Kidney blood filtration system
The rate of filtration is approximately 125 ml/min or 180 liters each day. As the volume of blood in human body is typically about 7 to 8 liters, the entire blood in the body gets filtered approximately 20 to 25 times each day Kidneys regulate the composition of the blood by a combination of three processes: Filtration, Reabsorption and Secretion.
Filtration: The blood flows through the glomerulus in kidneys with high pressure as the efferent (outgoing) arteriole is narrower than the afferent (incoming) arteriole. This hydrostatic pressure causes the liquid part of the blood to filter out from the glomerulus into the renal tubule. This process filters nearly twenty percent of the plasma and non – cell elements from the blood into the inside of the nephron. The blood gets filtered under pressure through the walls of the glomerular capillaries and Bowman's capsule. The filtrate is composed of water, glucose, small proteins and ions such as sodium, potassium and chloride. The rate of filtration is approximately 125 ml/min or 180 liters each day. As the volume of blood in human body is typically about 7 to 8 liters, the entire blood in the body gets filtered approximately 20 to 25 times each day.
The amount of any substance that gets filtered is the product of the concentration of that substance in the blood and the rate of filtration. So the higher the concentration, the greater the amount filtered or the greater the filtration rate, the more substance gets filtered. The filtrate only includes small molecules and water and red blood cells are not filtered. Therefore, no blood appears in the urine under normal conditions and blood in your urine indicates a kidney problem. This filtration process is much like the making of espresso or cappuccino. In a cappuccino machine, water is forced under pressure through a fine sieve containing ground coffee; the filtrate is the brewed coffee. The arrangement of the glomerular capillaries in series with the peritubular capillaries is important to maintain a constant pressure in the glomerular capillaries, and thus a constant rate of filtration, despite momentary fluctuations in blood pressure. Once the filtrate has entered the Bowman's capsule, it flows through the lumen of the nephron into the proximal tubule.