1. The key elements of an organ essential to its functioning, as distinct from the capsule that encompasses it and other supporting structures.

The parenchyma is therefore opposed to the connective tissue framework, or stroma, of an organ. The parenchyma of the testis consists of what are called the seminiferous tubules.

2. Etymology: from the Greek word parenchyma, "that which is poured in". It reflects the error of an ancient idea that the inner substance of solid organs like the liver, spleen, and kidneys was formed by blood that was "poured into it".