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

The spleen is part of the lymphatic system as it plays a crucial role in filtering blood, removing old or damaged red blood cells, and is involved in the immune response. Located in the upper left part of the abdomen, the spleen contains white blood cells that help fight infections and diseases. It also stores platelets and white blood cells, contributing to the body's overall immune function.

In contrast, the heart, liver, and pancreas are not components of the lymphatic system. The heart is primarily part of the circulatory system, responsible for pumping blood throughout the body. The liver has various functions, including detoxification and metabolic processes, and plays significant roles in the digestive system. The pancreas is involved in both endocrine functions related to hormonal regulation of blood sugar and exocrine functions related to digestion. Understanding the specific roles of these organs helps clarify their distinct functions outside of the lymphatic system.