How does the immune system works ? ( in 3 steps )

Anatomy of the Immune System

.The immune system is a mobile, circulatingsystem. However, there are some fixed anatomical structures which are important to its function:

immune cells are made within the bone marrow during haematopoiesis

the thymus gland is situated just in front of the heart in the mediastinum. It is active throughout life, but is at its largest in childhood and decreases in size after puberty. It is where lymphocytes mature and receive their immunological “education” before being released into the bloodstream.

mature lymphocytes migrate to lymph nodes, which are small bean-like structures situated along the lymphatic vasculature throughout the body. These filter lymph and provide a site for antigen presentation to the adaptive immune system. Lymph is then returned to the systemic circulation via the thoracic duct, which joins with the left subclavian vein.

the spleen is basically a massive lymph node and is, therefore, another site of antigen presentation to mature lymphocytes. It is part of the reticulo-endothelial system which filters blood and removes old cells, tissue debris, pathogens and immune complexes. It also stores red blood cells and immature monocytes.

finally, the liver is also a site of antigen presentation and contains its own cohort of phagocytes and lymphocytes. This is a vital role, as the liver filters large volumes of potentially contaminated venous blood from the gastrointestinal (GI) tract. It also synthesises acute phase proteins such as CRP in response to infection.