Chapter 17 Platelets and Hemostasis

What are the two mechanisms that limit the size of clots as they form?

1. Rapidly moving blood disseminates clottingfactors before they can initiate a clotting cascade. 2. Activated clotting factors are inhibited.

What are the steps to platelet plug formation.

1. When endothelium are damaged, platelets become sticky and spiky, adhering to each other and the damaged vessel wall. 2. Once attached, other platelets are attracted to the site of injury, activating a positive feedback loop for clot formation.

What is a thrombus?

A thrombus is a clot that forms and persists in an unbroken blood vessel and if large enough may block blood flow to tissues.

What is an Embolus?

An embolus is a thrombus that breaks away from a vessel wall and can become lodged in a small diameter blood vessel which can also restrict blood flow.

What are used to clinically to prevent undesirable clotting?

Aspirin, Heparin, and Warfarin.

What is clot retraction?

Clot retraction is a process in which the contractile proteins within platelets contract and pull on neighboring fibrin strands, squeezing plasma from the clot and pulling damaged tissue edges together.

What are factors that promote clotting in coagulation?

Factors that promote clotting are called clotting factors, or procoagulants; those that inhibit clot formation are called anticoagulants.

What does Fibrinolysis do?

Fibrinolysis removes unneeded clots through the action of the fibrin-digesting enzyme, plasmin.

What are the three phases of the clotting process?

Formation of prothrombin activator, conversion of prothrombin to thrombin, and the formation of fibrin mesh from fibrinogen in the plasma.

How can impaired liver function cause a bleeding disorder?

Impaired liver function results in a lack of synthesis of procoagulants, which may be due to a shortage of vitamin K, or diseases such as hepatitis or cirrhosis.

What are the two pathways to the formation of prothrombin activator?

Intrinsic pathway and extrinsic pathway

What is Hemophilia?

It is a genetic condition that results in a deficiency of factors VIII, IX or XI.

What are platelets?

Platelets are cell fragments from megakaryocytes that help stop bleeding. They form a temporary seal when a blood vessel breaks.

When do platelets enter the blood?

Platelets enter the blood when a megakaryocyte sends cytoplasmic extensions through a sinusoid wall, ruptures, and releases platelets.

What is repair stimulated by?

Repair is stimulated by platelet-derived growth factor (PDGF).

What is the extrinsic pathway?

The extrinsic pathway is triggered through an endothelium-derived protein factor, called tissue factor III, and can ovvur very rapidly.

What is the intrinsic pathway?

The intrinsic pathway is named that because all factors necessary are present within the blood, it is a slower clotting pathway.

What is the last factor that limits clot growth or formation?

The vascular endothelium is smooth and intact, platelets are prevented from clotting.

What does Thrombin do?

Thrombin catalyzes the reactions that convert fibrinogens to fibrin, which forms strands that form the structure of a clot.

What is another factor that limits clot growth or formation?

Thrombin that is not bound to fibrin is inactivated by antithrombin III as well as heparin

Thromboembolic disorders result from what?

Thromboembolic disorders result from conditions that cause undesirable clotting, such as roughening of vessel endothelium, slow flowing blood, or blood stasis.

What is Thrombopoietin?

Thrombopoietin is a hormone that regulates the formation of platelets, which takes place by repeated mitosis of megakaryocytes without cytokenesis.

What are the three steps that occur in rapid sequence during hemostasis?

Vascular Spasm, Platelet Plug Formation, and Coagulation.

What are vascular spasms?

Vascular spasms are the immediate vasoconstriction response to blood vessel injury and become more efficient with increased tissue damage.