1. Thrombocytes 2-Life span =8-12 days
1-Minute round or oval discs (2-4 ) non-nucleated
2-Life span =8-12 days
3- number = – /mm3
removed by tissue macrophage as spleen so,the number increases after spleenectomy.
increases during exercise,
pregnancy,
high altitude,
surgical trauma
spleenectomy
It decreases during
menstruation
4-They are formed in the bone marrow as buds on the surface of megakaryocytes and released into the blood under stimulation of thrombopoietin from the kidney

2. Platelet structure 1- mucopolysaccharide surface coat
important in adhesion and aggregation of platelets
Glycoproteins
A- bind with the Von Willebrand factor
which are necessary for platelet adhesion to the damaged
endothelial cells.
B-act as fibrinogen receptors.
2- Plasma membrane: is formed of 3 layers and invaginates inside to form open membrane system and contain phospholipids.
This membrane is the basis structure of platelet factor 3 (PF3)

3. 3- Beneath the membrane there are:
a- Microfilaments
of actin, myosin and thrombasthenin
b- Microtubules
maintains the disc shape of the platelets.
4- The platelets contain 3 types of granules:
a- Dense granules
ADP,serotonin and calcium.
b- Specific (Alpha) granules
contain platelet growth factor, beta thromboglobulin,
fibrinogen ,clotting factors as V, XIII
platelet factor 4 (PF4) which is heparin antagonist factor.

4. c- Dense tubular system
contains calcium and may be site of synthesis
of prostaglandin and thromboxane A2
5- The platelets also contain mitochondria, glycogen and lysosomes which contain hydrolytic enzymes

5. Von Willebrand factor (VWF):
an adhesive protein
formed by :-
A-the vascular endothelial cells and secreted in the plasma.to be bound to clotting factor VIII
B- megakaryocytes and stored in the platelets.