Colloid Osmotic Pressure

Colloid Osmotic Pressure is a process that happens at the capillary beds to help ensure that we maintain fluid volume within our blood vessels and as a result adequate blood pressure we lose fluid volume we lose pressure in this picture we see an arterial entering a capillary bed and a venule leaving the capillary bed as we discussed in a previous video there's higher pressure on the arterial end of the capillary bed and lower pressure on the venule end of the capillary bed at the capillary blood bed is where exchange occurs oxygen leaves the capillary glucose ions hormones any number of things needing to gain access to our tissues and cells of those tissues they will move from the capillary bed into the interstitial space and then into the cells so transport happens a number of ways there's paracellular transport between endothelial cells there's transport across the endothelial cells and there's transport via fenestrations in the capillary bed and what we're going to talk about here oh bulk flow transport it's going to be fluid leaving the capillary bed accompanying the fluid is going to be everything i just suggested ions hormones glucose and oxygen so if we look at this this is an example of bulk flow fluid is leaving and all of the constituents within the blood plasma i shouldn't say all of it but a number of the constituents of the blood plasma that are needed by the tissues and the cells the force that is pushing this fluid out is the hydraulic pressure or the blood pressure coming down the arterial end now what we see in orange here are plasma proteins plasma proteins are too large to leave the capillary bed certainly there are some proteins that do leave the bloodstream via the capillary bed via exocytosis but we're not concerned about those we're talking about these plasma proteins which i have drawn in orange right here they are not going to be filtered and filtered is the movement of substances from the capillary bed into the interstitial fluid the plasma proteins will not get filtered via this bulk flow because they are too large so one example that the silverthorne textbook actually gives for this type of capillary bed are soaker hoses in a garden that have very tiny perforations that just let water seep out of those hoses and that's the same idea here one thing we have to understand though is that there is blood pressure helping this just like there's pressure moving down a hose so once we lose all of that fluid from the capillary bed that fluid is in the interstitial space and the plasma proteins remain in the capillary bed we now see them at the venule end of the capillary bed now i want to back up to this previous slide here i'm not suggesting there are now more plasma proteins in the venous end of that capillary bed but there is a higher concentration because we've lost the water so i just don't know how to draw a higher concentration other than put in place more plasma proteins so what i'm trying to suggest right here is that they there is a higher concentration of plasma proteins due to the loss of water from the arterial end of the capillary bed now because there's a higher concentration of plasma proteins here and when i say higher it's certainly higher than was in the arterial end of the capillary bed but also higher than we see in the interstitial fluid and certainly i don't have any solutes drawn in the interstitial fluid but it's going to be loaded with solutes but there's going to be a higher concentration of solutes due to the plasma proteins in the venous end of this capillary bed and that high concentration of solutes is going to draw water back into the capillary bed so we don't lose that fluid volume it's being drawn back into the capillary bed via the process of osmosis where water is moving to an area of high soluble concentration the solutes in this case are the plasma proteins this is significantly important in maintaining blood pressure that is colloid osmotic pressure at the capillary beds is significantly important in maintaining the fluid volume in our vascular system and this may not seem like a big deal because we're just dealing with one capillary bed here but there are millions if not trillions of capillary beds throughout the whole body that are constantly losing fluid due to bulk flow and that is fluid that we need to get back into our blood vessels to maintain blood pressure if we lose blood volume the volume of the fluid decreases pressure is going to decrease accordingly which we do not want to happen so colloid osmotic pressure is the mechanism by which our cardiovascular system maintains blood pressure.