiplication of T cells in culture?

A. Phytohemagglutinin (Correct Answer)
B. Chemotactic factor
C. Leukotrienes
D. Prostaglandins

Explanation: ***Phytohemagglutinin*** - **Phytohemagglutinin (PHA)** is a plant lectin that acts as a mitogen, non-specifically stimulating **T cells** to proliferate in culture. - It works by binding to cell surface glycoproteins, activating signaling pathways that lead to cell division and **clonal expansion** of T cells. *Chemotactic factor* - **Chemotactic factors** are substances that attract cells to a specific site, like chemokines attracting leukocytes to inflammation. - They are involved in cell migration and homing, not direct stimulation of **T cell proliferation**. *Leukotrienes* - **Leukotrienes** are inflammatory mediators derived from arachidonic acid, involved in allergic reactions and asthma. - They primarily influence **smooth muscle contraction**, vascular permeability, and leukocyte recruitment, not T cell multiplication. *Prostaglandins* - **Prostaglandins** are lipid compounds involved in various physiological processes, including inflammation, pain, and fever. - While they can modulate immune responses, they generally have **immunosuppressive effects** on T cells rather than enhancing their multiplication.

Question 498: All of the following are true about blood coagulation, except which of the following?

A. Factor X directly activates both intrinsic and extrinsic pathways. (Correct Answer)
B. Calcium is required in several steps of coagulation.
C. Extrinsic pathway is activated by tissue factor released from damaged tissues.
D. Intrinsic pathway can be activated in vitro by contact with collagen.

Explanation: ***Extrinsic pathway is activated by contact with negatively charged surfaces*** - The **extrinsic pathway** is actually activated by tissue factor, not by contact with negatively charged surfaces [1]. - This statement is therefore **incorrect**, making it the exception among the other statements. *Factor X is part of both intrinsic and extrinsic pathways* - Factor X is indeed a key component involved in both the **intrinsic** and **extrinsic pathways** of coagulation, leading to the common pathway [1]. - The presence of Factor X is crucial for the conversion of prothrombin to thrombin in both pathways [2]. *Calcium is required in several steps of coagulation* - Calcium (**factor IV**) is essential for several reactions in the coagulation cascade, playing a pivotal role in both pathways [1]. - It acts as a cofactor that facilitates various enzyme-substrate interactions necessary for the coagulation process [2]. *Intrinsic pathway can be activated in vitro* - The **intrinsic pathway** can be activated in vitro using substances like kaolin or glass that promote contact activation [1]. - This means the statement is not an exception, as it's true regarding the properties of the intrinsic pathway. **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. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Blood And Bone Marrow Disease, pp. 582-583.

Question 499: What does the plateau of oxygen-hemoglobin dissociation curve signify?

A. Hb is almost fully saturated with O₂ (Correct Answer)
B. All oxygen is released to tissues
C. No oxygen is available for binding to Hb
D. None of the above

Explanation: ***Hb is almost fully saturated with O₂*** - The **plateau phase** of the oxygen-hemoglobin dissociation curve represents the region where hemoglobin is nearly fully saturated with oxygen (typically **97-100% saturation**). - At this stage, nearly all available **hemoglobin binding sites** are occupied by oxygen molecules, even with only moderate increases in partial pressure of oxygen (PO₂). - This plateau occurs at **PO₂ above 60-70 mmHg**, providing a **safety margin** for oxygen loading in the lungs despite variations in alveolar PO₂. - The flat plateau ensures stable oxygen saturation even with minor fluctuations in inspired oxygen or at moderate altitudes. *No oxygen is available for binding to Hb* - This is incorrect as the plateau region occurs at **high partial pressures of oxygen**, meaning plenty of oxygen is available in the environment. - If no oxygen were available, hemoglobin saturation would be minimal, corresponding to the **lowest point on the curve**, not the plateau. *All oxygen is released to tissues* - The plateau shows **high oxygen saturation**, meaning oxygen is tightly bound to hemoglobin, not released. - Oxygen release to tissues primarily occurs in the **steep portion of the curve** at lower PO₂ values (20-40 mmHg), typical of metabolically active tissues. - The steep part allows for **efficient oxygen unloading** in response to small changes in tissue PO₂. *None of the above* - This is incorrect because the first option accurately describes the physiological significance of the plateau phase as representing near-maximal hemoglobin saturation.

Question 500: Which type of hypoxia is associated with reduced oxygen delivery to tissues despite normal arterial oxygen content?

A. Stagnant hypoxia (related to blood flow issues) (Correct Answer)
B. Ischemic hypoxia (inadequate blood supply)
C. Anemic hypoxia (due to reduced hemoglobin functionality)
D. Histotoxic hypoxia (cells cannot utilize oxygen due to toxins)

Explanation: ***Stagnant hypoxia (related to blood flow issues)*** - **Stagnant hypoxia**, also known as **circulatory hypoxia**, is characterized by **reduced oxygen delivery to tissues despite normal arterial oxygen content**. - The **oxygen content (CaO2)** in arterial blood is normal, but **oxygen delivery (DO2)** is reduced due to **decreased blood flow** or **reduced cardiac output**. - Conditions like **heart failure**, **shock**, or **localized vascular obstruction** reduce tissue perfusion, preventing adequate oxygen from reaching the tissues. - This perfectly matches the question stem: normal arterial O2 content but impaired delivery. *Anemic hypoxia (due to reduced hemoglobin functionality)* - **Anemic hypoxia** occurs when the **oxygen-carrying capacity of blood** is reduced due to decreased **functional hemoglobin**. - While **PaO2** (partial pressure) may be normal, the **arterial oxygen content (CaO2) is REDUCED** because CaO2 depends on hemoglobin concentration. - Conditions like **anemia** or **carbon monoxide poisoning** reduce the amount of oxygen that can be carried in blood. - This does NOT match the question stem because arterial oxygen content is reduced, not normal. *Histotoxic hypoxia (cells cannot utilize oxygen due to toxins)* - In **histotoxic hypoxia**, both **arterial oxygen content** and **oxygen delivery** are normal. - The problem is at the **cellular level** where cells cannot utilize oxygen despite adequate supply. - **Cyanide poisoning** inhibits **cytochrome oxidase** in mitochondria, preventing cellular respiration. - Does not match because delivery is normal, not reduced. *Ischemic hypoxia (inadequate blood supply)* - **Ischemic hypoxia** is a **localized form of stagnant hypoxia** caused by **regional blood flow obstruction**. - Examples include **arterial occlusion** in **stroke** or **myocardial infarction**. - While this involves reduced delivery, it's a subset of stagnant hypoxia and less precise than the primary answer.

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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