Concept of parenchyma. The main parenchymal tissues, their structure, location in plant organs, functions

The kidneys are a paired organ that is part of the urinary system. They regulate the process of hemostasis through the function of urine formation.

The surface of the kidneys is covered with parenchyma. The kidney parenchyma performs the most important functions in the body: controlling the level of electrolytes, purifying the blood. Thus, the kidneys are parenchymal organs. We will find out further what it is and what diseases it is susceptible to.

What it is?

Renal parenchyma is the tissue that makes up the kidneys. It consists of two layers: the medulla and the cortex.

Under a microscope, the cortex is visible as many small balls entwined with vessels. In them urinary fluid is formed. The medulla contains millions of pathways through which urinary fluid enters the renal pelvis.

Normal sizes adult kidneys:

length - up to 120 mm;
width - up to 60 mm.

The thickness of the parenchyma changes throughout life. The normal indicators are as follows:

Children under 16 years old - 13-16 mm.
Adults 17-60 years old - 16-21 mm.
After 60 years - 11 mm.

The cortical layer of the parenchyma has thickness from 8 to 10 mm. The structure of the parenchyma is not homogeneous and differs in individual characteristics.

Sometimes an organ structure such as partial doubling of the kidney occurs. In this case, a parenchymal constriction (bridge) is visualized, which divides the organ into two parts. This is a variant of the norm and does not cause concern to a person.

Read our article about the normal size of the kidney CL in adults and children.

Functions of parenchyma

The parenchyma is very vulnerable; it is the first to react to any pathological processes in the body. As a result, the parenchyma decreases or increases.

If the changes are not age-related, a full examination should be performed to identify the underlying cause.

The main function of the parenchyma is urine excretion, which takes place in two stages:

formation of primary urine;
formation of secondary urine.

The glomerular system of the kidneys absorbs fluid entering the body. This is how primary urine is formed. Then the reabsorption process begins, during which nutrients and some water are returned to the body.

Parenchyma ensures the removal of waste and toxins and maintains a normal volume of fluid in the body.

What are the dangers of changes in parenchyma?

Based on the thickness of the parenchyma, the doctor can judge the condition of the kidneys. Changes in the parenchyma indicate an inflammatory process in the kidneys, which developed as a result of untimely treatment of renal disease.

Thinning

We can talk about thinning of the parenchyma if its thickness is less than 1 cm.

This indicates serious renal pathologies that have long-term chronic course. If the disease proceeds slowly, then the parenchyma becomes thinner gradually. During an exacerbation, thinning occurs rapidly and the organ may lose its functions, which poses a direct threat to life.

The main causes of thinning:

kidney infections;
viral diseases (flu);
kidney inflammation;
inappropriate treatment of kidney diseases.

Thickening

An increase in the size of the parenchyma is also a symptom of serious kidney damage. Among these diseases:

With any pathological change in the parenchyma, the basic function of the kidneys is disrupted. They are no longer able to remove harmful substances from the body. The patient appears signs of intoxication:

temperature increase;
pain when urinating;
swelling of the legs and arms;
, changing its color.

If one kidney is affected, the second compensates for the impairment, taking over all functions. The greatest danger is damage to both kidneys. If the disease is neglected, the kidneys will never be able to function normally. The only chance to prolong life is regular kidney transplantation or kidney transplantation.

Tumors

Thickening of the parenchyma is dangerous because it increases the risk formation of growths in the kidneys. According to statistics, most growths are malignant in nature. The main symptoms are:

sudden weight loss;
phlebeurysm;
increased blood pressure;
sudden temperature changes.

If cancer is detected at an early stage, surgery is performed to remove the tumor or the entire kidney. Thus the patient's likelihood of survival increases.

Another common cause of thickening of the parenchyma is cystic growths. They are formed due to fluid retention in the nephrons. Typically, such cysts are up to 10 cm in size. After removal of the cyst, the renal parenchyma acquires normal thickness.

Echogenicity

Also an alarming symptom is increased echogenicity of the kidney. This condition is determined using ultrasound. Increased echogenicity indicates diseases such as:

diabetic nephropathy;
endocrine system disorders;
extensive inflammatory processes.

Diffuse changes in organs

Diffuse changes in the kidneys are not an independent disease, but a set of signs indicating pathological processes.

On ultrasound, the doctor identifies diffuse lesions (see photo below), which can be mild or severe. The final document describes parenchymal changes as follows:

Echoten, calculosis. This means the presence of sand or kidney stones.
Volumetric formations are cysts, tumors, inflammations.
Echo-positive formations of heterogeneous texture are a cancerous tumor.
Echo-negative lesions are necrotic lesions.
Anechoic formation - cyst.
Hyperechoic zone - lipoma, .
Uneven contour of the kidneys, asymmetry in size - pyelonephritis in an advanced stage.

Diffuse changes may manifest themselves with the following symptoms:

The appearance of blood in the urine.
Pain when urinating.
Lower back pain.
Chills.
Edema.

If the above symptoms appear, you should consult a doctor for differential diagnosis.

How to restore renal parenchyma?

Therapy depends on the cause of the pathology.

Inflammatory diseases treated with antibacterial drugs. The patient is also prescribed a special diet and bed rest. In cases of tumors and urolithiasis, surgical treatment is used.

Kidney tuberculosis treated with special anti-tuberculosis drugs: Isoniazid, Streptomycin. The duration of therapy is more than a year. At the same time, the affected organ tissue is removed.

You cannot self-medicate so as not to transfer the disease to an advanced stage, when irreversible changes occur in the kidney.

If changes in the renal parenchyma are suspected, a full examination should be performed in order to determine the choice of therapy. Most of these conditions are reversible.

How diffuse changes in the kidney parenchyma look on ultrasound, see the video:

Ground tissues make up most of the plant's body. By origin, the main tissues are almost always primary, formed from apical meristems. They consist of living parenchyma cells, often almost isodiametric, thin-walled, with simple pores. The main parenchyma is able to return to meristematic activity, for example during wound healing, formation of adventitious roots and shoots. Basic tissues are associated with the synthesis, accumulation and use of organic substances. Depending on the function performed, basic (typical), assimilation, storage and pneumatic basic tissues are distinguished. The main parenchyma does not have specific, strictly defined functions. It is located inside the plant body in fairly large arrays. Typical main parenchyma fills the core of the stem, the inner layers of the stem and root bark. Its cells form vertical and horizontal cords (rays), along which radial transport of substances occurs. Secondary meristems can arise from the main parenchyma. Assimilation parenchyma (chlorenchyma). Its main function is photosynthesis. Chlorenchyma is located in aboveground organs, usually under the epidermis. It is especially well developed in the leaves, less so in young stems. Characterized by the presence of intercellular spaces that facilitate gas exchange. The cells are thin-walled, with many chloroplasts in the wall layer of the cytoplasm. Their total volume can reach 70...80% of the protoplast volume. Storage parenchyma. Serves as a place for deposition of excess nutrients during a given period. Storage tissues consist of living thin-walled cells. They may contain many leucoplasts (starch), large vacuoles (sugars, inulin), many small vacuoles forming aleurone grains (protein), thick cell walls (hemicelluloses in date palm seeds), fat cells. Many plant products used by humans accumulate in these tissues. In cultivated food plants, the development of storage parenchyma is usually hypertrophied. Storage tissues are widespread and develop in a variety of organs. They can be found in potato tubers, beet roots, carrots, onion bulbs, grains of cereals, sunflower seeds, castor beans, as well as sugar cane stems, rhizomes, and roots. In plants of arid places - succulents (agaves, aloe, cacti) - water accumulates in the cells of the storage parenchyma, just like in plants of saline habitats (saltweed). Large water-bearing cells are found in the stems of cereals. The vacuoles of aquifer cells contain mucous substances with a high water-holding capacity. Air-bearing parenchyma (aerenchyma). Performs ventilation and partly respiratory functions, providing tissues with oxygen. Consists of cells of various shapes (for example, stellate) and large intercellular spaces. It is well developed in plant organs immersed in water (in the pedicels of water lilies, in the stems of cotton grass, whitewing, pondweed, and in the roots of reeds). This name combines the tissues that make up the bulk of the various organs of the plant. They are also called performing, main parenchyma or simply parenchyma. The ground tissue consists of living parenchyma cells with thin walls. There are intercellular spaces between the cells. Parenchyma cells perform a variety of functions: photosynthesis, storage of reserve products, absorption of substances, etc. The following main tissues are distinguished. Assimilation, or chlorophyll-bearing, parenchyma (chlorenchyma) is located in the leaves and bark of young stems. The cells of the assimilative parenchyma contain chloroplasts and carry out photosynthesis. Structure and functions. The main function of assimilation tissues is photosynthesis. It is in these tissues that the bulk of organic substances are synthesized and the energy received by the Earth from the Sun is bound.

The process of photosynthesis determines the character of the entire biosphere of our planet and makes it suitable for human life. Assimilation tissues have a relatively simple structure and consist of fairly uniform thin-walled parenchyma cells. Their wall layer of cytoplasm contains numerous chloroplasts. This arrangement has a certain adaptive meaning: the cell contains a large number of chloroplasts, which shade each other to the least extent and are close to the source of CO 2 coming from outside. Depending on lighting conditions and gas exchange, chloroplasts move easily (as can be clearly seen in Elodea leaves). In some cases, an increase in the surface of the wall layer of cytoplasm, and therefore the number of chloroplasts in the cell, is achieved by the fact that the membrane forms folds, protruding cells, as in pine needles. As observations using an electron microscope and mathematical calculations have shown, in a growing chlorenchyma cell the number of chloroplasts quickly increases by 5 or more times; the number of ribosomes and thylakoids in them also increases. The total volume of chloroplasts can reach 70-80% of the total volume of the cellular protoplast. After photosynthesis has reached its maximum, reverse changes are observed in the adult cell, which determine aging. However, if chloroplasts are formed in growing cells in all plants within 5-10 days, then the duration of their existence and the rate of aging can vary from a few weeks (in grasses, deciduous trees) to several years (for example, in evergreens). Location in the plant body. Assimilation tissues in the plant body most often lie directly under the transparent skin (epidermis), which ensures gas exchange and good lighting. The chlorenchyma contains large intercellular spaces that facilitate the circulation of gases. Translucent through the transparent epidermis, chlorenchyma gives green color to leaves and young stems. Sometimes chlorenchyma is located deep in the stem, under the mechanical tissue or even deeper, around the vascular bundles. In the latter case, it is probably not the synthesis of carbohydrates that is of main importance, but the release of oxygen during respiration. This oxygen is consumed during respiration by the internal tissues of the stem, primarily by the living cells of the vascular bundles, the respiration of which is necessary for intensive activity associated with the conduction of substances. Chlorenchyma is also present in flower organs and fruits. In rare cases, it is also formed in roots accessible to light (in aerial roots, in the roots of aquatic plants). Storage parenchyma is located mainly in the core of the stem and root bark, as well as in the reproductive organs - seeds, fruits, bulbs, tubers, etc. Storage tissue can also include water-storing tissue of plants in arid habitats (cacti, aloe, etc.). Structure and functions. Substances synthesized by the plant or taken in from the outside can be deposited as reserves. All living cells are capable of accumulating reserve substances. Storage tissues are spoken of in cases where the storage function comes first. Storage tissues are widespread in many plants and in a wide variety of organs. They are stored in seeds and serve for the future development of the embryo. Annual plants that go through their entire life cycle in one season usually do not have significant deposits of substances in their vegetative organs. Perennial plants accumulate reserves of substances both in ordinary roots and shoots, and in specialized organs - tubers, rhizomes, bulbs, using up these reserves after dormant periods. Storage tissues consist of living, most often parenchymal cells. Types of reserve substances. Substances accumulate in solid or dissolved form. Starch and storage proteins are deposited in the form of solid grains. In some plants, hemicelluloses, which are part of the shells, can serve as a reserve substance. For example, many hemicelluloses are found in the thick cell walls of date palm seeds. During seed germination, hemicelluloses are converted by enzymes into sugars mobilized by the seedling.

Sugars accumulate in dissolved form, for example, in the roots of beets, carrots, onion bulbs, in the stalks of sugar cane, in the pulp of grapes, watermelon, etc.

Plants that periodically lack water sometimes form special water-bearing storage tissues. Most often, these tissues consist of large, thin-walled parenchyma cells that contain mucus that helps retain water. The absorptive parenchyma is most typically represented in the absorptive zone of the root by a layer of cells with root hairs (epiblema). Aerenchyma is especially well expressed in the underwater organs of plants, in aerial and respiratory roots. It has large intercellular spaces interconnected into one ventilation network. Functions of intercellular spaces. In all organs and almost all tissues there are intercellular spaces that form connected systems. Despite the fact that the intercellular systems communicate with the external atmosphere through numerous passage holes in the integumentary tissues, the gas composition in the intercellular spaces is very different from the gas composition of the atmosphere, since cells in the process of their life activity (photosynthesis, respiration, evaporation) release some gases into the intercellular spaces and absorb other. Living conditions and the general organization of a particular plant determine the nature of the circulation of gases through the intercellular spaces necessary for normal life. Quite often, plants develop tissue with very large intercellular spaces. The structure of aerenchyma. Most often it represents a kind of modification of the parenchyma. However, the cells in it can have very different shapes, and large intercellular spaces arise with different combinations of cells. In the peduncle of the egg capsule, the aerenchyma is composed of rounded cells, and in the stem of the rush plant - stellate. Sometimes the aerenchyma includes mechanical, excretory and other cells. Aerenchyma reaches especially strong development in plants that live in an environment that impedes normal gas exchange and the supply of internal tissues with oxygen, for example, in plants immersed in water or growing in swampy soil. Direct experiments have shown that oxygen from above-ground organs enters rhizomes and roots through the intercellular spaces. Absorbing tissues play an important role in plant life. Through them, water and substances dissolved in it enter the plant body from the external environment. They are very different in structure and in distribution among higher plants. The most important is the rhizoderm (Greek. chasuble-- root; dermis- skin) - the outer layer of cells on all young roots. Through the rhizoderm, water is absorbed into the root from the soil and substances dissolved in it are absorbed. The remaining types of absorbent tissues are found either in certain systematic groups, or their presence is associated with adaptation to special conditions of existence. Therefore, they will be considered in more detail when describing the corresponding organs or groups of plants. Velamen is especially well developed on the aerial roots of orchids. They can be seen on the underside of the floating leaves of the egg capsule.

More often, parenchyma cells have a round, less often elongated shape. Characterized by the presence of developed intercellular spaces. The spaces between cells together form a transport system - apoplastic In addition, the intercellular spaces form the “ventilation system” of the plant. Through stomata, or lenticels, they are connected to atmospheric air and provide an optimal gas composition inside the plant. Developed intercellular spaces are especially necessary for plants growing in marshy soil, where normal gas exchange is difficult. This parenchyma is called aerenchyma.

Parenchyma elements, filling the gaps between other tissues, also serve as a support. Parenchyma cells are living, they do not have thick cell walls, like sclerenchyma. Therefore, mechanical properties are provided by turgor. If the water content drops, which leads to plasmolysis and wilting of the plant.

Assimilation parenchyma formed by thin-walled cells with many intercellular spaces. The cells of this structure contain many chloroplasts, which is why it is called chlorenchyma. Chloroplasts are located along the wall without shading each other. In the assimilation parenchyma, photosynthesis reactions occur, which provide the plant with organic substances and energy. The result of photosynthetic processes is the possibility of the existence of all living organisms on Earth.

Assimilation tissues are present only in the illuminated parts of the plant; they are separated from the environment by a transparent epidermis. If the epidermis is replaced by opaque secondary integumentary tissues, the assimilation parenchyma disappears.

Storage parenchyma serves as a container for organic substances that are temporarily not used by the plant organism. In principle, any cell with a living protoplast is capable of depositing organic substances in the form of various types of inclusions, but some cells specialize in this . Energy-rich compounds are deposited only during the growing season and are consumed during the dormant period and in preparation for the next growing season. Therefore, reserve substances are deposited in vegetative organs only in perennial plants.

The storage container can be ordinary organs (shoots, roots), as well as specialized ones (rhizomes, tubers, bulbs). All seed plants store energetically valuable substances in the seeds (cotyledons, endosperm). Many plants in arid climates store not only organic matter, but also water . For example, aloe stores water in its fleshy leaves, and cacti store water in their shoots.

Mechanical fabrics

The mechanical properties of plant cells are ensured by:

· rigid cell membrane;

· turgidity, that is, the turgor state of cells.

Despite the fact that almost all tissue cells have mechanical properties, there are tissues in the plant for which mechanical properties are basic. This collenchyma And sclerenchyma. They usually function in interaction with other tissues. Inside the body of the plant, they form a kind of frame. That's why they are called reinforcing.

Not all plants have equally well expressed mechanical tissues. Plants living in an aquatic environment require much less internal support than plants living on land. The reason is that aquatic plants require less internal support. Their body is largely supported by the surrounding water. Air on land does not create such support, since it is less dense than water. It is for this reason that the availability of specialized mechanical fabrics becomes relevant.

The improvement of internal supporting structures occurred in the process of evolution.

Collenchyma. It is formed only by living cells elongated along the axis of the organ. This type of mechanical tissue is formed very early, during the period of primary growth. Therefore, it is important that the cells remain alive and retain the ability to stretch along with the stretching cells that are nearby.

Features of collenchyma cells:

· uneven thickening of the shell, as a result of which some parts of it remain thin, while others thicken;

· shells do not become lignified.

Collenchyma cells are arranged differently relative to each other. In cells located nearby, thickenings form on the corners facing each other. This type of collenchyma is called corner In another case, the cells are arranged in parallel layers. The cell membranes facing these layers are greatly thickened. This lamellar collenchyma. Cells may be loosely arranged, with abundant intercellular spaces - This is loose collenchyma. This type of collenchyma is often found in plants on waterlogged soils.

Collenchyma is of particular importance in young plants, herbaceous forms, and in parts of plants where secondary growth does not occur, such as leaves. In this case, it is laid very close to the surface, sometimes just under the epidermis. If the organ has edges, then thick layers of collenchyma are found along their ridges.

Collenchyma cells are functional only in the presence of turgor. A lack of water reduces the effectiveness of collenchyma and the plant temporarily withers, for example, cucumber leaves drooping on a hot day. After filling the cells with water, the functions of collenchyma are restored.

Sclerenchyma. The second type of mechanical fabrics. Unlike collenchyma, where all cells are living, sclerenchyma cells are dead. Their walls are very thick. They perform a mechanical function. A strong thickening of the shell leads to disruption of the transport of substances, as a result of which the protoplast dies. Lignification of the membranes of sclerenchyma cells occurs when the plant organ has already completed its growth. Therefore, they no longer interfere with the stretching of surrounding tissues.

Depending on the shape, two types of sclerenchyma cells are distinguished - fibers and sclereids.

Fibers They have a highly elongated shape with very thick walls and a small cavity. They are somewhat smaller than wood fibers. Often longitudinal layers and cords form under the epidermis. In the phloem or xylem they can be found singly or in groups. In the phloem they are called bast fibers, and in the xylem – libriform fibers.

Sclereids, or stony cells, are represented by round or branched cells with thick membranes. In the plant body they can be found singly (supporting cells) or in groups. It should be noted that the mechanical properties strongly depend on the location of the sclereids. Some of the sclereids form continuous layers, as, for example, in the shells of nuts or in the seeds of fruits (stone fruits).

The kidneys are the main organ of the human excretory system, thanks to which metabolic products are removed from the body: ammonia, carbon dioxide, urea.

They are responsible for the removal of other substances, organic and inorganic: excess water, toxins, mineral salts.

All these functions are performed by the parenchyma - the tissue from which this organ consists.

The renal parenchyma consists of two layers:

cortex, located immediately under the renal capsule. It contains the renal glomeruli, in which urine is formed. The glomeruli are covered with a huge number of vessels. There are more than a million glomeruli themselves in the outer layer of each kidney;
medulla. Performs an equally important function in transporting urine through a complex system of pyramids and tubules into the calyces and further into the pelvis. There are up to 18 such tubules, grown directly into the outer layer.

One of the main roles of the renal parenchyma is to ensure the water and electrolyte balance of the human body. The contents - vessels, glomeruli, tubules and pyramids - form the nephron, which is the main functional unit of the excretory organ.

The thickness of the renal parenchyma is one of the main indicators of its normal functioning, since it can fluctuate under the negative influence of microbes.

But its size can also change with age, which must be taken into account when conducting an ultrasound examination.

So, in young and middle-aged people, the kidney parenchyma (normal value) is 14-26 mm.

In persons over 55 years of age, the kidney parenchyma (size and normal) is no more than 20 mm. The normal thickness of the kidney parenchyma in old age is up to 11 mm.

Parenchymal tissue has a unique ability to recover, so it is necessary to promptly treat diseases.

Study

Diagnostic procedures make it possible to determine the structure of the kidney tissue, examine the internal state of the organ, and identify diseases in time to quickly take measures to prevent their spread and aggravation.

Parenchymal tissue can be examined in several ways:

If deviations in the size of parenchymal tissue from the generally accepted norm are detected, it is necessary to contact a specialist for further examination and treatment.

The decision on the choice of diagnostic method should be made by the doctor based on the medical history.

Diffuse changes in the renal parenchyma

Often, patients are faced with the conclusion of an ultrasound or CT scan: diffuse changes in parenchymal tissue. Don't panic: this is not a diagnosis.

Diffuse means numerous changes in the renal tissue that do not fit within the normal limits. Which ones exactly can only be determined by a doctor after conducting additional examination using tests and monitoring the patient.

Signs of diffuse changes in the renal parenchyma in acute renal failure

Changes may include increased echogenicity of the renal parenchyma, thinning of the renal parenchyma, or vice versa, thickening, fluid accumulation and other pathologies.

Enlargement and swelling of the renal parenchyma may indicate the presence of microliths (stones in the renal parenchyma), chronic diseases, and atherosclerosis of the renal vessels.

For example, with a parenchyma cyst, tissues are compressed, which negatively affects the processes of formation and excretion of urine from the body.

In most cases, a single cyst does not require treatment, unlike polycystic disease, which is dangerous for the body as a whole.

Multiple parenchymal cysts must be removed surgically.

If the kidney parenchyma is thinned (unless we are talking about elderly patients), it may indicate the presence of advanced chronic diseases. If they were not treated, or the therapy was inadequate, the parenchymal layer becomes thinner and the body is unable to function normally.

To detect diseases at an early stage, do not neglect the diagnostics recommended by your doctor.

Focal changes

Focal changes are neoplasms that can be either benign or malignant. In particular, a simple cyst is benign, while solid parenchymal tumors and complex cysts are most often carriers of cancer cells.

A neoplasm can be suspected based on several signs:

blood impurities in the urine;
pain in the kidney area;
a tumor noticeable on palpation.

The listed symptoms, if present together, unmistakably indicate the malignant nature of the pathology.

Unfortunately, they usually appear in an advanced stage and indicate global dysfunction.

The diagnosis is made based on research:

computed tomography;
nephroscintigraphy;
biopsies.

Additional methods for studying focal changes that allow us to determine the presence of a blood clot, the location of the tumor, and the type of vascularization necessary for effective surgical treatment:

aortography;
arteriography;
cavography.

X-ray and computed tomography of the bones of the skull, spine, as well as CT of the lungs are auxiliary methods of examination if the spread of metastases is suspected.\

Parenchyma is the main tissue that makes up most of the plant body, within which highly specialized tissues are differentiated. The term “basic tissues”, proposed by the German botanist J. Sachs, has become generally accepted. Tissues are basic because during ontogenesis, during the development of a seedling from a seed, they serve as a monolithic basis for apexes, from which plant organs of various structures develop. The range of functions of the main tissues can change due to the physiological plasticity of parenchyma cells. However, at all levels of specialization, the main tissues retain their characteristic features. Parenchyma cells are always living, isodiametric in shape. The shells are thin, with simple pores, less often thickened and lignified. In typical cases, intercellular spaces are well developed. Cells of the main parenchyma do not lose the ability to divide and can return to the meristematic state, for example, during wound healing, regeneration, and the formation of adventitious roots. There are several groups of main tissues.

ASSIMILATING, OR CHLOROPHYLLONING, TISSUE (CHLORENCHYMA)

The main function of assimilation tissues is photosynthesis. It is in these tissues that the bulk of organic substances are synthesized and the energy received by plants from the sun is bound.

Chlorenchyma cells are thin-walled, contain chloroplasts, which are located in one layer along the walls, without darkening each other. Chlorenchyma, facing the sunny side, has an oblong cell shape and is called columnar, or palisade. In this type of chlorenchyma, photosynthesis reactions are actively occurring. On the back side of the cell, chlorenchyma is round in shape, with large intercellular spaces, and is called spongy chlorenchyma. Chlorenchyma lies directly under the epidermis, which provides good lighting and gas exchange in the stem. Shining through the transparent skin, chlorenchyma colors the young parts of plants green. Sometimes it is located deep in the stem around the fascicles or more superficially under the mechanical tissue. In this case, its function is associated with supplying the internal tissues of the stem and, first of all, living cells of the vascular bundles with oxygen, which is formed during the process of photosynthesis. In rare cases, chlorenchyma is formed in roots accessible to light (in air, in the roots of aquatic plants).

STORAGE FABRICS

Substances coming from the external environment or synthesized by the plant can be stored. Mass deposition of organic substances occurs only in specialized storage tissues, which are the main type of tissue in a number of organs.

Reserve substances accumulate in certain parts of the plant: in trees and shrubs - in the parenchyma cells of the bark, medullary rays, wood parenchyma of trunks and roots, and in young shoots - in the medullary cells. Perennial herbaceous plants have specialized storage organs - roots, bulbs, tubers, rhizomes. The reserves of organic substances accumulated in the summer are spent in the spring on the formation of young shoots and roots. In fruits and seeds, storage parenchyma forms the basis of organs.

The specialization of storage tissues is determined to a large extent by the composition of the accumulated products. Substances accumulate in a soluble or solid state. High molecular weight reserve compounds are deposited in the seeds in the form of solid grains (proteins, starch); fats are represented by hydrophobic lipids. Most often, two (protein and starch or protein and fats) or all three types of main storage substances are present in the storage tissues of seeds. In tubers, rhizomes, and pericarps, the level of water content changes only slightly as they ripen, so proteins and lipids rarely accumulate here. In these organs, reserve products are usually high-molecular carbohydrates (starch, inulin, hemicellulose) or water-soluble sugars (root vegetables of beets, carrots, fruit pulp, watermelon).

The difference in the chemical nature of reserve substances leads to tissue specialization. Thus, starch deposition occurs in amyloplasts, vacuoles serve as storage sites for proteins and sugars, lipid droplets accumulate directly in the hyaloplasm, and hemicellulose accumulates in the cell membrane.

Plants that periodically lack water sometimes form special water-bearing storage tissues. Most often, these tissues consist of large, thin-walled parenchyma cells that are filled with a mixture of mucus and water. Aquiferous parenchyma is found in the stems and leaves of succulent plants (cacti, agaves, aloe).

AIR-BEARING TISSUE (AERENCHYMA)

All plant organs and tissues contain intercellular spaces that carry out gas exchange and communicate with the external environment through openings in the integumentary tissues. In the process of life activity (photosynthesis, respiration, evaporation), plants release some gases into the intercellular spaces and absorb others, therefore the gas composition in the intercellular spaces is very different from the atmospheric one. The nature of the circulation of gases through the intercellular spaces, which ensures normal life activity, is determined by the type of plant and living conditions. In many cases, a tissue with large intercellular spaces and the predominant function of gas exchange (ventilation) is formed in plants. This tissue is called aerenchyma.

Rice. 15. Air-bearing parenchyma in the stem of pondweed brilliant:

1 - cuticle, 2 - epidermis, 3 - cells of the pneumatic parenchyma, 4 - pneumatic cavities, 5 - endoderm

Aerenchyma comes in various configurations. In some cases, large star-shaped parenchyma cells form bridges and large cavities filled with air remain between them (reed, rush), in others - small parenchyma cells, arranged in a chain, surround the air cavity (pondweed, egg capsule, calliper).

Aerenchyma is well developed in marsh and aquatic plants, in which normal gas exchange is difficult. In addition to aeration, air cavities inside the stem and in the leaves allow the plant to float freely in water. Aerenchyma also performs a mechanical function: its structure, reminiscent of a honeycomb, most densely and economically ensures the strength and elasticity of plant body organs in an aquatic environment.

SUCTION TISSUE

EXCRETORY TISSUE

Unlike animals, whose metabolism is always associated with the continuous release of nitrogenous decomposition products, in plants there is reutilization, or accumulation, of both incoming and synthesized substances throughout life with partial losses in the form of leaf fall, branch fall, peeling of the outer layers of the crust and etc. Many woody plants retain organic matter in the form of dead tissue for hundreds of years, without interrupting growth and increasing phytomass.

Rice. 16. Excretory tissues of various plants:

A - outer oil gland on a parsley leaf, B - excretory duct in the root of parsley in a cross section, epithelial cells surrounding the excretory duct are visible, C - idioblasts with essential oil, in the central part of the petiole of a geranium leaf, D - resin duct in pine wood Eldar on a longitudinal-tangential section, D - a container for essential oil in the peel of a tangerine fruit, E - a group of cells in a Caucasian beech leaf with tannins (1 and 2); these cells are located around the vascular bundle (3) across the leaf blade from the lower to the upper epidermis

The classification of secretory (excretory) complexes is based on their location. Some are located on the surface of the above-ground parts of the plant and secrete the secretion outward - external excretory tissues; others are localized inside organs, are not directly connected with the external environment and have the form of channels (passages) or cavities - internal excretory tissues.

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