Parenchyma

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Parenchyma is the bulk of a substance. In animals, a parenchyma comprises the functional parts of an organ and in plants parenchyma is the ground tissue of nonwoody structures.

The term parenchyma is New Latin, f. Greek παρέγχυμα - parenkhuma, "visceral flesh", f. παρεγχεῖν - parenkhein, "to pour in" f. para-, "beside" + en-, "in" + khein, "to pour".[1]

In animals[edit]

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 portion of a tissue that lies outside the circulatory system and often is responsible for carrying out the specialized functions of the tissue".[2]

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:

OrganParenchyma
brainneurons and glial cells
heartmyocyte
kidneynephron
liverhepatocyte
lungsLung 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
ovaryFollicles with egg cells
pancreasIslets of Langerhans and Pancreatic acini
spleenwhite pulp and red pulp
placentaplacental 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[edit]

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.

References[edit]

  1. ^ Parenchyma at eMedicine Dictionary
  2. ^ Weinberg (c. 2014). The Biology of Cancer.