Medical Devices

Abstract

15 Medical Deviceswith leukocyte and platelet numbers being approximately 1/600 and 1/20 that of erythrocytes, respectively.The erythrocyte is disc-shaped, 7.5-8.5 μm in diameter, and 1-2.5 μm thick, but is thinner at its central region. Functionally, erythrocytes contain hemoglobin, which combines very rapidly with oxygen (as discussed later).There are various types of leukocytes, the main function of which is to protect against infection. Macrophages, one type of leukocytes, engulf and digest various foreign particles and bacteria that have passed into the interstitial spaces. Lymphocytes exist as two types: (i) B cells, which produce antibodies (i.e., various immunoglobulins) and (ii) T cells, which destroy foreign cells, activate macrophages, and regulate the production of antibodies by B cells. Complements are proteins in plasma that assist the functions of antibodies in a variety of ways.Clotting -the coagulation of blood -involves a series of very complicated chain reactions that are assisted by enzymes. In the final stage of blood clotting, the protein fibrinogen, which is soluble in plasma, becomes an insoluble fibrin, which encloses the red cells and platelets, with the latter component playing an important role in the clotting process. If a blood vessel is injured, clotting must occur to stop further bleeding. However, clotting must not occur in blood that is flowing through the blood vessels or through artificial organs. Within the blood vessels, blood does not coagulate due to the existence of antithrombin and other anticoagulants. Serum is the plasma from which fibrinogen has been removed during the process of clotting, and can be obtained by stirring and then centrifuging the clotted blood.Heparin, an anticoagulant that is widely used to prevent blood coagulation flowing through artificial organs, is a mucopolysaccharide that is obtained from the liver or lung of animals. It is also possible to prevent blood clotting in vitro by the addition of oxalic acid or citric acid; these combine with the Ca 2+ ions that are required in clotting reactions and block the process.Hemolysis is the leakage of hemoglobin into liquid such as plasma, and is due to disruption of the erythrocytes. Within the body, hemolysis may be caused by some diseases or poisons, whereas hemolysis outside the body, as in artificial organs, is caused by physical or chemical factors. If erythrocytes are placed in water, hemolysis will occur as the cells rupture due to the difference in osmotic pressure between water and the intracellular liquid. Hemolysis in artificial organs and their accessories occurs due to a variety of physical factors, including turbulence, shear, and changes of pressure and velocity. It is difficult, however, to obtain any quantitative correlation between the rates of hemolysis and such physical factors.The body fluids can be regarded as buffer solutions, with the normal pH values of the extracellular fluids (including blood) and intracellular fluids being 7.4 and 7.2, respectively.Plasma or serum can be regard...