Which of the following organs is NOT part of the digestive system?

The spleen is not part of the digestive system; it is primarily associated with the lymphatic system and plays a key role in immune function and the recycling of iron from red blood cells. The digestive system includes organs that are involved in the process of breaking down food, absorbing nutrients, and expelling waste.

The esophagus, for example, is a muscular tube that connects the throat to the stomach and is essential for transporting food. The stomach is a hollow organ that holds food while it is mixed with stomach enzymes and acids, further aiding in digestion. The liver, which is a vital organ in the digestive system, produces bile to help digest fats and processes nutrients absorbed from the small intestine.

In contrast, the spleen's functions are focused on filtering blood and helping fight infections, rather than contributing to the digestive process.