Lymphatic system: characteristics, parts and functions

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

In the blood flow the red blood cells or red blood cells, responsible for transporting oxygen to each and every one of the tissues of our body, with the help of hemoglobin. Also circulate through this liquid white blood cells or leukocytes, cell bodies responsible for identify and eliminate endogenous and exogenous pathogens, either specifically or nonspecifically. Blood is essential to understand the immune system, but if we only talk about it, we leave something very important in the pipeline.

Indeed, in this article we will talk about the great forgotten of 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 everything about this enigmatic fluid system, read on.

• Related article: "Leukocytes: what are they, types and functions in the human body"

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 harmful events for the body (exposure to chemicals, presence of allergic substances or cancer cells, for example). Conceiving life today without the action of immune mechanisms would be impossible.

The lymphatic system carries fluid (lymph, more specifically) throughout the body through a network of thin tubules. For this reason, it is the second circulatory system of the body, and some authors consider it as an accessory part of the blood, since it ends up flowing into 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, as well as the circulating lymph itself. We dissect each of these parts in the following lines.

1. Bone marrow

The bone marrow is spongy tissue found inside some bones in the body (and it 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 pluripotential 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 500,000 million red blood cells are produced in it per day. It is an effective and tireless machinery when it comes to cell production.

2. Spleen

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

Due to its link with immune activity, infections, certain types of cancer or Liver diseases can cause enlargement of the spleen, a condition known as splenomegaly. This condition often has no symptoms, but when it does, it usually manifests as swelling in the upper left abdominal area.

3. Scam

The thymus is the organ of the lymphatic system where T lymphocytes grow and multiply. It is located in the chest, behind the breastbone, 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 understanding adaptive immunity, as they directly attack foreign bodies specifically and produce cytokines, biological substances that help activate other cellular components of the system immune.

4. Lymph nodes

Lymph nodes are small structures that contain lymphocytes, which are essential to fight diseases and respond to them 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 the lymph is filtered. There are hundreds of connected lymph nodes throughout the body: to give you an idea, only in the armpit there are between 20 and 40 of these unique structures.

Also, the lymph nodes differentiate between peripherals and internal. The former are easily palpable, as they are found under the skin, and their inflammation can indicate various pathologies. In many of these cases, a dry lymphadenopathy or adenopathy occurs, which corresponds to the inflammation of the lymph nodes due to infectious processes, cancerous tumors, HIV and tuberculosis, among other. Lymph node enlargement is a clear clinical sign of disease.

• You may be interested in: "Swollen Glands: Causes and Warning Symptoms"

5. Lymphatic vessels

Lymphatic vessels are located throughout the body, and are larger than blood capillaries. Almost all lymphatic vessels contain specialized valves, which allow lymph to flow in only one direction and clotting does not occur.

Lymph

How can we leave the liquid that gives its name to the entire system and is the reason for being of all the previously named structures in the inkwell? Lymph is a practically transparent liquid that is produced from excess fluid that leaves the blood capillaries into the intercellular space. This unique liquid contains white blood cells, proteins, fats and salts and, unlike the circulatory system with the heart, it does not have a pumping device to transport it throughout the Body.

The lymph circulates thanks to the muscular contractions of the body itself, 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 cell bodies. that may have entered tissue fluids.

Functions of the lymphatic system

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

• Interstitial fluid drainage: this system captures excess fluids from the blood capillaries and returns them to the blood after circulating through it.
• Fat transport: after a copious 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, T lymphocytes and macrophages present in lymph nodes and other organs recognize and destroy foreign substances.

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

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

Resume

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 you can live without some of the lymphoid organs such as the spleen, their absence can dramatically decrease the ability to respond to exogenous infections and other internal processes harmful. Without a doubt, the importance of the lymphatic system as a whole has been more than justified in these lines.

Bibliographic references:

• Enlarged spleen (splenomegaly), mayoclinic.org. Picked up on January 19 in https://www.mayoclinic.org/es-es/diseases-conditions/enlarged-spleen/symptoms-causes/syc-20354326.
• Definition of the lymphatic system, NIH. Picked up on January 19 in https://www.cancer.gov/espanol/publicaciones/diccionario/def/sistema-linfatico.
• The lymphatic system, Leukemia and lymphoma society. Picked up on January 19 in 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 in 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.