When we are attacked by microorganisms and foreign particles the body fights against those pathogens
The system in charge of this task is called Immune System and is able to distinguish harmful agents like viruses, worms or parasites that your body needs to distinguish from the cells and healthy tissues themselves to function properly. Detection is complicated because pathogens can evolve rapidly and deceive our immune system and allow pathogens to infect you causing serious illness.
In humans, the gastrointestinal tract, also called the digestive tract, is the organ system that when consuming your food is in charge of digesting them to extract energy and nutrients. The main functions of the gastrointestinal tract are ingestion, digestion, absorption and excretion and constitutes 70% of the immune system. This is where most of the body's biological processes are developed to protect you against diseases by identifying and killing pathogenic and tumor cells.
Disorders in the immune system can cause illness. Immunodeficiency occurs when the immune system is less or more active than normal, resulting in recurrent and life-threatening infections.
Immunodeficiency can be the result of a genetic disease, such as combined severe immunodeficiency, or being produced by drugs or an infection, such as the acquired immunodeficiency syndrome (AIDS) that is caused by the HIV retrovirus.
In contrast, autoimmune diseases are a consequence of a hyperactive immune system that attacks normal tissues as if they were foreign organisms.
Common autoimmune diseases include Hashimoto's thyroiditis, rheumatoid arthritis, type 1 diabetes mellitus, and lupus erythematosus. Immunology covers the study of all aspects of the immune system that have significant relevance to human health and disease.