3. Physiology
        3.6. Haematology
            3.6.1. Blood cells
3.6.1.1. Platelet

Platelet

[Ref: KB:p209; WG21:p533; PK1:p245-249]

Characteristics of platelet

Life cycle of platelet

Production

Pluripotent stem cells in bone marrow
--> Megakaryoblast
--> Masophilic megakaryocyte
--> Granular megakaryocytes
--> Mature megakaryocytes
--> Fragmentation of megakaryocytes
--> Platelets

Whole process takes 10 days

New platelets are stored in spleen for 36 hours before release

Elimination

Old platelets are removed by reticuloendothelial system in spleen and liver

Regulation

Main regulator of platelet production
= Thrombopoietin

Thrombopoietin receptors

Thrombopoietin receptors are present on platelets

Thus low platelet count
--> Less thrombopoietin is bound
--> More thrombopoietin is available to stimulate platelet production

Vessel walls as well as platelets contain von Willebrand factor

vWF forms complex with factor 8
--> Regulation of factor 8 level

Life expectancy

Distribution

Structures

Membrane

Receptors for thrombin
Membrane glycoprotein

[PK1:p248]

Glycoprotein Ia/IIa
= Facilitates adhesion to collagen

Glycoprotein Ib, IIb, and IIIa
= Required for attachment of platelets to vWF (thus the vascular subendothelium)
* especially GpIb/IX

Glycoprotein IIb-IIIa
= Binds to fibrinogen
= Required for platelet-to-platelet aggregation

Cytoplasm

Actin, myosin, glycogen, lysosomes, mitochondria

2 types of granules (dense granules and alpha-granules)

Dense granules
Alpha-granules

Function of platelet

2 main functions

  1. Formation of temporary plug
  2. Serves as a surface on which coagulation factors can act (PF3)

See also Hemostasis

Other notes

ATP is mostly produced by anaerobic glycolysis
* But there is some aerobic metabolism



Table of contents  | Bibliography  | Index