لخّصلي

Formation of blood ( hematopoiesis ) Sites of hematopoiesis During pregnancy , blood is formed at the following sites : Yolk sac : - Forms blood during the intrauterine life , first trimester Liver & spleen : -Form blood during the intrauterine life , second trimester After delivery , the liver and spleen may resume their hemopoietic activity in children suffering from chronic anemia [ this is known as extramedullary hematopoiesis ] Bone marrow ) : - Forms blood during the intrauterine life , third trimester ( and then after delivery ) ; called red marrow ( active marrow ) -Found in almost all bones during pregnancy After delivery , blood is formed at the following sites : The red bone marrow - After delivery , the red bone marrow starts to be replaced gradually by yellow marrow ( inactive marrow ) - At about the age of 20y the red marrow is confined to : 。 Flat bones Skull , sternum , ribs , scapula , vertebrae & iliac bone • Ends of long bones " epiphyses " not the shaft " diaphysis " • Small bones of hands & feet - About 75 % of the cells in the red bone marrow are WBC precursors and only 25 % are RBC precursors ; inspite of the fact that RBC count is over 500 times more than the WBC count . This indicates the longer life span of RBCs . The core of medical physiology ( 1 ) - 3rd edition Page 134

Formation of blood ( hematopoiesis ) Sites of hematopoiesis During pregnancy , blood is formed at the following sites : Yolk sac : - Forms blood during the intrauterine life , first trimester Liver & spleen : -Form blood during the intrauterine life , second trimester After delivery , the liver and spleen may resume their hemopoietic activity in children suffering from chronic anemia [ this is known as extramedullary hematopoiesis ] Bone marrow ) : - Forms blood during the intrauterine life , third trimester ( and then after delivery ) ; called red marrow ( active marrow ) -Found in almost all bones during pregnancy After delivery , blood is formed at the following sites : The red bone marrow - After delivery , the red bone marrow starts to be replaced gradually by yellow marrow ( inactive marrow ) - At about the age of 20y the red marrow is confined to : 。 Flat bones Skull , sternum , ribs , scapula , vertebrae & iliac bone • Ends of long bones " epiphyses " not the shaft " diaphysis " • Small bones of hands & feet - About 75 % of the cells in the red bone marrow are WBC precursors and only 25 % are RBC precursors ; inspite of the fact that RBC count is over 500 times more than the WBC count . This indicates the longer life span of RBCs . The core of medical physiology ( 1 ) - 3rd edition Page 134