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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.
|brain||neurons and glial cells|
|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)|
In plants, "parenchyma" is one of the three main types of ground tissue. Parenchyma cells make up the bulk of the soft parts of plants.