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 παÏÎγχυμα - parenkhuma, "visceral flesh", f. παÏεγχεῖν - parenkhein, "to pour in" f. para-, "beside" + en-, "in" + khein, "to pour".
In plants
In plants, "parenchyma" is one of the three main types of ground tissue, and the most common. It can be distinguished through their thin cell wall as compared to other cells. Parenchyma cells make up the bulk of the soft parts of plants, including the insides of leaves, flowers and fruits (but not the epidermis or veins of these structures).
In animals
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 is often responsible for carrying out the specialized functions of the tissue".
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: