People tend to think about blood as this red liquid.  Actually, the red part isn't liquid at all.  The liquid portion of the blood (the blood minus all the cells and cell parts) is called the plasma.  Plasma is a yellowish, clearish, somewhat thick liquid.  We saw it in lab, above the red blood cells and the white blood cells.  You will learn that blood plasma contains a lot more than just water.

    Consider for a moment that blood travels to and through all the tissues of the body.  The blood has to supply all the cells of the body with nutrients and remove all those cells' wastes.  Therefore, the blood has to become intimately associated with these cells.  I have tried to show how this might look in the schematic here.

    You see, all the cells contain fluid, the extracellular space contains fluid, and the blood contains fluid (its plasma).  All of these fluids are in communication with one another.  The plasma interacts with the fluid of the extracellular space, and the fluid of the extracellular space interacts with the fluid of the tissue cells.  Also, the plasma interacts with the fluid of the blood cells.

    If anything messes up the plasma, the extracellular space fluid and the intracellular fluid will also get messed up.  What do I mean by "messed up?"  Well, fluids have to be balanced.  One type of fluid balance is osmotic balance... if the fluid outside of a cell and the fluid inside a cell are isotonic to one another, they will be balanced and cells won't shrink or swell.  Another type of fluid balance is pH... if the blood maintains a pH that the cells can live with, all is good.  Because these types of fluid balances are crucial, they will be discussed on separate web pages under this one.

© 2006 STCC Foundation Press
written by Dawn A. Tamarkin, Ph.D.