The Lymphatic System

The lymph system is a collection of thin tubes that carries colourless liquid called lymph. As discovered in the circulatory system, blood travels around the body and delivers oxygen and other nutrients. On its journey, fluid leaks into the bodies tissues and it is this fluid which makes the lymph, along with substances such as fibrinogen, water and lymphocytes. It travels around the tissues of the body and carries white blood cells. After travelling around the body, lymph enters one of the major lymphatic vessels, the thoracic duct, which begins near the lower part of the spine and collects lymph from the pelvis, abdomen, and lower chest. This duct runs up through the chest and empties into the blood through a large vein near the left side of the neck. The right lymphatic duct is the other major lymphatic vessel and collects lymph from the right side of the neck, chest, and arm, and empties into a large vein near the right side of the neck. This means that lymph is continuously emptied into the blood where it mixes with the plasma. The system has no heart or arteries, but capillaries that extend into most tissues, which run parallel to the blood capillaries. In conclusion, Lymph is formed when plasma seeps from the blood into the surrounding tissues and becomes tissue fluid where it is collected by the lymph vessels. The main function of the lymphatic system is to fight infection, distribute excess fluid and transport fats around the body.

Nodes

Throughout the miles of lymph vessels, there are small round nodes or glands which are bean shaped structures covered in a capsule of connective tissue. They are packed full with lymphocytes which are used to filter the lymph. These structures are made of lymphatic tissue and here the white blood cells fight infection, that is why sometimes these glands can be felt, for example in the armpits, in the groin and neck, as the lymph nodes trap bacteria or viruses that they cannot destroy immediately. The lymph node may swell and become painful and sore. Some nodes cannot be felt, for example those in the abdomen, chest and pelvis. Occasionally the lymph nodes can trap cancer cells that it cannot destroy. The nodes then become swollen but not necessarily painful. This is why it is so important to check any swollen lymph node as cancers can develop in the lymph system.

Lymph

As lymph flows through the node, lymphocytes (white blood cells) are added, which leaves the lymph cleaner due to breaking down bacteria. Lymph drains through around 8 – 10 nodes before returning to the blood. Most lymph nodes are solitary but some can be found in clusters. For example, a cluster is found in the ileum of the small intestine. These large masses of lymph nodules are known as Peyer’s patches.

Lymph Vessels – carry lymph

These are microscopic, thin walled tubes which branch, interconnect and extend into almost all tissues of the body. They look like blood capillaries but they contain a larger inner space and also have a closed end. Lymph capillary walls are made up of overlapping cells that swing slightly inward when fluid outside the capillary pushes against them. This allows the milky fluid to enter the capillary, and is now referred to as lymph. Small amounts of diffuse lymphatic tissue are found in virtually every organ of the body.

Lymph capillaries join to form larger vessels called lymphatic’s or sometimes called lymph veins. Lymphatic’s are found in the subcutaneous tissue of the skin, following the same path as veins. Lymph vessels contain valves to prevent the back flow of lymph and they allow lymph to travel through lymphatic nodes.

Lympahtic

Lymphatic Ducts – collects lymph

Thoracic duct is the principal vessel of the lymphatic system and carries lymph as well as a substance called chyle, which is a milk fluid that contains lymph and emulsified fats. It begins in the abdomen and runs to the neck where it empties into the venous blood stream at the left subclavian vein. This duct receives the lymph from smaller vessels of the lower limbs and the upper left side of the head and neck.

Right lymphatic duct is a vessel that collects lymph from the right upper side of the body and drains it into the right subclavian vein.

Cisterna Chyli vessels drains lymph from the intestines which is laden with digested fats.

Bone Marrow

Bone marrow is found in the hollow of bones and is a spongy material that makes red and white blood cells and plasma. Once mature enough, two types of white blood cells, lymphocytes and myeloid cells made by the bone marrow enter the bloodstream and circulate around the body. The lymphocytes also circulate in the lymph system. These cells only live for a few days so it is essential that the bone marrow constantly renews the old ones.

There are four main organs that are involved with the lymphatic system. They are the spleen, thymus, tonsils and adenoids.

The Spleen

This organ is found in the upper left abdominal cavity and is the largest lymphatic organ in the body. The spleen consists of two types of tissue called the white and red pulp. The white pulp consists mainly of lymphocytes and the red pulp consists of venous sinuses which are filled with blood and cords of lymphatic cells.

The function of the spleen is to filter blood, similar to the way lymph nodes filter lymph, but it also breaks down and destroys old red blood cells, which have a life span of around 120 days. The spleen holds extra blood that can be released into the circulatory system if needed.

The Thymus

As already discovered, the thymus is an endocrine gland but it also helps to produce white blood cells, so that puts it in the lymphatic system as well.

The Tonsils

The tonsils are two glands in the back of your throat, and they help to protect the entrance of the digestive system by preventing bacteria from entering. When the tonsils become infected, a condition called tonsillitis occurs. The lymphoid tissues in the back of the mouth at the top of the throat that normally help to filter out bacteria.

The Adenoids

The adenoids are lumps of tissue found at the back of the nose above the tonsils but are only present in children as they begin to shrink by the age of 7. The appendix also needs to be mentioned as, although its function is unclear, it has a rich supply of lymph tissue.

Pathologies of the Lymphatic System

DiseaseMeaning
OedemaSoft tissue swelling – fluid retention.
Hodgkin’sCancer of the lymphatic system.
Non Hodgkin’s lymphomaCancer of the lymphoid tissue.
Glandular feverViral infection causing sore throat and temperature.
LymphadenitisAn infection of the lymph nodes.
LupusAn autoimmune disease where the body starts to attack healthy cells, tissues and organs.