THE COMPONENT OF THE BLOOD

The principal component of the blood plasma, which comprises over half of the total bood volume, is water. Our bodies are 70% water, our cells all function in a watery environment, and the blood is responsible for bringing adequate hydration to all of our tissues. The blood fluid also contains dissolved ions that are crucial for cell function. These ions are principally sodium, potassium, chloride, hydrogen, magnesium, and calcium. The plasma also transport iron, which is vital for crucial tissues enzymes but is particularly important for the structure and function of red blood cells.
The proteins of the blood plasma can be broadly divided into three classes: carrier proteins, immunoproteins, and coagulation proteins. The carrier functions of plasma proteins is threefold. First, the plasma proteins can bind molecules in the plasma, there by diminishing the nonspecific diffusion of these molecules into the tissues or their nonspecific interractions with blood and tissue cells. Second, complexes of carrier protein and molecules bound to them may be recognized by particular cells with a high degree to of specifity. In this way molecules such as iron can be directly targeted to cells that requaire them. Finally, plasma protein can diminish the toxic effect of certain molecules in the plasma by binding to them and by carrying these neutralize d toxins to specific sites, where they can be eliminate. Examples of these three carrier functions are evident for the plasma proteins describe in the following paragrahp.
The chief plasma protein is albumin. Comprising two-thirds of the mass of plasma protein, albumin is the major source of the osmotic pressure of thep plasma. In this sense albumin can be said to be a carrier of water, and when the serum albumin level declines the tissues of the body become edematous. Albuminis also a carrier of many compounds, examples of which are bilirubin and other bile pigments, and of free fatty acids. albumin doesn’t bind all such moleculeswith very high avidity, but because of the high albumin concentration, the proportion of these molecules that remain uncomplexed in the plasma is small. Another class of carrier proteins are the lipoproteins,which transport cholesterol, triglycerid, and phospholipid between tissues. Two plasma protein are particularly important for the transport of nutrients needed by the blood. One of these protein is transferrin, which carries iron to developing red blood cells. The second carrier is a class of proteins called transcobalamins, protein that transport cobalamins, vital cofactors for DNA synthesis in blood cells and other tissues.
Another set of carrier proteins complex to substances that may not ordinarily be present in the plasma but appear following injury or tissue dstruction. Haptoglobin is a protein that binds hemoglobin if this principal red blood cell connstituent appears in the plasma because of red blood cell destruction. A protein with a similar function is hemopexin, which bind to free heme released from denatured hemoglobin. Two proteins, alpha-1-antiprotease and alpha-2-macroglobulin, bind and neutralize proteolytic enzymes release from destroyed tissues and phagocytic leucocytes. The protease antiprotease-antiprotease complexes are avidly cleared from the circulation by mononuclear phagocytes. These antiprotease also function in the tissues. Injury and inflammation frequently increase the permeability of blood vesssels, allowing plasma constituent ti leak into the injured area. The antiproteases participate in the neutralization of proteolytic enzymes activated by the injury and inflammatory processes. An other ”anti-inflammatory” plasma protein is a copper binding protein called ceruloplasmin. Ceruloplasmin participates in the detoxification of oxygen free radicals that are released during inflammation by phagocytic cells. In addition, ceruplasmin is required to prevent the accumulation of copper in tissues, where it can have toxic effects. A conginetal disorder in which ceruloplasmin is absent, Wilson’s disease, is associated with extensive tissue damage, including red blood cell destruction.
Aside from nutrition, defense is the major function of the blood. Both cell and humors participate in this defense. The blood humors active in defense against invading micro-organism are the immunoproteins, the immunoglobulins, and the complemen proteins.
One of the tasks of the blood is to maintain the integrity of its conduit, the vascular system. As in defense against infection, cells and humors cooperate in this endeavor. The humoral arm of this defense is the coagulation system, a series of plasma proteins that interact to produce gelatinous plugs for sealing breaks and leaks in the vasculature. A variety of condition activate the coagulation protein. The solidificattion of plasma as a result of this activation is due to the formation of a network of strands composed of the protein fibrin. Between the strands of fibrin are water, salts, and the majority of plasma proteins. By centrifugation of the clot, these compound can be squeezed out; collectively they are called the serum. One of the stimuli for blood coagulation is contact with of the plasma with foreign surface such as glass or plastic. Therefore, any attempt to remove blood from the vascular system results in activation of the clotting system unless coagulation is inhibited in some way. For a number of diagnostic procedures involving blood and for blood blood transfusion it is inconvenient to have clotting occur. The coagulation system is very dependent on the presence of inonized calcium, so that if calcium is lowered by means of a suitable chelating agent coagulation is inhibited. Blood can be drawn into a container containing a sufficient quantity of sodium citrate or else ethylenediaminetetraasetic acid (commonly called EDTA) to complex all of the free calcium and will not clot. A system of proteins complementary to the coagulation proteins inhibits the coagulation system. It prevents the whole circulation from clotting up at once, if exposed locally to one of the many coagulation activators, and also break down formed clots when they are no longer needed. This system is called the fibrinolytic system.

key words: blood, tranobalamins, fibrinolytic system, Ceruloplasmin
(Bernard M. Babior & Thomas P. Stossel ; Hematology A Pathophysiological Approach, 1-3)