what is this thing called lymph? some more…
Canto: So we learned a lot about lymph recently, but strangely enough, it made us hungry for more. So, it has two functions, circulatory and immunological. I’d like get more detail on both those functions, and in particular I’d like to know more about lymphocytes, what they are, how they’re made and what they do.
Jacinta: Sounds like a plan. So first, lymph in the circulatory system. Here’s what I’ve gleaned from an online video. This system brings oxygen and nutrients to all our bodily tissues, as well as removing waste materials. Ultimately this feeding and removal process occurs in the smallest vessels, the capillaries, which penetrate into tissues and organs. Nutrient-rich blood plasma moves out of capillaries ‘at the arterial end of capillary beds, while tissue fluid containing wastes reabsorbs back in at the venous end’.
Canto: Okay, whoa. First, I have difficulty separating left from right, and east from west, what they call directional dyslexia. I also, in a probably related way, have problems with arteries and veins. One goes into the heart, the other goes out….
Jacinta: Haha, think arteries away (AA), and that’s all you need to know. I have the same problem, quelle surprise!
Canto: So I get that nutrient-rich ‘blood plasma’, presumably some kind of mixture of blood and plasma, moves out of arterial capillaries into tissues, to feed and energise and rejuvenate them and such, but I’ve never heard of capillary beds, and ’tissue fluid’ sounds a bit questionable…
Jacinta: These are all good issues to raise. Apparently there’s a whole capillary bed network. So, getting back to basics, our cardiovascular system is this super-complex network of veins, arteries and capillaries that move oxygen, nutrients, hormones and waste materials to and from our tissues and organs. It’s often analogised as something like a city road network, highways with off-ramps leading to main roads, side-roads and such. And capillary beds are the network of smaller vessels leading into and out of particular tissues. Anyway here’s a useful definition from a medical website:
Capillaries do not function independently. The capillary bed is an interwoven network of capillaries that supplies an organ. The more metabolically active the cells, the more capillaries required to supply nutrients and carry away waste products. A capillary bed can consist of two types of vessels: true capillaries, which branch mainly from arterioles and provide exchange between cells and the circulation, and vascular shunts, short vessels that directly connect arterioles and venules at opposite ends of the bed, allowing for bypass.
If all of the precapillary sphincters in a capillary bed are closed, blood will flow from the metarteriole directly into a thoroughfare channel and then into the venous circulation, bypassing the capillary bed entirely. This creates what is known as a vascular shunt.
And, since I know you’re wondering:
A metarteriole is a short microvessel in the microcirculation that links arterioles and capillaries. Instead of a continuous tunica media, they have individual smooth muscle cells placed a short distance apart, each forming a precapillary sphincter that encircles the entrance to that capillary bed.
And as for tunica media, I won’t quote, I’ll put it in my own words. Arteries and veins have three-layered linings called tunicae. The tunica media, as the name suggests, is the middle layer between the inner tunica intima and the outer tunica externa. The make-up and structure of this layer (and the others) varies in relation to the size of the artery. For example, there’s a lot more tissue in the layers of the aorta, the body’s largest artery.
Canto: Great, and yes, intrinsically interesting, but let’s return to lymph. So the lymphatic system is a ‘cleaning up’ and drainage system among other things. There are some 700 lymph nodes throughout the body – armpits, groin, throat, and in the intestines where they’re involved in the absorption of fat. A node in this context is a bean-like structure which filters the lymph passing through it. It contains lots of lymphocytes for combating/consuming pathogens. If the system fails to function properly, oedema or lymphoedema results (a swelling or puffiness). As well as these numerous tiny nodes, there’s the spleen, a multifunctional lymphatic organ located on the left side of our bodies next to the stomach. It produces a range of cells including many types of white blood cells such as murderous macrophages and of course lymphocytes. The spleen is divided into a ‘red pulp’ and a smaller ‘white pulp’ section, and I could go into greater detail about T cell zones and B cell zones and the various functions of these cells and their subdivisions.
Jacinta: Yes I think we have a general sense in that the lymphatic system of nodes and spleen improves circulation through removal and replacement, and immunity through renewal of ageing cells and production of lymphocytes and other antibody-type cells. All of this started with our attempt to get a handle on CFS or ME/CFS or CFIDS and its relation to the immune system. It’s been an interesting little journey into an unknown land for us, and my impression is that there’s still a lot to be learned even by researchers steeped in lymph, so to speak.
Canto: Yes, and it’s given us some little background into immunology and the amazing complexity of the animal body…
References
https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/lymphatic-system
https://en.wikipedia.org/wiki/Lymphatic_system
https://en.wikipedia.org/wiki/Metarteriole
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