Parenchyma

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Parenchyma

A ground tissue of plants chiefly concerned with the manufacture and storage of food. The primary functions of plants, such as photosynthesis, assimilation, respiration, storage, secretion, and excretion—those associated with living protoplasm—proceed mainly in parenchymal cells. Parenchyma is frequently found as a homogeneous tissue in stems, roots, leaves, and flower parts. Other tissues, such as sclerenchyma, xylem, and phloem, seem to be embedded in a matrix of parenchyma; hence the use of the term ground tissue with regard to parenchyma is derived. The parenchymal cell is one of the most frequently occurring cell types in the plant kingdom. See Plant anatomy, Plant physiology

Typical parenchyma occurs in pith and cortex of roots and stems as a relatively undifferentiated tissue composed of polyhedral cells that may be more or less compactly arranged and show little variation in size or shape. The mesophyll, that is, the tissue located between the upper and lower epidermis of leaves, is a specially differentiated parenchyma called chlorenchyma because its cells contain chlorophyll in distinct chloroplastids.

This chlorenchymatous tissue is the major locus of photosynthetic activity and consequently is one of the more important variants of parenchyma. Specialized secretory parenchymal cells are found lining resin ducts and other secretory structures. See Photosynthesis, Secretory structures (plant)

Parenchyma

 

(1) The fundamental tissue in plants. Parenchyma is composed of cells having a polyhedral shape, with the various diameters differing very little from each other. The cells form homogeneous aggregates in the plant body and fill the spaces between other tissues. They serve as part of the conductive and mechanical tissues. As a result of functional specialization of protoplasts, parenchyma cells may perform assimilative, excretive, and other functions. The presence of intercellular substances, especially in diffuse parenchyma with vacuoles, determines the tissue’s role in gas exchange. Parenchyma cells serving support functions may be elongated, branched, or stellate; their walls are thick and often lignified. Living parenchyma cells are capable of division. Phellogen (cork cambium) or, in unusually thick plants, cambium is formed (for example, in beets and certain lianas).

(2) In animals, parenchyma is the phylogenetic precursor of true tissue. It is divided into primary parenchyma and mixed parenchyma. The former is a bond of homogeneous cells without systematic organization. The cells are not fused in a syncytium or separated by interstitial matter (as in the embryos of certain hydroids in the morular stage). Mixed parenchyma is an aggregate of heterogeneous cells distributed randomly, as in the bodies of Acoela. At times, the term “parenchyma” is used to designate the principal functional tissue of the liver, spleen, lungs, and glands. It is also used to designate striated muscle tissue.

parenchyma

[pə′reŋ·kə·mə]
(botany)
A tissue of higher plants consisting of living cells with thin walls that are agents of photosynthesis and storage; abundant in leaves, roots, and the pulp of fruit, and found also in leaves and stems.
(histology)
The specialized epithelial portion of an organ, as contrasted with the supporting connective tissue and nutritive framework.
References in periodicals archive ?
In place of hypodermal fibers, multiple layers of parenchyma cells compose a zone of cells which are smaller and more densely staining than those of the parenchymatous zone subjacent to the secretory epidermis (Fig.
After anthesis, the ovary presents uniseriate outer epidermis and mesophyll with three tissue regions: 1) An outer parenchymatous region, with thin-walled cells that vary in size and shape, and may present druses; 2) A middle region that originates from the middle meristem and consists of elongated cells that are oriented obliquely or transversely to the longitudinal axis of the ovary; and 3) An inner region that is uniseriate and has short palisade-like cells.
Thyroid morphology of animals treated with PTU was characterized by the presence of parenchymatous goiter with intra- and interfollicular adenomatosis.
Beneath the epidermis, a few layers of small, rounded parenchymatous cells were filled with red-brown unidentified contents.
This revealed midden deposits containing fragmented animal bone, whole and fragmented shells, bone tool fragments, lithic debitage and plant remains including charred parenchymatous tissues and nut fragments.
These bundles were immediately adjacent to photosynthesizing chlorophyllous parenchymatous cells, in the outer extremities of the rachis and presumably functioned to transport nascently synthesized assimilates into the tissues of the rachis.
Bacterial invasion occurs mostly during the dry period, particularly during late gestation, and leads to glandular damage in parenchymatous tissue.
Many cases of herpesvirus infection are associated with inclusion bodies and necrotizing lesions in the parenchymatous organs.
At the dose of 50 mg/kg, mild parenchymatous degeneration of cells of renal tubules, moderate congestion and mild hemorrhage were observed.
The stems pith, medullary rays and cortex are very extensively parenchymatous.
Blue stain, or sap stain, is a phenomenon caused by pigmented micro-fungi growing primarily in the parenchymatous tissue of sapwood where starch and sugars are available.
Necropsy of the dogs showed hemorrhagic enteritis, abundant serosanguineous fluid in the abdominal cavity, and severe lesions in the parenchymatous organs.