Which organ is NOT involved in the formation of blood elements?

The kidneys are primarily involved in the regulation of various physiological functions, including the maintenance of electrolyte balance, blood pressure control, and waste elimination through urine production. While they play a significant role in erythropoiesis by producing erythropoietin, a hormone that stimulates red blood cell production in the bone marrow, they do not directly participate in the formation of blood elements themselves.

In contrast, the liver is involved in synthesizing various components necessary for blood clotting and metabolism of nutrients that can influence blood formation. The red bone marrow is the primary site for the production of all blood cells, including red blood cells, white blood cells, and platelets. Additionally, the spleen plays a role in filtering blood and recycling components of red blood cells, but it does not produce blood cells. Therefore, the kidneys do not directly contribute to the formation of blood elements, making them the correct option in this context.