The Immune System . Chapter 21. Immune System. functional system rather than organ system Hematopoetic Vasculature Lymphatic. Fig 21.1. Innate vs. Adaptive Immune System – Introduction. Innate: structural defenses; responds to nonspecific foreign substances
*Humoral and/or cell mediated
= Site of lymphocyte origin
Red bone marrow
= Site of development of immunocompetence as B or T cells; primary lymphoid organs
= Site of antigen challenge & final differentiation to activated B & T cells
Circulation in blood
Lymphocytes destined to become T cells migrate to the thymus & develop immunocompetence there. B cells develop immunocompetence in red bone marrow.
After leaving the thymus or bone marrow as naive immunocompetent cells, lymphocytes “seed” the lymph nodes, spleen, & other lymphoid tissues where the antigen challenge occurs.
Immunocompetent, but still naive, lymphocyte migrates via blood
Lymph nodes, spleen, & other lymphoid tissues
Mature (antigen-activated) immunocompetent lymphocytes circulate continuously in the bloodstream & lymph & throughout the lymphoid organs of the body.
Activated immunocompetent B & T cells recirculate in blood & lymph