A clean educational flowchart titled "Lymphoid System" showing the classification of lymphoid organs. Top level: "Lymphoid System" box with subtitle "Enables lymphocytes to encounter antigens; initiates adaptive immune responses" Second level splits into two branches: Left branch: "Primary (Central) Lymphoid Organs" - Sites of antigen-INDEPENDENT lymphocyte proliferation - B & T lymphocytes differentiate from stem cells into mature naïve effector cells - Sub-boxes: "Bone Marrow" and "Thymus" Right branch: "Secondary (Peripheral) Lymphoid Organs" - Provide environment for lymphocytes to interact with each other, accessory cells, and antigens - Initiate antigen-specific primary immune responses - Sub-boxes: "Lymph Nodes", "Spleen", "Peyer's Patches", "Tonsils & Adenoids", "Appendix", "MALT (Mucosa-Associated Lymphoid Tissue)" Also a separate node: "Blood & Lymphatic Vessels" - Carry lymphocytes to and from lymphoid structures (also considered lymphoid organs) Use a clean medical education style with color-coded boxes (blue for primary, green for secondary, purple for vessels), arrows connecting levels, white background