Coagulation (secondary hemostasis)

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Coagulation (secondary hemostasis)


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USMLE® Step 1 questions

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Coagulation (secondary hemostasis)

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USMLE® Step 1 style questions USMLE

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A lab study is simulating secondary hemostasis. In the study, both the intrinsic and extrinsic pathways of coagulation lead to the formation of the active form of factor X (Xa). Which of the following is the correct order of events to occur afterward?  

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coagulation cascade and p. 418


coagulation cascade and p. 418


coagulation and kinin pathways p. 420

Clotting factors p. 69

Coagulation p. 69

Coagulation cascade components p. 418

Coagulation disorders p. 433

mixed platelet/coagulation p. 435

Coagulation pathways p. 420

Combined pathway for coagulation p. 420

Contact activation pathway for coagulation p. 420

Extrinsic pathway p. 206

coagulation p. 420

warfarin and p. 444

Granzyme B

extrinsic pathway and p. 206

Hemostasis p. 415

coagulation p. 419

Heparin p. 443

in coagulation cascade p. 420

Intrinsic pathway p. 206

for coagulation p. 420

coagulation defects of p. 433


coagulation cascade in p. 418


extrinsic pathway and p. 206

TNF- α p. 106

extrinsic pathway and p. 206

Vitamin K

coagulation cascade p. 420

Warfarin p. 444

coagulation cascade p. 420


Hemostasis can be broken down into hemo referring to blood or bleeding and stasis meaning to stop - so together it means stopping bleeding. Hemostasis has two phases: primary and secondary hemostasis.

In primary hemostasis, platelets aggregate to form a plug at the site of an injured blood vessel. While these platelets are aggregating, coagulation, or secondary hemostasis starts.

This is where numerous enzymes that are always floating around in the blood called clotting factors get proteolytically activated, meaning that activation happens when a small piece is chopped off - a bit like pulling the pin out of a grenade.

These factors activate one another, eventually leading to the activation of fibrin or factor Ia. That results in a fibrin mesh which forms around the platelet plug to reinforce it and hold it together.

Without primary and secondary hemostasis, our body would suffer massive blood loss from even the most minor injuries--imagine losing all of your blood volume from something as simple as a pinprick!

So let’s get into the details of secondary hemostasis. The process of forming the fibrin mesh begins via two pathways --the extrinsic and intrinsic pathways.

The intrinsic pathway is called intrinsic because all of the factors required to activate it are intrinsic, or found within the blood.

Conversely, the extrinsic pathway is called extrinsic because it’s activated by tissue factor found extrinsically, or outside of the blood.

Both pathways can become activated independently and ultimately culminate in the activation of factor X, which then proceeds to activate the rest of the coagulation cascade via the common pathway.

Let's start with the extrinsic pathway. It starts when trauma damages the blood vessel, and exposes the cells under the endothelial layer, like smooth muscle cells, which have tissue factor or factor III in their membrane.


Coagulation is the process of formation of a blood clot. It is secondary hemostasis that occurs after vascular damage has occurred and platelets have been activated. Its purpose is to form the fibrin mesh necessary to stabilize the platelet plug to stop bleeding. Coagulation happens in a series of steps called the coagulation cascade, which is a series of enzymatic reactions that leads to the conversion of fibrinogen to fibrin. The final product is a stable plug that stops the bleeding. Factors XII, XI, IX, VIII, VII, V, and IV are essential for the initiation of coagulation. Proteins C and S inhibit the coagulation cascade by inactivating factors Va and VIIIa, respectively.


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  6. "Thrombus formation in vivo" Journal of Clinical Investigation (2005)
  7. "Remodeling the Blood Coagulation Cascade" Journal of Thrombosis and Thrombolysis (2003)

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