Interstitial fluid
The interstitial fluid is essentially comparable to plasma. The interstitial fluid and plasma make up about 97% of the ECF, and a small percentage of this is lymph.
Interstitial fluid is the body fluid between blood vessels and cells,[7] containing nutrients from capillaries by diffusion and holding waste products discharged by cells due to metabolism.[8][9] 11 litres of the ECF is interstitial fluid and the remaining three litres is plasma.[6] Plasma and interstitial fluid are very similar because water, ions, and small solutes are continuously exchanged between them across the walls of capillaries, through pores and capillary clefts.
Interstitial fluid consists of a water solvent containing sugars, salts, fatty acids, amino acids, coenzymes, hormones, neurotransmitters, white blood cells and cell waste-products. This solution accounts for 26% of the water in the human body. The composition of interstitial fluid depends upon the exchanges between the cells in the biological tissue and the blood.[10] This means that tissue fluid has a different composition in different tissues and in different areas of the body.
The plasma that filters through the blood capillaries into the interstitial fluid does not contain red blood cells or platelets as they are too large to pass through but can contain some white blood cells to help the immune system.
Once the extracellular fluid collects into small vessels (lymph capillaries) it is considered to be lymph, and the vessels that carry it back to the blood are called the lymphatic vessels. The lymphatic system returns protein and excess interstitial fluid to the circulation.
The ionic composition of the interstitial fluid and blood plasma vary due to the Gibbs–Donnan effect. This causes a slight difference in the concentration of cations and anions between the two fluid compartments.
https://en.wikipedia.org/wiki/Extracellular_fluid#Interstitial_fluid
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