Where is filtrate made

Note that the kidneys filter much more fluid than the amount of urine that is actually excreted about 1. This is essential for the kidneys to rapidly remove waste and toxins from the plasma efficiently. Reabsorption is the movement of water and solutes from the tubule back into the plasma. Reabsorption of water and specific solutes occurs to varying degrees over the entire length of the renal tubule.

Bulk reabsorption, which is not under hormonal control, occurs largely in the proximal tubule. Some substances can also pass through tiny spaces in between the renal epithelial cells, called tight junctions. As filtrate passes through the nephron, its osmolarity ion concentration changes as ions and water are reabsorbed. Finally, in the distal convoluted tubule and collecting duct, a variable amount of ions and water are reabsorbed depending on hormonal stimulus.

The final osmolarity of urine is therefore dependent on whether or not the final collecting tubules and ducts are permeable to water or not, which is regulated by homeostasis. Reabsorption throughout the nephron : A diagram of the nephron that shows the mechanisms of reabsorption. Hydrogen, creatinine, and drugs are removed from the blood and into the collecting duct through the peritubular capillary network.

Tubular secretion is the transfer of materials from peritubular capillaries to the renal tubular lumen; it is the opposite process of reabsorption. This secretion is caused mainly by active transport and passive diffusion. Usually only a few substances are secreted, and are typically waste products. Urine is the substance leftover in the collecting duct following reabsorption and secretion. The mechanisms by which secretion occurs are similar to those of reabsorption, however these processes occur in the opposite direction.

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. The glomerulus then, is this really loopy structure; there's a lot of spinning that goes on here, then we branch off again, and this gives us the same arteriole, this is the same vessel we just started off with, so we're going this way, and spinning around and coming out, as one single vessel, but we call this part of it, the "efferent" arteriole: "efferent," meaning that we have left the glomerulus.

And that of course leaves this ball-like structure over here, that's going to be known as the glomerulus. Now the thing about the glomerulus that's really interesting: it's the main site for filtration, where we take blood that came in from the renal artery, and we push out a whole bunch of fluid, that we're then going to take out some ions, and some water, and some waste, and we'll get rid of the waste or the extra ions.

The glomerulus is where we take blood and turn it into filtrate, and let the rest of the blood flow on. So this efferent arteriole is gonna turn into a capillary, and then it's gonna go into venules, and then collect back, and come out as the renal vein; we'll talk about that in a later video, when I talk about other parts of the nephron. The glomerulus though, just leaks out fluid, and it needs to be caught somewhere.

That fluid that leaks out is caught in a capsule, that's kind of hugging the glomerulus right here. So I'm gonna draw it, like that, and it kinda keeps going this way, and this is gonna continue on, into the rest of our nephron, but this thing right here, it's a capsule, and actually it has a name; it's named after a British scientist, "Doctor Bowman," so we call this, "Bowman's Capsule.

The inside right here is just open space, so they call it, "Bowman's Space" as well, so it's just space that's gonna collect our filtrate. So at this point, you should be asking yourself, "Why is it that we're gonna have fluid leak out here? So the point where the arteriole meets Bowman's Capsule, there's a lot going on. Recall, that when we have a vessel, I'll draw half of it, like that, right there, and it's kind of going this a way, okay, so that's our vessel that's right here.

This vessel's got a lot of good stuff, like our red blood cells, our white blood cells, platelets, some really really big proteins, so I'm just gonna draw something really big, right here; that's a giant protein, and it's not gonna leak out into our Bowmans' Capsule.

So, this stuff kinda moves along that way, then again, we've got other things like ions, so I'm gonna write, "Sodium" right there.