The lymphatic system is critical to the body’s ability to maintain immunity to illnesses. It is composed of tissues, vessels, and organs, such as; tonsils, lymph nodes and the spleen. The lymphatic system works with the cardiovascular system to filter foreign substances through these tissues; allowing them to be removed. 

Organs within the lymphatic system contain large quantities of white blood cells that defend the body against invading infectious agents, such as; microorganisms. When a foreign substance enters the body, it triggers the white blood cells to attack; releasing antibodies and histamines as they fend off the intruder. However, beyond viruses, bacteria, and other pathogens, there are other invaders that attack the human body. 

The allergic response  

Allergies are the result of the immune system overreacting to foreign substances. An allergic response can be mild to life-threatening. Below is an outline of a typical allergic response:

• First Exposure to Allergen: Upon first exposure to an allergen, it is flooded with white blood cells, and the immune system begins to produce antibodies to combat the response.
• Second Exposure to Allergen: During the second exposure, the body increases production of antibodies. 
• Histamines Are Released: An inflammatory response occurs as white blood cells release chemicals, such as histamines. 

Severities of allergic reactions 

There are various levels of allergic reactions the body can have: 

• Allergic rhinitis relates to exposure to allergens that cause irritation to the nose and throat linings. Allergens that frequently cause this irritation are; dust, pollen and pet hair. Common symptoms include; watery or stinging eyes, sneezing, coughing, and itchiness.  
• Food allergies occur when the immune response to particular foods is over-reactive. Common triggers foods include; nuts and seafood. After consuming the triggering food, symptoms can occur immediately or develop over several hours. Frequent symptoms to food allergy reactions include;  mouth and throat swelling, vomiting, skin rashes, and diarrhoea.
• Anaphylaxis is an extreme reaction to an allergen. Anaphylaxis occurs when hypersensitivity to an allergen causes the entire body to react in an immune response. Vast quantities of histamines are released; leading the blood pressure within the body to drop. The rare and extreme immune response can lead to restriction of the airways and is potentially fatal. When exposed to a foreign substance, secondary exposure results in a faster response that is more severe than the first; regardless of whether the substance is a pathogen or allergen. 

||Biology||Article||Physiology||All Year Levels||