PARENCHYMA: CHARACTERISTICS, FUNCTIONS, ANIMAL AND PLANT - BIOLOGY - 2025

Parenchyma is a histological term used to define both a tissue (botany) and the functional part of an organ (zoology). The word derives from the Greek παρέγχυμα, which means substance of the organs.

In plants, the parenchyma comprises a large part of, or mainly, the so-called fundamental tissue or ground tissue. It is a little specialized tissue composed of living cells, which remain alive even after maturity; it also presents great physiological complexity.

Cells of the parenchyma of a pine stem. Taken and edited from Berkshire Community College Bioscience Image Library

In animals, the parenchyma serves to define the functional tissue of the organs. The term parenchyma was first used by the Greek physician and anatomist Erisistratus to refer to various human tissues.

On the other hand, the first to use it in botany was the botanist and father of plant anatomy, Nehemiah Grew.

characteristics

As already mentioned, the parenchyma is a term that defines both plant and animal tissues, and in each of them it has very different characteristics and types of cells.

Vegetable parenchyma

The plant parenchyma is characterized by its low degree of specialization and by making up most of the plant mass. It is made up of an abundant number of cells, with complex physiology, that present vacuoles and have thin primary walls, although these walls rarely become thick.

Cell division of plant parenchymal cells occurs through the mitotic process, and their cells are alive even after reaching maturity (a feature that distinguishes them from some other plant tissues).

These cells have various types of shapes that depend on their specific location in the plant and its role in the plant. They can be imperfect spherical, starry, polyhedron-shaped and can also be branched.

Parenchymal cells have air-filled spaces in their corners. They generally do not have chloroplasts (with some exceptions), but they do have leukoplasts. Its vacuoles are characteristic for the storage of tannins and other compounds.

This tissue is found in the plant in structures such as the soil tissue, the root bark, in regions of the xylem, the phloem, and also in leaves, flowers and fruits, but never in the woody parts.

Animal parenchyma

The animal parenchyma is characterized by being composed of highly specialized cells that perform the function of specific organs. Usually this tissue occupies most of the organ.

Because they are highly specialized fabrics, their components vary greatly. However, they always represent the functional part of an organ. The non-functional part is represented by the stroma, a supporting or supporting tissue (usually of the connective type).

In cellophane organisms (without a coelom), the term is used to define a relatively spongy mass of cells that occupy or fill the interior of the body. This type of parenchyma is formed from epidermal (ectodermal) cells, during the early stages of embryonic development.

Types

-Vegetable parenchyma

Chlorophyll

This type of plant parenchyma has an abundance of chloroplasts. Its cells are more or less cylindrical and perpendicular to the surface, and are separated by spaces. They are found under the epidermis of the green areas of the plant (stems, leaves, etc.).

At least two subtypes of chlorophyll tissues are known: lagoon tissue, located in the part where there is less incidence of light on the leaves. And the palisade tissue, located in the part where there is a greater incidence of sunlight on the leaf.

Backup

It does not present chloroplasts. The tissue is abundant in structures such as rhizomes, aerial stems, roots and tubers (such as potatoes, beets and carrots), seeds, fruit pulps, sugarcane stem, cotyledons, among others.

Airship

Also known as aerénquima. It is a tissue made up of irregular cells, separated by large spaces between one cell and another. Aeriferous tissues are characteristic of aquatic plants or humid environments. The tissue is found in both the roots and stems.

Aerenchymal tissue can be formed by three different mechanisms: schizogeny, lysogeny, and expansigenia. The first one occurs by cell differentiation, during the development of the organ.

Lysogeny is only possible under environmental stress and gaseous spaces are formed by cell death. Finally by expansigenia, a process that is not recognized by some botanists, which occurs without the need for cell junctions to disappear.

Aquifer

It is a type of tissue capable of storing water; It can store much more water than other tissues, thanks to large, vacuolated, thin-walled cells.

This tissue is found in underground organs. It is characteristic of plants that inhabit dry environments such as cacti (prickly pears and cacti, for example).

-Animal parenchyma

Due to the high specificity of the parenchymal tissues of animals, they are divided into at least four types, which are the most general and basic known :

Muscular

From the embryological point of view, it derives from the mesoderm. It is made up of myocytes or muscle fibers. There are three types of muscle tissue; cardiac, smooth and skeletal. Each one is differentiated according to its function, appearance and form.

Nervous

This tissue derives from the outer layer, which covers the embryo and which will also give rise to the epidermis (the ectoderm). It is made up of highly specialized nerve cells, called neurons and glia. These cells group together to form the central and peripheral nervous systems.

Connective

This tissue is of mesenchymal origin (mesoderm). It is the main constituent tissue of animals. They present several types of cells and a set of extracellular materials (extracellular matrix), which are a combination of collagen and elastic fibers, and a substance rich in glycosamicoglycans and proteoglycans.

Epithelial

It is a tissue that generally derives or comes from the ectoderm. Covers almost the entire body of animals. It makes up more than 60% of the body's cells. There is no extracellular matrix in this type of tissue. It extends to all the complex evaginations of the body that form the liver, lungs, sweat glands, among many more.

Histological section through the testicular parenchyma of a wild boar. Taken and edited from Mikael Häggström at English Wikipedia

Features

-Vegetable parenchyma

Chlorophyll

This type of parenchyma mainly fulfills photosynthetic functions, thanks to the numerous chloroplasts it contains. Regarding the two subtypes, palisade chlorophyll focuses on photosynthetic processes, while intercellular spaces are formed in the lagoon that facilitate respiration and water exchange.

Backup

The reserve parenchyma fulfills storage functions throughout different organs of the plant. Among the main substances that they reserve are the crystals of proteins, salts, pigments, carbohydrates (sugars), also, and mainly water, among many others.

These reserve substances vary depending on the plant species and the environment where they develop. However, what makes storage possible are the large central vacuoles, which function as the main reserve organelle.

Airship

This type of tissue develops mainly in aquatic plants (hydrophytes), its function is to leave large intercellular spaces, which serve for the conduction of gases in the plant, allowing aeration, especially when these are found in muddy, flooded or flooded.

Aquifer

The aquifer parenchyma is hyper specialized for water storage. Although all the cells of the plant necessarily store water, these with their large cells with thin walls and large vacuoles, are responsible for retaining water.

This parenchyma is more and better developed in plants that live in environments lacking water and require this tissue to survive prolonged periods of drought.

-Animal parenchyma

Epithelial

The epithelial tissue fulfills the functions of protection, storage of body fluids and internal and external transport, facilitating the absorption and secretion of substances.

An example of an epithelial parenchyma is the corpuscles and renal tubules (of the kidney) that have the function of filtering the blood and later forming urine.

Connective

The functions of the parenchyma or connective tissue are many, among which the transport of nutrients, diffusion of waste, storage of fat (energy), immune activity, among others. An example of a connective parenchyma is blood cells, especially lymphocytes from the spleen.

Nervous

The nervous parenchyma is a tissue whose functions are among the most complex known; it is responsible for coordination, transmission of the nerve impulse through long distances within the body and the immediate response. They do this through the organ called the brain and the nerve cells and glia.

Muscular

This tissue is responsible for almost all types of movement that organisms present, including those that are not voluntary. Muscle tissue also performs functions of protecting organs, producing heat and maintaining body posture.

An example of a muscle parenchyma is the cardiac muscle cells. These fulfill the function of generating contraction and relaxation movements, necessary for the blood to be propelled through the circulatory system.

Another example is that of the muscle cells of the iris (in the eye), which are responsible for contraction (iris sphincter) and dilation (iris dilator muscle) of the pupil in the presence of abundant or scarce light, respectively.

References

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