index
Adults can produce 180L of urine every day and night, but the final urine output every day is only 1 ~ 2l. It can be seen that about 99% of the water in the original urine is reabsorbed into the blood when it passes through the renal tubules and collection tubes. From the comparison of components, the final urine is also very different from the original urine, for example, the original urine contains glucose, but the final urine does not; The final urine contains more creatinine and ammonia than the initial urine. It shows that the original urine must pass through the action of renal tubules and collecting tubes to generate the final urine.
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Factors affecting glomerular filtration
The influence of the change of the permeability and filtration area of glomerular filtration membrane on glomerular filtration function has been described before. The effects of glomerular capillary blood pressure, plasma colloid osmotic pressure, intracapsular pressure and renal plasma flow on glomerular filtration function were further analyzed.
Glomerular capillary blood pressure
If the systemic arterial blood pressure changes, it should affect the blood pressure of glomerular capillaries. Because renal blood flow has self-regulation mechanism, arterial blood pressure changes in 10.7? /FONT & gt； In the range of 24kPa(80-45mmHg), the glomerular capillary blood pressure remained stable, but the glomerular filtration rate remained basically unchanged (Figure 8-5). However, when the arterial blood pressure drops below 10.7kPa(80mmHg), the glomerular capillaries will decrease accordingly, so the effective filtration pressure will decrease and the glomerular filtration rate will also decrease. When the arterial blood pressure drops below 5.3-6.7 kPa (40-50 mHg), the glomerular filtration rate will drop to zero, so there is no urine. In the late stage of hypertension, the afferent arteriole contracts due to sclerosis, and the glomerular capillary blood pressure can be significantly reduced, so the glomerular filtration rate decreases, resulting in glomerular oliguria.
Intracapsular pressure
Under normal circumstances, the renal capsule pressure is relatively stable. Ureteral obstruction caused by calculus of renal pelvis or ureter, tumor compression or other reasons can obviously increase renal pelvis pressure. At this time, the pressure in the capsule will also increase, leading to the decrease of effective filtration pressure and glomerular filtration rate. If the concentration of some drugs is too high, crystals can be precipitated in the acidity of renal tubular fluid; In some diseases, excessive hemolysis and hemoglobin will block the renal tubules, which will also lead to the increase of pressure in the capsule and affect glomerular filtration.
Plasma colloid osmotic pressure.
Under normal circumstances, the plasma colloid osmotic pressure of the human body effectively filtering the signal body will not change greatly. However, if the whole body plasma protein concentration is significantly reduced, the plasma colloid osmotic pressure will also be reduced. At this time, effective filtration pressure will increase, and glomerular filtration rate will also increase. For example, rapid intravenous injection of normal saline will increase glomerular filtration rate, and one of the reasons may be the decrease of plasma colloid osmotic pressure.
Renal plasma flow
Renal plasma flow has a great influence on glomerular filtration rate, mainly affecting the position of filtration balance. If the renal plasma flow increases, the rising speed of plasma colloid osmotic pressure in glomerular capillaries slows down, and the filtration balance is close to the end of efferent arteriole, so the effective filtration pressure and filtration area increase, and the glomerular filtration rate increases accordingly. If the renal blood flow is further increased, the rising speed of plasma colloid osmotic pressure will be further slowed down, the total length of glomerular capillaries will not reach the filtration balance, and the glomerular filtration rate will be further increased. On the contrary, when the renal plasma flow decreases, the plasma colloid osmotic pressure rises faster, the filtration balance approaches the end of the afferent arteriole, the effective filtration pressure and filtration area decrease, and the glomerular filtration rate also decreases (Figure 8-8). Under pathological conditions such as severe hypoxia and toxic shock, renal blood flow and renal plasma flow will be significantly reduced due to sympathetic nerve excitation, and glomerular filtration rate will also be significantly reduced. Glomerular filtration rate refers to the amount of filtrate produced by both kidneys per unit time, which is about 1.25ml/min for normal adults. The ratio of glomerular filtration rate to renal plasma flow is called filtration fraction. The renal plasma flow per minute is about 660ml, so the filtration fraction is125/660×100% ≈19%. The results showed that about 1/5 of the plasma flowing through the kidney was filtered from the glomerulus into the capsule cavity, resulting in protourine. Glomerular filtration rate and filtration fraction are indicators to measure renal function.
index
Adults can produce 180L of urine every day and night, but the final urine output every day is only 1 ~ 2l. It can be seen that about 99% of the water in the original urine is reabsorbed into the blood when it passes through the renal tubules and collection tubes. From the comparison of components, the final urine is also very different from the original urine, for example, the original urine contains glucose, but the final urine does not; The final urine contains more creatinine and ammonia than the initial urine. It shows that the original urine must pass through the action of renal tubules and collecting tubes to generate the final urine.
Edit this paragraph
Factors affecting glomerular filtration
The influence of the change of the permeability and filtration area of glomerular filtration membrane on glomerular filtration function has been described before. The effects of glomerular capillary blood pressure, plasma colloid osmotic pressure, intracapsular pressure and renal plasma flow on glomerular filtration function were further analyzed.
Glomerular capillary blood pressure
If the systemic arterial blood pressure changes, it should affect the blood pressure of glomerular capillaries. Because renal blood flow has self-regulation mechanism, arterial blood pressure changes in 10.7? /FONT & gt； In the range of 24kPa(80-45mmHg), the glomerular capillary blood pressure remained stable, but the glomerular filtration rate remained basically unchanged (Figure 8-5). However, when the arterial blood pressure drops below 10.7kPa(80mmHg), the glomerular capillaries will decrease accordingly, so the effective filtration pressure will decrease and the glomerular filtration rate will also decrease. When the arterial blood pressure drops below 5.3-6.7 kPa (40-50 mHg), the glomerular filtration rate will drop to zero, so there is no urine. In the late stage of hypertension, the afferent arteriole contracts due to sclerosis, and the glomerular capillary blood pressure can be significantly reduced, so the glomerular filtration rate decreases, resulting in glomerular oliguria.
Intracapsular pressure
Under normal circumstances, the renal capsule pressure is relatively stable. Ureteral obstruction caused by calculus of renal pelvis or ureter, tumor compression or other reasons can obviously increase renal pelvis pressure. At this time, the pressure in the capsule will also increase, leading to the decrease of effective filtration pressure and glomerular filtration rate. If the concentration of some drugs is too high, crystals can be precipitated in the acidity of renal tubular fluid; In some diseases, excessive hemolysis and hemoglobin will block the renal tubules, which will also lead to the increase of pressure in the capsule and affect glomerular filtration.
Plasma colloid osmotic pressure.
Under normal circumstances, the plasma colloid osmotic pressure of the human body effectively filtering the signal body will not change greatly. However, if the whole body plasma protein concentration is significantly reduced, the plasma colloid osmotic pressure will also be reduced. At this time, effective filtration pressure will increase, and glomerular filtration rate will also increase. For example, rapid intravenous injection of normal saline will increase glomerular filtration rate, and one of the reasons may be the decrease of plasma colloid osmotic pressure.
Renal plasma flow
Renal plasma flow has a great influence on glomerular filtration rate, mainly affecting the position of filtration balance. If the renal plasma flow increases, the rising speed of plasma colloid osmotic pressure in glomerular capillaries slows down, and the filtration balance is close to the end of efferent arteriole, so the effective filtration pressure and filtration area increase, and the glomerular filtration rate increases accordingly. If the renal blood flow is further increased, the rising speed of plasma colloid osmotic pressure will be further slowed down, the total length of glomerular capillaries will not reach the filtration balance, and the glomerular filtration rate will be further increased. On the contrary, when the renal plasma flow decreases, the plasma colloid osmotic pressure rises faster, the filtration balance approaches the end of the afferent arteriole, the effective filtration pressure and filtration area decrease, and the glomerular filtration rate also decreases (Figure 8-8). Under pathological conditions such as severe hypoxia and toxic shock, renal blood flow and renal plasma flow will be significantly reduced due to sympathetic nerve excitation, and glomerular filtration rate will also be significantly reduced. /view/679348.htm#4