Blood and Immunity Practice Questions

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

Intrinsic pathway. ***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.

Q: Senescent RBCs are mainly attacked in:

Spleen. ***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**.

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

Neutrophils. ***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.

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

Vasoconstriction. ***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.

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

Phytohemagglutinin. ***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.

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

Hb is almost fully saturated with O₂. ***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 1

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

Accepted Answer

Intrinsic pathway

Answer

Extrinsic pathway

Answer

Fibrinogen function

Answer

Platelet function

Question 2

Senescent RBCs are mainly attacked in:

Accepted Answer

Spleen

Answer

Liver

Answer

Bone Marrow

Answer

Lymph Nodes

Question 3

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

Accepted Answer

PMNs actively migrate to the gingival crevicular fluid as part of the immune response.

Answer

PMNs function mainly as antigen-presenting cells in oral tissues.

Answer

Granulocytes found in the gingival connective tissue.

Answer

None of the options.

Question 4

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

Accepted Answer

Neutrophils

Answer

Basophils

Answer

B lymphocytes

Answer

Eosinophils

Question 5

Transmigration of white blood cells across the endothelium is called?

Accepted Answer

Diapedesis

Answer

Margination

Answer

Rolling

Answer

Pavementing

Question 6

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

Accepted Answer

Vasoconstriction

Answer

Fibrin deposition

Answer

Platelet adhesion

Answer

Thrombosis

Question 7

Which substance enhances the multiplication of T cells in culture?

Accepted Answer

Phytohemagglutinin

Answer

Chemotactic factor

Answer

Leukotrienes

Answer

Prostaglandins

Question 8

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

Accepted Answer

Factor X directly activates both intrinsic and extrinsic pathways.

Answer

Calcium is required in several steps of coagulation.

Answer

Extrinsic pathway is activated by tissue factor released from damaged tissues.

Answer

Intrinsic pathway can be activated in vitro by contact with collagen.

Question 9

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

Accepted Answer

Hb is almost fully saturated with O₂

Answer

All oxygen is released to tissues

Answer

No oxygen is available for binding to Hb

Answer

None of the above

Question 10

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

Accepted Answer

Stagnant hypoxia (related to blood flow issues)

Answer

Ischemic hypoxia (inadequate blood supply)

Answer

Anemic hypoxia (due to reduced hemoglobin functionality)

Answer

Histotoxic hypoxia (cells cannot utilize oxygen due to toxins)

Blood and Immunity — MCQs

Blood and Immunity — MCQs

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