Fascia or interstitium – what’s the difference?

Fascia or interstitium? Two different terms for the body’s “newly discovered” largest organ. The criteria for defining an organ is that the structure should be the same in the tissue wherever you look and that the function is also the same, no matter where you look. Fascia or interstitium is the body’s architectural framework with its continuous flow, which an American research group now considers to be the body’s largest organ.

Already more than a hundred years ago, Franklin Mall described the body’s reticular network, made up of collagen, elastin, glycosaminoglycans, and other extracellular components, which surround cells, inside and between all organs. The network has biological and mechanical functions in creating the body’s architecture and entire physiology. This knowledge has also led to the creation of custom organ transplants in regenerative medicine. It has been confirmed that the network extends beyond the boundaries of individual organs and involves nearby structures, such as the abdominal cavity with the liver, intestines, and kidneys. With its vascular system and surrounding fibrous sheaths, a structural continuity is created across all organ borders, which has also been recognized previously between the fascia of the intestinal mesentery and the connective tissue in the intestinal wall.

In recent times, decellularization of whole sheep fetuses has also shown that the connective tissue network is continuous throughout the body and that connective tissue in nerve tissue creates a coherent structure between the nervous system and other tissues. Dissections of humans have similarly shown the continuous network throughout the body, including the fascia of the skin and fascia in and around various organs and organ systems.

The spaces between the network’s fibers have been seen as empty spaces, as previous microscopy techniques with fixation created artifacts. However, it has previously been proposed, especially in osteopathy, that these connective tissue networks contain fluid and represent a body-wide communication network, even if detailed microscopic confirmation has been lacking. Now it has been shown that there is a continuous fluid flow between different tissue areas and in and between organs, and the fluid flow is not limited to being contained within an organ. It is thus a continuous interstitial space and is filled with hyaluronic acid, which is involved in regulating the fluid flow. The fluid-filled interstitial space with its network, the fascia, is vital for the body’s entire physiology, molecular signaling, communication, cell migration, regeneration, immune system, transport and more, and can also spread malignant cells and infectious diseases.

  • Benias, P. C. et al. Structure and distribution of an unrecognized interstitium in human tissues. Sci. Rep. 8, 4947 (2018).
  • Cenaj, O. et al. Evidence for continuity of interstitial spaces across tissue and organ boundaries in humans. Commun Biol. 4, 436 (2021).
  • Guimberteau, J. C., Armstrong, C. Architecture of Human Living Fascia: Cells and Extracellular Matrix as Revealed by Endoscopy (2015).
  • Mall, F. P. A study of the structural unit of the liver. Am. J. Anat. 5, 277–308 (1906).
  • Wiig, H. & Swartz, M. A. Interstitial fluid and lymph formation and transport: physiological regulation and roles in inflammation and cancer. Physiol. Rev. 92, 1005–1060 (2012).