Fragments of cytoplasm covered with a membrane with no nucleus (not true cells).
Origin: megakaryocytes.
Size: 2 - 4 μm.
Life span: 5-10 days.
Shape: oval or rounded discs.
Number: 150.000 - 400.000 / mm3.
Histol., LN.1&2 Dr.Mona Farouk Level 1- Semester 2- Block 3- Module 3B- IBL
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Function: (Haemostasis)
1. Serotonin → V.C.
2. Platelet aggregation.
3. Red thrombus (coagulation)
Thromboblastin changes prothrombin into thrombin → change fibrinogen into fibrin network → attraction of RBCs → closes blood vessels and stops bleeding.
3- Granulomere:
• α granules: fibrinogen.
• β granules: mitochondria.
• δ granules: serotonin, ATP, ADP and calcium.
• λ granules: lysosomes.
• Glycogen granules.
Active(red) bone marrow
structure 1. Stroma of fixed cells •Reticular branched cells •Fat cells •Endothelial cells •Osteogenic cells •Pericyte cells 2. Bl. Sinusoides 3. Free cells
Sites:
-In foetus: most of the bone.
- In adult:
•Flat bone
•Sternum.
• Ribs and clavicle.
•Vertebrae.
Function: 1. Formation of blood cells. 2. Destruction of old RBCs. 3. Storage of iron. 4. Storage of fat.
InActive (yellow) bone marrow
1.Stroma of fixed cells: • Undiff. Mesencymal cells • Macrophage • Reticular cells 2. Large number of adipose cells 3. No free cells
- Present in adults:
•In shafts of long bone. 1. Storage of fat 2. On need , it changes into active red bone marrow.
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