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function
Standard value
The difference between plasma and serum
Concept and calculation method of plasma clearance rate
Significance of plasma clearance rate determination
[Edit this paragraph] function
The functions of plasma protein are: maintaining plasma colloid osmotic pressure; Form a blood buffer system and participate in maintaining blood acid-base balance; Transport nutrients and metabolites, plasma protein is hydrophilic colloid, and many water-insoluble substances combine with it to become water-soluble substances; Nutritional function, amino acids produced by plasma protein decomposition can be used to synthesize tissue protein or oxidative decomposition to supply energy; Participate in coagulation and immunity. Inorganic salts in plasma mainly exist in ionic state, and the total amount of positive and negative ions is equal, maintaining electric neutrality. These ions play an important role in maintaining crystal osmotic pressure, acid-base balance and normal neuromuscular excitability. The chemical composition of plasma often changes in a certain range, among which the concentrations of glucose, protein, fat and hormones are most easily affected by nutritional status and body activities, while the concentration of inorganic salts changes in a smaller range. The relatively constant physical and chemical properties of plasma are the main manifestations of internal environment homeostasis.
[Edit this paragraph] Normal value
The total plasma osmotic pressure is 3 1.3 milliosmotic pressure /L, which is equivalent to 7 atmospheres (5330 mm Hg, 1 mmHg = 0. 1.33 kPa), in which the colloid osmotic pressure does not exceed 1.5 milliosmotic pressure/L (25mm Hg). PH7.35~7.47. Relative viscosity to water is 1.6 ~ 2.4.
[Edit this paragraph] The difference between plasma and serum
Plasma is a cell-free liquid obtained by centrifugal precipitation of whole blood leaving blood vessels after anticoagulation, which contains fibrinogen (fibrinogen can be converted into fibrin and has coagulation effect). If Ca2+ is added to the plasma, it will coagulate again, so there is no free Ca2+ in the plasma. Serum is a liquid released by blood coagulation in vitro. It has no fibrinogen, but contains free Ca2+. If Ca2+ is added, the serum will not coagulate again. In addition, another difference between plasma and serum is that there are much fewer coagulation factors and much more coagulation products in serum. In addition, the serum contains specific antibodies (such as antitoxin or lectin) immune serum (antibiotic serum).
[Edit this paragraph] The concept of plasma clearance rate and its calculation method
Clearance rate is a very important concept in renal physiology, because it provides an index to evaluate the ability of kidney to exclude certain substances. Refers to the number of milliliters of a substance contained in plasma that is completely cleared by the kidney in a unit time (usually per minute), and the number of milliliters of a substance completely cleared by plasma is called the plasma clearance rate (ml/min) of the substance. U (concentration of a substance in urine mg/ 100ml) V (urine volume per minute ml/min) P (concentration of a substance in plasma mg/ 100ml) Now, the clearance rate of inulin (I) is taken as an example for further explanation. Inulin is a kind of polysaccharide with a molecular weight of about 5200, which is harmless to people. Because of its small molecular weight, it can be filtered when passing through glomeruli in blood, and will not be reabsorbed or secreted in renal tubules. When determining the inulin clearance rate, the inulin solution was slowly injected intravenously into the body to keep its concentration in plasma at 1mg/ 100ml, and then the urine of the subject was collected for several minutes, and then the urine volume per minute (v, ml/min) was calculated, and the inulin concentration in the urine was determined (u, mg//kloc). If v is 1ml/min, u is 125mg/ 100ml, and p is 1mg/ 100ml, the clearance rate CI of inulin is 125ml/min. What needs to be pointed out here is that the so-called plasma ml number that completely removes a substance per minute is only a theoretical calculation. In fact, the kidney may not completely remove a substance in a certain milliliter of plasma, but may only remove a part. It's just that the amount of substances removed by the kidney per minute is equivalent to the amount of substances contained in several milliliters of plasma.
[Edit this paragraph] Significance of determination of plasma clearance rate
(The total amount of substances excreted by GFR kidney per minute (U V) should be equal to the algebraic sum of glomerular filtration and reabsorption and secretion of renal tubules and collecting ducts. If a substance is neither reabsorbed nor secreted, then the plasma clearance rate of this substance is GFR. Inulin is the substance that meets this condition. Theoretically, the following formula can be applied: U V = F P-R+S F represents the filtered plasma volume per minute, that is, GFR represents the reabsorption volume and S represents the secretion volume, which is the same as the formula of inulin plasma clearance rate, and CI = GFR = 125ml/min. (II) Inference of renal tubular function Through the determination of GFR and plasma clearance rate of other substances, we can infer which substances can be reabsorbed by renal tubules and which substances are secreted by renal tubules. Of course, these substances must be able to pass freely through the filter membrane. For example, the plasma clearance rates of urea and glucose are less than CI, urea is 70ml/min, and glucose is 0, indicating that urea is partially reabsorbed and glucose is completely reabsorbed. But it cannot be inferred that there is no secretion of this substance. As long as reabsorption exceeds secretion, its plasma clearance rate can still be less than 125ml/min. If the reabsorption is equal to the secretion, the plasma clearance rate can also be equal to 1.25ml/min. If the reabsorption amount of a substance is less than the secretion amount or there is no reabsorption, the plasma clearance rate of the substance is greater than 125ml/min. (3) Determination of renal blood flow If a substance (concentration P) in plasma can be completely removed by filtration and secretion after one week of renal circulation, that is, the concentration of the substance in renal venous blood is close to zero, the amount of the substance discharged from urine per minute (U V) should be equal to the amount contained in the plasma passing through the kidney per minute, that is, X represents the plasma flow of the kidney. For example, iodine nitrate and sodium p-aminohippurate are substances that meet this condition. Therefore, the plasma clearance rate of these two substances can represent the plasma flow, which is about 660ml/min in human kidney. The ratio of glomerular filtration rate to renal plasma flow is called filtration fraction. According to the renal plasma flow and red blood cell volume, the renal blood flow can be calculated, which is about 1200ml/min, accounting for 1/5 ~ 1/4 of the cardiac output.