Reabsorption in the PCT, Loop of Henle, and DCT – Urine Formation (Nursing)

00:01 So now let's take a look at reabsorption as it occurs through the different parts of the nephron.

00:08 First, we start with the proximal convoluted tubule, which is the first area after the glomerulus.

00:15 The proximal convoluted tubule is the site of most of the absorption of the Nephron.

00:21 All nutrients such as glucose and amino acids will be reabsorbed in this part of the Nephron.

00:29 About 65% of the sodium ions and our filtrate as well as water will also be a reabsorbed in this area.

00:39 Other ions, almost all of our uric acid and about half of their urea in the filtrate will also be reabsorbed here.

00:49 So if we take a look at this or to recap we're going to have secondary active transport of our nutrients like glucose and amino acids with sodium ions on the apical side of the cells.

01:05 Also in these cells on both the apical and basolateral side.

01:10 We have aquaporins which are going to allow for the transport of water across the cell.

01:18 Lastly lipid soluble substance are able to move directly through the cell by just passively diffusing into and out of the cell.

01:28 And also we have the paracellular route which allows for transport of certain substances between the cells.

01:36 On the basolateral side, we also have sodium potassium atpase pumps which allows for the movement of sodium and potassium out of these cells toward the peritubular capillaries.

01:52 After the proximal convoluted tubule we have the nephron loop.

01:57 The nephron loop is made up of two limbs.

02:00 First, you have the descending limb where mostly water will leave but solutes are impermeable and cannot get out.

02:09 We also have an ascending limb on the other side of the loop where this time water is impermeable and only solutes can go in and out.

02:20 The ascending limb has both, has two segments to it.

02:25 There's a thin segment which is going to be passive to sodium movement and a thicker segment, which is going to be passed at to sodium potassium and chloride ions by way of a sodium potassium to chloride symporter.

02:41 Also, there's a sodium and hydrogen ion and antiporter that's going to transport sodium into the cells.

02:50 Also some sodium can pass into the cell by way of the para cellular route found in the a sending limb portion of the nephron loop.

03:02 After the nephron loop we have the distal convoluted tubule as well as the collecting ducts.

03:10 Here, unlike in the proximal convoluted tubule where reabsorption was obligatory reabsorption here is going to be hormonally regulated.

03:21 The main hormones that are going to regulate this are antidiuretic hormone and aldosterone.

03:28 First starting with antidiuretic hormone.

03:30 It's released by posterior pituitary gland and causes the principal cells of the collecting duct to insert aquaporins in their apical membrane.

03:41 This increases water reabsorption.

03:45 An increased level of antidiuretic hormone will cause an increase in the amount of water that is reabsorbed from the filtrate back into the blood.

03:57 The second hormone is aldosterone.

04:00 Aldosterone is also going to target the collecting ducts and the principal cells in these collecting ducts as well as the distal convoluted tubule.

04:11 Aldosterone promotes the synthesis of apical, sodium and potassium channels as well as basolateral sodium potassium atpase pumps.

04:22 So that sodium may be reabsorbed.

04:25 With the reabsorption of sodium water will follow behind it.

04:31 This results in very little sodium actually leaving the body in the form of urine.

04:38 Without aldosterone, we would lose about 20 percent of our filtered sodium.

04:44 This however is incompatible of life.

04:47 The main function of aldosterone, however, is to increase our blood pressure and also to lead to the secretion of potassium thus decreasing our blood potassium levels.

05:01 Another important molecule that is important for reabsorption is the atrial natriuretic peptide.

05:09 This actually reduces blood sodium levels and thus results in a decrease in our blood volume, which will subsequently result in a decrease in our blood pressure.

05:21 This substance is released by the cardiac atrial cells.

05:26 If the blood volume or the blood pressure is high.

05:31 Finally, we have the parathyroid hormone.

05:35 Recall the parathyroid hormone is very important for the maintenance of our calcium levels in our body.

05:43 This hormone will act on the distal convoluted tubule to increase calcium reabsorption when calcium blood levels are low.