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Tissue fluid >> osmosis/diffusion >> blood vessel ?
when I'm checking a CE question..
the question is ask how the tissue fluid move into the venule...
Part of the points said the movement is caused by OSMOSIS...
Why not DIFFUSION? As plasma is also squeezed to the tissue fluid initially..?
Thz for answering.. =]
- ?Lv 51 decade agoFavorite Answer
When we are talking about the water component of the tissue fluid moving back into the venules, it has to be osmosis.
You are right: plasma is squeezed out of the tissue fluid because of 1) the higher pressures in the arterioles, 2) the narrowing of the vessels as blood moves into the capillaries and 3) the lower pressure in the tissue fluid - thus tissue fluid gets `pressed` out of the blood into the interstitial space through positive blood pressure.
Though remember: because of the squeezing of water into the interstitial space due to high blood pressure at the arteriole end, and large stuff in the blood cannot get through the capillary wall (e.g. albumin, etc), the osmotic pressure (concentration of solutes) in the blood increases. As blood passes through the capillaries, pressure drops due to peripheral resistance, but its osmotic pressure goes up. The positive force that squeezes water out into the interstitial space is gone at the venule end, and a force that pulls water back into the blood increases - that's why at the venule end water returns to the blood from the tissue fluid via osmosis.
Does that make sense? =)