Collecting Duct (CD): Transport Mechanism

00:01 The last little bit that we have in a nephron. Never thought we will get here and here we are already. One of those things during the journey at sometimes feels like it is perhaps a little taxing but once we actually get here, then it is not so bad and what do you want to do later is keep reviewing, reviewing, reviewing, be able to answer the questions that I have been posing at you. Be able to identify the patients that I have been giving you over and over again and that way the more number of times you go through this the easier it becomes and the more that you are able to integrate the material as needed. Where we are now is an epsilon or collecting duct. We took a look at this picture earlier once again quickly recap. We have the urine luminal side on the left. On the right is your blood interstitium. That green cell that you are seeing there is, in fact, the epithelial cell.

00:58 One will be the principal because we are in the collecting duct, the other one would be in fact your intercalated. Next what kind of receptors do we have here when dealing with two other major hormones? We have an aldosterone receptor and we have an ADH receptor known as V2 receptor. Aldosterone is what our topic here will be as we peruse through this lecture series and aldosterone could potentially work on two sides of the cell. If it is on the side of the luminal membrane or apical, it then works on the ENAC.

01:30 What does that mean to you again? Epithelial Sodium Channel whereas if it works on your sodium-potassium pump that would be on the basolateral all in the hopes of doing what, please? Reabsorption of sodium. What kind of effect does aldosterone have on hydrogen? It gets rid of it. So therefore if you have excess and you have an increase in pH. It gets rid of your potassium, what kind of effect would that have? Obviously, if there is too much aldosterone, it results in hypokalemia. Once again if you have hypokalemia, then how is your patient going to present? Tired, fatigued because of muscles that are not working properly.

02:07 Finally, get difficult to reach the threshold, and the heart obviously is an issue. Collecting tubule when dealing with the principal cell let us look at sodium and potassium. If we are dealing with intercalated, the hydrogen. Aldosterone results in increased sodium reabsorption. And then ADH here as you see of two kidneys does as the V2 receptors. ADH, as we talked about earlier, is responsible for strictly inserting your aquaporin and as long as what the pending is to the osmolarity of the plasma. The example that I gave earlier was severe sweating. You taste yourself and you taste salty, but you are losing more fluid, are you not? So, therefore, it is hypotonic loss of sodium. When you are losing that amount of fluid, then you know that your plasma osmolarity increases. Your osmoreceptors are very sensitive up by the hypothalamus resulting in release of ADH, which then flows down in neurophysins in your infundibulum into the posterior pituitary and out it comes. Are we clear? It also has effect on your V1 receptors and vasopressin is what it is called.