BloodPeople have been donating blood since the early twentieth century to help accident victims and patients undergoing surgical procedures. Usually a pint of whole blood is donated, and it is thendivided into platelets, white blood cells, and red blood cells. People can donate blood (for red blood cells) about once every two months. Transfusing the blood from the donor to the recipient is straightforward. It involves taing the blood from a donor!s arm vein by means of a hypodermic syringe. The blood flows through a plastic tube to a collection bag or bottle that contains sodium citrate, which prevents the bloodfrom clotting. "hen the blood is given to a patient, a plastic tube and hypodermic needle are connected to therecipient!s arm. The blood flows down from the container by gravity. This is a slow process andmay last as long as # hours to complete the infusion of blood into the recipient. The patient is protected from being infected during the transfusion. $nly sterile containers, tubing, and needlesare used, and this helps ensure that transfused or stored blood is not e%posed to disease causing bacteria. &egative reactions to transfusions are not unusual. The recipient may suffer an allergic reactionor be sensitive to donor leuocytes. 'ome may suffer from an undetected redcellincompatibility. Une%plained reactions are also fairly common. lthough they are rare, other causes of such negative reactions include contaminated blood, air bubbles in the blood,overloading of the circulatory system through administration of e%cess blood, or sensitivity todonor plasma or platelets. Today, hospitals and blood bans go to great lengths to screen all blood donors and their blood.ll donated blood is routinely and rigorously tested for diseases, such as *I+ (which causesI'), hepatitis B, and syphilis. "hen the recipient is a newborn or an infant, the blood isusually irradiated to eliminate harmful elements. onated blood is washed, and the white bloodcells and platelets are removed. 'toring the blood sometimes re-uires a freeing process. To freee the red blood cells, a glycerolsolution is added. To unfreee, the glycerol is removed. The ability to store blood for long periods has been a boon to human
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