Parenchym

Parenchym, or parenchyma, is a term used in biology to describe the functional tissue of an organ, in contrast to the organ’s supportive framework (stroma). In plants, parenchym is the most common ground tissue and consists of living cells with relatively thin primary walls. Parenchym cells are usually rounded or elongated, with large central vacuoles and abundant cytoplasm. The tissue forms the soft, fleshy parts of the plant: the cortex and pith of stems, the mesophyll of leaves, and the flesh of roots and fruits. Because parenchym cells retain the capacity to divide, they participate in wound repair and regrowth, and they can store nutrients.

Specialized forms include chlorenchym, which contains chloroplasts and carries out photosynthesis in leaves and green stems; storage parenchym, which stores starch, oils, or fats; and aerenchym, which develops air-filled spaces to aid buoyancy and gas exchange in some aquatic plants. Parenchym can also be important in wound healing and regeneration in plants.

In animals, parenchym refers to the functional tissue of an organ as opposed to its stroma, the connective framework. Parenchymal cells perform the organ’s specific tasks, such as hepatocytes in the liver, renal tubule cells in the kidney, or neurons in the brain. The term is also used in pathology to describe tumors arising from parenchymal cells, e.g., carcinomas and other neoplasms, in contrast to tumors composed mainly of stromal tissue.

Parenchym thus denotes both a broad plant tissue type responsible for metabolism, storage, and photosynthesis, and a general term for the functional tissue of animal organs.