الفهرس 
PHYSIOLOGICAL ROLE OF BLOOD CELLS
Iron RecyclingOnly 14 pages are availabe for public view
 |  | from | 119 |  |  |
| | | from | 119 | | |
Abstract
Blood transfusion has been the solution for many disorders that affect the integrity of the circulatory system as well as the respiratory system in the way that includes oxygen carriage and delivery to tissues. Blood transfusion unfortunately has many drawbacks and complications e.g.: may be unavailable during crisis and emergency situations, non-compatible blood can cause serious reactions, carries the risk of contamination and spreading dangerous illnesses. Due to these disadvantages and the already low supplies of fresh blood and the costs and efforts done to screen and prepare safe blood, scientists and researchers worldwide have been trying to produce substances that can perform the different functions of blood and these substances have to be safer, more plentiful, available and if possible cheaper than regular blood or blood components.
Generally, these products are called blood substitutes, but the term blood substitutes mainly refers to the products that deal with substituting the function of red blood cells; oxygen carriage. These products have undergone a lot of development and available products are classified into: perfluorocarbon emulsions, hemoglobin based oxygen carriers, nanobiotechnology synthesized artificial red blood cells and hematopoietic growth factors.
Perfluorocarbons emulsions are completely synthetic inert products and are mainly classified into first and second generations. Hemoglobin based oxygen carriers use modified hemoglobin, conjugated hemoglobin, polymerized hemoglobin or encapsulated hemoglobin as the oxygen carrier. Nanobiotechnology synthesized artificial red blood cells, however, have encountered several problems, including low encapsulation efficiency, ready oxidation of hemoglobin, and adherence of hemoglobin to the outside of the vesicles – not to mention the very high cost and complexity of the production process.
Approximately 18 million units of platelets are transfused each year worldwide, about 80% goes to patients who are thrombocytopenic as a result of chemotherapy. Platelet substitutes are also available to restore platelet count and function in thrombocytopenic and thrombocytopathic patients. These substitutes are either fully synthetic or derived from outdated or modified platelets
Platelet substitutes include: Synthocytes which are microcapsules to which fibrinogen has been chemically linked, thrombospheres which are composed of cross-linked human albumin with human fibrinogen bound to the surface, infusible platelet membranes which are produced from outdated human platelets, red cells with surface-bound fibrinogen, lyophilized human platelets, freeze dried platelets, plateletsomes, factor Xa with phospholipid vesicles and platelet growth factors.
White blood cells however don’t have a substitute yet, except growth factors like: G-CSF (Granulocyte colony stimulating factor) that stimulate their production and maturation. G-CSF stimulates the production of white blood cells. In oncology and hematology, a recombinant form of G-CSF is used with certain cancer patients to accelerate recovery from neutropenia after chemotherapy. Further studies are currently underway for this exciting new class of drugs. The use of recombinant myeloid colony stimulating factors (CSF) such as G-CSF has also improved care of patients with severe leucopenia, allowing for increased production of endogenous myeloid cells.