BRAINCAKEPlatelets
Platelets (thrombocytes) are small fragments of cells, about 2 to 3 µm across. They are not complete cells: they have no nucleus, but they are surrounded by a cell surface membrane and contain some cytoplasm with mitochondria and granules.
Platelets are formed in the bone marrow when very large cells called megakaryocytes break up into thousands of fragments. There are about 150 000 to 400 000 platelets per mm3 of blood, and each one survives for only about 7 to 10 days before being removed by the spleen and liver.
The main role of platelets is to help stop bleeding when a blood vessel is damaged:
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More in Circulatory Systems
- Erythrocytes
- Leucocytes
- Granulocytes
- Agranulocytes
- Haemoglobin and Oxygen Transport
- Oxygen Dissociation Curve for Haemoglobin
- The Bohr Effect
- Fetal Haemoglobin
All 33 lessons in Circulatory Systems · All Edexcel AS-level Biology topics