we're talking uh taking a look here at part four uh and this is on page 71 and we're still continuing on now with the cells we're talking about passive transport and i'm going to show you a gross anatomy version of this where i've uh i've drawn a little picture of the heart here as you can see it's a little valentine and the heart pump the heart is a mucu muscular system it creates pressures with each um stroke volume of the heart we get a stroke and then we get a rest and we get a stroke and we get a rest and on the stroke we get usually somewhere in the vicinity of about 114 millimeters of mercury and the rest it drops down to about 75 the mean arterial pressure if you take um a third of the difference 13 and add it to the 75 you get 88 millimeters of mercury sometime in 20b i will be asking you to learn how to do that but right now i'm just doing it for you so you can see that's that's the mean arterial blood pressure and we're coming down the arterial system here we're coming down to a capillary bed uh we're off in the tissue somewhere where we have metabolizing cells okay so at this end of the capillary uh bed right here you can see that we've diminished the um mean arterial blood pressure to 55 millimeters of mercury over on this side on the venous side we drop off considerably to 10 millimeters of mercury pressure out in each case and then we have an osmotic pressure coming back in because there's so much protein in the blood in which we have 25 millimeters of mercury really pretty much constant osmotic pressure across the membrane here okay so over at this end where the hydrostatic pressure or the blood pressure is greater we're going to win and we're going to be having filtration of nutrient-rich solutes and solvent coming out there's water there's oxygen and then there's things that are dissolved and things that get transported across but generally speaking it's all dissolved and coming through okay and then over here at this side we have cells that have completed their metabolism and they have co2 and urea and other things to pass back and because the pressure from the inside of the blood vessel is so low that means the osmotic pressure is going to win and we get the cleaner okay we have capillary beds all over the place so these cells are near the venous end of somebody's capillary system these cells are over here by this venous side but they're also next to an arterial side somewhere so that's the gross anatomy here we are at the cellular anatomy and we have something that i refer to then as tonicity that's what we're supposed to be learning about in this uh part of the book here and we're looking actually at page 71 for this and so we have three different types of solutions here one solution right here this is the way a red blood cell is supposed to look it's round it's sort of dimpled in the middle where there used to be a nucleus and there is no one there is one no longer and so it looks like a little necco wafer and it's filled with hemoglobin and this is the relaxed look of a red blood cell and in this scenario we have something that's referred to as the isotonic state isotonic means that the tonicity or that is to say the electrolytes on one side of the membrane has the same sort of osmotic force as the electrolytes on the inside okay so that means that the movement of water across the membrane is more or less even in both directions so the cell can take on nutrients and it can also give out waste products it can also signal in an outward direction if necessary okay so that's the nature of the cell these cells don't really signal very much but they they do need to have a certain sort of flexibility in their size they have to be at this sort of isotonic state okay then we can change the solution and we'll change the dynamics of the membrane so in this case we have a solution that is um going to be very high in electrolytes and we call this one hypertonic hypertonic is sort of like your salad dressing which is a lot spicier and saltier than water okay so if you were to put your carrot sticks or your celery sticks into a solution like this a hypertonic solution that might be very salty and spicy then the water from inside the cells within the carrot or the celery will leave and we'll get this shrunken sort of looking uh cell right here where it's gone from this nice relaxed fall state to this very shrunken size it's diminished the water has left okay so then we move on to this scenario in which here is our little dimpled red blood cell and here's our red blood cell becoming very puffy and oversized and swollen and we call this solution hypotonic hypo meaning less than and so we have less tonicity hypotonic solution so there's perhaps just water here or there's water and very little electrolyte and so the water is leaving i'm sorry the water is moving from the outside and entering the cell it's moving down its diffusion gradient and the cell is becoming puffy and swollen okay so that's that particular scenario then we move on to active processes and we'll we'll consider that next