Lymphatic system: characteristics, parts and functions.

A summary of the functions and characteristics of the lymphatic system, important in our health.

We all know some curious facts about the circulatory system. For example, you may at least know that a human being has about 5 liters of Blood flowing through its arteries, veins and capillaries, or that the heart pumps all of the body's blood in just over a minute. This red fluid that gives us life is also one of the first contact of students with biology, which is why it is more than present in the general culture.

In the blood flow the red blood cells, responsible for transporting oxygen to each and every one of the tissues of our body, with the help of hemoglobin. Also circulating in this fluid are white blood cells or leukocytes, cellular bodies responsible for signaling and eliminating endogenous and exogenous pathogens, either specifically or non-specifically. Blood is essential to understand the immune system, but if we only talk about it, we are leaving something very important behind.

Indeed, in this article we will talk about the great forgotten of the human circulation: the lymphatic system. The human body produces approximately 3 liters of lymph per day, which is incorporated into the blood and circulates through small capillaries. If you want to know all about this enigmatic fluid system, read on.

What is the lymphatic system?

According to the National Cancer Institute (NIH), the lymphatic system can be defined as. the set of tissues and organs that produce, store and transport white blood cells, which are responsible for fighting infections and other deleterious events for the organism (e.g. chemical exposure, presence of allergic substances or cancer cells). (exposure to chemicals, presence of allergic substances or cancer cells, for example). It would be impossible to conceive of life today without the action of immune mechanisms.

The lymphatic system transports fluid (lymph, more specifically) throughout the body by means of a network of thin tubules. For this reason, it is the second circulatory system of the organism, and some authors consider it to be an accessory part of the blood systemIt ends up in the venous system, at the junction between the subclavian vein and the left jugular vein.

This system includes the bone marrow, spleen, thymus, lymph nodes and lymphatic vessels, in addition to the circulating lymph itself. We dissect each of these parts in the following lines.

1. Bone marrow

Bone marrow is a spongy tissue found inside some bones of the body (and has nothing to do with the spinal cord). (and has nothing to do with the spinal cord). In colloquial language it is known as marrow. All circulating blood cells (red blood cells, lymphocytes, macrophages, neutrophils and many more) are derived from a pluripotent hematopoietic stem cell, which is found in the bone marrow.

In an adult human, this type of tissue accounts for 4% of its total mass and approximately 500 billion red blood cells are produced in it per day. It is an effective and tireless machinery as far as cell production is concerned.

2. Spleen

The spleen is an organ that lies to the left in the body plane, just below the rib cage.. Its main function is immunological in nature, since as the blood passes through it, it filters antigens and in its germinal centers specific antibodies are formed for them, known as immunoglobulins. It is also a site of essential relevance for the elimination of old circulating red blood cells (splenic hemocateresis), which allows us to renew this essential cell type.

Because of its link to immune activity, infections, certain types of cancer or liver disease can cause enlargement of the spleen, a condition known as splenomegaly. Often, this condition has no symptoms, but when it does it usually manifests as a swelling in the upper left abdominal area.

3. Thymus

The thymus is the organ of the lymphatic system where T lymphocytes grow and multiply.. It is located in the thorax, behind the sternum, in front of the heart. Hematopoietic progenitor cells (remember that they are formed in the bone marrow) come here to develop, acquiring the name of thymocytes.

T lymphocytes are essential for the understanding of adaptive immunity, as they directly attack foreign bodies in a specific way and produce cytokines, biological substances that help to activate other cellular components of the immune system.

4. Lymph nodes

Lymph nodes are small structures containing lymphocytes, which are essential for fighting disease and responding to it in the short and long term.. They are formations that are located in the path of the lymphatic vessels, forming chains or clusters, through which lymph is filtered. Throughout the body there are hundreds of lymph nodes connected to each other: to give you an idea, in the armpit alone there are between 20 and 40 of these unique structures.

In addition, lymph nodes are differentiated are differentiated between peripheral and internal. The former are easily palpable, as they are located under the skin, and their inflammation can indicate various pathologies. In many of these cases there is a lymphadenopathy or adenopathy, which corresponds to inflammation of the lymph nodes due to infectious processes, cancerous tumors, HIV and tuberculosis, among others. The increase in volume of the lymph nodes is a clear clinical sign of disease.

5. Lymphatic vessels

The lymphatic vessels are located throughout the body, and are larger than the blood capillaries.. Almost all lymphatic vessels contain specialized valves, which allow the lymph to go in one direction only and do not cause clotting.

Lymph

How can we leave out the fluid that gives its name to the entire system and is the raison d'être of all the structures previously mentioned? Lymph is a practically transparent fluid that is produced from the excess fluid that flows out of the blood capillaries into the intercellular space..... This unique fluid contains white blood cells, proteins, fats and salts and, unlike the circulatory system with the heart, it has no pumping apparatus to transport it throughout the body.

Lymph circulates thanks to the body's own muscular contractions, since its purpose is to return to the circulatory system. In addition to containing immune cells and nutrients, it is also responsible for transporting foreign substances, damaged cells and cancerous cellular bodies that may have entered the tissue fluids.

Functions of the lymphatic system

We have painted a general picture of the functioning and usefulness of the lymphatic system in the previous lines, but it never hurts to make a general summary to finish. Below is a list of the most important functions of the lymphatic a list of the most important functions of the lymphatic system:

• Drainage of interstitial fluid: this system captures excess fluids from the blood capillaries and returns them to the blood after circulating through it.
• Transport of fats: after a large meal, up to 2% of the body's fats can be found in the lymph. These fats are essential for cellular nutrition.
• Immune response: B and T lymphocytes and macrophages in the lymph nodes and other organs recognize and destroy foreign substances.

Thus, the lymphatic system is involved in many more tasks than you might at first think: transports nutrients, serves as a fluid recycling mechanism and, most important of all, is one of the essential bases for the immune response..

For this reason, lymphadenopathy (inflammation of the lymph nodes) is an essential diagnostic element in the presence of many pathologies. For example, breast cancer can be detected by an axillary lymphadenopathy: when the tumor is present in a breast, the metastatic cells travel through the lymphatic system to the nearest lymph node (in this case in the armpit), causing it to swell and enlarge. This is a very powerful diagnostic tool before the tumor spreads to the rest of the body.

Summary

The functions of the lymphatic system can be defined in two basic pillars: transport and immunity.. Here leukocytes, the most important cell bodies for understanding the human immune system, both innate and acquired, are synthesized and transported.

Although it is possible to live without some of the lymphoid organs such as the spleen, their absence can drastically diminish the ability to respond to exogenous infections and other harmful internal processes. Undoubtedly, the importance of the lymphatic system as a whole has been more than justified in these lines.

Bibliographic references:

• Enlarged spleen (splenomegaly), mayoclinic.org. Retrieved January 19 from https://www.mayoclinic.org/es-es/diseases-conditions/enlarged-spleen/symptoms-causes/syc-20354326.
• Definition of the lymphatic system, NIH. Retrieved January 19 from https://www.cancer.gov/espanol/publicaciones/diccionario/def/sistema-linfatico.
• The lymphatic system, Leukemia and lymphoma society. Retrieved January 19 from https://www.lls.org/sites/default/files/file_assets/PS54S_SP_BloodCells_LymphaticSystem_2019.pdf.
• Introduction to the lymphatic system, merckmanuals.com. Picked up on January 19 at https://www.merckmanuals.com/es-us/hogar/trastornos-del-coraz%C3%B3n-y-los-vasos-sangu%C3%ADneos/trastornos-del-sistema-linf%C3%A1tico/introducci%C3%B3n-al-sistema-linf%C3%A1tico.