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What Is Hemostasis?

Hemostasis

Hemostasis is a term you’ll see in medical sources quite frequently, especially in texts concerning blood and clotting. Here’s a quick rundown of everything you need to know about hemostasis, what it means, and how it works.

Hemostasis Definition

Hemostasis refers to the normal way a person’s body prevents and stops bleeding or loss of blood. The result of hemostasis is the blockage of any breaks or tears in blood vessels. Proper hemostasis is important for maintaining the smooth flow of blood through unbroken blood vessels. Problems with hemostasis usually result in excessive bleeding, if hemostasis doesn’t occur, or blood clots, if the processes involved in hemostasis occur too easily.

The Steps of Hemostasis

In a healthy individual, hemostasis involves three distinct parts. Primary hemostasis refers to the body’s first several actions to fix an injury. During primary hemostasis, the blood vessels surrounding the injury site contract to reduce blood flow, and a plug of platelets forms to fill the hole. Secondary hemostasis is the next part of the process. During secondary hemostasis, plasma forms a clot. This is a complex process that involves many factors working together to form the clot and many inhibitors preventing the clot from forming improperly. Finally, fibrinolysis is the process of removing the clot once the blood vessel has healed.

In a healthy person, this process only occurs when it’s necessary to stop bleeding and the clot is quickly dissolved after the wound has healed. Hemostasis is often discussed when a medical condition, drug, or other factor interferes with the normal operation of this process.

What Is Primary Hemostasis?

The first step of hemostasis, primary hemostasis, is a vital part of the body’s reaction to injury. Primary hemostasis starts when an injury is recognized and the body begins to take action. The first step is to produce a protein called collagen, which attracts blood platelets and causes them to adhere to one another. This will eventually result in the formation of a plug of platelets that begins to seal the injury.

The next part of primary hemostasis occurs as these platelets interact with the blood vessels surrounding them. In order to reduce leakage from the injury, the blood vessels in the surrounding area will begin to contract. This will reduce circulation and help stem the bleeding.

Imagine you’ve got a leak in your hose. Turning down your hose will reduce the amount of water that’s spurting out and make it easier to form a patch or seal. This is similar to the constriction of blood vessels during primary hemostasis. Similarly, you’ll want a solid object that you can use to plug the leak. With primary hemostasis, this solid object is the platelet plug.

Primary hemostasis usually takes several minutes and results in a fairly effective seal being made between the platelet plug and the rupture in the blood vessel. Once this is complete, the process of secondary hemostasis begins.

What Is Secondary Hemostasis?

If primary hemostasis is turning down our hose and applying a patch, secondary hemostasis is sealing that patch into place. During secondary hemostasis, a very complicated set of reactions take place that causes the production of fibrin. Fibrin is a fiber-like protein that will form a tough mesh on top of the platelet plug that’s sealing the wound. During secondary hemostasis, this fibrin mesh will contract and harden, sealing the plug in place. Once this mesh has finished forming, the clot is complete and will effectively block further leakage of blood while the wound heals.

In order to produce fibrin for this process, the body needs access to certain compounds in your blood. If these compounds can’t be found or the process doesn’t get started properly, bleeding can quickly turn into a serious health risk. People with hemophilia and similar disorders often have issues completing secondary hemostasis. Conversely, if factors cause the body to produce excess fibrin or fail to dissolve it after a wound has healed, this tough, durable protein can cause blood clots that narrow or block blood vessels.

Secondary hemostasis ends when the clot is securely locked in place behind a fibrin mesh. After secondary hemostasis, the body waits for the wound to heal before proceeding further.

What Is Fibrinolysis?

As the body produces a clot during secondary hemostasis, it weaves something called plasminogen into the fibrin mesh. Plasminogen is an enzyme that sticks to fibrin and waits for the body to give it a signal. Once it’s activated, it turns into something called plasmin that breaks down the fibrin mesh into small pieces. Eventually, the pieces become small enough to be dealt with by various agents in the blood or processed by the kidney and liver.

The proteins that activate plasminogen are found in the walls of blood vessels. As the wound heals, these proteins leak out very slowly. It takes several days for enough plasminogen to leak out and cause the fibrin mesh to break down. The rate at which these proteins enter the bloodstream is carefully calibrated to match the rate at which the body heals. When everything works properly, the clot begins to break apart just as the wound finishes healing.

Hemostasis: The Body’s Answer To Bleeding

Hemostasis is a word with two parts: hemo, which corresponds to blood, and stasis, which means ‘stay the same’ or ‘preserve.’ This fits nicely with the hemostasis definition above: its the body’s way of keeping blood trapped inside the blood vessels in which it belongs. Hemostasis involves three parts: primary hemostasis, where the body limits blood flow and forms a solid plug of platelets to block the leak, and secondary hemostasis, which involves forming a tough protein mesh that locks the platelet plug in place. Finally, fibrinolysis occurs, giving the body an opportunity to break down the clot after the healing process has sealed the injury more permanently.

All three parts of hemostasis are complex and vital processes that are vital to healthy bodily function. Issues with hemostasis can result in hemorrhage, thrombosis, embolism, and other issues related to improper flow of blood. Failure to form or secure a clot leads to uncontrolled bleeding (or hemorrhage) while forming too many clots or failing to properly break down clots after the injury has healed can lead to blocked blood vessels (or thrombosis). In a healthy person, however, these processes are balanced, allowing wounds to heal and keeping blood where it belongs.

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