Parenchyma

Parenchyma is a term used in biology to describe the functional tissue of an organ in animals and the principal tissue of the plant ground tissue system. In plants, parenchyma is a flexible, living tissue composed of parenchyma cells with thin primary cell walls. The cells are usually alive at maturity, often isodiametric or polyhedral, and capable of cell division. Parenchyma forms most of the soft tissues of leaves, stems, roots, and fruits and can differentiate into specialized tissues such as chlorenchyma, aerenchyma, and storage parenchyma.

Chlorenchyma contains chloroplasts and carries out photosynthesis, particularly in leaves; palisade and mesophyll tissues are composed largely of chlorenchyma. Aerenchyma has extensive air spaces that facilitate buoyancy and gas exchange in aquatic plants. Amylenchyma and other storage parenchyma store starch, oils, and proteins in tubers and seeds. Parenchyma is typically alive after differentiation and can dedifferentiate to form a wounding response or repair damaged tissue.

In animals, parenchyma refers to the functional tissue of an organ as distinct from its stroma, the supportive and connective framework. The parenchymal cells perform the organ’s essential tasks, such as hepatocytes in the liver or neurons and glia in the brain. The term is often used in biopsy and pathology to describe tissue that carries out the organ’s function, with stroma including the extracellular matrix and blood vessels. Parenchyma is present in many organs, including the lung and kidney.