 Hello and welcome to Physiology Open. In this video, we will talk about the concept of Gibson and equilibrium. Gibson and equilibrium explains how charged particles distribute themselves across a semi permeable membrane in the presence of another charged particle to which the membrane is not permeable. By understanding Gibson and equilibrium, we get to know why concentration of ions is different inside the cells as opposed to its outside environment that is interstitial flow and why this leads to generation of a potential across the membrane. Let's start from the very beginning like when there was no cell, only sea. So the ions are distributed throughout the whole environment. Now with the origin of a cell which is surrounded by a semi permeable membrane, things started to change. So now we have a cell separated from its surroundings by a semi permeable membrane. Now suppose initially both the sides have same ions. For sake of simplicity, we will take only two ions. Okay say on both sides, concentration of ions is same. Say 5 potassium ions on each side and 5 chloride ions also on each side. We are taking very small and arbitrary numbers here. You may think how is it possible? There will be definitely more ions in the sea. Well correct but the concept remains the same. We may start for any number of ions each side but the physical processes will remain the same that is what we are discussing here. So for ease of understanding, we are taking some numbers here. Anyways so where were we? Yeah 5 5 each of positive and negative ions on either side of the cell membrane which is semi permeable. But now inside the cell we add proteins to which the cell membrane is impermeable. We are adding inside the cell because it is the cell which will start producing the proteins. So I am adding say 6 proteins. So now what will happen is that the other ions to which the cell membrane is permeable will redistribute across the membrane. Why will they redistribute? After all their concentration is same on both sides? But see if we are talking about an uncharged molecule say suppose glucose molecules. Then it moves along only its concentration gradient until the concentration on both sides becomes equal. But for a charged substance there are two forces which govern its movement. One its concentration gradient and the other its electrical gradient. Concentration gradient depends on actual number of ions while the electrical gradient depends on the net charge. So since proteins have been added which are negatively charged even though there is no concentration gradient for the ions but the net charge on one side has changed. So there is a development of an electrical gradient. So we said initially there are 5 potassium ions, 5 chloride ions and 6 proteins this side. So we will see how much is the net charge by adding all positive and negative ions. This side there is a net negative charge of 6. Now same thing will do on the other side of the membrane. Here net charge is zero. So see due to proteins which is an impermeant ion or we can say the non-diffusable ion and an electrical gradient of 6 has been established with negativity inside the cell and positivity outside. This negativity will attract the positive ions and repel negative ions. So an electrical gradient for positive ions develops from outside to inside and for negative ions will be from inside to outside. So let's say one potassium ion moves from outside to inside. So here potassium ion will become 4 while inside it will become 6 ions. So you see now due to this difference in the number of ions a concentration gradient for them has developed from inside to outside and electrical gradient will also change. So with the decrease in positive charge outside and increase in positive charge inside there will be an electrical gradient of 4 now from outside to inside and a concentration gradient of 2 for potassium from inside to outside. But what about chloride? See we have said earlier that electrical gradient for chloride that is whether our negative ion is from inside to outside. Even with this change gradient of 4 it is still from inside to outside. So say one chloride ion moves from inside to outside. This will increase chloride ions outside from 5 to 6 and decrease an ion inside so it will become 4 here. So there is a concentration gradient established from outside to inside for chloride. So now for chloride a concentration gradient established from outside to inside of 2 while electrical gradient will decrease from 4 to 2. So at this point you see the chloride concentration gradient is balanced by its electrical gradient and similarly the potassium concentration gradient is also balanced by its electrical gradient. So the net driving forces have become 0. So what has happened at equilibrium? Concentration gradient of ions is balanced by their electrical gradient. So at equilibrium concentration of ions is different on each side. Inside potassium is more and chloride is less while outside it's opposite. Now there are certain general things which we can deduce from this distribution of ions. One keeps on an equation states that in the presence of a non-diffusable ion the diffusable ions distribute themselves so that at equilibrium their concentration ratios are equal. That is potassium inside divided by the potassium outside is equal to chloride outside divided by the chloride inside. Check whether for us it's coming okay or not. Yes 6 by 4 this side and 6 by 4 other side also. Now if we cross multiply on cross multiplying it will give us the Gibbs Tornon equation. Second number of total ions is more on the side of the presence of non-diffusable ion. You count and see this side is 16 ions and the other side is 10 ions. So basically number of osmotically active particles are more on one side of the membrane. This will lead to movement of water from outside to inside and hence cell swelling and rupture. This doesn't happen for a cell because of the presence of sodium potassium ad paste which constantly throws out more ions than what it brings in. But you can imagine what will happen when sodium potassium ad paste stops functioning. It will lead to entry of water, cell swelling and ultimately rupture. Now this difference in concentration of ions which we are seeing here between inside and outside of the cell is also seen across capillary wall since more proteins are present in plasma compared to the interstitial fluid. Thus in plasma a little more concentration of ions is there compared to interstitial fluid. Okay and finally one more point since the equilibrium occurs at the point when electrical gradient is balanced by the concentration gradient that means there remains some difference in charges across the membrane. So a potential is developed across the membrane due to this electrical difference. Now remember two things here in this example we took very small numbers to make you understand but in actuality most of the fluid remains electro neutral and there is only a small difference in charges which accumulate just near the membrane and with this small difference in charges only there is development of the potential. Second the potential generated here is passive see no ATP is acquired it is just passive redistribution of ions which generates the potential difference. But how much potential is developed? Well it depends on the concentration of ions inside and outside the membrane and on the valency of the ion. More on this will be dealt in video on resting membrane potential and Nernst equation. Thanks for watching the video if you like did do like and share the video and don't forget to subscribe to the channel Physiology Open. Thank you.