What Are the Medical Uses of Blood Plasma?

The main role of plasma is to carry blood cells, transport substances needed to maintain human life activities, and waste generated in the body. Plasma is the intercellular substance of connective tissue. Plasma is an important part of the blood and is a pale yellow liquid (due to the presence of bilirubin). Among the chemical components of plasma, water accounts for 90 ~ 92%, the other 10% is mainly solute plasma protein, and contains electrolytes, nutrients, enzymes, hormones, cholesterol, and others. An important part of. Plasma protein is a general term for a variety of proteins, which can be divided into albumin, globulin, and fibrinogen by salting out.

Plasma is the extracellular fluid of blood cells and is an important part of the internal environment of the body. It plays an important role in communicating the internal and external environment of the body. The composition of plasma can change correspondingly due to the metabolic activity of the body and the external environment, but under normal circumstances, the body keeps the composition of plasma relatively constant through various regulatory effects. When the body is sick, some of the components in plasma can change beyond the normal range, so the determination of plasma components can provide a basis for the diagnosis of certain diseases ^[2]

Plasma is the liquid component of blood,

Plasma is the whole blood leaving the blood vessel after anticoagulation treatment, and then centrifuged to obtain a cell-free liquid, which contains

Plasma plasma clearance

Plasma clearance is an important concept in kidney physiology because it provides an indicator of the ability of the kidneys to exclude a substance. It refers to how many milliliters of plasma can be completely removed by the kidney in a unit time (generally per minute). The number of milliliters of plasma that has been completely removed from a substance is called the plasma clearance of the substance ( ml / min).

U (concentration of a substance in urine mg / 100ml)

V (ml / min urine output per minute)

P (concentration of a substance in plasma mg / 100ml)

Let's take the clearance rate of inulin (inulin, I) as an example, and explain it further. Inulin is a polysaccharide with a molecular weight of about 5,200. It is harmless to humans. Because of its small molecular weight, it can be filtered through the glomeruli in the blood, and is not reabsorbed or secreted in the renal tubules.

When measuring the inulin clearance rate, slowly inject the inulin solution into the body to keep its concentration in plasma at 1mg / 100ml, and then start to collect the urine of the subject for several minutes, and then calculate the urine volume per minute ( V, ml / min), and the concentration of inulin in the urine (U, mg / 100 ml) was measured.

If measured V is 1ml / min U is 125mg / 100ml

P is 1mg / 100ml

The clearance CI of inulin was 125 ml / min.

It should be pointed out here that the so-called plasma ml that completely clears a substance per minute is only a theoretically estimated value. In fact, the kidney does not necessarily completely remove a certain substance in a certain milliliter of plasma, it may only remove a part of it. However, the amount of the substance that the kidney clears every minute is equivalent to how many milliliters of plasma contains the substance. The amount.

GFR GFR in plasma

The total amount of certain substance (U · V) excreted by the kidney per minute should be equal to the algebraic sum of the excess glomerular filtration and the reabsorption and secretion of tubules and collecting ducts. If a substance is neither reabsorbed nor secreted, the plasma clearance of that substance is GFR. Inulin is a substance that meets this condition. In theory, the following formulas can be applied:

U · V = F · P-R + S

F is the amount of plasma filtered per minute, which is GFR

R is the amount of reabsorption

S stands for secretion

Same as the formula of inulin plasma clearance, CI = GFR = 125ml / min.

Plasma function speculation

Through the determination of GFR and the determination of the plasma clearance of other substances, it can be inferred which substances can be reabsorbed by the renal tubules and which are secreted by the renal tubules. Of course, these materials must be free to pass through the filter membrane. For example, the plasma clearance of urea and glucose is less than Cl, urea is 70ml / min, and glucose is 0, indicating that urea is partially reabsorbed and glucose is fully reabsorbed. However, it cannot be inferred that there is no secretion of this substance, as long as the reabsorption amount exceeds the secretion amount, its plasma clearance rate can still be less than 125ml / min; if the reabsorption amount is equal to the secretion amount, its plasma clearance rate can also be equal to 125ml / min; If the amount of reabsorption of a substance is less than the amount of secretion or no reabsorption, the plasma clearance of the substance is greater than 125ml / min.

Determination of plasma renal blood flow

If a certain substance in the plasma (its concentration is P), it can be completely removed by filtration and secretion after one week of renal circulation, that is, the concentration of this substance in renal venous blood is close to 0, The amount excreted from the urine in minutes (U · V) should be equal to the amount contained in the plasma of the substance per minute passing through the kidney, that is, X represents the plasma flow of the kidney.

Such as iodide and p-amino urate are substances that meet this condition. Therefore, the plasma clearance of these two substances can represent the plasma flow, and it is calculated that the human renal plasma flow is about 660ml / min. The ratio of GFR to renal plasma flow is called the filtration fraction.

From the renal plasma flow, and then based on the hematocrit, the renal blood flow can be calculated.

Renal blood flow is about 1200ml / min, which accounts for about 1/5 ~ 1/4 of cardiac output ^[2] .