AS Biology, a bit confused

[rexsun]

Hi guys.
I'm doing chapter 8 at this moment and was confused by the sentence, on page 150, which states' If the protein concentration and rate of loss from plasma are not in balance with the concentration and rate of loss from tissue fluid, there can be a build-up of tissue fluid, called oedema.'
I understand it as saying proteins can be lost from plasma as well as tissue fluid, and when these two rates of loss do not balance, oedema exists.
But can proteins be lost from plasma through gaps in the squamous epithelium of capillaries? I feel a bit unsure because I think proteins cannot be lost from capillaries as they are too large.
Can somebody please be kind and help me out? Really confused there...

Thanks much!

 

[Muhammad Amer]

Two opposing forces control the movement of fluid between the capillaries and the surrounding tissues: Blood pressure tends to drive fluid out of capillaries, and the presence of blood proteins tends to pull fluid back (osmotic pressure). Now, many blood proteins are too large to pass through the gaps between squamous endothelium, and they remain in the capillaries. These dissolved proteins are responsible for much of the blood’s osmotic pressure (the pressure produced by the difference in solute concentration across a membrane). The difference in osmotic pressure between the blood and the interstitial/tissue fluid opposes fluid movement out of the capillaries. What the statement is trying to say is that if, for some reason (elephantiasis, weak capillary walls or other medical conditions), too much protein leaves the blood with the tissue fluid, there won't be sufficient concentration of protein to "pull" the tissue fluid back into the blood, thus it will accumulate in the interstitial space or tissue as oedema.

That is what I've understood from your question, bear in mind that I'm also a student so do seek confirmation from somebody else, or perhaps your teacher would be willing to aid.

One last thing: I'm interested in knowing what book you are talking about, so if you'd be kind enough, please tell me its title.