Jako de Prize asked:
How are blood cells made?
We put this to Professor Adrian Newland:
Adrian - Blood cells are made in the bone marrow. In the bone space - in particular in the pelvis, in the bones of the back, the ribs and the sternum. They’re made from stem cells that then incorporate protein, iron, all the building blocks of haemoglobin that then encapsulate in cells that are pushed out into the blood. Many millions of cells every day.
Jaco du Preez asked the Naked Scientists: How are blood cells created? What do you think? Jaco du Preez, Tue, 2nd Sep 2008
This is a good site but it's quite technical.