Blood and Immunity Practice Questions

Q: Which of the following is a procoagulant protein?

Thrombin. ***Thrombin*** - Thrombin is a key **procoagulant enzyme** that catalyzes the conversion of fibrinogen to fibrin in the clotting cascade [2] [3]. - It activates platelets and enhances thrombus formation, playing a crucial role in **hemostasis** [1] [2]. *Protein C* - Protein C functions as an **anticoagulant**; when activated, it inactivates factors Va and VIIIa to decrease clot formation [1]. - Low levels or dysfunction of Protein C lead to increased thrombotic risk, indicating its role in **regulating coagulation** rather than promoting it. *Protein S* - Like Protein C, Protein S is involved in the **anticoagulation pathway**, serving as a cofactor to activated Protein C. - It assists in the inactivation of the procoagulant factors Va and VIIIa, thereby reducing coagulation. *Thrombomodulin* - Thrombomodulin is a receptor that binds thrombin, altering its activity from procoagulant to anticoagulant by activating Protein C. - Its primary function is to regulate coagulation rather than to promote clot formation, underscoring its role in **coagulation inhibition**. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Blood And Bone Marrow Disease, pp. 582-583. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Hemodynamic Disorders, Thromboembolic Disease, and Shock, p. 130. [3] 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: A baby's blood group was determined as O negative. Which of the following blood groups can the baby's mother or father not have?

AB Negative. ***AB Negative*** - A parent with **AB blood type** cannot have an O blood type child because an individual with AB blood type only has A and B alleles to pass on (i.e., *I A I B * genotype). - For a child to have **O blood type**, they must inherit the *i* allele from both parents (*ii* genotype), which is impossible if one parent is AB. *A Positive* - A parent with **A positive blood type** can have an O negative child if their genotype is *I A i* for A/B/O and *Rr* for Rh factor. - The child would inherit the *i* allele from this parent and the *r* allele for Rh, along with the same from the other parent. *B Positive* - Similar to A positive, a parent with **B positive blood type** can have an O negative child if their genotype is *I B i* and *Rr*. - The child would inherit the *i* allele from this parent and the *r* allele for Rh, along with the same from the other parent. *O positive* - A parent with **O positive blood type** can certainly have an O negative child; their genotype would be *ii* for A/B/O and *Rr* for Rh factor. - The child would inherit the *i* allele from this parent and the *r* allele for Rh.

Q: Among the blood cells, which has the longest lifespan?

Erythrocytes. ***Erythrocytes*** - Erythrocytes (red blood cells) have the **longest consistent lifespan** among blood cells at approximately **100-120 days** in circulation. - They are produced in the bone marrow and removed by the **reticuloendothelial system** (primarily spleen and liver) when they become senescent. - This predictable lifespan makes RBCs the blood cells with the longest average survival time. *Lymphocytes* - While some **memory lymphocytes** can survive for months to years, the **majority of lymphocytes are short-lived** (days to weeks). - The question asks about blood cells in general, not the specialized subset of long-lived memory cells. - Most naive and activated lymphocytes undergo apoptosis within days. *Neutrophils* - Neutrophils are **short-lived granulocytes**, typically circulating for only **6-12 hours** in the bloodstream. - Their primary role is in acute inflammation and bacterial defense, after which they undergo apoptosis. *Eosinophils* - Eosinophils have a short lifespan, circulating for **6-12 hours** in the blood before migrating into tissues. - They are primarily involved in allergic reactions and defense against parasitic infections.

Q: What is the primary function of Langerhans' cells?

Antigen presenting cells. ***Antigen presenting cells*** - Langerhans' cells play a critical role as **antigen presenting cells** (APCs) in the immune system, facilitating the activation of T-cells [1][2]. - They are found in the **epidermis** and are essential in initiating immune responses against pathogens [1][3]. *Seen in auto immune conditions* - While Langerhans' cells may be involved in autoimmune responses, they are not exclusively seen in these conditions. - Their primary function isn't linked to autoimmunity but rather to **immunological surveillance** and **antigen presentation** [1]. *Phagocytic cells* - Langerhans' cells are not primarily **phagocytic**, as their main role focuses on presenting antigens rather than directly engulfing pathogens [1]. - Phagocytic cells include macrophages and neutrophils, which are more involved in **directly consuming foreign particles**. *Seen in chronic infection* - Although Langerhans' cells can participate in the immune response during infections, they are not specifically characterized as being prominent in **chronic infections**. - Chronic infections are typically associated with different immune cell dynamics, involving other cells such as **plasma cells** and **T-cells**. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, p. 200. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 207-208. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Skin, p. 1144.

Q: The clot formed after the coagulation cascade is not stable unless extensive cross-linking occurs. This is done by what?

Factor XIII. ***Factor XIII*** - **Factor XIII** (fibrin-stabilizing factor) is crucial for cross-linking fibrin strands, forming a stable clot [1][2]. - This enzyme catalyzes the conversion of soluble fibrin into insoluble fibrin by creating **covalent bonds** between fibrin molecules. *Thrombin* - While **thrombin** is essential for converting fibrinogen to fibrin, it does not facilitate the cross-linking of fibrin strands. - Thrombin acts primarily in the early stages of the coagulation cascade and is not responsible for clot stabilization. *Plasmin* - **Plasmin** is involved in fibrinolysis, the breakdown of fibrin clots, rather than stabilizing them. - It works to dissolve clots after they have formed, which is the opposite of the function required for cross-linking. *High molecular weight kininogen* - This protein is a precursor in the **kallikrein-kinin system** and is involved in the inflammatory response, not in clot stabilization. - High molecular weight kininogen assists in **bradykinin** formation but does not play a role in cross-linking fibrin for stable clots. **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: NO acts on platelets through what mechanism?

cGMP. ***cGMP (inhibits platelet activation)*** - **Nitric oxide (NO)** diffuses into platelets and activates **guanylate cyclase**, leading to an increase in intracellular **cyclic guanosine monophosphate (cGMP)**. - Elevated **cGMP** levels then activate protein kinase G, which phosphorylates various proteins involved in platelet signaling, ultimately inhibiting **platelet activation**, adhesion, and aggregation. *cAMP (modulates platelet function through other pathways)* - While **cAMP** also plays a role in inhibiting platelet aggregation, it is primarily generated through the activation of **adenylyl cyclase** by agents like **prostacyclin (PGI2)**, not directly by NO. - NO's direct effect on platelets is mediated by **cGMP**, not **cAMP**. *Adenosine (vasodilator)* - **Adenosine** is a nucleoside known for its **vasodilatory** properties and can also influence platelet function, but it is not the primary mechanism by which NO acts on platelets. - **Adenosine** exerts its effects by activating specific **purinergic receptors** on the platelet surface, distinct from NO's intracellular signaling pathway. *TXA2 (a mediator of platelet aggregation and vasoconstriction)* - **Thromboxane A2 (TXA2)** is a potent **pro-aggregatory** and **vasoconstrictive** eicosanoid produced by platelets through the **cyclooxygenase pathway**. - NO's action on platelets is to *antagonize* the effects of **TXA2**, promoting **platelet inhibition** rather than mediating it.

Q: Which of the following cell types is not a precursor of erythrocytes?

Myeloblast. ***Myeloblast*** - **Myeloblasts** are immature precursor cells that differentiate into **granulocytes** (neutrophils, eosinophils, basophils) within the myeloid lineage. - They are part of **granulopoiesis**, not erythropoiesis, and thus do not give rise to red blood cells. *Proerythroblast* - The **proerythroblast** is the earliest recognizable precursor cell in the erythroid lineage that develops from the common myeloid progenitor. - It differentiates into basophilic, polychromatophilic, and orthochromatic erythroblasts. *Normoblast* - **Normoblasts** (also known as erythroblasts) represent an intermediate stage in erythrocyte maturation, encompassing basophilic, polychromatophilic, and orthochromatic forms. - These cells undergo progressive hemoglobin synthesis and nuclear condensation, eventually leading to nuclear extrusion. *Reticulocyte* - A **reticulocyte** is an immature red blood cell that still contains ribosomal RNA, giving it a reticular appearance when stained with supravital dyes. - Reticulocytes mature into fully functional **erythrocytes** within 1-2 days after being released from the bone marrow into circulation.

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**.

Question 1

Which of the following is a procoagulant protein?

Accepted Answer

Thrombin

Answer

Protein S

Answer

Thrombomodulin

Answer

Protein C

Question 2

A baby's blood group was determined as O negative. Which of the following blood groups can the baby's mother or father not have?

Accepted Answer

AB Negative

Answer

A Positive

Answer

B Positive

Answer

O positive

Question 3

Among the blood cells, which has the longest lifespan?

Accepted Answer

Erythrocytes

Answer

Neutrophils

Answer

Eosinophils

Answer

Lymphocytes

Question 4

What is the primary function of Langerhans' cells?

Accepted Answer

Antigen presenting cells

Answer

Involved in immune responses

Answer

Phagocytosis of pathogens

Answer

Keratinocyte production and maintenance

Question 5

The clot formed after the coagulation cascade is not stable unless extensive cross-linking occurs. This is done by what?

Accepted Answer

Factor XIII

Answer

Plasmin

Answer

Fibrinogen

Answer

Kininogen

Question 6

NO acts on platelets through what mechanism?

Accepted Answer

cGMP

Answer

Adenosine

Answer

cAMP

Answer

TXA2

Question 7

Which of the following cell types is not a precursor of erythrocytes?

Accepted Answer

Myeloblast

Answer

Proerythroblast

Answer

Normoblast

Answer

Reticulocyte

Question 8

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

Accepted Answer

Intrinsic pathway

Answer

Extrinsic pathway

Answer

Fibrinogen function

Answer

Platelet function

Question 9

Senescent RBCs are mainly attacked in:

Accepted Answer

Spleen

Answer

Liver

Answer

Bone Marrow

Answer

Lymph Nodes

Question 10

Although more than 400 blood groups have been identified, the ABO blood group system remains the most important in clinical medicine because it is essential for safe blood transfusions. Which of the following statements about the ABO blood group system is correct?

Accepted Answer

In the ABO blood group system, antibodies are present in plasma when the corresponding antigen is absent on red blood cells.

Answer

The ABO blood group system divides blood into four groups: A, B, AB, and O.

Answer

The ABO blood group system was the first blood group system to be discovered in 1901.

Answer

ABO antigens are found in most body tissues and fluids.

Blood and Immunity — MCQs

Blood and Immunity — MCQs

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