Considering that you have 7 to 8 liters of blood in your body, this means that your entire blood volume gets filtered approximately 20 to 25 times each day! Also, 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.
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. Renal secretion is different from reabsorption because it deals with filtering and cleaning substances from the blood, rather than retaining them. The substances that are secreted into the tubular fluid for removal from the body include:.
Many pharmaceutical drugs are protein-bound molecules thatDiagram showing the basic physiologic mechanisms of the kidney and the three steps involved in urine formation. Tubular secretion occurs throughout the different parts of the nephron, from the proximal convoluted tubule to the collecting duct at the end of the nephron.
The movement of these ions also helps to conserve sodium bicarbonate NaHCO 3. The typical pH of urine is about 6. Urine that is formed via the three processes of filtration, reabsorption, and secretion leaves the kidney through the ureter, and is stored in the bladder before being removed through the urethra. At this final stage it is only approximately one percent of the originally filtered volume, consisting mostly of water with highly diluted amounts of urea, creatinine, and variable concentrations of ions.
Privacy Policy. Skip to main content. Urinary System. Search for:. Physiology of the Kidneys. Overview of Urine Formation Urine is formed in three steps: filtration, reabsorption, and secretion. Learning Objectives Summarize the steps in urine formation. Key Takeaways Key Points Filtration involves the transfer of soluble components, such as water and waste, from the blood into the glomerulus.
Reabsorption involves the absorption of molecules, ions, and water that are necessary for the body to maintain homeostasis from the glomerular filtrate back into the blood.
Secretion involves the transfer of hydrogen ions, creatinine, drugs, and urea from the blood into the collecting duct, and is primarily made of water. Blood and glucose are not normally found in urine. Key Terms urine : A liquid excrement consisting of water, salts, and urea, which is made in the kidneys then released through the urethra. Glomerular Filtration Glomerular filtration is the renal process whereby fluid in the blood is filtered across the capillaries of the glomerulus.
Learning Objectives Explain the process of glomerular filtration in the kidneys. Key Takeaways Key Points The formation of urine begins with the process of filtration. Fluid and small solutes are forced under pressure to flow from the glomerulus into the capsular space of the glomerular capsule.
Blood entering the glomerulus has filterable and non-filterable components. Filterable blood components include water, nitrogenous waste, and nutrients that will be transferred into the glomerulus to form the glomerular filtrate. Non-filterable blood components include blood cells, albumins, and platelets, that will leave the glomerulus through the efferent arteriole. Glomerular filtration is caused by the force of the difference between hydrostatic and osmotic pressure though the glomerular filtration rate includes other variables as well.
Key Terms glomerulus : A small, intertwined group of capillaries within nephrons of the kidney that filter the blood to make urine. What organ system does the liver belong to? What is the major function of the kidney? What role do the kidneys play in diabetes type 2? What is the function of the renal artery and the renal vein? See all questions in Excretory System.
Impact of this question views around the world. You can reuse this answer Creative Commons License. Glomerular filtration is the renal process whereby fluid in the blood is filtered across the capillaries of the glomerulus.
Glomerular filtration is the first step in urine formation and constitutes the basic physiologic function of the kidneys. It describes the process of blood filtration in the kidney, in which fluid, ions, glucose, and waste products are removed from the glomerular capillaries. Many of these materials are reabsorbed by the body as the fluid travels through the various parts of the nephron, but those that are not reabsorbed leave the body in the form of urine. Blood plasma enters the afferent arteriole and flows into the glomerulus, a cluster of intertwined capillaries.
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