الفهرس 
RED BLOOD CELL PHYSIOLOGYOnly 14 pages are availabe for public view
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Abstract
The final goal of any transfusion medicine is to create a transfusion system with no side effects and with more effective medical care.
Continud research and better understanding of the unique physiology of red blood cells and their interaction with the surrounding environment has helped in developing newer generations of ideal red blood cells substitutes.
Hopefully, as red blood cells substitutes are developed and enter routine clinical use, the need for blood transfusions in different clinical settings will decrease. Large –scale production of red blood cells substitutes would also help to meet the anticipated increase in demand for blood as the population ages and the blood donor pool diminishes. Furthermore, it will overcome the problem of cross matching, short shelf life, and the concern about the adverse effects of blood transfusion.
Two distincit pathways of development have emerged in the search for clinically employable artificial red blood cell substitutes: Hemoglobin- based oxygen carriers and perfluorocarbon emulsions. Recently, there is a third natural different way using the umbilical cord blood transplantation as a source of hematopoietic stem cells with greater capability to produce mature red blood cells.
Hemoglobin- based oxygen carriers (HBOCs) include various types. Polymerized hemoglobin, conjugated hemoglobin, and the new recombinant human hemoglobin with desired characteristics. A soluble Polyhemoglobin–catalase–superoxide dismutase is being studied as an oxygen carrier with antioxidant properties. New artificial red blood cells that are more like red blood cells are being developed. One is based on hemoglobin lipid vesicles. A more recent one is based on nano-dimension artificial red blood cells containing hemoglobin and RBC enzymes with biodegradable polymer membrane like –polylactic acid.
Currently, hemoglobin based oxygen carriers represent an interesting class of red blood cell substitutes, which are undergoing advanced clinical trials. The therapeutic goal of these compounds is to avoid, delay, or reduce blood transfusion in different surgical and medical situations of acute hemoglobin deficiency. Their main advantages include availability in large volumes, storage for prolonged periods, rapid administration without cross matching, and sterilisation by pasteurisation. Their main known disadvantages are reduced circulation half-life, hemodynamic, and gastrointestinal perturbations, probably related to nitric oxide (NO) scavenging. Moreover, it causes alterations of biochemical and hematological parameters.
Perfluorocarbon emulsions (PFCEs) are chemically inert compounds. Unlike hemoglobin based oxygen carriers, they have the following advantages: they do not react with oxygen or other gases, increase the oxygen solubility in the plasma, the dissolved oxygen is not subjected to the effects of allosteric modifiers, and facilitate effortless transfer of oxygen from the red cells to the tissue. Unfortunately, complement activation has been a major clinical problem with perfluorocarbon emulsions, in addition to the decreasing platelet counts, increased body temperature, and short half life. Furthermore, the patients generally have to breathe 70–100% oxygen in order for the products to carry enough oxygen.
Red blood cells substitutes with different properties might target the diversity of clinical indications, spanning from blood loss in trauma and surgery by avoiding or delay ing the use of blood transfusion, hemodilution, organ preservation, regional perfusion of ischemic tissues, as well assensitization of solid tumors to X-rays and chemotherapy.
It is important to remember that artificial red blood cells substitutes are not blood substitute; they cannot replace red blood cells. The only functions they serve are oxygen transport, delivery, and blood volume expansion
Artificial red blood cells substitutes cannot be ready for clinical use without years of research and development followed by time consuming clinical trials. Thus, despite many years of intense efforts, the ideal red blood cells substitutes continue to elude researchers and there is still no product ready for commercial use even in the western world However, uptill now there are no documented clinical trials about the routine clinical use of artificial red blood cell substitutes in Egypt.
Umbilical cord blood transplantation has become an accepted source of related and unrelated hematopoietic stem cell transplantation for bone marrow reconstitution as it harbor some advantages like rapid availability, greater tolerance to Histocompatibility leucocytic antigen (HLA) disparity, and lower incidence of graft versus host disease. On the other hand, there are different challenges facing its use like, the risk of post-transplant infection, the risk of genetic disease transmission, and the limited number of nucleated cell dose.
Umbilical cord blood transplantation can be used as a substitute for bone marrow transplantation and to decrease the need for future regular blood transfusion in various clinical settings as, thalassemia, sickle cell anemia, bone marrow failure, and hematological malignancies.
There should be urgent motivations in Egyptian blood banks to find red blood cells substitutes to over come the problem of transfusion-transmitted infections especially Hepatitis viruses and the inherited risks together with the increased cost of chronic red blood cell transfusion.Therefore, there are great efforts to benefit from the umbilical cord blood transplantation in different medical settings.
Egypt witnessed a very specific medical advancement as a group of private laboratories are set to open the first private umbilical cord blood bank, with the approval from the Ministry of Health.