Corpus: Parenchyma

The term parenchyma refers to the organ-specific tissue in contrast to the interstitial connective tissue, the stroma. The function of an organ is largely performed by the parenchyma.

The parenchyma consists of specialised cells, the parenchyma cells. As a whole, they fulfil the actual function of the organ. The liver parenchyma, for example, consists of hepatocytes, the thyroid parenchyma of thyrocytes.

The stroma, on the other hand, does not fulfil any organ function, but is essentially responsible for the tissue architecture and supply of the parenchyma. Accordingly, it contains fibre elements as well as supplying and draining vessels and nerves.

Parenchyma and interstitial connective tissue are not strictly separate anatomical compartments, but form a close functional unit at the microscopic level. Parenchymal cells and stromal cells co-ordinate their cell activity by influencing each other biochemically, e.g. through growth factors.

Embryologically, the parenchyma is usually derived from the ectoderm or endoderm.

In everyday clinical language, the term "parenchyma" is usually used in a less differentiated way. In imaging, it usually simply refers to the interior of an organ, e.g. in contrast to the organ capsule.