The lymphatic system consists of a fluid (lymph), vessels that transport the lymph, and organs that contain lymphoid tissue.
Lymphatic Organs Lymphatic organs are characterized by clusters of lymphocytes and other cells, such as macrophages, enmeshed in a framework of short, branching connective tissue fibers. The lymphocytes originate in the red bone marrow with other types of blood cells and are carried in the blood from the bone marrow to the lymphatic organs. When the body is exposed to microorganisms and other foreign substances, the lymphocytes proliferate within the lymphatic organs and are sent in the blood to the site of the invasion. This is part of the immune response that attempts to destroy the invading agent.
Lymphatic Organs: Lymph Nodes||Tonsils||Spleen||Thymus
Referrence:Lymphatic System(Chinese Version)
The lymphatic system is a vast drainage network that returns water, proteins, and other substances from body tissues back to the bloodstream. It is made up of ducts, called lymph vessels or lymphatics, and carries lymph, a clear, watery fluid that resembles blood plasma.
The lymphatic system is closely connected with the blood and circulatory system. In fact, some scientists consider this system to be part of the circulatory system because lymph comes from blood and returns to blood, and because its vessels are very similar to the veins and capillaries of the blood system.
Throughout the body, wherever there are blood vessels, there are lymph vessels, and the two systems work together.
How Are the Spleen and Lymphatic System Necessary for Living? The entire lymphatic system flows from the body tissues toward the bloodstream, returning fluid to the blood. If this didn't happen, our body tissues would become swollen. For example, when a body part swells, it may be because there is too much fluid in the tissues in that area. The lymph vessels collect that extra fluid and carry it back to the circulatory system through the lymphatic system.
This process is crucial because water, proteins, and other molecules continuously leak out of tiny blood capillaries into the surrounding body tissues. This lymph fluid has to be drained, so it returns to the blood by way of the lymphatic vessels. These lymph vessels also prevent the fluid from flowing back into the tissues.
The lymphatic system also has a big role in defending the body against germs - like viruses, bacteria, and fungi - that cause disease. Harmful foreign materials are filtered out by lymph nodes, small masses of tissue that lie along the network of lymphatic vessels. These nodes contain lymphocytes (pronounced: lim-fuh-sites), a type of white blood cell, some of which produce antibodies, special proteins that fight off infection. Antibodies and white blood cells also stop infections from spreading through the body by trapping germs and destroying them.
The spleen also plays an important part in a person's immune system. Like the lymph nodes, the spleen contains lymphocytes that make antibodies. These antibodies weaken or kill bacteria, viruses, and other organisms that cause infection. Also, if blood passing through the spleen carries damaged cells, white blood cells called macrophages (pronounced: ma-kru-fay-jiz) in the spleen will destroy the damaged cells and clear them from the bloodstream.
In fact, the spleen is so important in defending the body against infections that when the spleen is missing, the body is at much greater risk of serious infection. That's why kids and teens who have lost their spleens through injuries or diseases like sickle cell disease need to have special immunizations and often need to go to the hospital when they have a fever.
Basic Anatomy The lymphatic system is a network of very fine vessels or tubes called lymphatics that drain lymph from all over the body. Lymph is made up of water, protein molecules, salts, glucose, urea (the main component of urine), lymphocytes, and other substances.
Lymphatics are found in every part of the body except the central nervous system. In addition to the lymphatic vessels, the major parts of the lymphatic system are the:
bone marrow spleen thymus gland lymph nodes tonsils Other organs, including the heart, lungs, intestines, liver, and skin, also contain lymphatic tissue.
Lymph nodes are round or kidney-shaped, and range in size from very tiny to 1 inch in diameter. They are usually found in groups in different places throughout the body, including the neck, armpit, chest, abdomen, pelvis, and groin. Most lymph nodes and lymphatic tissue are within or near the gastrointestinal tract, but the easiest to feel are in the front portion of the neck.
Lymph nodes drain lymph from the body tissues that are most nearby, which is why a doctor may feel carefully for enlarged lymph nodes in your neck if you have a throat infection or may feel your armpit if you have signs of a skin infection of the arm.
Lymphocytes are white blood cells in the lymph nodes that produce antibodies to help the body fight infection. Two types of lymphocytes are T cells and B cells. Immunoblasts are lymphocytes that become stimulated and enlarged when they encounter foreign substances.
The body's biggest lymphatic vessel is the thoracic duct, which begins near the lower part of the spine. The thoracic duct collects lymph from the lower limbs, pelvis, abdomen, and lower chest. It 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 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.
The spleen is found on the left side of the abdomen. Unlike other lymphoid tissue, red blood cells flow through it. The spleen helps control the amount of blood and blood cells that circulate through the body and helps destroy damaged cells.
Normal Physiology (How the Body Works Normally) Lymph is drained by the lymph capillaries out of the lymphatic system. Fluid moves more slowly than blood, pushed along mainly by a person's breathing and contractions of the skeletal muscles. The walls of blood capillaries are very thin, and they have many tiny openings to allow gases, water, and chemicals to pass through to nourish cells and to take away waste products. Lymph leaks out of the blood capillaries, where it bathes the body tissues and is termed interstitial (pronounced: in-ter-stih-shul) fluid.
Lymph vessels recycle the interstitial fluid and return it to the bloodstream. They collect the fluid from all of the body's tissues and then empty it into large veins in the upper chest, near the neck.
Lymph nodes are made of a mesh-like network of tissue. Lymph enters the lymph node and works its way through passages called sinuses. The nodes contain macrophages, cells that engulf and destroy bacteria, dead tissue, and other foreign matter, removing them from the bloodstream. Macrophages are called phagocytic (pronounced: fa-guh-sit-ick) cells because of the way they engulf and consume (phagocytize) foreign matter. After the lymph has passed through the lymph nodes, it returns to the veins, where it re-enters the bloodstream.
When a person has an infection, germs and the white blood cells fighting them collect in great numbers in the lymph nodes. If the throat is infected, for example, the lymph nodes of the neck may swell. Sometimes the phagocytic cells may not be able to destroy all of the germs, and a local infection in the nodes may result.
Because the lymphatic system extends to the far reaches of the body, when a person has cancer, the cancer cells can sometimes spread along the lymphatic system. This is why lymph nodes near a cancerous growth are sometimes removed with the growth.
Diseases, Conditions, and Disorders (Stuff That Can Go Wrong) Because the lymphatic system branches through most of the parts of the body, it may be involved in a wide range of conditions. Diseases may affect the lymph nodes, the spleen, or the collections of lymphoid tissue that occur in certain areas of the body.
Disorders of the lymph nodes
Lymphadenopathy (pronounced: lim-fad-en-ah-puh-thee). Most lymph nodes in the body can't be felt easily unless they become swollen or enlarged. Lymphadenopathy is an increase in the size of a lymph node or nodes, most often because of a nearby infection (for example, lymphadenopathy in the neck might be the result of an infection of the throat). Less commonly, swelling of the lymph nodes can be due to an infiltration of cancerous cells. If lymphadenopathy is generalized (meaning that the swelling is present in several lymph node groups throughout the body), it usually indicates that the person has a disease that involves the entire body. Lymphadenitis, or adenitis, is an inflammation (swelling, tenderness, and sometimes redness and warmth of the overlying skin) of the lymph node due to an infection of the tissue in the node itself. In kids, this condition most commonly involves the lymph nodes of the neck. Lymphomas. A group of cancers that result when lymphocytes undergo changes and start to multiply out of control. The involved lymph nodes enlarge, and the cancer cells crowd out healthy cells and may form tumors (solid growths) in other parts of the body. Disorders of the spleen
Splenomegaly (pronounced: spleh-no-meh-go-lee), or enlarged spleen. In kids and teens, the spleen is usually small enough that it can't be felt by pressing on the abdomen, but the spleen can enlarge to several times its normal size with certain diseases. There are many possible reasons for this including various blood diseases and cancers, but the most common cause in children is infection (particularly viral infections). Infectious mononucleosis, a condition usually caused by the Epstein-Barr virus (EBV), is one of many viral infections that can cause the spleen to enlarge. Kids and teens with an enlarged spleen should avoid contact sports because they can have a life-threatening loss of blood if their spleen is ruptured. Disorders of other lymphoid tissue
Tonsillitis. This common condition occurs when the tonsils, the collections of lymphoid tissue in the back of the mouth at the top of the throat, are involved in a bacterial or viral infection that causes them to become swollen and inflamed. The tonsils normally help to filter out bacteria and other microorganisms to aid the body in fighting infection. Symptoms include sore throat, high fever, and difficulty swallowing. The infection may also spread to the throat and surrounding areas, causing pain and inflammation (this is called pharyngitis).
Glossary
antibodies: chemicals produced by white blood cells to fight bacteria, viruses, and other foreign substances immunoblasts: lymphocytes that become stimulated and enlarged when they encounter foreign substances interstitial fluid: fluid that leaks out of capillaries (the tiniest blood vessels) and bathes body tissues lymph: pale fluid that bathes the body tissues, passes into lymphatic vessels, and is discharged into the blood by way of the thoracic duct; it consists of a liquid resembling blood plasma and contains white blood cells lymph nodes: organized masses of lymphoid tissue that are distributed along the branching system of lymphatic vessels; they contain numerous lymphocytes and other cells that filter bacteria, dead tissue, and foreign matter from the lymph that flows through them lymph vessels: channels or ducts that contain and transport lymph; also called lymphatics lymphocytes: white blood cells macrophages: white blood cells that remove damaged cells from the bloodstream spleen: organ found on the left side of the abdomen; it helps control the amount of blood and blood cells that circulate through the body and helps destroy damaged cells thoracic duct: major lymphatic vessel, which begins near the lower part of the spine and collects lymph from the lower limbs, pelvis, abdomen, and lower chest; lymph flowing through the duct eventually empties into a large vein in the upper chest and returns to the bloodstream
The lymphatic system has three primary functions. First of all, it returns excess interstitial fluid to the blood. Of the fluid that leaves the capillary, about 90 percent is returned. The 10 percent that does not return becomes part of the interstitial fluid that surrounds the tissue cells. Small protein molecules may "leak" through the capillary wall and increase the osmotic pressure of the interstitial fluid. This further inhibits the return of fluid into the capillaries, and fluid tends to accumulate in the tissue spaces. If this continues, blood volume and blood pressure decrease significantly and the volume of tissue fluid increases, which results in edema (swelling). Lymph capillaries pick up the excess interstitial fluid and proteins and return them to the venous blood. After the fluid enters the lymph capillaries, it is called lymph. The second function of the lymphatic system is the absorption of fats and fat-soluble vitamins from the digestive system and the subsequent transport of these substances to the venous circulation. The mucosa that lines the small intestine is covered with fingerlike projections called villi. There are blood capillaries and special lymph capillaries, called lacteals, in the center of each villus. The blood capillaries absorb most nutrients, but the fats and fat-soluble vitamins are absorbed by the lacteals. The lymph in the lacteals has a milky appearance due to its high fat content and is called chyle.
The third and probably most well known function of the lymphatic system is defense against invading microorganisms and disease. Lymph nodes and other lymphatic organs filter the lymph to remove microorganisms and other foreign particles. Lymphatic organs contain lymphocytes that destroy invading organisms.