Everything is simple here. Through the kidneys and with sweat, water comes out, which was part of the blood, and water is pumped out through the lymphatic vessels, which could not get into the blood.
Well, that is, this water really wanted to get into the blood, it strove there, but it did not work out. And this water was left to splash in the intercellular space. There, between the cells, about a quarter of all our water is poured.
All this spilled water was at one time in the blood, but then flowed out through microscopic holes in the capillaries. This is normal. Through such holes, the capillaries drain useful substances, and take waste back.
Ladybugs
You can imagine our cages as cows on a farm, peacefully standing in their stalls, and under their nose they are fed from our capillaries.
Since nothing in our body spills out in a dry form, then the food for our cells is drained in the form of an aqueous solution.
Waste and excess water are absorbed back into the bloodstream. But all the excess water cannot be absorbed into the blood through the wall of the capillaries. Because the capillaries, although small, still have pressure, and water tends to escape from them out into the intercellular space.
There are, of course, osmosis and other cunning mechanisms in the capillaries that allow you to collect some of the water, but the water will still remain spilled between the cells.
Pepper
Plus, large proteins are constantly falling out of the capillaries, which may be needed for something in the intercellular space, or maybe they just fell out of the capillary.
Imagine that it is like pepper, which we pour from the pepperpot into our plate. If you sprinkled too much, then you can't put these pieces of ground pepper back into the pepper shaker through those very small holes. Pepper has to be loaded in some other way.
Lymph
So the water remaining between the cells is collected by the lymphatic vessels. They literally pump out and suck in this fluid, and then centrally deliver it through a special pipeline into one of the large veins near the heart. So all the extra intercellular water is again in the blood. The circle is complete.
Complicated? Yes. But you can't do without it. Because in addition to food and waste, all sorts of large proteins, microbes and other debris will be scattered between the cells, which will never get back into the bloodstream. This is where the lymphatic vessels are needed.
Hooligans
If some microbe does not want to leave the intercellular space, then there are specially trained cells in the lymph that will literally drag such a bully by the scruff to the nearest lymph node.
All sorts of large proteins that spilled out, which had no chance to squeeze back into the blood through small holes in the capillaries, and indeed any garbage lying around idle, will also be sucked in there.
Wipers
Well, it's as if hot and cold water, electricity and heat are supplied to your apartment building, waste water is pumped out, solid household waste, and for the whole business it was paid regularly, then even in the most ideal conditions you will need a cleaner and a janitor who will clean up the remnants of the tenants garbage. So? Well, the lymphatic vessels are the very same wipers, without which the adjacent territory would quickly become cluttered.
