Just about all vertebrates have an organ called the "spleen". The spleen has a similar structure to a large lymph node and acts primarily as a blood filter. The spleen plays important roles in regard to red blood cells and the immune system. The spleen removes old blood cells and holds a reserve of blood, which can be valuable in the case of shock. The spleen also synthesizes antibodies in its white pulp and removes antibody-coated bacteria and antibody-coated blood cells by way of blood and lymph node circulation.
![](//4.bp.blogspot.com/-wUXMZ4Lrgqc/VEU9eFwJGDI/AAAAAAAAC9s/frUSBYtU8vU/s280/Illu_spleen.jpg) |
Image courtesy US Government |
![Spleen under microscope Spleen under microscope at 40x magnification.](//4.bp.blogspot.com/-TUbmkMIISuE/VEU_CCZAriI/AAAAAAAAC94/Q_wDYo4yCxA/s280/Spleen-40x-total.jpg) |
Spleen captured under the microscope at 40x magnification. |
![Spleen under microscope Spleen under the microscope at 100x magnification.](//4.bp.blogspot.com/-Re2dnSPD5FY/VEU_Go_sZJI/AAAAAAAAC-I/ySJqYl40HYI/s280/Spleen100x-total.jpg) |
Spleen captured under the microscope at 100x magnification. |
![Spleen under microscope Spleen captured under microscope at 400x.](//1.bp.blogspot.com/-PjXbuJwZC8o/VEU_Ezz4vnI/AAAAAAAAC-A/Gza7esrBN44/s280/Spleen-400x-total.jpg) |
Spleen captured under the microscope at 400x magnification. |