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The following points highlight the five types of human lymphatic system. The types are: 1. Lymph 2. Lymphatic Capillaries 3. Lymphatic Vessels 4. Thoracic Duct 5. Right Lymphatic Duct.
Type # 1. Lymph:
This colourless fluid 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 the tissue fluid and lymph has lower protein contents.
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As compared to the tissue fluid, the lymph contains very small amount of nutrients and oxygen but contains abundant carbon dioxide and other metabolic wastes. Amoeboid shaped white blood corpuscles may be present in the lymph.
Type # 2. Lymphatic Capillaries:
They lie close to the blood capillaries but differ from them to the extent that they end blindly. Moreover, they have extremely thin walls. They are composed of a single layer of endothelial cells. The lymphatic capillaries of intestine absorb the digested fats. They are milky in appearance and are, therefore, called the lacteals (lactos-milk).
Type # 3. Lymphatic Vessels:
The lymphatic capillaries unite to form larger lymphatic vessels. They are composed of an outer coat of fibrous tissue, middle coat of muscular tissue and an inner lining of endothelial cells. The lymphatic vessels have numerous valves.
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Lymph nodes:
These are small oval or bean shaped structures located along the length of lymphatic vessels. Lymph nodes are most numerous in the thoracic mediastinum, on the posterior abdominal wall in the abdominal mesenteries, and in the pelvis, neck and proximal ends of the limbs.
Lymphatic nodes perform the following main functions:
(i) Both B-lymphocytes and T-lymphocytes are produced here.
(ii) Macrophages of the lymph nodes remove bacteria, foreign material and cell debris from the lymph.
(iii) B-lymphocytes change to plasma cells that produce antibodies against invading antigens, while T-lymphocytes attack cells that are ‘foreign’ to the host body.
Type # 4. Thoracic Duct:
The lymphatic vessels of left side unite to form a thoracic duct. This duct begins at the cisterna chyli, which is a sac-dilation situated in front of the first and
second lumbar vertebrae. The thoracic duct contains several valves. It discharges its lymph into the left subclavian vein.
Type # 5. Right Lymphatic Duct:
The lymphatic vessels of the right side of the thorax, head and neck unite to form the right lymphatic duct. It is about 1 cm in length. It discharges its lymph into the right subclavian vein.
