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what is this thing called lymph?

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Canto: So in the last post, lymph glands, or nodes or whatever, got a passing mention, and I realise I’ve lived a pretty full lifetime without having much of an idea of this substance – is it a solid, liquid or gas, or is it delightfully ethereal, like qi?

Jacinta: Okay, let’s explore. The Better Health Channel, an Australian website, manages to give a point by point summary of the lymphatic system without really explaining what lymph actually is. For example, here are a couple of points that come close, but not very….

  • The lymph nodes monitor the lymph flowing into them and produce cells and antibodies which protect our body from infection and disease.
  • It maintains fluid levels in our body tissues by removing all fluids that leak out of our blood vessels.

From which we can deduce that it’s a fluid, since it flows.

Canto: The book we’ve been reading on CFS and its symptoms gives, en passant, this useful information on lymph nodes:

The lymph nodes are tender in multiple areas, such as in the front and back of the neck, armpits, elbows and groin…. One of the most characteristic symptoms is pain in the sub-auricular lymph nodes, the nodes located under the ear and behind the angle of the jaw.

Jacinta: Wow, they bin everywhere. And yes it does sound a bit like qi, some energy force that just needs to be needled at the nodes.

Canto: Time for some science. Lymph comes from Latin, lympha, ‘water’. So, very fluid. Here’s what Wikipedia says on its structure:

Lymph has a composition similar but not identical to that of blood plasma. Lymph that leaves a lymph node is richer in lymphocytes than blood plasma is. The lymph formed in the human digestive system called chyle is rich in triglycerides (fat), and looks milky white because of its lipid content.

Which sounds like the lymph nodes are where lymphocytes are produced. Lymphocytes are a type of leukocyte or white blood cell.

Jacinta: Well, here’s what I’ve come up with, to start things off.

The lymphatic system is the system of lymphoid channels and tissues that drains extracellular fluid from the periphery via the thoracic duct to the blood. It includes the lymph nodes, Peyer’s patches, and other organized lymphoid elements apart from the spleen, which communicates directly with the blood.

And what, you might ask, is the thoracic duct? Not to mention Peyer’s patches. The thorax, I think, is basically that part of the body covered by the rib cage, which includes the heart, the lungs and other organs, perhaps the spleen, perhaps the pancreas, the liver, the stomach, I’m very vague about it all. Anyway, the thoracic duct is an essential part of the lymphatic system, so here’s some more essential info about it:

The lymph from most of the body, except the head, neck, and right arm, is gathered in a large lymphatic vessel, the thoracic duct, which runs parallel to the aorta through the thorax and drains into the left subclavian vein. The thoracic duct thus returns the lymphatic fluid and lymphocytes back into the peripheral blood circulation.

So from this it’s clear that blood and lymph seem to circulate and work together in some respects.

Canto: It’s annoying that lymph is described as the ‘stuff of the lymphatic system’ or in the lymph nodes/vessels, etc etc. It reminds me of dormative virtue, somehow. Then again, it’s a bit like blood. What’s blood? It’s the stuff that comes out of us when we cut ourselves. Most people don’t know much beyond that – except for one key fact. It’s red, and it pools all over the floor in murder dramas. What colour is lymph? Have we ever seen a pool of it? Do we every lymph to death? Why can’t we turn lymph into a verb?

Jacinta: Okay, enough of the deepities. This really is a fascinating topic, and tracing the discovery of lymph, chyle, and the lymphatic system, starting with Hippocrates some 2400 years ago, would be the best, or at least the most interesting way to learn about the stuff, IMHO. I’ve found a recent series of pieces, The discovery of lymphatic system in the seventeenth century, which I’d love to read, but they’re behind a paywall, because we impoverished dilettantes need to be kept from accessing such things. They do give us access to the abstracts though. Here’s the abstract from part one:

The early history of lymphatic anatomy from Hippocrates (ca. 460–377 B.C.) to Eustachius (1510–1574). The presence of lymphatic vessels and lymph nodes was reported by ancient anatomists without any accurate knowledge of their true functions. Lymph nodes were described as spongy structures, spread over the whole body for the support of vulnerable body parts. Digestion was explained as being the resorption of clear chyle from digested food by the open endings of chyle vessels. The first insights into the place of lymphatic components within nutrition emanated from the medical school of Alexandria (fourth century B.C.) where vivisection was a common practice. Herophilus and Erasistratus described mesenteric veins [relating to the mesentery, a fold of membrane that attaches the intestine to the abdominal wall] full of clear liquid, air or milk. For Galen of Pergamum, (104–210) mesenteric lymph nodes also had a nutritional function. He described three different types of mesenteric vessels, namely, the arterial vessels, for the transport of spirituous blood to the intestines; the venous side branches of the portal vein, for the transport of nutritive blood from the liver to the intestines; and small vessels, from the intestines to the mesenteric lymph nodes (serous lymph vessels?). According to Galen, chyle was transported via the above-mentioned mesenteric venous vessels from the intestines to the portal vein and liver, where it was transformed into nutritive blood. This doctrine would be obliterated in the seventeenth century by the discovery of systemic circulation and of the drainage of chyle through a thoracic duct to the subclavian veins.

Canto: Hmmm. Chyle? Peritoneum? Subclavian?

Jacinta: Chyle’s a milky, fatty fluid (containing lymph), formed in the small intestine during digestion. It flows into those lymph vessels known as lacteals. These are special ‘lymph capillaries’ where the lipids ‘are colloidally suspended in chylomicrons’ My guess is that ‘chylomicrons’ are itty-bitty chyle bits. Colloidal suspension is ‘a stable phase showing little tendency to aggregate and separate from the aqueous phase’, according to ScienceDirect. The peritoneum is ‘the serous membrane that lines the abdominal cavity’. Other serous membranes are the pleura and the pericardium. They are two-layered membranes ‘lubricated by a fluid derived from serum’. The subclavian veins (and arteries) are those running from the neck down the left and right arms.

Canto: Serum?

Jacinta: Comes from the blood, and rich in proteins.

Canto: So it seems that lymph, or the lymphatic system, has a few functions. Three in particular are highlighted by a NIH website relating to cancer. First, it returns interstitial fluid – fluid that leaks from blood capillaries into the spaces between cells – to the venous blood. This is a sort of recycling process – a regular leakage and a regular return. The returned fluid is called lymph. The second function connects it to the digestive system. Fats and fat soluble vitamins are absorbed and transported to the venous circulation. This happens through those aforementioned lacteals. The small intestines are lined with villi, little finger-like projections, in the centre of which are blood capillaries, and lacteals, aka lymph capillaries. The blood and the lymph thus act together, with the blood capillaries absorbing most of the nutrients and the lymph capillaries absorbing the fatty stuff. And this high fat content lymph is called chyle. And the third function – the most well-known function according to my source – is immunological:

Lymph nodes and other lymphatic organs filter the lymph to remove microorganisms and other foreign particles. Lymphatic organs contain lymphocytes that destroy invading organisms.

Jacinta: A reasonably good dummies intro to lymph and the lymphatic system, IMHO, and it’s not really surprising that it took a while to work out what it was all about. We certainly don’t know ourselves, but we know a bit more than we did.

Canto: Yes, much more to learn, about lymphoid tissue, capillaries, vessels and that big thoracic duct. And since much of this info comes from the National Cancer Institute (in the US), the connection with cancer, positive or negative, might be worth exploring….

References

David Bell, The disease of a thousand names, 1991

https://en.wikipedia.org/wiki/Lymph

https://en.wikipedia.org/wiki/Lymphocyte

https://www.ncbi.nlm.nih.gov/books/NBK27092/

https://www.ncbi.nlm.nih.gov/books/NBK10759/def-item/A3018/

https://www.ncbi.nlm.nih.gov/books/NBK10759/def-item/A3298/

https://en.wikipedia.org/wiki/Mesentery

https://www.sciencedirect.com/topics/engineering/colloidal-suspension

https://training.seer.cancer.gov/anatomy/lymphatic/

https://training.seer.cancer.gov/anatomy/lymphatic/components/

Written by stewart henderson

March 31, 2023 at 8:30 pm