Blood and Immunity Practice Questions

Q: Endothelial cells synthesize which of the following substances?

Factor VIII. ***Factor VIII (Correct Answer)*** * Endothelial cells synthesize and secrete **von Willebrand factor**, a carrier protein for **Factor VIII**; they also produce Factor VIII itself, playing a crucial role in hemostasis. * **Weibel-Palade bodies** within endothelial cells are storage sites for both von Willebrand factor and Factor VIII, which are released upon endothelial activation. *Incorrect: Fibrinogen* * **Fibrinogen** is primarily synthesized by the **liver** and is a key component of the coagulation cascade, forming the fibrin clot. * While endothelial cells play a role in regulating coagulation, they are not the primary site of **fibrinogen production**. *Incorrect: Factor-X* * **Factor X** (Stuart-Prower factor) is a coagulation factor that is **synthesized in the liver** and is vitamin K-dependent. * Endothelial cells do not synthesize Factor X; instead, they *regulate* its activation and activity through various mechanisms. *Incorrect: Factor-XII* * **Factor XII** (Hageman factor) is a protein of the contact activation pathway of coagulation, primarily **synthesized by the liver**. * Endothelial cells influence the activation of Factor XII on their surface but do not **produce** this coagulation factor themselves.

Q: The principal site for granulocytic hemopoiesis in the adult human is:

Red bone marrow. ***Red bone marrow*** - In adult humans, **red bone marrow** is the primary site for all types of **hematopoiesis**, including granulocytic hemopoiesis. - It contains **hematopoietic stem cells** that differentiate into myeloid and lymphoid lineages, producing mature blood cells. *Liver* - The liver is a major site of **hematopoiesis during fetal development**, especially in the second trimester. - In adults, the liver only resumes hematopoietic function under conditions of **extramedullary hematopoiesis**, such as severe bone marrow failure. *Spleen* - The spleen is involved in **hematopoiesis** during fetal life and can also contribute to **extramedullary hematopoiesis** in adults when red bone marrow is compromised. - However, it is not the principal site for normal, ongoing granulocytic hemopoiesis in healthy adults. *Yellow bone marrow* - **Yellow bone marrow** primarily consists of **adipocytes (fat cells)** and has limited hematopoietic activity. - While it can convert to red bone marrow under extraordinary demand, it is not the principal site for granulocytic hemopoiesis.

Q: Which of the following agents is least likely to be found in plasma?

Thrombin. ***Thrombin*** - **Thrombin** is an active enzyme that converts **fibrinogen to fibrin** during coagulation. Its presence in significant amounts in plasma would lead to widespread, uncontrolled clotting. - Due to its potent procoagulant activity, thrombin is typically present in circulation only transiently and in very low concentrations, being rapidly inactivated by **antithrombin** and other inhibitors. *Fibrinogen* - **Fibrinogen** is a large plasma protein that is a precursor to fibrin and is crucial for **blood clot formation**. - It is a normal and abundant component of plasma, synthesized by the liver, and is continuously present in significant concentrations. *Prothrombin* - **Prothrombin** (Factor II) is the inactive precursor of thrombin, synthesized by the liver with the help of **vitamin K**. - It circulates in the plasma in relatively high concentrations, ready to be activated into thrombin upon injury. *Calcium ion* - **Calcium ions (Ca2+)** are essential **cofactors** for many steps in the coagulation cascade. - They are continuously present in plasma and play vital roles in bone health, muscle contraction, and nerve function, in addition to coagulation.

Q: Activated protein C inhibits the clotting mechanism by inactivating which of the following clotting factors?

Factor Va and Factor VIIIa. ***Factor Va and Factor VIIIa*** - **Activated protein C (APC)** functions as a natural anticoagulant by specifically inactivating the activated forms of **Factor V (Va)** and **Factor VIII (VIIIa)**. - By inactivating these cofactors, APC effectively downregulates the functioning of the **prothrombinase complex** and **tenase complex**, thereby slowing down thrombin generation and subsequent fibrin formation. *Factor III and Factor VIIIa* - **Factor III (tissue factor)** initiates the extrinsic coagulation pathway, but it is not directly inactivated by activated protein C. - While **Factor VIIIa** is a target of APC, the combination with Factor III makes this option incorrect. *Factor VIIIa and Factor IX* - **Factor VIIIa** is indeed inactivated by APC. - However, **Factor IX** (the inactive zymogen) and its activated form **Factor IXa** are not direct targets for inactivation by APC; Factor IXa remains active to participate in the tenase complex until its co-factor Factor VIIIa is inactivated. *Factor Va and Factor VII* - **Factor Va** is a known target for inactivation by APC. - **Factor VII** (the inactive zymogen) and its activated form **Factor VIIa** are not inactivated by APC; Factor VIIa plays a role in the initiation of coagulation by forming a complex with tissue factor.

Q: Cell type which lacks HLA antigen is:

Erythrocytes. ***Erythrocytes*** - Mature **erythrocytes** (red blood cells) lack a nucleus and therefore do not express **MHC/HLA antigens** on their surface. This is critical for their role in oxygen transport without triggering immune responses. - While other blood cells like leukocytes express HLA antigens, erythrocytes are a notable exception, making them less immunogenic in certain contexts. *Monocytes* - **Monocytes** are **antigen-presenting cells** and express both **MHC Class I and Class II** molecules (HLA-A, B, C, DR, DP, DQ) on their surface. - These HLA antigens are crucial for monocytes to present antigens to T lymphocytes and initiate immune responses. *Platelets* - **Platelets** express **MHC Class I (HLA-A, B, C)** antigens on their surface. - These HLA antigens can be a target for alloantibodies, contributing to conditions like **post-transfusion purpura** and **neonatal alloimmune thrombocytopenia**. *Neutrophils* - **Neutrophils** are granulocytes that express **MHC Class I (HLA-A, B, C)** antigens on their surface. - While their primary role is phagocytosis, the presence of HLA Class I allows them to be recognized by the immune system and can be relevant in transfusion reactions.

Q: Endothelial cells synthesize:

Von Willebrand Factor. ***Von Willebrand Factor*** - **Endothelial cells** are the primary site of synthesis and storage for **Von Willebrand factor (vWF)**. - **vWF** is crucial for primary hemostasis, mediating **platelet adhesion** to subendothelial collagen and acting as a carrier protein for **Factor VIII**. *Factor X* - **Factor X** (Stuart-Prower factor) is a **vitamin K-dependent coagulation factor** synthesized primarily in the **liver**. - It plays a central role in both the intrinsic and extrinsic pathways, ultimately converting **prothrombin to thrombin**. *Factor XII* - **Factor XII** (Hageman factor) is a component of the **intrinsic coagulation pathway** and is primarily synthesized in the **liver**. - It is activated upon contact with negatively charged surfaces and initiates the **intrinsic cascade**. *Fibrinogen* - **Fibrinogen** (Factor I) is a large plasma glycoprotein predominantly synthesized by **hepatocytes in the liver**. - It is converted into **fibrin** by thrombin, forming the meshwork of a stable clot.

Q: Tissue factor activates which coagulation pathway?

Extrinsic pathway. ***Extrinsic pathway*** - **Tissue factor (TF)**, also known as factor III, is a transmembrane glycoprotein found on extravascular cells that initiates the **extrinsic pathway** of coagulation when exposed to blood. - TF binds to **factor VIIa** to form the TF-VIIa complex, which then activates factor X and factor IX, leading to thrombin generation. *Contact pathway* - The contact pathway, also known as the **intrinsic pathway**, is initiated when factor XII comes into contact with negatively charged surfaces. - It does not involve tissue factor as its primary activator. *Intrinsic pathway* - The intrinsic pathway is initiated by activation of **factor XII** on contact with negatively charged surfaces and involves factors XI, IX, and VIII. - It works in parallel with the extrinsic pathway but is not directly activated by **tissue factor**. *Common pathway* - The **common pathway** is where the intrinsic and extrinsic pathways converge, starting with the activation of **factor X**. - While tissue factor contributes to the activation of factor X (via the extrinsic pathway), it does not directly activate or initiate the common pathway itself; its role is upstream.

Q: What is the major hemoglobin present in an adult?

HbA. ***HbA*** - **Hemoglobin A (HbA)** is the primary and most abundant form of hemoglobin found in healthy adult red blood cells, constituting about 95-98% of total hemoglobin. - It consists of two **alpha (α)** and two **beta (β)** globin chains (α2β2). *HbA2* - **Hemoglobin A2 (HbA2)** is a minor adult hemoglobin, making up only about 2-3% of total hemoglobin in adults. - It is composed of two **alpha (α)** and two **delta (δ)** globin chains (α2δ2). *HbA1c* - **Hemoglobin A1c (HbA1c)** is a glycated form of HbA, where glucose molecules are irreversibly bound to the N-terminus of the beta globin chains. - While present in adults, its proportion reflects average blood glucose levels over the past 2-3 months and is not the major form of hemoglobin. *HbA1b* - **HbA1b** is another minor glycated hemoglobin component, similar to HbA1c but present in even smaller quantities. - It is a subset of the HbA1 fraction and does not represent the major adult hemoglobin.

Q: Which of the following substances is primarily synthesized and secreted by mast cells?

Histamine. ***Histamine*** - **Histamine** is a key mediator of immediate hypersensitivity reactions, primarily synthesized and stored in the **granules of mast cells** and basophils. - Upon activation, mast cells release histamine, which causes **vasodilation**, increased vascular permeability, and smooth muscle contraction, contributing to allergic symptoms. - Histamine is considered the **primary and most important mediator** released by mast cells in allergic and inflammatory responses. *Adrenaline* - **Adrenaline (epinephrine)** is a hormone and neurotransmitter primarily produced by the **adrenal medulla**. - It plays a crucial role in the **"fight or flight" response**, affecting heart rate, blood pressure, and metabolism, and is not associated with mast cell synthesis. *Acetylcholine* - **Acetylcholine** is a major neurotransmitter in the **parasympathetic nervous system** and at neuromuscular junctions. - It is synthesized and released by neurons to transmit signals, and not by mast cells. *Heparin* - **Heparin** is also synthesized and stored in mast cell granules and has anticoagulant properties. - However, while mast cells do produce heparin, **histamine** is considered the **primary and most clinically significant** substance synthesized and secreted by mast cells, particularly in the context of immediate allergic responses. - The question emphasizes "primarily," making histamine the best answer as it is the principal mediator of mast cell-related allergic reactions.

Q: Anemia in chronic renal failure is due to.

Decreased erythropoietin production. ### Decreased erythropoietin production - The kidneys are the primary site for **erythropoietin (EPO)** production, a hormone essential for **red blood cell production** in the bone marrow [1]. - In chronic renal failure, damaged kidneys are unable to produce adequate amounts of EPO, leading to **normochromic, normocytic anemia** [1]. *Iron deficiency* - While **iron deficiency** can contribute to anemia in chronic renal failure due to blood loss or poor absorption, it is not the primary cause of anemia associated with **chronic kidney disease (CKD)** itself. - Iron deficiency anemia typically presents as **microcytic, hypochromic anemia**. *Hypoplastic bone marrow* - **Hypoplastic bone marrow** (aplastic anemia) or marrow failure is a rare cause of anemia and is not typically associated with chronic renal failure. - Anemia in chronic kidney disease is due to a lack of EPO stimulation, not necessarily an inherent problem with the bone marrow's ability to produce cells. *Decreased folate levels* - **Folate deficiency** can cause **megaloblastic anemia**, which is characterized by large, immature red blood cells. - While patients with chronic renal failure may have nutritional deficiencies, global decreased folate levels are not the primary or most common cause of anemia in chronic renal failure.

Question 1

Endothelial cells synthesize which of the following substances?

Accepted Answer

Factor VIII

Answer

Fibrinogen

Answer

Factor-X

Answer

Factor-XII

Question 2

The principal site for granulocytic hemopoiesis in the adult human is:

Accepted Answer

Red bone marrow

Answer

Spleen

Answer

Yellow bone marrow (primarily fat storage)

Answer

Liver

Question 3

Which of the following agents is least likely to be found in plasma?

Accepted Answer

Thrombin

Answer

Fibrinogen

Answer

Prothrombin

Answer

Calcium ion

Question 4

Activated protein C inhibits the clotting mechanism by inactivating which of the following clotting factors?

Accepted Answer

Factor Va and Factor VIIIa

Answer

Factor III and Factor VIIIa

Answer

Factor VIIIa and Factor IX

Answer

Factor Va and Factor VII

Question 5

Cell type which lacks HLA antigen is:

Accepted Answer

Erythrocytes

Answer

Monocytes

Answer

Platelets

Answer

Neutrophils

Question 6

Endothelial cells synthesize:

Accepted Answer

Von Willebrand Factor

Answer

Factor XII

Answer

Factor X

Answer

Fibrinogen

Question 7

Tissue factor activates which coagulation pathway?

Accepted Answer

Extrinsic pathway

Answer

Common pathway

Answer

Contact pathway

Answer

Intrinsic pathway

Question 8

What is the major hemoglobin present in an adult?

Accepted Answer

HbA

Answer

HbA2

Answer

HbA1c

Answer

HbA1b

Question 9

Which of the following substances is primarily synthesized and secreted by mast cells?

Accepted Answer

Histamine

Answer

Adrenaline

Answer

Acetylcholine

Answer

Heparin

Question 10

Anemia in chronic renal failure is due to.

Accepted Answer

Decreased erythropoietin production

Answer

Iron deficiency

Answer

Hypoplastic bone marrow

Answer

Decreased folate levels

Blood and Immunity — MCQs

Blood and Immunity — MCQs

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