Body contours, swollen lymph nodes and dehydration, 3 facts about the lymph system you may not know.
Updated: Feb 9, 2020
Fact 1: The lymph system is responsible for the fine contours of your body such as the appearance of tendons and veins that stand out from your skin.
For the purposes of the lymphatic system we can consider our body in two parts, the superficial system and the deep system. The deep system is everything under the deep fascia, which is like a very tight, tough elastic stocking enclosing your muscle body, which in turn encloses all your vital organs.
Under this elastic bodysuit, the muscles and organs are in a high pressure environment which means the lymph vessels and veins get a lot of support for fluid return, especially when your muscles are pumping under that bodysuit.
It's a different story in the superficial system between the skin and the deep fascia where the skin is not such a tight 'stocking', so many more lymph vessels are needed to remove tissue fluid. 80% of all the lymph vessels in your body are in the subcutaneous compartment and the initial lymph plexus branches densely just a few mm below the skin where it plays a role in barrier defences by removing anything that crosses the skin barrier.
Although pumping of large lymph vessels is often slow and not very forceful, it is continuous and never stops.
The lymph system acts like a vacuum cleaner with the nozzle vacuuming cleaning the under-surface of your skin which also contributes to maintaining a sub-atmospheric environment within the compartment. The atmosphere is only a few mmHg higher but this is enough to compress the tissue slightly. Structures like tendons and veins are not so easily compressed and 'stand out'. Likewise the hollow at the back of your heel is formed by the atmosphere compressing the soft tissue which fills the space between bones of the ankle and the Achilles tendon. These contours at the hand and heel are lost during lymphatic failure.
Fact 2: The endothelial cells in your lymph vessels can detect the contents of the lymph and influence smooth muscle contraction in the lymphangions.
Q: We all know that lymph nodes swell when we have an infection, but why?
A: Because lymph endothelium is monitoring the contents of the lymph and communicating with the smooth muscle in the anion wall and through complex coordination controls the lymph is moved along the vessel as needed. This involvement of the endothluim in lymphatic pumping is very important during infections when cells in the efferent lymphatics, detecting a high pathogenic load in the lymph, trigger vaso-constriction of the lymph angion, reducing outflow and trapping the harmful material inside the node to be processed. As the pathogenic load decreases endothelial cell signalling stops and normal lymph pumping is restored.
Fact 3: Your lymph system is protecting your body from dehydration and helping to maintain venous blood volume
The loose connective tissue is comprised of tissue fibres and cells the composition and architecture of which will vary depending on location. But regardless of location the space between the fibres and cells is filled with an amorphous ground substance, which in the loose connective tissue is formed by glucos-amino-glycans, principally hyaluronic acid (HA).
These huge molecules have a bottle brush like structure with millions of fibres that can attach and hold free water molecules. This imparts the property of thixotrophy to the tissues and protects the tissue cells from fluid fluctuations in the bath (read previous posts on this topic). If overall hydration drops, the body responds by prioritising water to maintain central blood pressure, really all that matters is maintaining blood flow between the heart lungs and brain. The HA takes up free water molecules and lymph flow is reduced. This in turn reduces other lymph related activities such as barrier defences and immune support.
Often when I talk to people affected by lymphoedema about drinking more water, they complain that they are already up all night going to the bathroom. But it is the lack of water during the day that causes this problem.
Once the body is at rest and in the horizontal position (which changes all the tissue pressures), the free water is released and taken up by venous capillaries. This venous resorption does not happen in the subcutaneous tissue during standing/sitting, read other posts on this topic. Fluid that is removed by the lymph system is also returned to venous blood capillaries within lymph nodes, and directly into veins at multiple places notably the subclavian vein.
To hydrate frequently during the day allows fluids to flow normally through the connective tissue bath and lymphatic pumping can carry on vacuum cleaning your tissues and keeping your body cells healthy.