During blood clotting - platelets release-

Options

A. Thrombin
B. Fibrinogen
C. Prothrombin
D. Thrombokinase and other blood clotting factor

Answer

### Step-by-Step Solution

1. **Understanding Blood Clotting**: Blood clotting is a complex process that prevents excessive bleeding when a blood vessel is injured. It involves various components, including platelets and clotting factors.

2. **Role of Platelets**: Platelets, also known as thrombocytes, play a crucial role in the clotting process. They are small cell fragments that aggregate at the site of injury and release substances that are essential for clot formation.

3. **Release of Thrombokinase**: During blood clotting, platelets release an enzyme called thrombokinase (also known as thromboplastin). This enzyme is critical for the conversion of prothrombin to thrombin.

4. **Conversion of Prothrombin to Thrombin**: Prothrombin is a plasma protein produced in the liver. Thrombokinase activates prothrombin, converting it into thrombin. This step is essential as thrombin is a key enzyme in the clotting cascade.

5. **Thrombin's Function**: Once formed, thrombin acts on fibrinogen, another protein synthesized in the liver. Thrombin converts fibrinogen into fibrin, which is the main structural component of a blood clot.

6. **Formation of Fibrin**: Fibrin strands weave through the platelets and red blood cells, forming a stable clot that seals the wound and prevents further bleeding.

7. **Other Factors**: In addition to thrombokinase, platelets also release other clotting factors that assist in the clotting process, ensuring the formation of a stable and effective blood clot.

### Final Answer
During blood clotting, platelets release thrombokinase and other clotting factors, which are essential for converting prothrombin to thrombin and fibrinogen to fibrin.