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Lymph nodes also contain specialized white blood cells for example, lymphocytes and macrophages designed to engulf and destroy damaged cells, cancer cells, infectious organisms, and foreign particles. Thus, important functions of the lymphatic system are to remove damaged cells from the body and to provide protection against the spread of infection and cancer. The lymphatic vessels drain into collecting ducts , which empty their contents into the two subclavian veins, located under the collarbones.

These veins join to form the superior vena cava, the large vein that drains blood from the upper body into the heart. The lymphatic system is a vital part of the immune system, along with the thymus, bone marrow, spleen, tonsils, appendix, and Peyer patches in the small intestine. The lymphatic system is a network of lymph nodes connected by lymphatic vessels.

This system transports lymph throughout the body. Lymph is formed from fluid that seeps through the thin walls of capillaries into the body's tissues. This fluid contains oxygen, proteins, and other nutrients that nourish the tissues. Some of this fluid reenters the capillaries and some of it enters the lymphatic vessels becoming lymph. Small lymphatic vessels connect to larger ones and eventually form the thoracic duct.

The thoracic duct is the largest lymphatic vessel. It joins with the subclavian vein and thus returns lymph to the bloodstream. Lymph also transports foreign substances such as bacteria , cancer cells, and dead or damaged cells that may be present in tissues into the lymphatic vessels and to lymph organs for disposal.

Lymph contains many white blood cells. All substances transported by the lymph pass through at least one lymph node, where foreign substances can be filtered out and destroyed before fluid is returned to the bloodstream. In the lymph nodes, white blood cells can collect, interact with each other and with antigens, and generate immune responses to foreign substances.

Lymph nodes contain a mesh of tissue that is tightly packed with B cells, T cells, dendritic cells, and macrophages. Harmful microorganisms are filtered through the mesh, then identified and attacked by B cells and T cells. Lymph nodes are often clustered in areas where the lymphatic vessels branch off, such as the neck, armpits, and groin. Blockage obstruction : Obstruction in the lymphatic system leads to an accumulation of fluid lymphedema.

Obstruction may result from scar tissue that develops when the lymph vessels or nodes are damaged or removed during surgery, by radiation therapy, by injury, or in tropical countries, by infection with a threadworm filariasis that blocks the lymphatic ducts. Infection: Infection may cause swollen lymph nodes because the lymph nodes are inflamed. Sometimes the lymph nodes themselves may become infected lymphadenitis by organisms that spread through the lymphatic system from the original site of infection. Cancer: Tumors may block the lymphatic ducts or may travel metastasize to lymph nodes near a tumor, interfering with flow of lymphatic fluid through the node.

Lymphatic circulation

Rarely, a tumor lymphangiosarcoma may develop in the lymphatic system. From developing new therapies that treat and prevent disease to helping people in need, we are committed to improving health and well-being around the world. The Merck Manual was first published in as a service to the community. Learn more about our commitment to Global Medical Knowledge.

Common Health Topics.

Commonly searched drugs. Please see our privacy policy for more information. Click here to return to the Medical News Today home page. The lymphatic or lymph system involves an extensive network of vessels that passes through almost all our tissues to allow for the movement of a fluid called lymph. Lymph circulates through the body in a similar way to blood. There are about lymph nodes in the body. These nodes swell in response to infection, due to a build-up of lymph fluid, bacteria, or other organisms and immune system cells.


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A person with a throat infection, for example, may feel that their "glands" are swollen. Swollen glands can be felt especially under the jaw, in the armpits, or in the groin area. These are, in fact, not glands but lymph nodes. They should see a doctor if swelling does not go away, if nodes are hard or rubbery and difficult to move, if there is a fever , unexplained weight-loss, or difficulty breathing or swallowing.

The lymphatic system has three main functions:. The system has special small vessels called lacteals. These enable it to absorb fats and fat-soluble nutrients from the gut. They work with the blood capillaries in the folded surface membrane of the small intestine. The blood capillaries absorb other nutrients directly into the bloodstream. Around 2 liters of fluid leak from the cardiovascular system into body tissues every day. The lymphatic system is a network of vessels that collect these fluids, or lymph.

Lymph is a clear fluid that is derived from blood plasma. The lymph vessels form a network of branches that reach most of the body's tissues. They work in a similar way to the blood vessels. The lymph vessels work with the veins to return fluid from the tissues. Unlike blood, the lymphatic fluid is not pumped but squeezed through the vessels when we use our muscles. The properties of the lymph vessel walls and the valves help control the movement of lymph.

However, like veins, lymphatic vessels have valves inside them to stop fluid from flowing back in the wrong direction. Lymph is drained progressively towards larger vessels until it reaches the two main channels, the lymphatic ducts in our trunk. From there, the filtered lymph fluid returns to the blood in the veins. The vessels branch through junctions called lymph nodes.

These are often referred to as glands, but they are not true glands as they do not form part of the endocrine system. In the lymph nodes, immune cells assess for foreign material, such as bacteria, viruses, or fungus. Lymph nodes are not the only lymphatic tissues in the body.

Lymphatic system: Definition, anatomy, function, and diseases

The tonsils, spleen, and thymus gland are also lymphatic tissues. In the back of the mouth, there are tonsils. These produce lymphocytes, a type of white blood cell, and antibodies. They have a strategic position, hanging down from a ring forming the junction between the mouth and pharynx. This enables them to protect against inhaled and swallowed foreign bodies. The tonsils are the tissues affected by tonsillitis. The spleen is not connected to the lymphatic system in the same way as lymph nodes, but it is lymphoid tissue. This means it plays a role in the production of white blood cells that form part of the immune system.

Its other major role is to filter the blood to remove microbes and old and damaged red blood cells and platelets. The thymus gland is a lymphatic organ and an endocrine gland that is found just behind the sternum. It secretes hormones and is crucial in the production, maturation, and differentiation of immune T cells.

Overview of the Lymphatic System

Bone marrow is not lymphatic tissue, but it can be considered part of the lymphatic system because it is here that the B cell lymphocytes of the immune system mature. During gestation, the liver of a fetus is regarded as part of the lymphatic system as it plays a role in lymphocyte development. Explore the model using your mouse pad or touchscreen to understand more about the lymphatic system. The lymph system has three main functions. The lymphatic system helps maintain fluid balance.

Lymphatic System: Crash Course A&P #44

It returns excess fluid and proteins from the tissues that cannot be returned through the blood vessels. The fluid is found in tissue spaces and cavities, in the tiny spaces surrounding cells, known as the interstitial spaces. These are reached by the smallest blood and lymph capillaries. Around 90 percent of the plasma that reaches tissues from the arterial blood capillaries is returned by the venous capillaries and back along veins. The remaining 10 percent is drained back by the lymphatics. Each day, around liters is returned. This fluid includes proteins that are too large to be transported via the blood vessels.

Loss of the lymphatic system would be fatal within a day. Without the lymphatic system draining excess fluid, our tissues would swell, blood volume would be lost and pressure would increase. Most of the fats absorbed from the gastrointestinal tract are taken up in a part of the gut membrane in the small intestine that is specially adapted by the lymphatic system. The lymphatic system has tiny lacteals in this part of the intestine that form part of the villi. These finger-like protruding structures are produced by the tiny folds in the absorptive surface of the gut.

Lacteals absorb fats and fat-soluble vitamins to form a milky white fluid called chyle. This fluid contains lymph and emulsified fats, or free fatty acids. It delivers nutrients indirectly when it reaches the venous blood circulation. Blood capillaries take up other nutrients directly. The third function is to defend the body against unwanted organisms. Without it, we would die very soon from an infection. Our bodies are constantly exposed to potentially hazardous micro-organisms, such as infections. However, pathogens often do succeed in entering the body despite these defenses.

In this case, the lymphatic system enables our immune system to respond appropriately. If the immune system is not able to fight off these micro-organisms, or pathogens, they can be harmful and even fatal. A number of different immune cells and special molecules work together to fight off the unwanted pathogens.


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The lymphatic system produces white blood cells, known as lymphocytes. There are two types of lymphocyte, T cells and B cells. They both travel through the lymphatic system. As they reach the lymph nodes, they are filtered and become activated by contact with viruses, bacteria, foreign particles, and so on in the lymph fluid. From this stage, the pathogens, or invaders, are known as antigens.

As the lymphocytes become activated, they form antibodies and start to defend the body. They can also produce antibodies from memory if they have already encountered the specific pathogen in the past. Collections of lymph nodes are concentrated in the neck, armpits, and groin. We become aware of these on one or both sides of the neck when we develop so-called "swollen glands" in response to an illness. It is in the lymph nodes that the lymphocytes first encounter the pathogens, communicate with each other, and set off their defensive response. Activated lymphocytes then pass further up the lymphatic system so that they can reach the bloodstream.

Anatomy of the Circulatory and Lymphatic Systems

Now, they are equipped to spread the immune response throughout the body, through the blood circulation. The lymphatic system and the action of lymphocytes, of which the body has trillions, form part of what immunologists call the "adaptive immune response. The lymphatic system can stop working properly if nodes, ducts, vessels, or lymph tissues become blocked, infected, inflamed, or cancerous. Cancer that starts in the lymphatic system is known as lymphoma. It is the most serious lymphatic disease. Hodgkin lymphoma affects a specific type of white blood cell known as Reed-Sternberg cells.

Non-Hodgkin lymphoma refers to types that do not involve these cells. Cancer that affects the lymphatic system is usually a secondary cancer. This means it has spread from a primary tumor , such as the breast, to nearby or regional lymph nodes. Sometimes, a lymph node swells because it becomes infected.

The nodes may fill with pus , creating an abscess. The skin over the nodes may be red or streaky. Localized lymphadenitis affects the nodes near the infection, for example, as a result of tonsilitis. Generalized lymphadenitis can happen when a disease spreads through the bloodstream and affects the whole body.