What Is Lymph and lymphatic system: Function, Conditions & Disorders

Little known, but very important, the lymphatic system allows lymph to flow through body tissues, draining every corner of the body before pouring into the thoracic veins. Parallel to the cardiovascular system, the lymphatic system opposes excessive accumulations of fluids in the tissues and is considered the bulwark of defense of our body. In fact, along the lymphatic pathways there are organs, called lymph nodes, capable of producing so-called lymphocytes, a special series of white blood cells responsible for eliminating 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 noticeable and painful to the touch (hence the expression “having swollen lymph nodes”).

The lymphatic system is made up of a complex system of vessels, very similar to the venous and arterial circulatory system. Unlike blood, lymph is not pushed by cardiac activity, but flows through 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 you remain 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 (precisely to ensure that the force of gravity facilitates lymphatic drainage).

Similar to those of the cardiovascular system, the smaller lymphatic vessels, called capillaries, are found in the peripheral regions of the body and, coming together, give rise to increasingly larger vessels, until they flow into the thoracic duct. Unlike blood capillaries, lymphatic capillaries have a blind end and are equipped with an even thinner wall, made up of cells separated by large openings. The lymph transported by the thoracic duct, uniting with that present in the vessels coming from the upper part of the body, flows at the level of the junction between the subclavian veins and the jugular vein.

At some junctions between the various lymphatic ducts, located in strategic points of the body, we find actual filtering stations called lymph nodes. Along the lymphatic system we also encounter the so-called lymphatic organs, responsible for the production and purification of lymph (thymus, spleen and bone marrow).

Transparent in color, 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 blood, lymph is particularly rich in lipids; in the article dedicated to the absorption of fats we in fact recalled how, after intestinal absorption, the lipid molecules are released into the lymphatic system in the form of particular lipoproteins called chylomicrons.

The larger lymphatic vessels are characterized by a succession of narrowings and dilations which are associated with actual valve insertions which, similarly to those of the venous system, prevent the reflux of the lymph, forcing it to flow in only one direction; 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.

The lymph derives directly from the blood and has a composition very similar to it, despite being richer in white blood cells and very poor in red ones. By 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, oxygen and nutrients can pass from the blood to the tissues which, in turn, release carbon dioxide and waste products into the bloodstream. 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, significant quantities of liquids can accumulate in the interstitial spaces due to the unfavorable osmotic gradient (passage of water from the lower concentrated solution to the higher concentrated one, i.e. from the blood to the interstitial spaces). This condition is defined as 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 reabsorption; this condition is typical of some diseases such as heart failure and protein-calorie malnutrition (kwashiorkor).

To keep your lymphatic system healthy it is very important to carry out regular physical activity, in order to promote the action of the “muscle pump”. When this healthy habit is combined with a balanced diet, the immune defenses maximize their effectiveness, thus preventing the lymphatic system from going haywire due to too much work. There are also particular massage techniques that help the lymphatic system to more effectively drain the liquid that stagnates in the peripheral areas (manual lymphatic drainage).