Lymphatics
General overview
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The lymphatic system is a major part of the body’s immune system that functions to:
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Collect, filter, and return excess interstitial fluid to the venous system
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Absorb fat and fat-soluble vitamins (from the villi of the small intestine)
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Help defend against microorganisms
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Parts of the lymphatic system
Lymph
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Lymph is interstitial fluid that has entered the lymphatic system; the quantitative composition of lymph varies in different tissues
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Lymph maintains the same basic composition of water, salts, plasma proteins (albumins, globulins, and fibrinogen), and white blood cells as the interstitial fluid it collects
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Fluid passes out of capillaries at the arterial end and bathes cells
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Osmotic pressure aids in the return of the fluid into the venous end of the capillary
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Excess interstitial fluid (containing waste and microorganisms such as bacteria) enters the lymphatic capillaries and is now called lymph
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The lymph is then filtered through lymph nodes and returned to the venous system
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Lymph contains plentiful lymphocytes and other white blood cells
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Lymph from the villi of the small intestine also absorbs fat and fat-soluble vitamins
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The absorbed fat makes the lymph from this area have a milky color, and it is now called chyle
Lymphatic vessels
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Lymphatic vessels carry lymph in only 1 direction—away from the tissue to rejoin the circulatory system
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Lymphatic capillaries are located throughout the tissue spaces within the cardiovascular capillary beds
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Lymphatic capillaries are composed of overlapping endothelial cells, which form a 1-way valve allowing the excess interstitial tissue fluid to enter the lymphatic capillary, but not lymph, which then must travel in the vessel away from the tissue
Lymph nodes
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Lymphatic vessels are connected to lymph nodes and filter the lymph
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Because lymphatic vessels are 1-way, lymph enters the lymph node through afferent lymph vessels, where it is filtered
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In addition to its filtration function, the lymph node has a rich supply of lymphocytes and other white blood cells that help provide an immune response to (foreign) microorganisms
Lymphatic ducts
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Lymphatic vessels conduct lymph to the venous system to rejoin the blood plasma
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There are 2 connections into the venous system at the junction of the internal jugular vein and the subclavian vein on both the right and left side of the body:
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Right lymphatic duct—carries lymph from right arm, right thorax, and right side of head
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Thoracic duct (left lymphatic duct)—carries lymph from remainder of the body
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Tonsils
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Tonsils are lymphatic tissue that are associated with the immune functions that defend the body
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Tonsils are part of the mucosa-associated lymphatic tissue (MALT) system of lymphoid tissue
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There are 4 sets of tonsils, together known as Waldeyer’s ring, located in the nasopharynx and oropharynx that guard against foreign microorganisms:
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Pharyngeal tonsils (adenoids)
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Tubal tonsils (very small, located at entrance of auditory tube in nasopharynx)
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Palatine tonsils (between palatoglossal and palatopharyngeal folds)
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Lingual tonsils (on posterior 1/3 of the tongue)
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Other lymphoid organs
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Thymus
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Spleen
Lymphatics of the head and neck
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There are multiple ways to classify lymphatics of the head and neck; 1 way is to divide lymph nodes into:
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Superficial nodes
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Deep nodes
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This classification results in 4 types of lymph nodes:
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Superficial lymph nodes of the head
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Deep lymph nodes of the head
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Superficial lymph nodes of the neck
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Deep lymph nodes of the neck
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Upper deep cervical
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Lower deep cervical
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After being filtered by lymph nodes (primary node), the lymph will connect to another lymph node and be filtered again (secondary node)
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Eventually, all lymph will drain into the inferior group of deep cervical lymph nodes where they join the jugular lymph trunks, which eventually create the right lymphatic duct (on the right side) and the thoracic duct (on the left side), which empties into the venous system at the junction of the internal jugular vein and the brachiocephalic vein
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