Source: Video and Images Created by Amanda Soderlind
Welcome to this lesson on reabsorption. In this lesson today, we will be discussing the role of reabsorption in urine formation. So reabsorption is also sometimes referred to as tubular reabsorption. So you might also hear it that way as well. So basically, reabsorption is the second step in urine formation.
So the first step is filtration, then comes reabsorption, and then come secretion. So it's a three-step process. And in this lesson, we're going to be focusing on this process right here of reabsorption.
So basically, urine formation as a whole, it's purpose is to basically make sure that only necessary products are excreted from the body. So urine formation takes place in the kidneys. And the nephrons will filter blood and produce urine in this three-step process. And that makes sure, as I said, that only necessary products are excreted from the body. So the body's not getting rid of any water or solutes that it actually should be keeping.
So in the step of urine formation called reabsorption, water and solutes are filtered from the blood in the first step called filtration. And then they move into the rest of the nephron here. So water and other solutes sometimes are really, really valuable, and our body doesn't want to get rid of them. So what needs to happen is that they need to be reabsorbed back into the blood so that the body can retain them.
So reabsorption takes place across the walls of the proximal tubules. So this here is the proximal tubule. So reabsorption is taking place across the walls of this proximal tubule here. And the walls of the proximal tubule are very, very thin. They're about one cell thick.
So solutes and water will leak out or be pumped out of the nephron tubule and will then leak into the peritubular capillaries. So we have these peritubular capillaries that kind of interweave within the nephron here. And then from there, they will be returned to the bloodstream. So then any remaining solutes that didn't leak back into the bloodstream will become a part of urine.
So usually during this step of reabsorption-- like I said, it mostly happens here in the proximal tubule-- it returns the vast majority of water and solutes, such as glucose, amino acids, and sodium, back to the blood. Between 95 to 100% of those solutes get returned back into the blood because our body needs them. But any remaining ones that do not get returned back to the blood will then become a part of urine. So this lesson has been an overview on the reabsorption stage of urine formation.
