The lymphatic system has three primary functions:
Fluid balance
The lymphatic system helps maintain fluid balance. It returns excess fluid and proteins from the tissues that cannot be returned through the blood vessels. The fluid is found in tissue spaces and cavities, in the tiny spaces surrounding cells, known as the interstitial spaces. These are reached by the smallest blood and lymph capillaries.
Around 90 percent of the plasma that reaches tissues from the arterial blood capillaries is returned by the venous capillaries and back along veins. The remaining 10 percent is drained back by the lymphatics.
Each day, around 2-3 liters is returned. This fluid includes proteins that are too large to be transported via the blood vessels. Loss of the lymphatic system would be fatal within a day. Without the lymphatic system draining excess fluid, our tissues would swell, blood volume would be lost and pressure would increase.
Absorption
Most of the fats absorbed from the gastrointestinal tract are taken up in a part of the gut membrane in the small intestine that is specially adapted by the lymphatic system.
The lymphatic system has tiny lacteals in this part of the intestine that form part of the villi. These finger-like protruding structures are produced by the tiny folds in the absorptive surface of the gut. Lacteals absorb fats and fat-soluble vitamins to form a milky white fluid called chyle.
This fluid contains lymph and emulsified fats, or free fatty acids. It delivers nutrients indirectly when it reaches the venous blood circulation. Blood capillaries take up other nutrients directly.
The immune system
The third function is to defend the body against unwanted organisms. Without it, we would die very soon from an infection.
Our bodies are constantly exposed to potentially hazardous micro-organisms, such as infections.
The body’s first line of defense involves:
- physical barriers, such as the skin
- toxic barriers, such as the acidic contents of the stomach
- “friendly” bacteria in the body
However, pathogens often do succeed in entering the body despite these defenses. In this case, the lymphatic system enables our immune system to respond appropriately. 
If the immune system is not able to fight off these micro-organisms, or pathogens, they can be harmful and even fatal. A number of different immune cells and special molecules work together to fight off the unwanted pathogens.
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