Platelets and the coagulation system work together to form clots during hemostasis and thrombosis. Platelets are produced by megakaryocytes and activated by various stimuli to form primary clots. The endothelial lining of blood vessels contains adhesion molecules that allow platelets and white blood cells to adhere during clotting and inflammation. The coagulation cascade involves platelet activation, coagulation factors, and fibrin polymerization to form clots. Several clinical tests evaluate coagulation and clotting disorders, including bleeding time, prothrombin time, activated partial thromboplastin time, and thrombin time. Prolonged or shortened results can indicate underlying hemostatic abnormalities or diseases.

1. Platelets,and CoagulationSystem
Fadel Muhammad Garishah, BSc

2. Thrombosis and Virchow’s
Triad

3. Platelets • Megakaryocytes’
daughters
• Actors of primary
thrombosis
• Activated and inhibited
by various stimuli
• Also involved in both
hemostatic and
immunity-inflammation
processes

4. Endothelial cells
• Lining of the vascular system
• Possessed various adhesion molecules for the adhesion of platelets, WBCs during
thrombosis and inflammation processes

5. Hemostasis – Thrombosis -
Fibrinolysis
http://www.hopkinsmedicine.org/hematology
/coagulation.swf

6. Platelet Activation

7. CoagulationCascadeand Fibrin
Polymerization

10. Fibrinolysis

12. Clinical Evaluation of
Thrombosis
• Clotting Time
• Bleeding Time
• Prothrombin Time
• Activated Partial Thromboplastin Time

13. Bleeding time
• Platelet functions to form clot
• Wound in superficial area -> normally 1-9 min stops
• Prolonged: platelet dysfunction, vWD, anticoagulant use,
uremia, liver failure, leukemias, MDS

14. Thrombin time
• Assess fibrin formation in plasma
• TT time < 20 seconds
• Shortened: hereditary, DIC, multple myeloma

15. Prothrombin Time
• Extrinsic factors and final common pathway
• Factor II, V, VII, X
• Adding Ca2+ and thromboplastin (activator) to blood sample,
and then measure the time
• PT 9,5 – 13,5 seconds
• INR < 1.
• Prolonged PT: warfarin use, def vit K, liver disease, deficiency
of F II, VIII, V, X, DIC, fibrinogen abnormalities, heparinization

16. PartialThromboplastinTimeorActivatedPartial
ThromboplastinTime
• Intrinsic coltting factors etc
• aPTT additional activator that speeds up PTT
• aPTT 30-40 seconds
• PTT 60 – 70 seconds
• Prolonged causes: Def F VIII, IX, XI, XII,
Fitzgeralnd/prekalikrein, vWD, hypofibrinogenemia, liver
cirrhosis, def vit K, , DIC, heparinization, coumarin inhibition
FI, IX and X
• Shortened: early DIC, cancers, hemorrhage,