Lymphatic system

The lymphatic system, or lymphoid system, is an organ system in vertebrates that is part of the immune system and complementary to the circulatory system. It consists of a large network of lymphatic vessels, lymph nodes, lymphoid organs, lymphatic tissue and lymph. Unlike the circulatory system, which is a closed system, the lymphatic system is open.

Lymph originates in the interstitial fluid that leaks from blood in the circulatory system into the tissues of the body. This fluid carries nutrients to the cells and collects waste products, bacteria, and damaged cells, before draining into the lymphatic vessels as lymph. The lymphatic system provides an accessory return route to the blood for this fluid.

The other main function is that of immune defense. Lymph contains waste products, bacteria, and proteins. The cells of the lymph are mostly lymphocytes. Important lymphoid organs include the lymph nodes, the spleen, the thymus, and the tonsils. Lymph is moved through the system by muscle contractions and eventually returns to the bloodstream through the subclavian veins.

Structure

The lymphatic system is a network of vessels, organs, and tissues that helps the body fight infections. It includes lymphatic vessels, lymph nodes, and lymphoid organs.

Primary lymphoid organs, such as the thymus and bone marrow, create immune cells called lymphocytes. The thymus helps these cells mature and learn to recognize harmful substances.

Secondary lymphoid organs, like lymph nodes and the spleen, house mature lymphocytes and help them find and fight invaders. Lymph nodes are small structures found throughout the body that filter lymph, a fluid that circulates through the lymphatic system. The spleen filters blood and also plays a role in immune responses.

Development

Lymphatic tissues start to form by the end of the fifth week when babies are growing inside their mothers. These tissues come from special sacs called lymph sacs, which come from veins. The first ones to appear are jugular lymph sacs near important veins in the neck. From there, tiny networks of lymphatic vessels spread to different parts of the body like the chest, arms, and head. The spleen grows from cells near the stomach, and the thymus comes from a small pouch in the throat area.

Function

The lymphatic system helps keep our body healthy in several important ways. It collects extra fluid from tissues and sends it back where it’s needed. It also helps carry fats and fatty acids from our food through special vessels called lymph vessels.

The lymphatic system is very important for our immune system. It helps our body fight germs by moving special cells, like white blood cells, to places where they can help protect us. When it finds something harmful, it starts a response to fight it off and keep us safe.

Clinical significance

Main article: Lymphatic disease

The lymphatic system is very important for fighting diseases, especially cancer. It helps carry cancer cells between different parts of the body, a process called metastasis. Lymph nodes can sometimes trap these cancer cells, which helps doctors detect and treat the disease.

When lymph nodes become enlarged, it is called lymphadenopathy. This can happen because of infections or inflammation. Sometimes, many lymph nodes in the body become enlarged, which can be caused by serious infections, diseases affecting connective tissue, or cancers.

Lymphedema is swelling that happens when the lymphatic system is damaged or not working properly. This can cause limbs, the face, neck, or abdomen to swell. In severe cases, the skin can become very thick. Lymphedema can also happen after lymph nodes are removed during surgery.

Cancer can also affect the lymphatic system. Lymphoma is a type of cancer that starts in the lymphatic tissue. There are two main types: Hodgkin lymphoma and non-Hodgkin lymphoma. Both are treated with special medicines and sometimes radiation.

History

Hippocrates, who lived in the 5th century BC, was one of the first to talk about the lymphatic system. He mentioned lymph nodes in his work. Later, in the 1st to 2nd century AD, Rufus of Ephesus identified several important parts, including the thymus.

In the 1600s, many scientists made important discoveries. Gabriele Falloppio described parts of the system, and Bartolomeo Eustachi found the thoracic duct in horses. Gaspare Aselli discovered lymphatic vessels in dogs, and Jean Pecquet showed how these vessels connect to the body's blood system. These discoveries helped scientists understand how the lymphatic system works.

More recently, researchers found that the lymphatic system even connects to the human brain, which changed what we know about the immune system.