What organ is included in the lymphatic system along with lymph glands and tonsils?

The spleen is a crucial organ within the lymphatic system as it plays several vital roles in the immune response and the maintenance of bodily fluids. It is responsible for filtering blood, removing old or damaged red blood cells, and helping produce lymphocytes, which are a type of white blood cell essential for fighting infections. The spleen also stores platelets and white blood cells, contributing further to the body's immune defense.

In contrast, the gall bladder, pancreas, and thyroid do not belong to the lymphatic system. The gall bladder is primarily involved in the storage and concentration of bile for digestion. The pancreas has both endocrine and exocrine functions, including the regulation of blood sugar and digestion, while the thyroid is an endocrine gland responsible for hormone production related to metabolism. Therefore, the role of the spleen in the lymphatic system is significant, linking it directly to immune function and fluid management in the body.