Question

Select the incorrect statement from the following: (a) Clot or coagulum is formed mainly by a network of fibrin in which the died and damaged formed element of blood are trapped. (b) Inactive fibrinogen is converted to fibrin by the hormone thrombin. (c) Prothrombin is converted into thrombin by the enzyme complex thrombokinase. (d) Platelet or injured tissue released certain factors which initiate coagulation.

Short answer

The incorrect statement is option B - Inactive fibrinogen is converted to fibrin by the hormone thrombin. Thrombin is not a hormone, but an enzyme.

Step-by-step solution

Analyze Option A

It states that the clot or coagulum is formed by a network of fibrin trapping the dead and damaged formed elements of blood. This is a correct statement because during blood clotting, fibrin forms a mesh that traps red blood cells and platelets, effectively forming a clot.

Analyze Option B

Option B refers to the conversion of inactive fibrinogen to fibrin by thrombin. However, it's wrong to calle thrombin a hormone. Thrombin is an enzyme that converts fibrinogen, a blood clotting factor that is normally dissolved in blood, into a fibrin clot. So, option B is the incorrect statement.

Analyze Option C

Option C is correct. It states that prothrombin is converted into thrombin by the enzyme complex thrombokinase, which is a correct part of the clotting process.

Analyze Option D

Option D is also correct. Platelets or injured tissues do release certain factors that initiate coagulation or blood clotting.

Key concepts

Fibrin Formation

When a blood vessel sustains damage, our bodies initiate an elaborate and crucial process to prevent excessive bleeding and facilitate healing. Fibrin formation is at the heart of this process, serving as the structural framework for blood clots. This process starts when the soluble protein fibrinogen is transformed into fibrin, which is an insoluble substance. The enzyme thrombin plays a pivotal role by cleaving fibrinogen into fibrin monomers, which spontaneously assemble into long, sticky fibers. These fibers then cross-link, thanks to the enzyme factor XIII, to create a strong and stable meshwork. This meshwork traps blood cells and platelets, which reinforces the initial platelet plug, effectively creating a stable clot that temporarily seals the breach in the blood vessel wall.

Understanding fibrin formation is essential, as it ensures that blood clots are strong enough to withstand the pressure of circulating blood, yet regulated not to cause unwanted blockages that can lead to conditions like strokes or heart attacks. To prevent incorrect information, one should avoid mistakenly referring to fibrin as 'fibrinogen', which is its soluble precursor, and recognize that fibrin itself is the result of a complex enzymatic reaction, not just a simple transformation of state.

Thrombin Role in Coagulation

The enzyme thrombin sits at the center of the blood clotting cascade and its role is multifaceted, influencing various aspects of hemostasis. It is a serine protease that is formed from its inactive precursor, prothrombin. When tissue injury occurs, the blood coagulation pathway is triggered, and thrombin is generated from prothrombin by the action of another complex of proteins and factors known as prothrombinase, which includes the enzyme thrombokinase. Thrombin then converts fibrinogen into fibrin and also activates factor XIII, which strengthens the clot.

Additionally, thrombin has a role in the activation of platelets and their aggregation at the site of injury. Importantly, while thrombin is crucial for coagulation, excess or uncontrolled production can be harmful, which is why its activity is finely balanced by anticoagulants in the blood. Therefore, it is crucial to understand that thrombin is not a hormone, as incorrectly stated in some sources, but rather an enzyme with a specific and essential function within the clotting process.

Blood Clotting Factors

A symphony of substances known as blood clotting factors work in tandem to achieve hemostasis. Each factor has a designated number, usually indicated by Roman numerals, and a specific role within the clotting cascade. This cascade can be divided into three main phases: the vascular phase, the platelet phase, and the coagulation phase.

Different factors are involved in each phase, starting with the vessel's response to injury, then the formation of a platelet plug, and finally the reinforcement of that plug with a fibrin clot. For instance, factor VII working with tissue factor initiates the process, while factors VIII and IX are central to amplifying the clotting signal. Factor X, once activated to Xa, plays a role in converting prothrombin to thrombin. It is important to understand that these clotting factors typically circulate in the plasma in inactive forms and are sequentially activated in response to injury. This sequential activation ensures that the body can quickly respond to bleeding while maintaining a balance to prevent excessive clotting. When explaining clotting factors, it's important to emphasize their complexity and interdependence to prevent oversimplification of the coagulation process.