The lymphatic system comprises colourless fluid lymph and a network of fine channels lymphatic capillaries (lacteals) and vessels (ducts), and the lymph nodes.
1. Lymph:
Lymph is a colourless fluid. It is a part of the tissue fluid which in turn is a part of blood plasma. So, the composition of tissue fluid and lymph is the same as that of blood plasma but tissue fluid and lymph have lower protein contents.
Lymph consists of a fluid matrix in which the white blood corpuscles or leucocytes are present. The lymph in the lymph capillaries lacks leucocytes, but receives them as it passes through the lymph nodes. Unlike blood, lymph does not have red blood corpuscles, platelets and plasma proteins. Lists the differences between blood and lymph.
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2. Lymph Vessels or Lymphatics:
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The lymph capillaries join to form the lymphatic vessels. These lymph vessels are like veins but have comparatively thin walls and numerous valves. The smaller lymphatic vessels unite to form larger vessels and they unite to form two main lymphatic ducts.
The lymph vessels at the right side of the head, neck and the right arm enter into a large vessel, the right lymphatic duct which opens into the right sub-clavian vein.
3. Lymph Nodes:
At specific points in the lymph vessels, there are enlargements like beads of a string. These are called lymph nodes. Lymph nodes contain lymphocytes, plasma cells and macrophages. The lymph is filtered through the lymph nodes. The macrophages remove microorganisms and foreign particles from the lymph. The lymphatic nodes also add lymphocytes and antibodies to the lymph from where these are carried to the blood.
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Lymph nodes are abundant in the regions of neck, armpit and groin. Tonsils and adenoids are masses of lymphatic tissues. Thymus and spleen are important lymphatic organs of the body.
Spleen is the largest lymph node found in our body. It produces antibodies, phagocytotic cells and destroys dead RBCs and platelets. In embryonic stage it produces RBCs. It also acts as reservoir of blood which is released during emergency.
Functions of the Lymph:
The lymph performs many functions.
i. It carries carbon dioxide and nitrogenous waste materials that diffuse into the blood through the tissue fluid.
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ii. It carries lymphocytes and antibodies from the lymph nodes to the blood.
iii. It transports fats (fatty acids and glycerol) from the intestine to the blood.
iv. It destroys microorganisms and foreign particles in the lymph nodes.
v. It drains excess tissue fluid from the intercellular spaces back into the blood.
vi. It carries the plasma protein macromolecules, synthesized in the liver cells and hormones, from endocrine glands to the blood.