In vertebrate animal anatomy and physiology, fluids in the body could vary in composition. For instance, if you consider the plasma found in the blood vessels, it would be different from the lymph of the lymphathic vessels, different from the cerebrospinal fluid of the central canal of spinal cord and ventricles of the brain, different from the endolymph and perilymph of the inner ear, different from the interstitial fluid of nervous tissues, and different from the interstitial fluid of bone tissues, cartilage tissues, and different from the interstitial fluid of other organs. Conditions of the extracellular/interstitial fluid may vary depending on conditions and locations. Even if some scientists now consider interstitial fluid as an organ known as the "interstitium" because of its continuity in the body of an organism, there are still variations. There is no absolute sameness in the interstitial fluid.

Thanks Mayer Calma,

but how about the interstitial fluid inside the same organ like liver, kidney or heart respectivel?

J

Let's take the case of the vertebrate kidney. The kidney cortex and the kidney medulla could also have variation in terms of the components of the interstitial fluid (eg. ion concentrations). There is no absolute sameness in the condition although we have certain ranges. How much difference are we concerned about? May I know why are you asking this question?

thanks for the valuable answer. it is just out of my curiosity.

one more quick question:

what if the ions are very soluble in water? Would their concentration vary spatially in the inter-connecting interstitial fluid in one same kidney?

I agree there’s never absolute sameness lets exclude the 1% bery close to cell membranes

the aforementioned 1% is not an evidenced data just to clarify the case if we only care about the bulk part of the interstitial fluid inside the same organ

Assuming we have two adjacent kidney cells (eg. tubular cells), depending on the processes they undergo (eg. rate of ion and water transport inside and outside the cells), there could still be variation in the immediate ECF/IF of those two cells. Although I would say in this case, the difference may be negligible.