internal organ; viscera
General term for internal organs of humans and animals. Used in medical, biological, and everyday contexts.
Organ transplants require donors.
We examine the condition of the internal organs with an endoscope.
He died in an accident, and with his family's consent, his organs were donated.
The doctors transplanted a new organ into the patient.
Years of drinking have weakened his organs.
器官 is the broader biological term covering any specialized body part (including sensory organs like eyes), while 臓器 refers specifically to internal organs such as the heart or liver.
臓器 refers to a specific organ and is used in medical/countable contexts, whereas 臓 by itself is not normally used as a standalone countable noun.
臓物 refers informally to entrails or offal, especially of animals in a food or butchering context, whereas 臓器 is the neutral medical term for organs in general.
Compound of 臓 (internal organs) and 器 (container, organ). The exact historical derivation is uncertain, but the kanji combination naturally conveys the meaning of bodily organs.
organ cloning