Platelets are a source of

Options

A. Fibrinogen
B. Calcium
C. Thromboplastin
D. Haemoglobin.

Answer

### Step-by-Step Text Solution

1. **Understanding Platelets**: Platelets, also known as thrombocytes, are small cell fragments in the blood that play a crucial role in the clotting process. They are derived from megakaryocytes in the bone marrow.

2. **Role of Platelets in Blood Clotting**: When there is an injury or cut in the blood vessel, platelets are the first responders. They aggregate at the site of injury and form a temporary plug to stop bleeding.

3. **Components Involved in Clotting**: The clotting process involves several components, including fibrinogen, calcium, hemoglobin, and thrombo-plastin. Fibrinogen is converted into fibrin, which forms a mesh that stabilizes the platelet plug.

4. **Analyzing the Options**:
- **Option A: Fibrinogen**: This is produced by the liver, not platelets. Therefore, platelets are not a source of fibrinogen.
- **Option B: Calcium**: Calcium is stored in bones and teeth and acts as a co-factor in the clotting process, but it is not produced by platelets.
- **Option C: Hemoglobin**: Hemoglobin is found in red blood cells (RBCs) and is responsible for oxygen transport. It is not associated with platelets.
- **Option D: Thrombo-plastin**: This is a substance that is released by platelets during the clotting process. It helps convert prothrombin into thrombin, which is essential for the conversion of fibrinogen to fibrin.

5. **Conclusion**: Based on the analysis, the correct answer is that platelets are a source of **thrombo-plastin**.