Limphatic system

The Lymphatic system is part of the vascular system and an important part of the immune system, composed of a large network of lymphatic vessels that carry a clear fluid called lymph (from Latin “lympha” meaning “water”) directionally towards the heart.  

Unlike the circulatory system, the lymphatic system is not a closed system. The human circulatory system processes an average of 20 liters of blood per day through capillary filtration, which removes plasma while leaving the blood cells. Roughly 17 liters of the filtered plasma is reabsorbed directly into the blood vessels, while the remaining three liters remain in the interstitial fluid. 

One of the main functions of the lymph system is to provide an accessory return route to the blood for the surplus three liters. 

The other main function is that of defense in the immune system. Lymph is very similar to blood plasma; it contains lymphocytes. It also contains waste products and cellular debris together with bacteria and proteins. Associated organs composed of lymphoid tissue are the sites of lymphocyte production. Lymphocytes are concentrated in the lymph nodes. The spleen and the thymus are also lymphoid organs of the immune system. The tonsils are lymphoid organs that are also associated with the digestive system. Lymphoid tissues contain lymphocytes, and also contain other types of cells for support. The system also includes all the structures dedicated to the circulation and production of lymphocytes (the primary cellular component of lymph), which also includes the bone marrow, and the lymphoid tissue associated with the digestive system. 


Functions of lymphatic system 

  • Helps rid body of toxins, waste, and other materials 
  • Transports lymph throughout body 
  • Lymph is filtered and screened through lymph nodes and then fluid return back to blood vessels 



  • Colorless fluid with white blood cells 
  • Bathes tissues and drains through lymphatic system into bloodstream 
  • Moves through capillary walls into fluid between cells  
  • Scans for microorganisms and returns lymph to circulatory system 


What happens to lymph after lymphatic system sends it back to circulatory system? 

  • Kidneys filter bodily waste  
  • Lymphatic system looks for infection 


What does the fluid between cells contain? 

  • Nutrients, dissolved oxygen, salts. 


    Parts of lymphatic system: 

               – lymph nodes 

               – thymus 

               – spleen  

               – blood 


               Lymph nodes 

  • is an organized collection of lymphoid tissue, through which the lymph passes on its way back to the blood 
  • act as filters, trapping microorganisms, stray cancer cells, and debris as lymph flows through node  
  • found in neck, armpit, and groin 



  • is a specialized primary lymphoid organ of the immune system 
  • produces T-cells for immune system to fight infection  
  • also part of endocrine system 



  • is an organ similar in structure to a large lymph node 
  • acts primarily as a blood filter 
  • filters blood as it flows through 
  • removes particulate matter and aged/damaged blood cells (mainly red blood cells) and stores platelets  
  • produces blood cells during fetal life 



  • is a body fluid in humans and other animals  
  • delivers necessary substances such as nutrients and oxygen to the cells 
  • transports metabolic waste products away from those same cells 


What systems is blood part of? 

  • Lymphatic and circulatory 


How much blood does the human body contain? 

  • 4-6 liters 


What does blood contain? 

        – 55% plasma 

        – red blood cells 

        – white blood cells 

        – platelets 



  • straw colored fluid  
  • 90% water and 10% dissolved gases, salts, nutrients, enzymes, hormones, waste, proteins, and cholesterol 


          Red blood cells 

  • transport oxygen  
  • average lifespan of 120 days before destroyed in liver and spleen 
  • red because of iron found in hemoglobin 



  • protein that binds oxygen in lungs and release it in capillary networks throughout body 


          White blood cells 

  • guard against infection, fight parasites, and attack bacteria 
  • WBC number increases during infection 



  • sticky substance 
  • cause blood to clot because of composition of plasma proteins and cell fragments