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can anyone tell me the difference? specifically in the case of liquid exchange in the capillaries. Thanks!
Prophecies said:Osmotic pressure describes the tendency of water to move into a solution via osmosis; hydrostatic pressure describes the tendency of water to stay where it is and not move out of solution (hydro = water, static = not moving). They are opposites...to help you remember, EK says:
"Students often think about osmotic pressure as the pressure pulling into a solution, and hydrostatic pressure as the pressure pulling out of a solution. Although this is technically incorrect because pressure is a scalar and has no direction, thinking about osmotic pressure in this way may give you some intuition about it."
As far as membrane transport/liquid exchange goes, here is how to think of it (from one of my physiology textbooks):
Imagine you have a container divided into into two compartments by a membrane permeable to water, but impermeable to some solutes. When there is only water in the container, the water moves back and forth across the membrane in equal amounts, so that the net water movement is zero.
If a solute to which the membrane is impermeable is added to one compartment of the container, the activity of the water molecules on the side containing the solute is reduced, so that the flow of water from that side is reduced. The flow of water into the solute-containing side continues as before, so that there is a net flow of water into the solute-containing side, which creates a hydrostatic pressure difference (the pressure required to keep the water static has decreased on one side). The osmotic pressure of the solution could be measured by determining the pressure required to move the water from one side to the other.
This principle is the same for the capillaries of the body. Hope this helps!
Prophecies said:Osmotic pressure describes the tendency of water to move into a solution via osmosis; hydrostatic pressure describes the tendency of water to stay where it is and not move out of solution (hydro = water, static = not moving). They are opposites...to help you remember, EK says:
"Students often think about osmotic pressure as the pressure pulling into a solution, and hydrostatic pressure as the pressure pulling out of a solution. Although this is technically incorrect because pressure is a scalar and has no direction, thinking about osmotic pressure in this way may give you some intuition about it."
As far as membrane transport/liquid exchange goes, here is how to think of it (from one of my physiology textbooks):
Imagine you have a container divided into into two compartments by a membrane permeable to water, but impermeable to some solutes. When there is only water in the container, the water moves back and forth across the membrane in equal amounts, so that the net water movement is zero.
If a solute to which the membrane is impermeable is added to one compartment of the container, the activity of the water molecules on the side containing the solute is reduced, so that the flow of water from that side is reduced. The flow of water into the solute-containing side continues as before, so that there is a net flow of water into the solute-containing side, which creates a hydrostatic pressure difference (the pressure required to keep the water static has decreased on one side). The osmotic pressure of the solution could be measured by determining the pressure required to move the water from one side to the other.
This principle is the same for the capillaries of the body. Hope this helps!
crys20 said:No offense dude but i hope you are not going into academia cause that is the most confusing explanation of a extremely simple subject taht i have ever seen.
crys20 said:I wouldnt say dont worry about it rather i would understand it as its a crucial topic in all of physio but dont worry it is easy.
just picture you have 2 containers seperated by a semipermeable membrane that only allows water across. Now you have a Left and Right side ( one on each sideo fthe membrane. Now say your goal is to see how much water you can get into the Right box so there are 2 ways you can get water into that Right sided compartment: So before taht you start by adding water into the left sided compartment and your goal is to get as much water from the left side to the right side through the membrane so first,
1. All that water you added to the left compartment is sitting there, lets say there are 10 gallons and you ahve 0 in the right side- so bam its like a flood gate, water will flow fast through the membrane from the left to right side since things flow from high to low( think of a water dam and what would happen if you took down the dam all of a sudden-the water would rush from one side across to the other side because all that water was building up on one side) ok so this is HYDROSTATIC pressure- when there is a difference in quantiity that forces flow from high to low.
now soon water will finish flowing when there are 5 gallons on each side, no more flow but yous till want more water on the right side so hwo do you do taht?
2. dump a ****load of salt into the right sidea nd make it mroe concentrated which will create a hypertonic solution on the right compared to pure water on the left so what will water due to equal things out? the salt sucks some water from left to right to make each side an equal tonicity or concentration---this "suckign" force is what is called Osmotic pressure.
So combine 1 and 2 and you get both a hydrostatic(driven by a High to low gradient force) and a osmotic(driven by a sucking action of solute driven by equalization of tonicity) and there you ahve it.
You're KIDDING me. I saw several questions on hydrostatic pressure on the MCAT. My sincere advice is DISREGARD THIS ADVICE ENTIRELY. The questions on hydrostatic pressure made me glad I studied ChemE.Prophecies said:I really wouldn't worry about the hydrostatic pressure part--it isn't very important for the MCAT. All you need to know about the topic is that osmotic pressure is used to move water into a solution, and you need to know the formula for osmotic pressure. Don't stress out about hydrostatic pressure
Prophecies said:Three things:
1.) To the person who said I shouldn't go into academia--like I said (but you obviously didn't read), that explanation did not come from me personally, because I don't know how to explain it accurately. All I did was provide sources (from ExamKrackers and from my physiology text book) to help describe the pressures. The explanation from the textbook includes a diagram which I could not post up. Sorry about that...no need to be so harsh.
2.) To the person who said nitpicked about hydrostatic pressure...I believe EK mentions that thinking of osmotic pressure as "pulling out" and hydrostatic as "pushing in" is not entirely accurate, but the best way to think of it for the MCAT. I also put that in my post...I did not mean to be misleading...only help people remember stuff for the MCAT.
3.) Hydrostatic pressure is not an important concept for the MCAT...osmotic pressure is. I think most people would agree that, instead of being confused about a subject that likely won't appear on the MCAT, one should focus on the topics that most certainly WILL be on the MCAT. To me it just seems like a waste of all that time to memorize something that won't be on the test. Yes, hydrostatic and osmotic pressures are VERY important concepts in physiology, but the poster is referring to the MCAT, not physiology.
Anyway, the OP understands the concept now and that is all that matters. Good luck to you!