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What is it?
The lymphatic system is central to the body’s ability to protect itself from disease by identifying and destroying pathogens (infectious agents). The lymphatic system works with the circulatory system. After the arterial blood has delivered oxygen, nutrients and hormones to the cells, 90% of that blood goes back to the circulatory system, taking the waste products from the cells with it. However, the remaining 10% of the fluid stays behind in the tissues as lymph, which is a yellowish, protein-rich fluid.
The lymph is circulated in its own system to the neck, where it passes back into the venous blood stream through the subclavian veins. Lymph only flows in one direction, unlike blood which loops through the body. On the way to the neck, it passes through lymph nodes which combat pathogens and remove excess waste.
Lymph nodes are an important part of the system. They are very small, oval shaped organs which trap foreign particles and help to filter them out of the body. The lymph nodes are filled with a fluid which contains lymphocytes, a type of white blood cell. Lymphocytes tackle foreign, potentially harmful organisms in the body by developing antibodies, which are specialized proteins. Lymphocytes can recognise the presence of a pathogen because of the abnormal proteins, known as antigens, which develop on the surface of the body’s cells.
There are two types of lymphocytes called B-cells (bursa-derived cells) and T-cells (thymus cells). B-cells primarily target bacterial antigens, which reside on the surface of the body’s cells. T-cells tackle viruses and other micro-organisms that hide inside the body’s cells.
The two cells tackle invading pathogens in different ways. B-cells produce large amounts of antibodies that neutralise toxins produced by bacteria. There are two types of T-cells which work together, known as helpers and killers. Helper T-cells identify invading pathogens and send out chemicals which warn the killer T-cells of the infection. These chemicals are called lymphokines. Killer T-cells destroy pathogens by combining its molecule with the pathogen molecule. This usurps the pathogen and prevents it from linking with any other of the body’s molecules and spreading.
All lymph nodes are connected by a network of lymphatic vessels, which transfer the lymph fluid from the tissues back in to the blood.
Five Quick Facts
- The lymphatic system doesn’t have a pump, like the heart. So, lymph is moved upwards from the body’s tissues to the neck by the movements of the muscles.
- When the lymphocytes are fighting infection, the lymph nodes will swell. This is sometimes called ‘swollen glands’. The nodes can become visible in the neck or groin and also under the arm.
- The lymphatic system circulates on average 1 to 2 litres of lymph fluid at any given time.
- Once the body has overcome a particular pathogen, it will be able to defend itself from every subsequent attack that same pathogen makes. This is because of memory cells, which allow the body to remember how it neutralised the pathogen initially. This is why vaccinations contain a small amount of the virus they are designed to defend against, as this gives the body a controlled opportunity to build up antibodies against it.
- HIV (human immunodeficiency virus) infects and destroys T-cells rendering the body susceptible to infections that might not otherwise affect healthy people.
How to remember it
The lymphatic system is like the body’s drainage system. It conveys excess fluid from all over the body back in to the blood circulation. The lymph nodes are very important because they filter the lymph of infectious pathogens and harmful waste before it is returned to the main blood stream. Without this intervention, infection and disease would be allowed to circulate throughout the body’s organs and tissues freely.
The circulatory system and the lymphatic system work together, but they are very different. Lymph moves in one direction through the body, unlike the circulatory system which transfers blood around the body in a continuous loop.
- Lymphatic: (lim-fat-ik)
- Lymph: (limf)
- Lymphoid: (lim-foid)
- Pathogen: (path-uh-juhn)
- Antibody: (ant-ee-bod-ee)
- Lymphocyte: (lim-fur-sayt)
- Antigen: (ant-ee-juhn)
- Circulatory: (sir-kyuh-luh-tawr-ee)
- Arterial: (ahe-teer-ee-uhl)
- Subclavian: (suhb-kley-vee-uhn)
- Thymus: (thahy-muhs)
- Lymphokine: (lim-fuh-kahyn)