Organ (anatomy)

An Organ was a complex system in an organism which typically performed a vital process which kept the organism alive.

A heart was an organ used to pump blood through the body. Time Lords had two hearts. (TV: Spearhead from Space, et al)

A stomach was an organ in the digestive tract use by many species to digest food and some by others as a form of communication. (TV: Flatline)

Time Lords possessed an organ called an exo-spleen. (TV: The Tsuranga Conundrum)

A lung was an organ primarily used for respiration. (TV: Smith and Jones) Though some species could uses them aggressively. (TV: Boom Town)