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What is the primary function of coagulation in the body?
Hemophilia prevents the body from effectively clotting blood.
True
Name the two main types of coagulation pathways.
Extrinsic pathway and Intrinsic pathway
Coagulation factors are produced by __________.
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Match the following coagulation factors with their corresponding functions:
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Which substance is used as an anticoagulant to obtain plasma from blood?
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Serum is obtained by adding anticoagulants to whole blood and then centrifuging.
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What are the three main types of blood cells?
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____ is the spontaneous arrest of blood loss from injured blood vessels.
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Match the anticoagulants with their sources:
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What happens during coagulation?
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Anticoagulants are substances that promote clot formation.
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What is the normal range of erythrocytes in blood?
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What is the role of Prostaglandin I2 (PGI2) in platelet activation?
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Thromboxane A2 (TXA2) decreases intracellular calcium levels in platelets.
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What enzyme is responsible for breaking down cAMP in platelets?
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ADP activates platelets by lowering the levels of the platelet inhibitor __________.
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Match the following elements with their roles in platelet function:
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What initiates the intrinsic pathway of coagulation?
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Platelets have a life span of around 30 days.
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What is the role of glycoproteins on the platelet surface?
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The __________ pathway is triggered by tissue factors outside the blood.
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Match the following processes with their descriptions:
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Which of the following stimuli do platelets interact with during activation?
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Activated platelets do not participate in clot formation.
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What is the final product of the clot formation process?
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Which glycoprotein binds to collagen during platelet adhesion?
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Thromboxane A2 (TXA2) is released from activated platelets and promotes platelet aggregation.
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What are the names of two receptors responsible for binding ADP on activated platelets?
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Collagen exposure occurs due to endothelial ______ from vascular injury.
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Match the receptors with their corresponding activation mechanism:
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What is the role of fibrinogen in platelet aggregation?
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Protease-activated receptors are not involved in platelet aggregation.
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Name one potent platelet agonist released from dense granules.
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Study Notes
Blood Components
- Plasma is the liquid component of blood, obtained by centrifuging blood after adding an anticoagulant (e.g., sodium citrate or heparin).
- Serum is the liquid component of blood, obtained by centrifuging clotted blood.
Blood Vessels
- Arteries carry oxygenated blood away from the heart.
- Arterioles are small arteries.
- Veins carry deoxygenated blood back to the heart.
- Venules are small veins.
Blood Cells
- Erythrocytes (Red Blood Cells - RBC) are responsible for oxygen transport and are present in a range of 4.2-6.1 million/μl.
- Leukocytes (White Blood Cells - WBC) are responsible for immune function and are present in a range of 5-10 k/μl.
- Platelets (Thrombocytes) are cell fragments involved in blood clotting and are present in a range of 250-500 k/μl.
Hemostasis
- Hemostasis is the process of stopping bleeding from injured blood vessels, essential for survival.
- Coagulation refers to the conversion of fluid blood into a gel (clot) to prevent excessive blood loss.
- Thrombosis is a pathological process where clots (thrombi) form and obstruct blood flow, potentially leading to organ damage.
- Anticoagulants are substances that inhibit blood coagulation.
Anticoagulants in Nature
- Mosquitoes (Anopheles and Culex) use anticoagulants in their saliva to prevent blood clotting while feeding.
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Leeches (Hirudo medicinalis) produce two anticoagulants:
- Hirudin: inhibits thrombin, an enzyme crucial in clot formation.
- Antistasin: inhibits Factor Xa, another key enzyme in coagulation.
Studying Coagulation and Anticoagulants
- Coagulation is essential for preventing excessive blood loss but can also contribute to medical complications like hemophilia.
- Studying coagulation and anticoagulants allows us to treat conditions like Disseminated Intravascular Coagulation Disorder (DIC) by preventing or controlling blood clotting.
Physiology of Coagulation
- Coagulation is initiated by injury or stasis (stagnation of flow).
- Platelets and coagulation factors play critical roles in the process.
- Coagulation factors (I-XIII) are proteins involved in the coagulation cascade.
- Activated platelets, fibrin, and red blood cells (RBCs) contribute to the formation of a thrombus (clot).
Coagulation Factors and Pathways
- Coagulation factors are glycoproteins produced by hepatocytes, mostly existing as inactive zymogens.
- The coagulation cascade involves a series of steps where active coagulation factors activate inactive ones through proteolytic cleavage.
- Extrinsic pathway is activated by exposure of tissue factor (TF) to blood.
- Intrinsic pathway is activated by contact of Factor XII with anionic surfaces like collagen.
- The goal of both pathways is to convert soluble fibrinogen into insoluble fibrin, the main component of a blood clot.
Platelet Involvement in Coagulation
- Platelets provide a phospholipid surface crucial for the assembly of calcium-dependent coagulation complexes.
- Thrombin activates platelets to aggregate.
- Platelet activation and blood coagulation are interconnected events for clot formation.
Coagulation Pathways
- Contact Activation pathway (Intrinsic): initiated by factors within blood.
- Tissue Factor pathway (Extrinsic): initiated by factors outside blood.
- Both pathways contribute to clot formation.
Steps in Clot Formation
- Vasoconstriction (narrowing of blood vessels): triggered by endothelial cells releasing endothelin at the injury site.
- Platelet Adhesion: platelets stick to the exposed subendothelium.
- Platelet Activation: platelets undergo changes leading to granule release and shape changes.
- Platelet Aggregation: platelets clump together to form a plug.
- Fibrin Formation: a mesh-like structure forms from fibrinogen.
- RBC and Platelet Incorporation: red blood cells and more platelets are incorporated into the fibrin mesh for complete clot formation.
Platelets
- Platelets are small cell fragments originating from megakaryocytes in the bone marrow.
- They lack nuclei (anucleated) and have a lifespan of approximately 10 days.
- Their surface contains numerous glycoproteins (GP) that serve as receptors for adhesiveness, interacting with proteins in blood and subendothelial matrices (e.g., fibrinogen, fibronectin, von Willebrand Factor).
Platelet Activation and Aggregation
- Platelets normally do not adhere to the shielded subendothelium of healthy blood vessels.
- Injury exposes collagen, leading to platelet adhesion mediated by GPVI and GPIb.
- GPVI binds to collagen, while GPIb binds to von Willebrand factor (vWF).
Platelet Secretion
- Activated platelets release contents from their dense granules, including:
- ADP (adenosine diphosphate)
- Serotonin
- Activated platelets also produce TXA2 (thromboxane A2).
Platelet Activation by ADP and TXA2
- ADP and TXA2 activate platelets through their respective receptors :
- P2Y1 and P2Y12 are receptors (GPCRs) for ADP.
- Thromboxane A2 receptor (GPCR) is activated by TXA2, the major product of COX-1.
- Activation of these receptors leads to activity of the fibrinogen-binding glycoprotein GPIIb/IIIa, promoting platelet aggregation.
Platelet Activation by Thrombin
- PAR1 and PAR4, protease-activated receptors (GPCRs) on platelets, are activated by thrombin (clotting factor IIa).
- This activation also leads to activity of GPIIb/IIIa and promotes platelet aggregation.
Platelet Aggregation
- Fibrinogen acts as a bridge linking activated platelets together, facilitating aggregation.
Platelet Inhibitor: Prostaglandin I2 (PGI2)
- Prostaglandin I2 (PGI2), produced by endothelial cells, inhibits platelet aggregation through its receptor (GPCR), raising cAMP levels.
- cAMP is a platelet inhibitor, preventing aggregation in the presence of agonists.
- Phosphodiesterases are enzymes that degrade cAMP, reversing its inhibitory effects on platelet activation.
Thromboxane A2 Formation by COX
- Cyclooxygenase (COX), an enzyme, plays a role in the formation of thromboxane A2 (TXA2) from arachidonic acid.
Platelet Activation by Thromboxane A2
- TXA2 activates platelets by increasing intracellular calcium levels.
Platelet Activation: Morphological Changes
- Resting platelets have a smooth, disc-like shape.
- Upon activation, they spread out and develop lamellipodia (thin protrusions) and filopodia (thin projections).
- Fully activated platelets contract due to actin filament bundling and crosslinking, and myosin contraction.
Platelet Activation by ADP
- ADP activates platelets by reducing cAMP levels (a platelet inhibitor) and increasing intracellular calcium levels.
Clot Formation Summary
- The process involves a combination of factors, including vasoconstriction, platelet adhesion and activation, platelet aggregation, fibrin formation, and red blood cell and platelet incorporation into the fibrin mesh.
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Description
Explore the essential components of blood, including plasma, serum, and various blood cells. Understand the roles of blood vessels in circulation and the crucial process of hemostasis. This quiz covers critical information about how blood functions in the body.
