Platelet Functions and Characteristics

Questions and Answers

What is the initial function of activated platelets at a site of vascular injury?

To attract additional platelets and form a platelet plug (correct)

To convert fibrin into fibrinogen

To activate coagulation factors for rapid clotting

To release fibrinogen into the blood

How long does it take for a clot to begin developing after a severe vascular trauma?

In 15 to 20 seconds (correct)

In 5 to 10 seconds

Immediately upon injury

Within 1 minute

What substances are secreted by activated platelets that contribute to further platelet activation?

Calcium and thrombin

Collagen and von Willebrand factor

Prothrombin and fibrinogen

Thromboxane A2 and ADP (correct)

What role does fibrin play in the formation of a blood clot?

It forms threads that stabilize the platelet plug Signup and view all the answers

What happens to the platelet plug when the trauma to the vascular wall is minor?

It remains loose until additional platelets are activated Signup and view all the answers

Which factors initiate the blood coagulation process?

Activator substances from the traumatized vascular wall and platelets Signup and view all the answers

What condition allows the platelets to adhere effectively to the tissues?

Their sticky surfaces due to ADP secretion Signup and view all the answers

Following the formation of a loose platelet plug, what is the next step in hemostasis?

Conversion of fibrinogen to fibrin Signup and view all the answers

What substance released from traumatized platelets plays a significant role in clotting reactions?

Platelet factor 3 Signup and view all the answers

What is the function of activated Factor XI in the intrinsic pathway?

To activate Factor IX Signup and view all the answers

Which factor is specifically missing in classic hemophilia?

Factor VIII Signup and view all the answers

What is the primary difference between the intrinsic and extrinsic clotting pathways?

Intrinsic pathway begins in the blood, while extrinsic starts with tissue trauma Signup and view all the answers

What combination is required for the activation of Factor X?

Activated Factor VIII, calcium ions, and phospholipids Signup and view all the answers

Which condition is associated with a deficiency of platelets?

Thrombocytopenia Signup and view all the answers

The formation of prothrombin activator occurs when activated Factor X combines with which factors or substances?

Factor V and platelet or tissue phospholipids Signup and view all the answers

Which statement about the intrinsic pathway is accurate?

It is slower, typically requiring 2-6 minutes for clotting Signup and view all the answers

What initiates the extrinsic pathway of prothrombin activator formation?

Release of tissue thromboplastins Signup and view all the answers

Which element is required for the activation of factor X in the extrinsic pathway?

Calcium Signup and view all the answers

What complex is formed when tissue thromboplastin combines with factor VII?

Tissue thromboplastin-factor VII complex Signup and view all the answers

In the intrinsic pathway, what is activated by trauma to blood or exposure to collagen?

Factor XII Signup and view all the answers

What role does activated factor X play in the formation of prothrombin activator?

It combines with tissue thromboplastin and calcium. Signup and view all the answers

Which components are necessary to form prothrombin activator?

Activated factor X, phospholipids, and factor V Signup and view all the answers

What occurs after the formation of activated factor X in the extrinsic pathway?

Combination with tissue phospholipids to form prothrombin activator Signup and view all the answers

What is the initial step in the intrinsic pathway of prothrombin activator formation?

Activation of factor XII Signup and view all the answers

What is the primary role of prothrombin in the coagulation process?

It serves as the inactive precursor to thrombin. Signup and view all the answers

How does prothrombin convert to thrombin?

Through the action of prothrombin activator in the presence of Ca2+. Signup and view all the answers

What effect does a greater degree of trauma to the vessel wall have on thrombin production?

It increases the quantity of prothrombin activator available. Signup and view all the answers

What is the molecular weight of prothrombin?

68,700 Signup and view all the answers

What is unique about the amount of thrombin produced during clotting?

It can coagulate vastly more blood than is present. Signup and view all the answers

Which factor affects the concentration of prothrombin in plasma?

Presence of vitamin K. Signup and view all the answers

What is the concentration range of fibrinogen in plasma?

100 to 700 mg/dL Signup and view all the answers

What preventive measures exist against excessive intravascular clotting during clotting mechanisms?

Regulatory mechanisms in the body to prevent excessive thrombin activity. Signup and view all the answers

What is the role of thrombin in the blood clotting process?

It activates fibrin monomer from fibrinogen. Signup and view all the answers

What happens during the polymerization of fibrin monomers?

Fibrin monomers create loose strands of fibrin. Signup and view all the answers

What role do calcium ions play in clot stabilization?

They activate fibrin-stabilizing factor (factor XIII). Signup and view all the answers

Which components are primarily involved in the clot retraction process?

Platelets and contractile proteins. Signup and view all the answers

What characterizes the composition of the blood clot after coagulation?

It contains a stable meshwork of fibrin threads and trapped cells. Signup and view all the answers

Which statement about fibrinogen levels in liver disease is true?

Liver disease decreases fibrinogen concentrations. Signup and view all the answers

What is primarily responsible for the contraction during clot retraction?

Actin and myosin from platelets. Signup and view all the answers

How does the structure of the formed clot change over time?

It is transformed into a denser and tighter configuration. Signup and view all the answers

Study Notes

Platelet Activation and Aggregation

Irregularly shaped platelets have numerous filopods that extend from their surfaces upon activation.
Contractile proteins within platelets facilitate the release of granules containing active factors.
Activated platelets become sticky, adhering to collagen and von Willebrand factor in damaged tissues.
Platelets secrete large amounts of ADP, which activates nearby platelets, causing further aggregation at the injury site.
A platelet plug forms, initially loose but effective for small vascular openings and subsequently reinforced by fibrin threads.

Coagulation Process

Blood clotting is the final stage of hemostasis, converting fibrinogen into fibrin to completely block blood loss.
Initial clot formation occurs within 15-20 seconds for severe trauma and 1-2 minutes for minor injuries.
The clotting process initiates through activator substances from the traumatized vascular wall, platelets, and blood proteins.

Formation of Prothrombin Activator

The coagulation process begins with the formation of prothrombin activator, converting prothrombin into thrombin.
Two main pathways to activate prothrombin: extrinsic and intrinsic.

Extrinsic Pathway

Begins with tissue damage, leading to the release of tissue thromboplastin (factor III).
Tissue thromboplastin and factor VII combine with calcium ions to activate factor X, forming activated factor X (Xa).
Activated factor X combines with phospholipids and factor V to create prothrombin activator.

Intrinsic Pathway

Initiated by trauma to blood or exposure to collagen beneath endothelial cells.
Activated factor XII initiates this pathway, subsequently activating factor XI, IX, and then X.
Factor IXa, in conjunction with activated factor VIII and calcium, activates factor X, mirroring the last step of the extrinsic pathway.

Comparison of Pathways

The extrinsic pathway is rapid (15 seconds), while the intrinsic pathway is slower (2-6 minutes).
Both pathways converge at factor X, leading into the common pathway for clotting.

Prothrombin Characteristics

Prothrombin (factor II) is an α2 globulin synthesized in the liver with a molecular weight around 68,700.
Dependent on vitamin K for synthesis; concentrations fluctuate with liver health.
Converts to thrombin on the surface of platelets, driven by prothrombin activator.

Thrombin Function

Thrombin acts as a proteolytic enzyme with a molecular weight of 33,700, produced in excess during coagulation.
One mL of thrombin can coagulate up to 3 liters of blood, indicating a potential risk for intravascular clotting.

Fibrinogen and Fibrin Conversion

Fibrinogen is a high-molecular-weight plasma protein (340,000) synthesized in the liver.
Thrombin converts fibrinogen into fibrin monomers, which polymerize into loose fibrin strands.
Fibrin-stabilizing factor (factor XIII) strengthens the fibrin strands into a stable meshwork.

Blood Clot Retraction

Post-coagulation, the clot, composed of a fibrin mesh and entrapped cells, begins to contract within 30-60 minutes.
Platelets play a crucial role in clot retraction, binding fibrin fibers together and aiding in the meshwork compression.
Contraction is driven by platelet contractile proteins activated by thrombin and calcium ions.

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Description

This quiz explores the unique features and roles of platelets in the body, including their irregular forms, contractile proteins, and adhesion properties. Understand how these characteristics contribute to their function in hemostasis and the release of chemical factors. Test your knowledge on the importance of platelets in tissue repair and coagulation.