Which of the following organs is part of the lymphatic system?

The spleen is indeed a vital organ of the lymphatic system. Its primary role is to filter blood and help the body fight infections. The spleen contains lymphocytes and other immune cells that respond to pathogens in the bloodstream. By filtering out old or damaged blood cells and microorganisms, the spleen contributes significantly to maintaining a healthy immune response.

The lymphatic system is crucial for both fluid balance in the body and the immune system, and the spleen plays a key role in those functions. It helps produce lymphocytes, which are essential for adaptive immunity, and also serves as a reservoir for blood. The other options listed—skin, liver, and stomach—do not belong to the lymphatic system. The skin serves as a protective barrier, the liver is involved in metabolic processes and detoxification, and the stomach plays a role in digestion. These functions, while important, do not pertain to the lymphatic system's structure or roles in immunity and fluid regulation.