The Interstitium: The Discovery of a Third Circulatory System
The Interstitium: The Body as an Interconnected Fluid Network
For generations, anatomy education described two primary fluid circulation systems within the human body:
The cardiovascular system, which circulates blood through arteries, veins, and capillaries.
The lymphatic system, which helps regulate fluid balance, immune activity, and waste removal.
Emerging research now suggests the body may also function through a third large-scale fluid network known as the interstitium — an interconnected system of fluid-filled spaces woven throughout connective tissue and fascia. Rather than seeing the body as isolated structures organized like separate compartments, this perspective reveals the body more as a continuous, communicating network.
This understanding aligns deeply with the foundational principles of SAYF Myofascial Education: everything is connected.
What Is the Interstitium?
The interstitium refers to microscopic fluid-filled spaces within connective tissue that exist throughout the body — beneath the skin, around organs, surrounding muscles, and woven through fascial layers.
In 2018, researchers using advanced endomicroscopy imaging identified these previously overlooked spaces within connective tissue layers. Rather than dense, solid walls of collagen, they discovered dynamic tissue networks supported by bundles of collagen and elastin surrounding fluid-filled channels. These spaces appear to act as shock absorbers, transport pathways, and communication corridors throughout the body.
Researchers later observed how substances such as tattoo ink particles traveled through these fascial and interstitial pathways more extensively than previously understood. Rather than remaining isolated near the skin surface, particles moved through deeper connective tissue spaces and into fascial networks.
This discovery shifted how many researchers conceptualize connective tissue: The body may function less like separate isolated parts and more like a continuous fluid communication system.
As Rebecca Wells, MD, one of the senior researchers involved in early interstitium studies, described: “The human body suddenly looked less like a patchwork quilt and more like a knitted blanket.”
Fascia as a Communication System
In SAYF Myofascial Foundations, fascia is not viewed simply as wrapping tissue around muscles. Fascia is:
a sensory organ,
a communication network,
a force-transmission system,
and potentially a major fluid transportation environment.
The fascial system contains nerves, blood vessels, lymphatic vessels, immune cells, mechanoreceptors, fibroblasts, and large amounts of interstitial fluid.
Movement, breath, pressure changes, muscular contraction, hydration, and tissue loading all influence how fluids move through these spaces. This is one reason why:
slow movement can change perception and pain,
diaphragmatic breathing can alter swelling and circulation,
foam rolling can influence tissue hydration and glide,
and why sustained stress or immobility can contribute to tissue stiffness and congestion.
The body is constantly exchanging information through tension, pressure, fluid movement, and sensory signaling.
Interstitial Fluid and the Role of Movement
Interstitial fluid exists between cells and connective tissues throughout the body. It helps transport nutrients, signaling molecules, immune cells, metabolic waste, hormones, and water. Unlike the cardiovascular system, the interstitial system does not have a central pump like the heart.
Instead, interstitial fluid movement is influenced by:
breath pressure changes,
muscular contractions,
fascial tension,
body position,
walking,
movement variability,
and tissue compression/decompression.
This has profound implications for understanding why movement matters so deeply for health.
Sedentary living reduces:
important fluid exchange,
tissue hydration,
fascial glide,
lymphatic return,
and mechanical stimulation of connective tissue.
Sustainable movement practices support:
circulation beyond blood flow,
tissue nourishment,
nervous system regulation,
fascial adaptability,
and whole-body communication.
Ancient Systems and Modern Science
Long before modern imaging technology revealed the complexity of connective tissue and interstitial fluid pathways, traditional systems of medicine described the body as an interconnected network through which energy, communication, and vitality move.
In Traditional Chinese Medicine, these pathways are described as meridians through which qi (chi) flows.
In yoga and Ayurveda, similar concepts exist through the understanding of nadis — energetic pathways through which prāṇa moves throughout the body and mind.
Both systems describe the body as deeply interconnected rather than mechanically separate. Modern fascial research is beginning to reveal intriguing parallels.
Studies have shown that many acupuncture points correspond closely with connective tissue planes, fascial intersections, and areas of increased interstitial fluid activity. Researchers have also observed injected tracers migrating through connective tissue pathways associated with traditional meridian lines rather than exclusively through blood vessels or superficial tissues alone.
This does not “prove” ancient energetic theories in a simplistic or reductionist way. However, it does suggest that connective tissue, fluid dynamics, mechanotransduction, and interstitial communication may play a much larger role in whole-body integration than modern anatomy models once recognized.
Why This Matters in SAYF Myofascial Education
Understanding fascia and the interstitium changes how we think about mobility, recovery, pain, breath, inflammation, movement efficiency, nervous system regulation, and healing.
In SAYF education, we emphasize:
fluid movement over rigid force,
adaptability over intensity,
progressive loading over aggressive stretching,
and awareness-based movement that improves communication throughout the system.
When fascia becomes dehydrated, compressed, guarded, or chronically overloaded, tissues often lose elasticity, glide, responsiveness, and efficient communication.
When movement, breath, hydration, pressure variation, and nervous system regulation improve, the body often responds with:
increased ease,
improved mobility,
better circulation,
reduced guarding,
and greater resilience.
The emerging science of fascia, fluid movement, and the interstitium is changing how we understand the body — not as isolated parts, but as an interconnected communication network influenced by breath, movement, pressure, hydration, and nervous system regulation.
This is exactly the kind of integrative, movement-based understanding we explore throughout the SAYF Myofascial Education Pathway.
Through May 31, 2026, we’re offering introductory pricing as we begin this next phase of SAYF Myofascial Education.
Where are you most inspired to start?
$200 off Myofascial Integration Certification (INTROMI)
$100 off Hatha Roll (INTROHR)
Dual Certification Advantage: If you choose to continue into both, the second program is offered at 40% off (code provided upon completion of the first).
This is a beautiful opportunity to engage the full pathway at a significantly reduced rate while deepening your understanding of fascia, movement, breath, fluid dynamics, nervous system support, and sustainable whole-body integration.
References & Research
Benias PC et al. Structure and Distribution of an Unrecognized Interstitium in Human Tissues. Scientific Reports. 2018.
Primo Vascular System / connective tissue meridian research related to acupuncture pathways.
Langevin HM & Yandow JA. Relationship of Acupuncture Points and Meridians to Connective Tissue Planes. The Anatomical Record. 2002.
The New York Times Magazine feature by Avraham Z. Cooper discussing emerging interstitium research and implications for medicine.