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Lymphatic System

The lymphatic system consists of a network of vessels and lymph organs, like lymph nodes, bone marrow, spleen and thymus. The fluid present in the lymphatic system is called lymph. Lymph is a transparent fluid derived from blood and other tissues, which accumulates in the interstitial spaces as the interstitial fluid. Lymph contains leucocytes, mainly the lymphocytes. This fluid has a composition similar to that of plasma, except that it is low in protein. Fine channels are called lymph vessels. Structurally, the lymph vessels are similar to that of veins, except for their thinner wall and more valves. Besides, a number of lymph nodes are present at intervals. These structures are made up of lymphoid tissues lying in the lymphatic vessels in which the foreign bodies (antigens) are filtered and destroyed by the lymphocytes. The lymphatic vessels, form blind-ended capillaries in the tissues. The system of lymphatic vessels is distributed in the limbs, abdomen, thorax and neck. The lymphatic vessels from the lower body parts extend upward to form the left thoracic duct, which receives the vessels from left arm, left side of head, and partly from thoracic region. This thoracic duct opens into the vein near the junction of left internal jugular vein and the subclavian vein. The lymphatic vessels from the right arm, the remaining thoracic parts, and the right side of the head, from the right lymphatic duct, which opens at the junction of right subclavian and internal jugular vein. Thus, the lymphatic system provides an accessory route for the flow of interstitial fluid into the blood. The lymphocytes present in the lymphatic system play important role in the defense against foreign agents or microbes.

The lymphatic system consists of
  1. lymph,
  2. lymph vessels, and
  3. lymph nodes.
Lymph is the name given to tissue fluid when it is in the lymph vessels. When the blood is circulating through the tissues, fluid filters from the blood plasma through the walls of the blood capillaries. Part of the this filtered fluid is reabsorbed into the capillaries. However, most of this fluid diffuses into a system of fine channels (lymph capillaries). These channels join, to form large lymphatic vessels. The fluid inside the lymph capillaries and lymph vessels called the lymph.
Lymph is a colourless fluid and is similar to the plasma of blood in composition; but the lymph from organs other than liver contains less proteins. The lymph contains several types of leucocytes such as (B cells and T cells) lymphocytes and granulocytes which play predominate roles in the immune systems.

Lymph Vessels
The lymphatic system is an open system consisting of a network of channels and lymph sinuses. Occurring beneath the skin, in the muscles, in the walls of digestive system and around the nervous system, lymph fluid from the sinuses flows into the lymph vessels and from there enters the veins. Two large lymphatic vessels which return lymph to the venous blood are the thoracic duct and the right lymphatic duct which open into the left and right subclavian veins respectively. The additional system of vessels from the lymphatic capillaries to the thoracic and right lymphatic duct constitute what is known as the lymphatic system. The lymph vessels have valves which direct the flow of the lymph towards the veins.

The Lymphatic System

Lymph Nodes
There are numerous nodular bodies on the lymph vessels. These appear as beads in a string. These nodules are known as lymph nodes. In the lymph nodes the lymph vessel breaks up into finer branches. Phagocytic white blood corpuscles (WBC) and macrophages, present in the lymph nodes, remove bacteria and foreign particles form the lymph. Lymph nodes also form lyumphocytes and antibodies which pass to the blood through the lymph. The neck, armpits and groin are regions where lymph nodes are found abundantly.

Function of the Lymphatic System
The lymphatic system has many functions. One of the important functions of lymph is to transport proteins to the blood plasma. The lymphocytes produced in the lymph nodes are responsible for the destruction of foreign bodies and harmful bacteria. They also produce antibodies. Another function of lymph is to convey lipids from the intestine to the blood stream.

The spleen is the largest lymphatic organ in the body. It serves three functions. It filters the disintegrated red blood cells from the blood flowing through it, acts as a reservoir of blood, and stores large amounts of blood, whenever there is haemorrhage (lose of blood), the spleen releases the reserve blood into circulation. In human embryos, the spleen is the site of formation of both red and white blood cells.

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