The parenchyma are the functional parts of an organ in the body. This is in contrast to the stroma, which refers to the structural tissue of organs, namely, the connective tissues.
In cancer, the parenchyma refers to the actual mutant cells of the single lineage, whereas the stroma is the surrounding connective tissue and associated cells that support it.
Early in development the mammalian embryo has three distinct layers: ectoderm (external layer), endoderm (internal layer) and in between those two layers the middle layer or mesoderm. The parenchyma of most organs is of ectodermal (brain, skin) or endodermal origin (lungs, gastrointestinal tract, liver, pancreas). The parenchyma of a few organs (spleen, kidneys, heart) is of mesodermal origin. The stroma of all organs is of mesodermal origin.
Examples include:
| Organ | Parenchyma |
| brain | neurons and glial cells |
| heart | myocyte |
| kidney | nephron |
| liver | hepatocyte |
| lungs | Lung parenchyma in its strictest sense refers solely to alveolar tissue with respiratory bronchioles, alveolar ducts and terminal bronchioles. However, the term is often used loosely to refer to any form of lung tissue, also including bronchioles, bronchi, blood vessels and lung interstitium. Source: Medical Dictionary - 'Parenchyma Of Lung' In turn citing: Stedman's Medical Dictionary. 2006 |
| ovary | Follicles with egg cells |
| pancreas | Islets of Langerhans and Pancreatic acini |
| spleen | white pulp and red pulp |
| placenta | placental villi, including the fetal vessels, and the maternal intervillous space; non-parenchyma comprises chorionic and decidual plates, fetal vessels of diameter >0.1 cm and intercotyledonary septa (Aherne, W. & Dunnill, M. S. (1966) Quantitative aspects of placental structure. J Path Bacteriol 91 123-139) |
Read more about Parenchyma: In Plants