Little known, but very important, the lymphatic system allows the lymph to flow into the body tissues, draining every corner of the body before flowing into the thoracic veins. Parallel to the cardiovascular system, the lymphatic system opposes excessive accumulations of fluids in the tissues and it is considered the bulwark of defense of our organism. Along the lymphatic pathways there are in fact organs, called lymph nodes, capable of producing the so-called lymphocytes, a special series of white blood cells dedicated to the elimination of hostile microorganisms. When the body is fighting an "infection, the lymph nodes accelerate the synthesis and transformation of these lymphocytes, thus increasing in volume and becoming appreciable and painful to the touch (hence the" expression "having swollen lymph nodes").
The lymphatic system consists of an articulated system of vessels, very similar to the venous and arterial circulatory system. Unlike the blood, the lymph is not pushed by cardiac activity, but flows in the vessels moved by the action of the muscles. By contracting and relaxing, these tissues work like a real pump.When this action fails, for example due to excessive immobility, the lymph tends to stagnate, accumulating in the tissues. This explains why feet and ankles swell when standing in a static position for a long time. For the same reason , when the leg is immobilized by a cast it is necessary to keep it raised above the level of the heart (just to make sure that the force of gravity facilitates the lymphatic drainage).
Similarly to those of the cardiovascular system, the smallest lymphatic vessels, called capillaries, are found in the peripheral regions of the body and, joining together, give rise to ever larger vessels, until they pour into the thoracic duct. Unlike the blood vessels. , the lymphatic capillaries have a blind bottom and are equipped with an even thinner wall, formed by cells separated by large openings. The lymph carried by the thoracic duct, joining that present in the vessels coming from the upper part of the body, of the junction between the subclavian veins and the jugular vein.
In correspondence of some junctions between the various lymphatic ducts, located in strategic points of the organism, we find real filtering stations called, in fact, lymph nodes. Along the lymphatic system we also meet the so-called lymphatic organs, responsible for the production and purification of lymph (thymus, spleen and bone marrow).
Transparent, straw yellow or milky depending on the case, the lymph contains sugars, proteins, salts, lipids, amino acids, hormones, vitamins, white blood cells, etc. Compared to the blood, the lymph is particularly rich in lipids; in the article dedicated to the absorption of fats we have in fact recalled how, after intestinal absorption, the lipid molecules are poured into the lymphatic system in the form of particular lipoproteins called chylomicrons.
The larger lymphatic vessels are characterized by the succession of narrowings and dilations associated with real valve insertions which, similarly to those of the venous system, prevent the reflux of the lymph forcing it to flow in one direction only; the wall of some of these vessels also has contractile capacity. All these anatomical peculiarities are fundamental to allow the unidirectional passage of the lymph: from the interstitial fluid of the tissues towards the systemic circulation, even against gravity.
This condition, called elephantiasis, is characterized by the conspicuous enlargement of the lower limbs due to the blockage of the lymphatic vessels by some parasites.
The lymph derives directly from the blood and has a composition very similar to it, although it is richer in white blood cells and very poor than red ones. Circulating in the interstitial spaces (including, that is, between one cell and another), it has the purpose of reabsorbing the plasma (liquid part of the blood) present in these areas. The very thin walls of the blood capillaries are in fact permeable to water and various substances; thanks to this permeability, the passage of oxygen and nutrients from the blood to the tissues can take place which, for their part, pour carbon dioxide and waste products into the bloodstream. The lymph represents an effective system through which the body collects liquids and waste material from the periphery and then conveys it to the purification organs (liver, kidneys, lungs, lymph nodes). From this point of view, the function of the lymphatic system is therefore very similar to that of the venous circulation.
When the precious lymphatic drainage system goes haywire, considerable quantities of liquids can accumulate in the interstitial spaces due to the unfavorable osmotic gradient (passage of water from the solution with a lower concentration to that with a higher concentration, i.e. from the blood to the interstitial spaces). This condition is called edema and, as mentioned, is the typical consequence of prolonged immobilization. In addition to inadequate lymphatic drainage, edema can be caused by increased capillary filtration compared to resorption; this condition is typical of some diseases such as heart failure and protein caloric malnutrition (kwashiorkor).
- capture and destroy pathogens foreign to the organism, producing and transforming the cells responsible for their neutralization
To keep your lymphatic system healthy it is very important to carry out regular physical activity, in order to favor the "muscle pump" action. When this healthy habit is associated with a "balanced diet, the immune defenses maximize their effectiveness, preventing so that the lymphatic system goes haywire from too much work. There are also particular massage techniques that help the lymphatic system to drain more effectively the liquid that stagnates in the peripheral areas (manual lymphatic drainage).
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