Parenchyma

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Parenchyma ( ancient Greek παρά para , German 'next to' , ancient Greek ἐγχεῖν enchein 'pour in'; literally 'that which is poured in next to' ) describes a tissue in biology that performs a certain function. The term was best known through Rudolf Virchow (1821–1902), who applied it to animal and plant tissue as part of his cellular pathology .

The parenchymal tissue is formed by the more or less differentiated or specific parenchymal cells . In contrast to this, vertebrates have cells that form the supporting tissue or support or framework tissue ( mesodermal connective tissue ). One also speaks of the interstitium (or stroma ) into which the parenchyma is "poured".

In vertebrates

Parenchyma refers to the tissue formed by the specific functional cells of an organ (e.g. the nephrons of the kidney , the alveoli of the lungs , the white and red pulp of the spleen ). In contrast to this is the interstitium (also called stroma ), the subdividing connective tissue that does not take on any actual organ function, but contains the supplying and draining vessels and nerves and which separates the organ from its surroundings and holds and supports it in its shape. The parenchyma is mostly derived from the ectoderm or the endoderm . So come z. B. the nerve cells of the ectoderm (neural groove).

Parenchymal tissue is usually differentiated from mesodermal connective tissue . This should like to express subliminally that this is derived from the mesoderm and is on a less high degree of differentiation . But also from the mesoderm specific organ structures develop such. B. smooth and striated muscles . The evolutionary origin from a certain germ leaf does not necessarily say anything about differences in differentiation.

With worms

In various worms such as B. Flatworms parenchyma "a tissue that fills the inside of the body and in which the organs are embedded".

With plants

Parenchyma cells in the ray of Picea abies

Most of the time, the cells that make up the tissue do not show any particular anatomical differentiation. Parenchymal cells are thin-walled cells of the basic tissue that make up the majority of non-woody (herbaceous) plant structures (although in some cases their cell walls can be lignified) and serve, for example, to store nutrients . A distinction is made between several types.

Palisade parenchyma

The palisade parenchyma or palisade tissue is a plant tissue that is found in the leaves of the higher plants below the upper epidermis. It consists of elongated, cylindrical cells and is mainly used for photosynthesis . Adjacent cells therefore resemble palisades if a leaf cross-section is viewed with a light microscope . It should be noted, however, that the cells of the palisade parenchyma are not only arranged in a row, but also to form a surface. Intercellular cells are rare in this tissue. Palisade parenchyma cells contain around three to five times as many chloroplasts as sponge parenchyma cells .

Leaves that are often exposed to sunlight (so-called sun leaves) have a multi-layered palisade parenchyma, while the palisade cells in shade leaves usually only form one layer so that the cells of the sponge parenchyma can also use the low light intensity.

Sponge parenchyma

Structure of a leaf with palisade fabric and sponge fabric

The sponge parenchyma or sponge tissue is a plant tissue of the foliage leaf, which in the leaf interior borders on the lower epidermis and above on the palisade parenchyma, or in equifacial leaves is surrounded by two palisade tissues . It consists of mostly irregularly shaped, often star-shaped cells (is then referred to as star parenchyma ), between which there are larger intercellular spaces . Compared to the palisade parenchyma, the sponge parenchyma contains fewer chloroplasts. It is primarily used for gas exchange during photosynthesis , which is favored by the intercellular system, as this results in the formation of large internal surfaces in the leaf. In the case of the trumpet tree, for example, 5100 m² of inner surface was measured with only 390 m² of outer leaf surface.

In general, a sponge parenchyma is only referred to as such if a palisade parenchyma is also present.

Chlorenchyma (assimilation parenchyma)

The chlorenchyma , also assimilation parenchyma , is the parenchyma that specializes in photosynthesis. It is a chloroplast-rich leaf tissue (mesophyll), which consists of the palisade layer and the sponge parenchyma. The sponge parenchyma is both chlorenchyma and aerenchyma.

  • Aerenchyma (star parenchyma) of a marsh plant

  • Storage parenchyma
    in the root of the celandine

Aerenchyma

Under Aerenchym refers to a form of vegetable raw tissue in the intercellular spaces are so far that a veritable "aerenchyma" arises. It occurs particularly in swamp and aquatic plants and serves to exchange gas in the submerged plant organs .

Hydrenchyma

Hydrenchyma can also be referred to as "water storage parenchyma ". It is mainly used by succulent plants to store water and has cells with very large vacuoles .

Storage parenchyma

Storage parenchyma is used to store nutrients such as starch, fats, proteins and water.

Web links

Wiktionary: Parenchyma  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. ↑ An earlier evidence for the use of the word: Schriften von Henrich Steffens , Second Volume, Breslau 1821 , p. 73 (in the form Parenchyma )
  2. ^ Pschyrembel, Willibald : Clinical Dictionary. Walter de Gruyter & Co, Berlin, 184th edition 1964, p. 658
  3. ^ A b Dagmar Reiche : Roche Lexikon Medizin Elsevier, Munich, 5th edition 2003, p. 1414
  4. ^ FA Brockhaus: The large foreign dictionary. Brockhaus Enzyklopädie, Leipzig 2001, ISBN 3-7653-1270-3 , p. 991
  5. ↑ Otto Grosser et al .: Outline of the human development history . Springer, Berlin 1966, p. 183
  6. ^ FA Brockhaus: The Great Brockhaus . Compact edition in 26 volumes, FA Brockhaus, Wiesbaden, 18th edition 1983, volume 16, p. 254

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