Blood Serum

Blood serum, the liquid part of blood, not containing fibrin or formed elements. Obtained as follows: blood collected in a vessel spontaneously clots, turning into a solid fibrin clot, which captures the blood's formed elements; when left standing, this clot squeezes out yellow-colored serum. The color of serum depends on the presence of bilirubin (0.5-1 mg%). The amount of bilirubin varies among different individuals but remains constant for the same person. An increase in bilirubin in serum has great clinical significance and indicates a disturbance in pigment metabolism (see Bilirubinemia, as well as Jaundice). Hematoporphyrin is not contained in normal serum but is found in it in pernicious anemia, acute yellow atrophy of the liver, and lead poisoning. Methemoglobin is found in serum in poisoning by aniline, nitrobenzene, and potassium chlorate, but is absent under normal conditions. Urobilin and urobilinogen are normally detected in trace amounts by some authors and are found in lobar pneumonia, in decompensated valvular defects, in infarctions of the lung, and in cholelithiasis. Lipochromes: lutein, xanthophyll, and carotene, which give serum its yellow color, have no clinical significance; they are of exogenous origin and depend on the type of food. In normal conditions, serum is transparent; after meals it often becomes turbid, chylous due to the admixture of tiny fat droplets. Chylous serum is observed in nephrosis. The specific gravity of serum is 1.028-1.032 and is determined mainly by its protein content, since the percentage of proteins is significantly higher than that of other dense substances (urea, sugar, NaCl). Under pathological conditions, fluctuations in the amount of urea, sugar, and fat do not substantially change the specific gravity of serum. Under pathological conditions, an increase in specific gravity is noted with strong physiological strains, under the influence of heat, and when fluid is removed. A decrease in specific gravity is observed in serum depleted of proteins, in edema in kidney patients, and in cachectic patients. The dry residue of serum is 19-23%. The water content in serum depends on metabolic processes in tissues, the excretory function of the kidneys, protein concentration, type of food, and water binding by plasma colloids. Under normal conditions, the amount of water in serum is constant (see Metabolism and Hydremia). The surface tension of plasma and blood serum is lower than that of water. The determination of surface tension and its significance in pathology-see Blood. All data regarding both viscosity and osmotic pressure and electrical conductivity of blood serum are also given there. The concentration of proteins in normal serum fluctuates between 6-8%; the main proteins of serum are: globulin-1.9-2.2% and albumins-4.5-6.5%. Fluctuations in the amount of proteins in serum and changes in the proportion of albumins and globulins have great clinical significance, but this question is far from resolution. The globulin fraction increases (absolutely and relatively) in all infections, and therefore has no differential diagnostic value. A connection between immune bodies and globulins is noted. Albumin of serum increases with muscular work and decreases in nephroses. In 1902, Reiss pointed out the close connection between the protein content in serum and its refraction; this made it possible to determine the amount of protein in serum with a refractometer. Fluctuations in refraction depend on several reasons: 1) from the exchange of fluid between blood serum and blood cells, between tissues and serum, 2) from the increase or decrease of crystalline substances in serum, 3) from the breakdown or formation of proteins. The refraction of serum changes little under the influence of physiological factors, such as food intake or the effect of hydrotherapeutic procedures. Long-term insufficient nutrition leads to a decrease in protein content in serum; muscular work has little effect on refraction. In acute infections, the amount of protein in serum falls and returns to normal during the recovery period; the exception is tuberculosis, in which an increase in the total amount of protein, especially globulin, is observed. In neoplasms, refraction is lowered; an increase in globulins in this case indicates tumor growth. When the tumor is irradiated, the amount of protein increases. Refractometry gives valuable indications in the study of water metabolism, in the study of metabolic diseases, and in kidney diseases. For detailed characteristics, as well as methods for determining proteins-see Blood. The reaction of serum is slightly shifted to the alkaline side from the neutral point-pH-7.3-7.4 at 38°. Fluctuations under normal conditions are small. The ability to maintain a constant active reaction depends on the presence of "buffer substances". Such substances are the bicarbonates, phosphates, and alkaline salts of proteins in serum. pH depends mainly on the ratio of two changing factors-carbonic acid and the alkaline bicarbonate of blood-and is maintained by respiration. Any decrease in the content of carbonic acid with unchanged bicarbonate causes an increase in pH, i.e., a deviation of the reaction to the alkaline side, while any decrease in bicarbonates with unchanged carbonic acid decreases pH and shifts the reaction to the acidic side. Under pathological conditions, the concentration of hydrogen ions can give significant deviations in both directions (see Blood). Carbohydrates-see Blood. Lipoids play a large role in cellular exchange processes and constitute an essential part of cell membranes. Under the name of lipoids are known neutral fats, fatty acids, phosphatides (lecithin), and cholesterol. Lipoids are extracted by alcohol or ether. One can distinguish: 1) alimentary lipemia-when consuming fat in food, 2) diabetic, 3) nephrotic, 4) anemic, and 5) in poisoning by phosphorus, alcohol, and ether (see Hypercholesterinemia and Lipemia). Inorganic substances are very unevenly distributed between serum and the formed elements of blood. An excess of potassium is contained in blood cells, while serum contains calcium and sodium. The mineral components of serum are in three forms: 1) in an ionized state, 2) in the form of undissociated molecules, in equilibrium with ions, 3) in a non-ionized compound with organic substances. Mineral substances in ionized or molecular form can be separated from those bound to colloids by dialysis or by passing through an ultrafilter, which retains colloids. Calcium is the only mineral element, a significant part of which is bound to colloids. (Methods of determination, as well as fluctuations under both physiological and pathological conditions-see Blood.) After removing proteins from serum by 15' precipitation by boiling or any precipitants, a certain amount of nitrogen remains in the filtrate, which is designated as residual nitrogen (RN) and consists of urea, uric acid, creatinine, indican, and amino acids. From the amount of these substances, one can judge the work of the excretory organs; the group of amino acids is very important for assessing protein metabolism (see Nephritis, Nephrosclerosis, Gout). Of the enzymes found in whole blood, lipase, protease, and phosphatase should be mentioned, which are mainly contained in serum (see Blood).

A. 11 koplena.