A summary on lymphatic architecture for students of Fundamental Lymphology.
The human lymph system is the most anatomically variable of all our body systems, so it can be a difficult system to describe and learn.
Historically considered a secondary system to the blood vasculature, and compounded by a lack of investigation on lymphatic function, the vital role of the lymph system in the health of all other systems has been significantly undervalued.
Now, 21st century research on lymphatic disorders is revealing fascinating new facts about this dynamic and fascinating system. So it has never been more important for students of lymphatic therapies to have a comprehensive understanding of the lymph pathways and the alternative mechanisms of tissue drainage.
Finding the drainage patterns
Despite the huge variation between individuals, there are some fundamental patterns in lymph drainage that we can use to map the location of the lymph vessels and nodes. But this requires two maps as the drainage patterns in the deep and superficial lymph systems are quite different.
Location, location, location
One body structure that is almost identical in all of us - the deep fascia - is a tough elastic stocking that encloses our muscle body and divides us into superficial and deep compartments.
In the deep system, our skeletal muscles further enclose and protect our visceral body; heart, lungs, gut, brain etc.
The deep fascia and skeletal muscles keep everything in the deep body in a high pressure state, which greatly assists the movement of venous blood and lymph toward the heart.
The superficial, or epifascial compartment surrounds the deep fascia and includes the skin and fatty layers that insulate, pad and protect us from the external world. Hair follicles and sweat glands, blood vessels and nerves, and 80% of all our lymph vessels, are located in the skin and subcutaneous tissue.
Most of the superficial lymph vessels are just 3-5 mm under the skin, where the initial lymph plexus forms a fine network of open ended vessels. Continuous pumping in the lymph collectors, pulls any invading microbes or unwanted molecules which have crossed the skin barrier, into the lymphatic system, removing them to the lymph nodes before they can reach the deeper body.
This image shows how ICG dye and a fluoroscope can be used to image the most superficial lymph collectors. This kind of imaging is useful to see where there are open skin pathways in a damaged lymph system.
Other forms of imaging such as lymphoscintigraphy are needed to show movement of lymph in the deeper tissues.
Taking each compartments separately, there are distinct patterns of draining for the major lymph collectors in each system.
Watersheds or perivascular bundles?
The superficial lymphatic system protects the body from invasion and maintains a slightly sub-atmospheric pressure in the superficial compartment.
Lymph formed under the skin is transported by collector vessels located above the deep fascia to superficial lymph nodes, also located above the deep fascia. Drainage pathways in the superficial system can be divided by three imaginary lines called watersheds, to make six major drainage areas.
Lymph vessels track in a relatively linear fashion toward lymph node basins at the base of the neck, armpits and groin on each side of the body. (Video from one of my online courses at Moving Lymph Online).
Further divisions of the lymph pathways within each watershed are are know as territories and relate to a subsection of skin such as either the radial or ulnar side of the hand etc.
Lymph node basins house both superficial and deep lymph nodes, and this is where most of the lymph collected in the superficial system passes into the deep system.
Generally, lymph carried by superficial lymph vessels will first empty into a superficial lymph node, but there are some exception such as the radial pathway. Not present in everyone, lymph vessels collecting from the skin of the radial hand pass into the deep system and follow the cephalic vein, emptying into either an infra- or supra-clavicular lymph node, by-passing the axilla.
There is also a sciatic pathways that bypasses the inguinal basin, but again not present in everyone.
What goes deep, stays deep
The lymphatic map in the deep system can made from a map of the arteries and veins as these three vessels primary travel within the same perivascular sheath throughout the deep body.
For drainage of the central nervous system a map of the cranial and spinal nerves can be used. Lymph collected from the brain is collected by perineural nerves mainly at the optic and olfactory cranial exists.
Peri-neural lymph vessels in the epidural spaces collect the lymph load from the spinal cord. Mesenteric lymph vessels follow the mesenteric veins.
What's in a name?
One advantage of being discovered late, is that lymph nodes and vessels are usually named for adjacent structures, so we don't need to learn a whole bunch of new names. Lymph nodes near the parotid salivary glands are called parotid lymph nodes, the lymph vessels returning fluid from the head are the jugular trunks etc.
Where are the lymphatic ?ducks?
Lymph vessels have a similar hierarchy to blood vessels with the smallest vessels in both systems called capillaries. Initially lymph vessels (lymphatic capillaries) pass the lymph via pre-collectors to the transporting collector vessels for deliver to the first lymph node in that pathway. Most lymph travels through multiple lymph nodes before being returned to the veins.
Ducts empty into veins
At the most proximal part of the system, processed lymph is delivered to the sub-clavian veins via the thoracic duct on the left, and the right lymphatic duct. Duct are the largest lymph collector vessels in the body.
Trunks empty into ducts
Each duct has at least three trunks which deliver lymph from the last lymph node in each pathway to the nearest duct.
The right lymphatic duct receives lymph from the jugular, subclavian and brocho-mediastinal trunks, from the head, arm/chest wall and thoracic cavity respectively. The same three trunks deliver lymph from the left upper body to the Thoracic Duct.
The thoracic duct also receives lymph from the intercostal trunks and cisterna chyli which is the convergence of the three trunk delivering lymph from the lower body. The left and right lumbar trunks carry lymph from the ipsilateral leg and abdomen, and the intestinal trunk delivers lymph carrying essential fatty nutrients from the gut which cannot be pick up by the blood vessels there.
Visualising the lymphatic system
Over the years I have tried to help clients understand their lymphatic system and whatever damage it has sustained. Since most lymphatic pathologies are irreversible, people affected by chronic oedema are faced with lifelong self-management, so it's important that they understand how their system works. I frequently use bathtubs, vacuum cleaners and hand pumps in my analogies, and have written other #TalkingLymph posts on the structure and function of the lymph vessels system.
Here is a guided visualisation of your lymph system from within.