3 blood platelets and bone marrow

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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 • Page | 15 • 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. • • for contact • [email protected] • • Telegram channel • https://t.me/drshereenhamed

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