Platelets and Hemostasis Quiz

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Questions and Answers

What is the role of tissue plasminogen activator (tPA) in the body?

It inhibits the production of prothrombin.

It promotes the formation of fibrin.

It converts plasminogen to plasmin. (correct)

It prevents the breakdown of thrombin.

How does plasmin affect thrombin?

It directly degrades thrombin into inactive fragments.

It activates thrombin into a more potent form.

It enhances thrombin activity.

It lyses fibrin and produces components that inhibit thrombin. (correct)

What condition is characterized by a deficiency in vitamin K?

Hemophilia A

Von Willebrand disease

Thromboembolism

Hemorrhagic disease (correct)

What is the inheritance pattern of hemophilia?

X-linked recessive Signup and view all the answers

Which substance produced by the liver delays fibrinolysis?

Antiplasmin Signup and view all the answers

What is the average normal concentration of platelets in the blood per microliter?

250,000/ul Signup and view all the answers

Which structure do platelets originate from in the bone marrow?

Megakaryocytes Signup and view all the answers

What occurs when platelets come into contact with a damaged vascular surface?

They swell and assume irregular forms. Signup and view all the answers

What is the primary role of von Willebrand factor in hemostasis?

To facilitate platelet adhesion to collagen. Signup and view all the answers

How do platelets attract additional platelets to an injury site?

By secreting ADP and thromboxane A2. Signup and view all the answers

What characterizes the initial platelet plug formed at a vascular opening?

It is a loose aggregation of activated platelets. Signup and view all the answers

What happens during the subsequent process of blood coagulation?

Fibrin threads form to stabilize the platelet plug. Signup and view all the answers

What factor causes platelets to become sticky during the hemostatic process?

Activation by thromboxane A2 Signup and view all the answers

What is one of the primary functions of platelets in hemostasis?

Release of vasoconstrictors to cause vessel spasm Signup and view all the answers

Which condition is characterized by a lower than normal platelet count?

Thrombocytopenia purpura Signup and view all the answers

Which of the following causes can lead to a high platelet count?

Chronic inflammatory disorders Signup and view all the answers

Which mechanism is primarily responsible for the temporary formation of a hemostatic plug?

Platelet reaction Signup and view all the answers

How does the body typically maintain blood in a liquid state despite the clotting process?

Fibrinolytic system Signup and view all the answers

What role does PDGF (platelet derived growth factor) play in the body?

Stimulating tissue repair Signup and view all the answers

What might prevent platelets from sticking to the endothelial lining of blood vessels under normal conditions?

Secretion of prostacyclin and NO Signup and view all the answers

What is the primary consequence of the spleen holding onto too many platelets?

Thrombocytopenia Signup and view all the answers

Study Notes

Platelets and Hemostasis

Platelets (thrombocytes) are minute discs, measuring 1 to 4 micrometers in diameter.
Formed in bone marrow from megakaryocytes, which are large cells of the hematopoietic series.
Megakaryocytes fragment into platelets within the bone marrow or soon after entering the blood, particularly as they pass through capillaries.
Normal platelet concentration in blood ranges between 150,000 and 400,000 per microliter, with an average of 250,000/µL.

Platelet Function

When platelets encounter a damaged blood vessel (especially collagen), they swell, become irregular, and extend pseudopods.
Their contractile proteins release granules containing bioactive factors causing them to adhere to collagen and von Willebrand factor.
Platelets release ADP and enzymes (thromboxane A2), activating more platelets and making them stickier.

Hemostasis

Hemostasis is the process of stopping bleeding by forming blood clots in the injured vessel wall.
The rest of blood remains fluid in the unaffected parts of the vascular system.

Mechanism of Hemostasis

Local vasoconstriction: Narrowing of the blood vessels to reduce blood flow to the injury site
Temporary hemostatic plug formation: Platelet activation, adherence and aggregation forms a temporary plug to stop bleeding.
Definitive hemostatic plug formation (blood coagulation): Blood clotting process leading to a permanent plug mediated by a complex cascade of protein interactions.
Repair of damaged blood vessel: Healing of the damaged blood vessel.

Clotting Mechanism

Two pathways: intrinsic and extrinsic.
Both result in activation of thrombin, which converts fibrinogen to fibrin, forming a mesh.
Platelets are essential in the clotting process adhering to fibrin strands forming a stable platelet plug.

Fibrinolytic System

The liver produces plasminogen (an inactive protein).
Thrombin and tissue plasminogen activator (tPA) convert plasminogen into plasmin (active enzyme).
Plasmin degrades fibrin, dissolving the clot.
tPA inhibitor (antiplasmin) and PAI-1 (plasminogen activator inhibitor) control fibrinolysis to ensure that clots aren't dissolved prematurely.

Variations in Platelet Count

Thrombocytopenia: Low platelet count (below 150,000/µL), potentially leading to bleeding. This condition can be caused by various factors: bone marrow not producing enough platelets, destruction of platelets by the body, or splenic retention of platelets.
Thrombocytosis: High platelet count (above 400,000/µL), which may indicate an underlying condition such as inflammatory disorders, malignancy or post splenectomy.

Disorders of Hemostasis

Vitamin K deficiency: This inhibits formation of prothrombin and factors VII, IX, and X in the liver, leading to bleeding.
Hemophilia: Genetic bleeding disorder, commonly transmitted from females (carrier) to males. It results from a deficiency in factors crucial for blood clotting.

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Description

Test your knowledge on the role of platelets in hemostasis and the processes involved in blood clot formation. This quiz covers platelet function, formation, and the physiological mechanisms of hemostasis. Perfect for students studying biology or medical sciences.