Liver
From Memory Alpha, the free Star Trek reference
The liver is an organ that is vital to metabolism. It filters toxins out of the blood and produces bile, which plays an important role in the digestive system.
The Vulcan heart is located where a Human's liver would be. (TOS: "Mudd's Women", "A Private Little War")
Liver was a delicacy among many species. Phlox was fond of chicken liver with grated cheese and slug liver was enjoyed by Ferengi and was served in Quark's. The Klingons eat the liver of bok-rats. (ENT: "Storm Front", DS9: "The Assignment", "Soldiers of the Empire")
By 2375, livers were able to be created synthetically, although they were in short supply during the Dominion War. (DS9: "When It Rains...")
Among the many organs found in a secret laboratory on a Vidiian planetoid was the liver of a Kazon. (VOY: "Phage")
After being exposed to a temporal energy surge in 2377, Chakotay had the liver of an eighty-year old man and the kidneys of a twelve-year old boy according to The Doctor. (VOY: "Shattered")
