Glomerular filtration rate

Glomerular filtration rate (GFR, glomerular filtration rate) refers to the unit time (usually 1min) within the two kidney to produce the amount of filtrate, the normal adult 80-120ml / min or so. The ratio of glomerular filtration rate to renal plasma flow is called the filtration fraction. Per minute renal plasma flow of about 660ml, so the filter score of 125/660 × 100% ≈ 19%. This result shows that the blood flow through the kidney about 1/5 from the glomerular filtration into the capsule cavity to produce urine. Glomerular filtration rate and filtration fraction are indicators of renal function.
Adults every day and night to produce the original urine volume up to 180L, but the daily discharge of urine volume is only 1 ~ 2L, visible urine through the renal tubular and collecting tube, about 99% of the water was reabsorbed back to the blood. And then from the composition of the comparison, the final urine and the original urine is also very different, such as the original urine containing glucose, no urine; and the final urine contains creatinine, ammonia and more than the original urine. Indicating that the original urine still need to pass through the role of renal tubular and collecting tube in order to generate the final urine.

Effective filter pressure
Refers to the difference between the power to promote ultrafiltration and the resistance to ultrafiltration.The power includes glomerular capillaries hydrostatic pressure and intracranial hypercapsular colloid osmotic pressure. Resistance includes plasma colloid osmotic pressure within the glomerular capillaries and hydrostatic pressure in the renal capsule.
Glomerular effective filtration pressure = (glomerular capillary hydrostatic pressure + intracapsular fluid colloid osmotic pressure) - (plasma colloid osmotic pressure + renal capsule pressure)
The plasma from the capillaries to filter the formation of tissue fluid - the effective filtration pressure.
Fold effective filter overpressure
Composition of effective filtration of the three factors in any factor changes, can affect the effective filtration pressure, thereby changing the glomerular filtration rate.
1, glomerular capillary blood pressure changes experiments show that arterial blood pressure in the 10.7 ~ 24.0kPa (80 ~ 180mmHg) range of changes in renal blood flow to maintain their own regulation can remain relatively stable, glomerular capillary blood pressure no significant change The On the mechanism of self-regulation, most people believe that arterial blood pressure, the ball artery of the smooth muscle by the stretch stimulation and contraction, blood flow resistance increases, so that glomerular blood vessels do not increase blood flow, blood pressure will not So that the effective filtration pressure and glomerular filtration rate did not change significantly; when the arterial blood pressure decreased, the ball artery wall diastolic, blood flow resistance decreased, so that the glomerular capillary blood flow will not be reduced, Blood pressure will not decline, and thus effective filtration pressure and glomerular filtration rate and no significant change. This shows that the body's regulation of glomerular filtration function is achieved through the regulation of renal blood flow itself to ensure that the body in the physiological state of normal urinary function. But if the arterial blood pressure dropped to 10.7kPa (80mmHg) below (such as large blood loss), beyond the renal blood flow regulation range, glomerular capillary blood pressure will be a corresponding decline in the effective filtration pressure decreased glomerular filtration The rate of reduction caused by oliguria, when the arterial blood pressure dropped to 5.3 ~ 6.7kPa (40 ~ 50mmHg), can lead to anuria. Hypertension late, due to the arterial arterial events and stenosis, the glomerular capillary blood pressure can also be significantly reduced, causing decreased glomerular filtration rate and lead to oliguria, and even anuria.
2, plasma colloid osmotic pressure changes in human plasma colloid osmotic pressure under normal circumstances will not be significant fluctuations. Only in the plasma protein concentration decreased, it caused the plasma colloid osmotic pressure decreased, so that the effective filtration of the glomerular filtration rate and filtration rate increased urine output. For example, intravenous input of a large number of saline caused by increased urine output is the main reason is that plasma protein was diluted, plasma protein concentration decreased, decreased plasma colloid osmotic pressure.
3, changes in renal capsule pressure under normal circumstances, renal capsule pressure is relatively stable. When the occurrence of urinary tract obstruction, such as renal pelvic stones, ureteral stones or tumor compression, can cause ipsilateral capsule pressure, so that the effective filtration pressure is reduced, the filtration rate decreased. In addition, some drugs, such as certain sulfonamides, are easily crystallized in the acidic environment of the tubules, or when some of the diseases cause hemolysis to contain hemoglobin, the drug crystals or hemoglobin can block the renal tubules and cause the capsule Increased pressure, resulting in effective filtration of the glomeruli and filtration rate decreased.
Folding plasma flow
Glomerular ball into the ball to the end of the ball, due to plasma colloid osmotic pressure gradually increased, resulting in effective filter pressure reduction. The rate of increase in plasma colloid osmotic pressure necessarily affects the rate of effective filtration pressure reduction. The rate of increase in plasma colloid osmotic pressure is closely related to glomerular plasma flow. When the plasma flow rate increased, the colloid osmotic pressure slowed down, the effective filtration pressure deceleration rate slowed down, the effective length of glomerular capillary formation filtrate prolonged, filtration rate increased; the contrary, glomerular plasma Flow reduction, glomerular capillary formation filtrate effective length shortened, reduced filtration rate. Under normal circumstances due to renal blood flow there is self-regulation, glomerular plasma flow can remain relatively stable, only in the body for strenuous exercise or in large blood loss, severe hypoxia and other pathological conditions, due to increased sympathetic nerve, renal vasoconstriction, So that renal blood flow and glomerular plasma flow was significantly reduced, it caused by decreased glomerular filtration rate.
Folding physical and chemical properties change
1, the size of glomerular filtration membrane permeability can be used to allow it to pass the molecular weight of the material to measure. Plasma small molecules are easily through the membrane size of the various channels; but macromolecules, such as molecular weight of 69000 plasma albumin is difficult to pass, but also the selective blocking of sialin protein, so it is in the filtrate Of the concentration does not exceed 0.2% of the plasma concentration; molecular weight of more than 69000 globulin, fibrinogen, etc. can not pass through the membrane. In addition, the plasma molecular weight of 64000 hemoglobin, which can be filtered, but it is associated with globin to form a complex form, and therefore can not pass. When a large amount of hemolysis occurs, the amount of hemoglobin contained in the blood exceeds the amount bound to the globin, and the hemoglobin that is not bound to the globin can be filtered out by the urine to form hemoglobinuria.
Under normal circumstances, the permeability of the membrane is relatively stable, only in the pathological changes only affect the composition of urine. Such as glomerular inflammation or hypoxia, often accompanied by proteinuria. In the past, it was considered that the permeability of the membrane was increased. The appearance of proteinuria is due to the lesion on the filter membrane with a negative charge of sialin to reduce or disappear, with negatively charged albumin homogeneous charge repulsion weakened, so that albumin easily filtered due. When the lesion caused by damage to the membrane, the red blood cells can also filter out the formation of hematuria.
2, glomerular filtration membrane total area of ​​about 1.5 to 2 square meters. People under normal circumstances, all the glomeruli are in the active state, so the filtration area remained stable. Pathological conditions, such as acute glomerulonephritis, glomerular capillary endothelial hyperplasia, swelling, the basement membrane is also swelling thickening, causing narrowing of the capillary stenosis or even complete occlusion, resulting in reduced effective filtration area, reduced filtration rate, There is no urine or even anuria.