| Primary Function |
T-cell maturation and education. It's where T-lymphocytes learn to distinguish self from non-self (central tolerance). |
Filter lymph and serve as sites for immune surveillance and activation of adaptive immune responses. |
Filters blood, removes old/damaged red blood cells, and mounts immune responses against blood-borne pathogens. |
| What it Filters |
Does not filter fluid; it's a primary lymphoid organ for cell maturation. |
Lymph fluid from surrounding tissues. |
Blood. |
| Key Cell Types |
Developing T-lymphocytes (thymocytes), epithelial cells, and macrophages. |
B-lymphocytes (in follicles), T-lymphocytes (in paracortex), macrophages, and dendritic cells. |
Red Pulp: Macrophages, red blood cells, platelets. White Pulp: B-lymphocytes and T-lymphocytes. |
| Key Structures |
Cortex (dense with immature T-cells) and Medulla (fewer, mature T-cells and Hassall's corpuscles). |
Cortex (with B-cell follicles), Paracortex (T-cell zone), and Medulla (with medullary cords and sinuses). |
Red Pulp: Sinusoids and splenic cords. White Pulp: Periarteriolar lymphoid sheaths (PALS) rich in T-cells and follicles with B-cells. |
| Life Cycle |
Large and active in childhood, undergoes involution (shrinks and is replaced by fat) after puberty. |
Functional throughout life. |
Functional throughout life, though it can be removed (splenectomy). |
| Vascular/Lymphatic Connection |
Has efferent lymphatics but no afferent lymphatics. |
Has both afferent (incoming) and efferent (outgoing) lymphatic vessels. |
Connected to the circulatory system via the splenic artery and splenic vein. Has efferent lymphatics but no afferent lymphatics. |