unit 2 aqa biology A level 2nd june

could some clarify tissue fluid for me that would be great

Tissue fluid is formed as a result of high blood pressure (also called hydrostatic pressure) at the arteriole end of the capillaries (the end the blood first passes through), which forces fluid out of the capillaries - this is tissue fluid, which is made up of glucose, amino acids, fatty acids, oxygen and salts. Large proteins remain in the capillaries as they're too large to get out.

The return of tissue fluid happens due to a fall in hydrostatic pressure at the venous end of the capillaries, so fluid is forced back into the capillaries - this time it contains waste materials and CO₂, picked up from the tissues (it delivered the useful components to the tissues). As well as the lower hydrostatic pressure, a reduction in water potential inside the capillaries (due to the proteins that remained there) causes water to enter the capillaries via osmosis.

Hope that helps :smile: