human anatomy and physiology here we are in episode three on the urinary system and fluid electrolyte and acid base balance in this particular episode we are focused in on the regulation of water in the human body as we've spoke about previously the human body consists primarily of water uh there are two main compartments with the in cellular fluid and the extracellular fluid on this particular slide now we are looking at the regulation of both water and electrolyte levels in the intracellular fluid what you can see here is that uh there are tight regulation of both Water and Electric levels regulation is controlled mainly by mechanisms that regulate uh the movement of solutes and water between the extracellular fluid and the intracellular fluid notably on the screen here you can see that lipid biolayer also known as a plasma membrane and that's what separates out both the intracellular fluid and the extracellular fluid compartments and thereby can regulate their fluid composition you can also note that there is a movement of solutes across the membrane and to accomplish this there are pores or ion Chann channels and active transport mechanisms that allow for ions such as sodium and potassium to move across the membrane while at the same time preventing larger proteins from doing so notably an unequal concentration of electrolytes on either side of a cell membrane will create an electrical charge difference on this next slide we look at the regulation of water and electrolytes in the intracellular fluid which depends on electrolyte balance and fluid balance and so an imbalance in fluid balance will cause an imbalance in electrolyte balance here what you can see if we follow this flow chart is that when you have a change in the concentration of sodium ions in the intracellular fluid such as a decrease this has an immediate impact on the interstitial fluid osmotic pressure which will also decrease as a result it becomes hypotonic compared to the osmotic pressure in the intracellular fluid as a result water will move by the process of osmosis from the interstitial fluid into the intracellular fluid I'm going to jump forward now to look at another diagram which highlights the extracellular fluid and the intracellular fluid and how the plasma membrane has pumps that facilitate the exchange of sodium and pottassium the sodium pottassium pump is showing here it requires ATP and the breakdown of ATP into a Denine diphosphate and inorganic phosphate and what this does is it is going to allow for the transfer of sodium out of the cytoplasm and into the extracellular fluid what you'll also notice is that the pump can transfer potassium out of the extracellular fluid and into into the cytoplasm although sodium and potassium can leak through pores into and out of cells respectively the high levels of potassium and low levels of sodium in the intracellular fluid are maintained by these sodium potassium pumps in the cell membrane once again I'd like to highlight that this is a form of active transport as these pumps use energy supplied by the breakdown of ATP to pump sodium out of the cell and to allows pottassium into the cell this next chart highlights four types of pressure that really modulate fluid and electrolyte levels in the plasma and interstitial fluid and how fluids will shift I've defined all four of these types of pressure at the bottom of your screen but essentially we have interstitial fluid hydrostatic pressure which is generated by the water in the interstitial fluid itself we have blood hydrostatic pressure which is generated by the water that's inside of the capillar iies that makes up the proportion a proportion of blood uh and as we've discussed in a preceding lecture episode The hydrostatic pressure within a vessel is highest at the arterial end when we're talking about capillary exchange we also have blood colloid osmotic pressure and that is generated largely by plasma proteins and retain contains water like a spongee we gave uh the example of the leaking bucket uh that has one Sponge versus has 10 sponges and how uh the bucket that has more sponges will retain more water this is Ain or it's an analogy to this osmotic pressure we also have interstitial fluid coloid osmotic pressure and this uh usually sits on close to zero uh millimeters of mercury and that's due to a lack of proteins that is typically um within the interstitial fluid so if we take each of these four pressures and we look at uh the comparing uh the sum of the hydrostatic pressures and the osmotic pressures you can see that when the blood hydrostatic pressure com combined with the interstitial fluid col osmotic pressure when those two are summed together and are equal to that of the interstitial fluid hydrostatic pressure and the blood Co coloid osmotic pressure that in fact you have no transfer of water between uh these compartments when they do not equal each other that is in fact when there's a net transfer of fluid in fact when the blood hydrostatic pressure and the inter fluid choid osmotic pressure are summed together and they are greater than the other two types of pressure then in fact fluid will shift out of the blood into the interstitial fluid in contrast when the blood hydrostatic pressure and the interstitial fluid coloid osmotic pressure are less than that of the interstitial fluid hydrostatic pressure and the blood coloid osmotic pressure that is when fluid will shift out of the interstitial fluid into the blood this is similar to what we observe uh in the kidneys with the um movement of fluid um that uh that exists and we've spoke about uh previously so that brings us now uh to this next example which just summarizes what we've talked about um in the preceding slides and we've also highlighted this in the preceding lecture episode once again when we're at the arterial end of a capillary and we're looking at um the capillary exchange and the likelihood of fluid moving out of or into the capillaries what happens is that as blood flows through the arterial end the capillary um due to um a high hydrostatic uh pressure within the blood fluid will tend to move out of the capillaries you will recall that the interstitial fluid coloid osmotic pressure tends to be quite low uh close to zero and therefore it's really relying on that BHP to be very high or that blood hydrostatic pressure um a very high blood hydrostatic pressure at the arterial end of the capillaries it was what is going to facilitate the movement of once again movement of fluid out of the capillaries on the opposing end when we're looking at the Venus end of the capillary so blood has flown through we've had some level of capillary exchange it equalizes out at the Venus end of the capillaries in fact the blood hydrostatic pressure tends to be much lower and the osmotic pressure now tends to be higher in this case uh what you see is that uh the fluid will move into the capillaries and this last slide really just highlights um a a clinical example so what we have here um is edema which is a classic example of fluid imbalance and in this case has occurred due to an allergy this may occur in any organ or tissue but common locations include the lungs brain uh and lower back and this POS a possible cause of Edema may be a decrease in the osmotic pressure within the blood due to a decreased concentration of plasma proteins you may also have edema when you have an increase in capillary blood pressure or that blood hydrostatic pressure due to the venous congestion of heart failure lastly if you have a retention of electrolytes especially sodium in the interstitial fluid this can also lead to edema and this may be caused by an increase in aldosterone secretion or kidney disease