Welcome back. So, today we want to talk about the renal
system, and we're, this is going to be the third of our lectures about the renal
system. And the things that we want to discuss
today, are, is, how the kidney then, is uses the tubular, the tubular
transporters to reabsorb materials that is to take it from the filtrate back into
the body or into the blood. And also to secrete materials bypassing
the filtration route that we talked about the last 2 times.
So, the specific learning objectives are first that we're going to explain the
importance of the peritubular capillary in the kidney cortex.
The secondly, we want to describe the cellular mechanism for transport of
materials from the tubule to the interior of the tubule, that is within the lumen,
across the cells and into the blood. And and we're going to use the glucose
transport as our, as our example. And then very briefly, we'll talk about
moving bicarbonate across this, this system.
Third, we want to talk about transcellular transport, that is the
movement across cells versus movement between cells, the paracellular pathways.
And this is the way that water, then, will move across this particular region
of the kidney. And and we'll also talk very briefly
about the solvent drag of potassium. Fourth, we will define the maximal
transport rate and the transport threshold for, for items that are using
transporters. And five, we'll dis, we'll consider
secretion. And secretion only very, very brief
briefly and then also we'll talk about secretion, in particularly secretion of
potassium, and again very briefly. So let's, let's revisit then our tubule
and that's what's drawn here. So we have the afferent arteriole, which
is feeding into the glomerulus, and that's our first capillary bed.
And that first capillary bed is drained by a second arteriole, and that's the
efferent arteriole. And the blood then drains into a, into
the, the second capillary bed, which is called the peritubular capillary.
And the peritubular capillary runs along the to, the renal tubule within, within
the the the kidney. We also have the, you know, tubule, and
that's what's diagrammed here. And around circling, around the
glomerulus, we have Bowman's capsule, and that's this.
And then from Bowman's capsule, we enter into the rest of the renal tubule.
And this is, the first region is the proximal convoluted tubule.
And then we'll go through the loops of Henle and eventually lead to the distal
tubules and, and the collecting duct and then out through the, the ureter.
So the process is, that we're talking about is the beginning between the
glomerulus and the in Bowman's capsule we have this filtration.
And the filtration will move solutes and water into the lumen of the renal tubule.
And we know that that's going to be governed by specific pressures, and
that's going to be hydrostatic pressure minus the oncotic pressures.
So now we want to move materials from the renal tubule back into the blood.
And this is going to be very important, because within 24 minutes, we can
completely exhaust the cardiovascular system if we do not bring the fluids the
water in particular back into the, into blood.