Blood and Immunity Practice Questions

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: The minimum platelet count required to maintain vascular integrity in the microcirculation is:

10,000-20,000. ***10,000-20,000/μL*** - This range represents the **critical threshold** for maintaining vascular integrity in the microcirculation. - A platelet count of **≥10,000/μL** is generally sufficient to prevent spontaneous bleeding and maintain hemostatic plugs in capillaries and small vessels. - Below 10,000/μL, the risk of **spontaneous bleeding** (petechiae, purpura) increases significantly due to inability to seal minor endothelial breaches. - This is the **standard transfusion threshold** used in clinical practice for prophylactic platelet transfusion in stable patients. *5,000-10,000/μL* - This is a **critically low range** where vascular integrity is already **compromised**. - Patients typically develop **petechiae and purpura** due to failure to maintain microvascular hemostasis. - This range indicates significant risk of spontaneous bleeding, not maintenance of integrity. *1,000-5,000/μL* - This represents **severe thrombocytopenia** with very high risk of life-threatening hemorrhage. - Spontaneous severe bleeding including **intracranial hemorrhage** and **GI bleeding** can occur. - Vascular integrity is severely compromised at this level. *20,000-30,000/μL* - While still classified as **thrombocytopenia**, this range provides a **comfortable margin of safety**. - Vascular integrity is well-maintained, and spontaneous bleeding is uncommon. - This exceeds the minimum requirement for microvascular integrity maintenance.

Q: Platelet adhesion is inhibited by what?

Nitric oxide. ***Nitric oxide*** - **Nitric oxide (NO)** is a potent **vasodilator** and **inhibitor of platelet adhesion** and aggregation. - It is released by **endothelial cells** and helps maintain blood vessel patency by preventing unwanted clot formation. *Substance P* - **Substance P** is a **neuropeptide** involved in pain transmission, inflammation, and neurogenic vasodilation. - It does not directly inhibit platelet adhesion; instead, it can induce **mast cell degranulation** and promote inflammatory responses. *IL-2* - **Interleukin-2 (IL-2)** is a **cytokine** primarily involved in the activation, proliferation, and differentiation of **T lymphocytes**. - It plays a crucial role in immune responses but has no direct role in inhibiting platelet adhesion. *Thrombin* - **Thrombin** is a key enzyme in the coagulation cascade that promotes platelet activation and aggregation. - It converts **fibrinogen** to **fibrin**, leading to clot formation, thus having an opposite effect to inhibiting platelet adhesion.

Q: Loose fibrin accumulated in a tight clot in the coagulation pathway is caused by which factor?

Factor XIII. ***Factor XIII*** - **Factor XIII** (fibrin-stabilizing factor) is responsible for **cross-linking fibrin monomers**, converting loose fibrin into a stable, insoluble clot [1]. - This cross-linking process strengthens the clot, preventing premature degradation and ensuring effective hemostasis [2]. *Factor X* - **Factor X** (Stuart-Prower factor) is a key enzyme in the coagulation cascade that, when activated to Factor Xa, forms part of the **prothrombinase complex** that converts **prothrombin to thrombin** [2]. - It does not directly cause the cross-linking of fibrin to form a tight clot. *Factor XI* - **Factor XI** (plasma thromboplastin antecedent) is involved in the intrinsic pathway, activating **Factor IX**. - Its primary role is in propagating the coagulation cascade, not in the final stabilization of the fibrin clot. *Factor XII* - **Factor XII** (Hageman factor) initiates the intrinsic pathway of coagulation and is involved in fibrinolysis and inflammation. - It does not directly influence the stability or cross-linking of the fibrin clot structure. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Hemodynamic Disorders, Thromboembolic Disease, and Shock, p. 130. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Blood And Bone Marrow Disease, pp. 582-583.

Q: Common site of haematopoiesis in the fetus is -

Liver. ***Liver*** - The **liver** is the **primary and most common site of hematopoiesis** during the fetal period, taking over from the yolk sac around the **second month of gestation**. - It remains the **dominant hematopoietic organ from the second to the seventh month of gestation**, making it the longest-serving primary site during fetal development. - This is why the liver is the correct answer to this question about the "common site" of fetal hematopoiesis. *Spleen* - The spleen contributes to hematopoiesis during the fetal period but is **not the primary or most common site**. - Its role is **secondary to the liver** and diminishes significantly as bone marrow becomes more active. *Bone marrow* - While it eventually becomes the **primary site of hematopoiesis in adults**, the bone marrow's role in fetal hematopoiesis becomes prominent **only in the late second and third trimesters** (after 5 months). - It gradually overtakes the liver as the main hematopoietic organ near term and postnatally. *Gut* - The **gut** is **not a site of hematopoiesis** at any stage of development. - Its primary function is digestion and absorption. **Note:** The yolk sac is the earliest site of hematopoiesis (0-2 months), but the liver serves as the primary site for the longest duration during fetal life.

Question 1

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 2

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 3

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

Accepted Answer

Vasoconstriction

Answer

Fibrin deposition

Answer

Platelet adhesion

Answer

Thrombosis

Question 4

Which substance enhances the multiplication of T cells in culture?

Accepted Answer

Phytohemagglutinin

Answer

Chemotactic factor

Answer

Leukotrienes

Answer

Prostaglandins

Question 5

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 6

The minimum platelet count required to maintain vascular integrity in the microcirculation is:

Accepted Answer

10,000-20,000

Answer

5000-10000

Answer

20,000-30,000

Answer

1000-5000

Question 7

Platelet adhesion is inhibited by what?

Accepted Answer

Nitric oxide

Answer

Substance P

Answer

IL-2

Answer

Thrombin

Question 8

Loose fibrin accumulated in a tight clot in the coagulation pathway is caused by which factor?

Accepted Answer

Factor XIII

Answer

Factor X

Answer

Factor XI

Answer

Factor XII

Question 9

Common site of haematopoiesis in the fetus is -

Accepted Answer

Liver

Answer

Spleen

Answer

Bone marrow

Answer

Gut

Blood and Immunity — MCQs

Blood and Immunity — MCQs

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