Which of the following is primarily filtered by the spleen?

• A. Blood
• B. Lymph
• C. Interstitial fluid
• D. Plasma

Answer: (A)

The spleen primarily functions to filter blood, making it essential for the immune response and the removal of old or damaged red blood cells. Situated in the upper left abdomen, the spleen plays a critical role in maintaining the body’s blood supply and recycling iron from hemoglobin. It filters out pathogens, debris, and cellular waste from circulating blood, thus contributing to both immune surveillance and hematological health.

Although lymph, interstitial fluid, and plasma are all important components of the body's fluid systems, they are not the primary focus of the spleen's filtering action. Lymph is filtered by lymph nodes, which are designed to trap and destroy pathogens and foreign substances that have entered through the lymphatic system. Interstitial fluid is the fluid that surrounds tissue cells and is involved in nutrient and waste exchange but does not pass through the spleen. Similarly, while plasma is a component of blood, the spleen specifically targets whole blood for filtering, rather than selectively filtering the plasma alone.

In summary, the role of the spleen is to manage and filter blood, ensuring that the body effectively removes damaged cells and potential threats to health, reinforcing its significance in the lymphatic and immune systems.