About the kidneys , you have any doubts, please click on this sentence, I'll give you the answer
Some substances are secreted from the plasma into the lumen by the cells of the nephron. Examples of such substances are ammonia (NH3). As in reabsorption, there are transporters on the cells that can move these specific substances into the lumen.
Now let's put all of these processes -- filtration, reabsorption and secretion -- together to understand how the kidneys maintain a constant composition of the blood. Let's say that you decide to eat several bags of salty (NaCl) potato chips at one sitting. The Na will be absorbed into your blood by your intestines, increasing the concentration of Na in your blood.
- Specialized proteins called transporters are located on the membranes of the various cells of the nephron.
- These transporters grab the small molecules from the filtrate as it flows by them.
- Each transporter grabs only one or two types of molecules. For example, glucose is reabsorbed by a transporter that also grabs sodium.
- Transporters are concentrated in different parts of the nephron. For example, most of the Na transporters are located in the proximal tubule, while fewer ones are spread out through other segments.
