What is the object of study of histology. Lecture topic: histology as a science, the subject of histology

What do we know about such a science as histology? Indirectly, one could get acquainted with its main provisions at school. But in more detail this science is studied in higher school (universities) in medicine.

At the level of the school curriculum, we know that there are four types of tissues, and they are one of the basic components of our body. But people who plan to choose or have already chosen medicine as their profession need to get acquainted with such a section of biology as histology in more detail.

What is histology

Histology is a science that studies the tissues of living organisms (humans, animals and others, their formation, structure, functions and interaction. This section of science includes several others.

As an academic discipline, this science includes:

• cytology (the science that studies the cell);
• embryology (the study of the process of development of the embryo, the features of the formation of organs and tissues);
• general histology (the science of the development, functions and structure of tissues, studies the characteristics of tissues);
• private histology (studies the microstructure of organs and their systems).

Levels of organization of the human body as an integral system

This hierarchy of the object of histology study consists of several levels, each of which includes the next one. Thus, it can be visually represented as a multi-level nesting doll.

1. organism. This is a biologically integral system, which is formed in the process of ontogenesis.
2. Organs. This is a complex of tissues that interact with each other, performing their main functions and ensuring that the organs perform basic functions.
3. fabrics. At this level, cells are combined together with derivatives. The types of tissues are being studied. Although they may be composed of a variety of genetic data, their basic properties are determined by the basic cells.
4. Cells. This level represents the main structural and functional unit of the tissue - the cell, as well as its derivatives.
5. Subcellular level. At this level, the components of the cell are studied - the nucleus, organelles, plasmolemma, cytosol, and so on.
6. Molecular level. This level is characterized by the study of the molecular composition of cell components, as well as their functioning.

Tissue Science: Challenges

As for any science, a number of tasks are also allocated for histology, which are performed in the course of studying and developing this field of activity. Among these tasks, the most important are:

• study of histogenesis;
• interpretation of the general histological theory;
• study of the mechanisms of tissue regulation and homeostasis;
• the study of such features of the cell as adaptability, variability and reactivity;
• development of the theory of tissue regeneration after damage, as well as methods of tissue replacement therapy;
• interpretation of the device of molecular genetic regulation, the creation of new methods, as well as the movement of embryonic stem cells;
• study of the process of human development in the embryonic phase, other periods of human development, as well as problems with reproduction and infertility.

Stages of development of histology as a science

As you know, the field of study of the structure of tissues is called "histology". What is it, scientists began to find out even before our era.

So, in the history of the development of this sphere, three main stages can be distinguished - pre-microscopic (until the 17th century), microscopic (until the 20th century) and modern (until now). Let's consider each of the stages in more detail.

premicroscopic period

At this stage, such scientists as Aristotle, Vesalius, Galen and many others were engaged in histology in its initial form. At that time, the object of study were tissues that were separated from the human or animal body by the method of preparation. This stage began in the 5th century BC and lasted until 1665.

microscopic period

The next microscopic period began in 1665. Its dating is explained by the great invention of the microscope in England. The scientist used a microscope to study various objects, including biological ones. The results of the study were published in the publication "Monograph", where the concept of "cell" was first used.

Prominent scientists of this period who studied tissues and organs were Marcello Malpighi, Anthony van Leeuwenhoek and Nehemiah Grew.

The structure of the cell continued to be studied by such scientists as Jan Evangelista Purkinje, Robert Brown, Matthias Schleiden and Theodor Schwann (his photo is posted below). The latter eventually formed which is relevant to this day.

The science of histology continues to develop. What it is, at this stage, Camillo Golgi, Theodore Boveri, Keith Roberts Porter, Christian Rene de Duve are studying. Also related to this are the works of other scientists, such as Ivan Dorofeevich Chistyakov and Pyotr Ivanovich Peremezhko.

The current stage of development of histology

The last stage of science, which studies the tissues of organisms, begins in the 1950s. The time frame is defined so because it was then that the electron microscope was first used to study biological objects, and new research methods were introduced, including the use of computer technology, histochemistry and historadiography.

What are fabrics

Let us proceed directly to the main object of study of such a science as histology. Tissues are evolutionarily arisen systems of cells and non-cellular structures that are united due to the similarity of structure and having common functions. In other words, tissue is one of the components of the body, which is an association of cells and their derivatives, and is the basis for building internal and external human organs.

Tissue is not exclusively made up of cells. The tissue may include the following components: muscle fibers, syncytium (one of the stages in the development of male germ cells), platelets, erythrocytes, horny scales of the epidermis (post-cellular structures), as well as collagen, elastic and reticular intercellular substances.

The emergence of the concept of "fabric"

For the first time the concept of "fabric" was applied by the English scientist Nehemiah Grew. While studying plant tissues at that time, the scientist noticed the similarity of cellular structures with textile fibers. Then (1671) fabrics were described by such a concept.

Marie Francois Xavier Bichat, a French anatomist, in his works even more firmly fixed the concept of tissues. Varieties and processes in tissues were also studied by Aleksey Alekseevich Zavarzin (the theory of parallel series), Nikolai Grigorievich Khlopin (the theory of divergent development) and many others.

But the first classification of tissues in the form in which we know it now was first proposed by the German microscopists Franz Leydig and Keliker. According to this classification, tissue types include 4 main groups: epithelial (boundary), connective (support-trophic), muscular (contractible) and nervous (excitable).

Histological examination in medicine

Today, histology, as a science that studies tissues, is very helpful in diagnosing the condition of human internal organs and prescribing further treatment.

When a person is diagnosed with a suspected presence of a malignant tumor in the body, one of the first appointments is a histological examination. This is, in fact, the study of a tissue sample from the patient's body obtained by biopsy, puncture, curettage, surgical intervention (excisional biopsy) and other methods.

Thanks to the science that studies the structure of tissues, it helps to prescribe the most correct treatment. In the photo above, you can see a sample of tracheal tissue stained with hematoxylin and eosin.

Such an analysis is carried out if necessary:

• confirm or refute the previously made diagnosis;
• establish an accurate diagnosis in the case when controversial issues arise;
• determine the presence of a malignant tumor in the early stages;
• monitor the dynamics of changes in malignant diseases in order to prevent them;
• to carry out differential diagnostics of the processes occurring in the organs;
• determine the presence of a cancerous tumor, as well as the stage of its growth;
• to analyze the changes occurring in the tissues with the already prescribed treatment.

Tissue samples are examined in detail under a microscope in a traditional or accelerated way. The traditional method is longer, it is used much more often. It uses paraffin.

But the accelerated method makes it possible to get the results of the analysis within an hour. This method is used when there is an urgent need to make a decision regarding the removal or preservation of the patient's organ.

The results of histological analysis, as a rule, are the most accurate, since they make it possible to study tissue cells in detail for the presence of a disease, the degree of organ damage and methods of its treatment.

Thus, the science that studies tissues makes it possible not only to investigate the suborganism, organs, tissues and cells of a living organism, but also helps to diagnose and treat dangerous diseases and pathological processes in the body.

HISTOLOGY
(tissue science)
TISSUE - common histological
elements (cells, fibers,
intercellular substance), combined
common origin, structure and
function performed

Fabric classification

epithelial tissues
characterized by a boundary position in the body
(usually on the border with the external environment), closed
arrangement of cells forming layers, practical
lack of intercellular substance, cell polarity.
Mesenchyme derivatives
an extensive group of tissues that develop from the embryonic
connective tissue dominated by
intercellular substance (tissues of the internal environment (blood and
lymph), connective and skeletal tissues).
Muscle tissues
have the ability to contract due to
which perform their main function of moving the body or its parts in space.
nervous tissue
characterized by the ability to excitability and
conduction of a nerve impulse, which
interacts with the external environment,
integration of individual parts of the body with each other.

epithelial tissues

Types of epithelium
integumentary
occupies in the body
borderline
position, separating
internal environment from
external and together with
that participates in
metabolism
between the body and
environment
Glandular
carries out
secretory function.
those. forming it
epithelial cells
synthesize and
secrete substances secrets involved
in different
processes

FUNCTIONS OF EPITHELIUM:
delimiting
Protective
(barrier)
excretory
Transport
Secretory
Suction
touch
(receptor)

Localization of various types
epithelium
Single layer flat
(mesothelium)
single layer
cubic
single layer
cylindrical
– glandular
– Kamchaty
– Flickering
Layered flat
– Non-keratinizing
- keratinizing
multilayer
transition
Pleura, peritoneum,
heart bag
Ovary, convoluted
nephron tubules
- Stomach
- Intestine, gallbladder
- Airways, uterine
pipes
- Cornea of ​​the eye, oral
cavity, esophagus
– Skin
Bladder,
ureter

glands

multicellular
unicellular
external
secretions
internal
secretions
external secretion
Simple
Simple
unbranched
branched
Simple
tubular
tubular
unbranched
gland
gland
alveolar
gland
Complex
branched
Simple
branched alveolar tubular
alveolar
gland
gland

Mesenchyme derivatives

Mesenchyme - (from the Greek mesenchio - I pour into the middle) -
embryonic rudiment of connective tissue, filling
spaces between germ layers.

Mesenchyme cells have a spindle-shaped or stellate shape, the processes of which form a mesh backbone. Intercells are located between cells

Mesenchyme cells are fusiform or
star-shaped, the processes of which form a reticulate
skeleton. Intercellular space is located between cells
substance with a gelatinous consistency.

Tissues of the internal environment (blood, lymph), connective tissues, skeletal (bone, cartilage) tissues develop from the mesenchyme. These are supporting tissues

Mesenchyme develops into tissues of the inner
media (blood, lymph), connective tissues,
skeletal (bone, cartilage) tissues. These are fabrics
support-trophic function.

Connective tissues

Connective tissue in its importance occupies in the body
special place. It is involved in the formation of the stroma of organs,
layers between other tissues, the dermis of the skin, the skeleton, as it were
connects dissimilar tissues or parts of these organs.
Multifunctional nature of connective tissues
determined by the complexity of their composition and organization
Connective tissue composition
Cellular elements
Non-cellular elements
fibroblasts
macrophages
Basic amorphous
substance
Plasma cells
mast cells
adventitial cells
Adipocytes
endothelial cells
Pericytes
Pigmentocytes
fibrous
structures

Connective tissue functions
Trophic
Protective
Plastic
support
Morphogenetic

Tissues of the internal environment

The blood and lymph are
main
types of fabrics
mesenchymal
origin,
forming together with
loose fibrous
connective tissue
internal environment
organism.

Blood functions:

Transport - the transfer of various substances.
Respiratory – transport of oxygen and carbon dioxide.
Trophic - the transfer of nutrients.
Excretory - removal of various toxins from the body,
formed in the course of his life.
Humoral - transport of hormones and other biologically
active substances.
Homeostatic - maintaining the constancy of the internal
body environment.
Heat-regulating - transfer of heat from deep-lying
organs to the surface for its scattering (which is essential for
large animals with a high metabolic rate).
Protective - ensuring humoral and cellular immunity,
folding ability.
Transfer of mechanical force (for example, for locomotion in
earthworms; to break the cuticle during molting in crustaceans;
for the movement of organs such as the siphon of bivalves and
etc.; for leg extension in spiders; for ultrafiltration in
renal capillaries).

Composition of the blood

Blood
Plasma
Cellular elements
red blood cells
Leukocytes
platelets

red blood cells

The number of red blood cells in an adult male is
3.95.5 1012/l, and in women - 3.7-4.9 1012/l of blood. However, the number
erythrocytes in healthy people may vary depending on
age, emotional and muscular load, actions
environmental factors, etc.
micrograph.
erythrocytes in
blood smear
person (x 1200)
scanning
electronic
microscopy
(x 3300)
scanning
electronic
microscopy
(x 4000)
coin columns
(x 900)

erythrocytes in the damaged vessel (x 2400)

Leukocytes

Leukocytes, or white blood cells, are colorless in fresh blood.
distinguishes them from stained erythrocytes. Their number averages
4-9 109/l.
An increase in the number of leukocytes is leukocytosis, a decrease is leukopenia.
Leukocytes
grainy
(granulocytes)
Neutrophils
49-79 %
Eosinophils
0,5-5 %
Non-granular
(agranulocytes)
Basophils
0-1 %
Lymphocytes
19-37 %
Monocytes
3-11 %

Skeletal connective tissues

cartilaginous
the cloth
Bone
the cloth

Cartilage types

Hyaline
cartilage
Fibrous
cartilage
elastic
cartilage

Bone

Cellular
elements
calcified
intercellular
substance
mineralized matrix:
osteoblasts
osteocytes
osteoclasts
inorganic part (50%)
organic part (25%)
water (25%)
organic matrix:
collagen
non-collagen proteins
glycosaminoglycans

Bone classification

lamellar
the cloth
coarse fibrous
the cloth

Compact matter

B
BUT
AT
Light microscopy (A - x 600, B - x 80, C - x 150)

Muscle tissues

Classification:
striated muscle
fabrics
(formed by fibers that have
transverse striation - skeletal
muscle)
smooth muscle tissue
(consist of cells that do not have a transverse
striation - the walls of the bronchi, stomach, intestines,
bladder and blood vessels)
cardiac muscle tissue
(muscular layer of the heart - myocardium)

Skeletal (somatic) muscle tissue

(muscles that ensure the movement of the body and its parts in space,
maintaining posture, oculomotor muscles, cavity wall muscles
mouth, tongue, pharynx, larynx, upper third of the esophagus, facial muscles)
Micrograph (x 300)

smooth muscle tissue

longitudinal cut smooth
muscle tissue.
Micrograph (x 480)
Structural-functional
unit of smooth muscle
mesenchymal tissue.
serves as a smooth myocyte
(smooth muscle cell).
Smooth myocytes
mononuclear cells
predominantly
fusiform, not
transverse
striation and
generators
numerous
connections with each other.

cardiac muscle tissue

BUT
B
Longitudinal section of the myocardium.
Micrograph (A - x 198, B - x 640).

nervous tissue

Made up of neurons
(neurocytes) that have
ability to produce
and conduction of nerve
impulses, and cells
neuroglia that perform
a number of subsidiary
functions (basic,
trophic, barrier,
protective, etc.) and
providing
activity of neurons.

Structure of dendrites (D) and axon (A) in a multipolar neuron, silver nitrate impregnation (x 320)

Micrograph of a neuron (x 1200)

Bipolar neurons of the peripheral ganglion stained with gold salts (x 320)

Classification of neurons

neuroglia

heterogeneous group of elements of the nervous tissue,
ensuring the activity of neurons and performing
nonspecific functions: supporting, trophic,
delimiting, barrier, secretory and
protective function.
Classification
macroglia
astrocytic glia
(astroglia),
oligodendroglia
ependymal glia
microglia
microgliocytes

Classification of nerve fibers

Type A fibers are thick, myelinated, with far
distant nodal intercepts. Spend
impulses with high speed (15-120 m/s);
subdivided into 4 subtypes (α, β, γ, δ) with
decreasing diameter and speed of conduction
impulse.
Type B fibers - medium thickness, myelinated,
smaller diameter than type A fibers, with finer
myelin sheath and lower speed
conduction of nerve impulses (5-15 m/s).
Type C fibers are thin, unmyelinated, conductive
impulses with a relatively low speed (0.5-2 m / s).

Interneuronal contacts (synapses)

The synapse is made up of 3
components:
the presynaptic part
postsynaptic part
and synaptic cleft.

The content of the article

HISTOLOGY, the science that studies animal tissues. A tissue is a group of cells that are similar in shape, size and function and in their metabolic products. In all plants and animals, with the exception of the most primitive, the body consists of tissues, and in higher plants and in highly organized animals, tissues are distinguished by a great variety of structure and the complexity of their products; combining with each other, different tissues form separate organs of the body.

Histology is the study of animal tissues; the study of plant tissues is usually referred to as plant anatomy. Histology is sometimes called microscopic anatomy, because it studies the structure (morphology) of an organism at the microscopic level (very thin tissue sections and individual cells serve as the object of histological examination). Although this science is primarily descriptive, its task also includes the interpretation of those changes that occur in tissues in normal and pathological conditions. Therefore, the histologist needs to be well versed in how tissues are formed in the process of embryonic development, what is their ability to grow in the postembryonic period, and how they undergo changes in various natural and experimental conditions, including during their aging and the death of their constituent cells.

The history of histology as a separate branch of biology is closely connected with the creation of the microscope and its improvement. M. Malpighi (1628-1694) is called the "father of microscopic anatomy", and therefore of histology. Histology was enriched by the observations and methods of research carried out or created by many scientists whose main interests lay in the field of zoology or medicine. This is evidenced by the histological terminology that immortalized their names in the names of the structures they first described or the methods they created: islets of Langerhans, Lieberkühn glands, Kupffer cells, Malpighian layer, Maximov stain, Giemsa stain, etc.

At present, methods for preparing preparations and their microscopic examination have become widespread, making it possible to study individual cells. These methods include frozen section technique, phase contrast microscopy, histochemical analysis, tissue culture, electron microscopy; the latter allows a detailed study of cellular structures (cell membranes, mitochondria, etc.). Using a scanning electron microscope, it was possible to reveal an interesting three-dimensional configuration of free surfaces of cells and tissues, which cannot be seen under a conventional microscope.

Origin of tissues.

The development of an embryo from a fertilized egg occurs in higher animals as a result of multiple cell divisions (crushing); the cells formed in this case are gradually distributed in their places in different parts of the future embryo. Initially, embryonic cells are similar to each other, but as their number increases, they begin to change, acquiring characteristic features and the ability to perform certain specific functions. This process, called differentiation, eventually leads to the formation of different tissues. All tissues of any animal come from three initial germ layers: 1) the outer layer, or ectoderm; 2) the innermost layer, or endoderm; and 3) the middle layer, or mesoderm. So, for example, muscles and blood are derivatives of the mesoderm, the lining of the intestinal tract develops from the endoderm, and the ectoderm forms integumentary tissues and nervous
system.

main types of fabrics.

Histologists usually distinguish four main tissues in humans and higher animals: epithelial, muscular, connective (including blood), and nervous. In some tissues, cells have approximately the same shape and size and are so tightly adjacent to each other that there is no or almost no intercellular space between them; such tissues cover the outer surface of the body and line its internal cavities. In other tissues (bone, cartilage), the cells are not so densely packed and are surrounded by the intercellular substance (matrix) that they produce. From the cells of the nervous tissue (neurons) that form the brain and spinal cord, long processes depart, ending very far from the cell body, for example, at the points of contact with muscle cells. Thus, each tissue can be distinguished from others by the nature of the location of the cells. Some tissues have a syncytial structure, in which the cytoplasmic processes of one cell pass into similar processes of neighboring cells; such a structure is observed in the germinal mesenchyme, loose connective tissue, reticular tissue, and can also occur in some diseases.

Many organs are composed of several types of tissues, which can be recognized by their characteristic microscopic structure. Below is a description of the main types of tissues found in all vertebrates. Invertebrates, with the exception of sponges and coelenterates, also have specialized tissues similar to the epithelial, muscular, connective, and nervous tissues of vertebrates.

epithelial tissue.

The epithelium may consist of very flat (scaly), cuboidal, or cylindrical cells. Sometimes it is multi-layered, i.e. consisting of several layers of cells; such an epithelium forms, for example, the outer layer of the human skin. In other parts of the body, for example in the gastrointestinal tract, the epithelium is single-layered, i.e. all of its cells are connected to the underlying basement membrane. In some cases, a single-layer epithelium may appear to be multi-layered: if the long axes of its cells are not parallel to each other, then it seems that the cells are at different levels, although in fact they lie on the same basement membrane. Such an epithelium is called multilayered. The free edge of epithelial cells is covered with cilia, i.e. thin hair-like outgrowths of protoplasm (such a ciliary epithelium lines, for example, the trachea), or ends with a “brush border” (the epithelium lining the small intestine); this border consists of ultramicroscopic finger-like outgrowths (so-called microvilli) on the cell surface. In addition to protective functions, the epithelium serves as a living membrane through which gases and solutes are absorbed by cells and released to the outside. In addition, the epithelium forms specialized structures, such as glands that produce substances necessary for the body. Sometimes secretory cells are scattered among other epithelial cells; an example is the mucus-producing goblet cells in the surface layer of the skin in fish or in the intestinal lining in mammals.

Muscle.

Muscle tissue differs from the rest in its ability to contract. This property is due to the internal organization of muscle cells containing a large number of submicroscopic contractile structures. There are three types of muscles: skeletal, also called striated or voluntary; smooth, or involuntary; cardiac muscle, which is striated but involuntary. Smooth muscle tissue consists of spindle-shaped mononuclear cells. The striated muscles are formed from multinuclear elongated contractile units with a characteristic transverse striation, i.e. alternating light and dark stripes perpendicular to the long axis. The cardiac muscle consists of mononuclear cells, connected end to end, and has a transverse striation; while the contractile structures of neighboring cells are connected by numerous anastomoses, forming a continuous network.

Connective tissue.

There are different types of connective tissue. The most important supporting structures of vertebrates consist of two types of connective tissue - bone and cartilage. Cartilage cells (chondrocytes) secrete around themselves a dense elastic ground substance (matrix). Bone cells (osteoclasts) are surrounded by a ground substance containing salt deposits, mainly calcium phosphate. The consistency of each of these tissues is usually determined by the nature of the basic substance. As the body ages, the content of mineral deposits in the ground substance of the bone increases, and it becomes more brittle. In young children, the main substance of the bone, as well as cartilage, is rich in organic substances; due to this, they usually have not real bone fractures, but the so-called. fractures (fractures of the "green branch" type). Tendons are made up of fibrous connective tissue; its fibers are formed from collagen, a protein secreted by fibrocytes (tendon cells). Adipose tissue is located in different parts of the body; This is a peculiar type of connective tissue, consisting of cells, in the center of which there is a large globule of fat.

Blood.

Blood is a very special type of connective tissue; some histologists even distinguish it as an independent type. The blood of vertebrates consists of liquid plasma and formed elements: red blood cells, or erythrocytes containing hemoglobin; a variety of white cells, or leukocytes (neutrophils, eosinophils, basophils, lymphocytes, and monocytes), and platelets, or platelets. In mammals, mature erythrocytes entering the bloodstream do not contain nuclei; in all other vertebrates (fish, amphibians, reptiles, and birds), mature, functioning erythrocytes contain a nucleus. Leukocytes are divided into two groups - granular (granulocytes) and non-granular (agranulocytes) - depending on the presence or absence of granules in their cytoplasm; in addition, they are easy to differentiate using staining with a special mixture of dyes: eosinophil granules acquire a bright pink color with this staining, the cytoplasm of monocytes and lymphocytes - a bluish tint, basophil granules - a purple tint, neutrophil granules - a faint purple tint. In the bloodstream, the cells are surrounded by a transparent liquid (plasma) in which various substances are dissolved. Blood delivers oxygen to tissues, removes carbon dioxide and metabolic products from them, and carries nutrients and secretion products, such as hormones, from one part of the body to another.

nervous tissue.

Nervous tissue is made up of highly specialized cells called neurons, which are concentrated mainly in the gray matter of the brain and spinal cord. A long process of a neuron (axon) stretches for long distances from the place where the body of the nerve cell containing the nucleus is located. The axons of many neurons form bundles, which we call nerves. Dendrites also depart from neurons - shorter processes, usually numerous and branched. Many axons are covered by a special myelin sheath, which is made up of Schwann cells containing a fat-like material. Neighboring Schwann cells are separated by small gaps called nodes of Ranvier; they form characteristic depressions on the axon. Nervous tissue is surrounded by a special type of supporting tissue known as neuroglia.

Tissue replacement and regeneration.

Throughout the life of an organism, there is constant wear or destruction of individual cells, which is one of the aspects of normal physiological processes. In addition, sometimes, for example, as a result of some kind of injury, there is a loss of one or another part of the body, consisting of different tissues. In such cases, it is extremely important for the body to reproduce the lost part. However, regeneration is possible only within certain limits. Some relatively simply organized animals, such as planarians (flatworms), earthworms, crustaceans (crabs, lobsters), starfish and holothurians, can restore body parts lost entirely for any reason, including as a result of spontaneous rejection (autotomy ). For regeneration to occur, it is not enough just to form new cells (proliferation) in the preserved tissues; newly formed cells must be capable of differentiation in order to ensure the replacement of cells of all types that were part of the lost structures. In other animals, especially vertebrates, regeneration is possible only in some cases. Tritons (tailed amphibians) are able to regenerate their tail and limbs. Mammals lack this ability; however, even in them, after partial experimental removal of the liver, under certain conditions, restoration of a rather significant area of ​​the liver tissue can be observed.

A deeper understanding of the mechanisms of regeneration and differentiation will undoubtedly open up many new possibilities for using these processes for therapeutic purposes. Basic research has already made a great contribution to the development of skin and cornea grafting techniques. Most differentiated tissues retain cells capable of proliferation and differentiation, but there are tissues (in particular, the human central nervous system) that, being fully formed, are not capable of regeneration. Approximately at the age of one year, the human central nervous system contains the number of nerve cells assigned to it, and although the nerve fibers, i.e. cytoplasmic processes of nerve cells are able to regenerate, cases of restoration of cells of the brain or spinal cord, destroyed as a result of injury or degenerative disease, are unknown.

Classical examples of the replacement of normal cells and tissues in the human body are the renewal of blood and the upper layer of the skin. The outer layer of the skin - the epidermis - lies on a dense connective tissue layer, the so-called. dermis, equipped with tiny blood vessels that deliver nutrients to it. The epidermis is composed of stratified squamous epithelium. The cells of its upper layers are gradually transformed, turning into thin transparent scales - a process called keratinization; eventually these scales slough off. Such desquamation is especially noticeable after severe sunburn of the skin. In amphibians and reptiles, shedding of the stratum corneum (molting) occurs regularly. The daily loss of superficial skin cells is compensated by new cells coming from the actively growing lower layer of the epidermis. There are four layers of the epidermis: the outer stratum corneum, under it is the shiny layer (in which keratinization begins, and its cells become transparent), below it is the granular layer (pigment granules accumulate in its cells, which causes darkening of the skin, especially under the action of solar radiation). rays) and, finally, the deepest - the rudimentary, or basal, layer (mitotic divisions occur in it throughout the life of the organism, giving new cells to replace the exfoliating ones).

The blood cells of humans and other vertebrates are also constantly updated. Each type of cell is characterized by a more or less definite lifespan, after which they are destroyed and removed from the blood by other cells - phagocytes ("cell eaters"), specially adapted for this purpose. New blood cells (instead of the destroyed ones) are formed in the hematopoietic organs (in humans and mammals - in the bone marrow). If blood loss (bleeding) or destruction of blood cells by chemicals (hemolytic agents) causes great damage to the blood cell populations, the hematopoietic organs begin to produce more cells. With the loss of a large number of red blood cells that supply tissues with oxygen, the cells of the body are threatened with oxygen starvation, which is especially dangerous for nervous tissue. With a lack of leukocytes, the body loses its ability to resist infections, as well as remove decayed cells from the blood, which in itself leads to further complications. Under normal conditions, blood loss is a sufficient stimulus for the mobilization of the regenerative functions of the hematopoietic organs.

Tissue responses to abnormal conditions.

When tissues are damaged, some loss of their typical structure is possible as a reaction to the violation that has occurred.

Mechanical damage.

With mechanical damage (cut or fracture), the tissue reaction is aimed at filling the resulting gap and reconnecting the edges of the wound. Weakly differentiated tissue elements, in particular fibroblasts, rush to the rupture site. Sometimes the wound is so large that the surgeon has to insert pieces of tissue into it to stimulate the initial stages of the healing process; for this, fragments or even whole pieces of bone obtained during amputation and stored in the "bank of bones" are used. In cases where the skin surrounding a large wound (for example, with burns) cannot provide healing, transplants of healthy skin flaps taken from other parts of the body are resorted to. Such grafts in some cases do not take root, because the transplanted tissue does not always manage to form contact with those parts of the body to which it is transferred, and it dies or is rejected by the recipient.

foreign objects.

Pressure.

Calluses occur with constant mechanical damage to the skin as a result of pressure exerted on it. They appear as well-known corns and thickenings of the skin on the soles of the feet, the palms of the hands and on other areas of the body that experience constant pressure. Removal of these thickenings by excision does not help. As long as the pressure continues, the formation of calluses will not stop, and cutting them off, we only expose the sensitive underlying layers, which can lead to the formation of wounds and the development of infection.

Methods for studying tissues.

Many special methods have been developed for the manufacture of tissue preparations for microscopic examination. There is also a special method called tissue culture that allows you to observe and study living tissues.

tissue culture.

Isolated pieces of tissues or organs are placed in nutrient solutions under conditions that exclude the possibility of infection with microbes. In this unusual environment, tissues continue to grow, exhibiting many of the characteristics (such as the need for nutrients, oxygen, a certain space, etc.) that are characteristic of them under normal conditions, i.e. when they are in a living organism. Cultivated tissues can retain many of their structural and functional features: fragments of the heart muscle continue to contract rhythmically, the skin of the embryo continues to grow and differentiate in the usual direction. However, sometimes cultivation reveals such properties of the tissue that are not expressed in it under normal conditions and could remain unknown. So, studying the structure of cells of abnormal neoplasms (tumors), it is not always possible to establish their belonging to a particular tissue or their embryonic origin. However, when grown in an artificial nutrient medium, they acquire features characteristic of the cells of a particular tissue or organ. This can be extremely helpful not only in correctly identifying the tumor, but also in identifying the organ in which it originally originated. Some cells, such as fibroblasts (connective tissue cells), are very easy to culture, which makes them valuable experimental objects, in particular in cases where a homogeneous material is needed for testing new drugs.

Growing tissue culture requires certain skills and equipment, but it is the most important method for studying living tissues. In addition, it allows obtaining additional data on the state of tissues studied by conventional histological methods.

Microscopic studies and histological methods.

Even the most superficial examination makes it possible to distinguish one tissue from another. Muscle, bone, cartilage and nerve tissue, as well as blood, can be recognized with the naked eye. However, for a detailed study, it is necessary to study tissues under a microscope at high magnification, which allows you to see individual cells and the nature of their distribution. Wet preparations can be examined under a microscope. An example of such a preparation is a blood smear; for its manufacture, a drop of blood is applied to a glass slide and smeared over it in the form of a thin film. However, these methods usually do not provide a complete picture of the distribution of cells, as well as the areas in which tissues are connected.

Living tissues removed from the body undergo rapid changes; meanwhile, any slightest change in the tissue leads to a distortion of the picture on the histological preparation. Therefore, it is very important to ensure its safety immediately after removing the tissue from the body. This is achieved with the help of fixatives - liquids of various chemical compositions that kill cells very quickly without distorting the details of their structure and ensuring that the tissue is preserved in this - fixed - state. The composition of each of the numerous fixatives was developed as a result of repeated experimentation, and the desired ratio of different components in them was established by the same method of repeated trial and error.

After fixation, the tissue is usually subjected to dehydration. Since rapid transfer to high concentration alcohol would lead to wrinkling and deformation of the cells, dehydration is carried out gradually: the tissue is passed through a series of vessels containing alcohol in successively increasing concentrations, up to 100%. The tissue is then usually transferred into a liquid that mixes well with liquid paraffin; most often xylene or toluene is used for this. After a short exposure to xylene, the tissue is able to absorb paraffin. Impregnation is carried out in a thermostat so that the paraffin remains liquid. All this so-called. wiring is done manually or the sample is placed in a special device that performs all operations automatically. Faster wiring is also used using solvents (for example, tetrahydrofuran) that can be mixed with both water and paraffin.

After a piece of tissue is completely saturated with paraffin, it is placed in a small paper or metal mold and liquid paraffin is added to it, pouring it over the entire sample. When the paraffin hardens, a solid block is obtained with tissue enclosed in it. Now the fabric can be cut. Usually, a special device is used for this - a microtome. Tissue samples taken during surgery can be cut after freezing, i.e. without dehydration and filling in paraffin.

The procedure described above has to be slightly modified if the tissue, such as bone, contains hard inclusions. The mineral components of the bone must first be removed; for this, the tissue after fixation is treated with weak acids - this process is called decalcification. The presence in the block of bone that has not undergone decalcification deforms the entire tissue and damages the cutting edge of the microtome knife. It is possible, however, by sawing the bone into small pieces and grinding them with some kind of abrasive, to obtain sections - extremely thin sections of the bone, suitable for examination under a microscope.

The microtome consists of several parts; the main ones are the knife and the holder. The paraffin block is attached to the holder, which moves relative to the edge of the knife in a horizontal plane, while the knife itself remains stationary. After one cut is obtained, the holder is advanced by means of micrometer screws a certain distance corresponding to the desired cut thickness. Sections can be as thin as 20 µm (0.02 mm) or as thin as 1–2 µm (0.001–0.002 mm); it depends on the size of cells in a given tissue and usually ranges from 7 to 10 microns. Sections of paraffin blocks with tissue enclosed in them are placed on a glass slide. The paraffin is then removed by placing the slides with sections in xylene. If it is necessary to preserve fatty components in sections, then instead of paraffin, carbovax, a synthetic polymer that is soluble in water, is used to fill the tissue.

After all these procedures, the preparation is ready for staining - a very important step in the manufacture of histological preparations. Depending on the type of tissue and the nature of the study, different staining methods are used. These methods, as well as methods for pouring fabric, were developed in the course of many years of experimentation; however, new methods are constantly being created, which is associated both with the development of new areas of research and with the advent of new chemicals and dyes. Dyes serve as an important tool for histological studies due to the fact that they are absorbed differently by different tissues or their individual components (cell nuclei, cytoplasm, membrane structures). Staining is based on the chemical affinity between the complex substances that make up the dyes and certain components of cells and tissues. Dyes are used in the form of aqueous or alcoholic solutions, depending on their solubility and the chosen method. After staining, the preparations are washed in water or alcohol to remove excess dye; after that, only those structures that absorb this dye remain colored.

In order to keep the preparation for a sufficiently long time, the colored section is covered with a coverslip smeared with some kind of adhesive, which gradually hardens. For this, Canadian balsam (natural resin) and various synthetic media are used. Preparations prepared in this way can be stored for years. Other methods of fixation (usually using osmic acid and glutaraldehyde) and other embedding media (usually epoxy resins) are used to study tissues in an electron microscope, which makes it possible to reveal the ultrastructure of cells and their components. A special ultramicrotome with a glass or diamond knife makes it possible to obtain sections with a thickness of less than 1 micron, and permanent preparations are mounted not on glass slides, but on copper meshes. Recently, techniques have been developed to allow a number of conventional histological staining procedures to be applied after the tissue has been fixed and embedded for electron microscopy.

The labor-intensive process described here requires skilled personnel, but mass production of microscopic specimens uses a conveyor technology in which many of the steps of dehydration, embedding, and even staining are performed by automatic tissue guides. In cases where an urgent diagnosis is needed, in particular during surgery, biopsy tissue is quickly fixed and frozen. Sections of such fabrics are made in a few minutes, they are not poured and immediately stained. An experienced pathologist can immediately make a diagnosis based on the general pattern of cell distribution. However, such sections are unsuitable for a detailed study.

Histochemistry.

Some staining methods allow you to identify certain chemicals in cells. Differential staining of fats, glycogen, nucleic acids, nucleoproteins, certain enzymes, and other chemical components of the cell is possible. Dyes are known that intensively stain tissues with high metabolic activity. The contribution of histochemistry to the study of the chemical composition of tissues is constantly increasing. Dyes, fluorochromes and enzymes have been selected that can be attached to specific immunoglobulins (antibodies) and, by observing the binding of this complex in a cell, identify cellular structures. This area of ​​research is the subject of immunohistochemistry. The use of immunological markers in light and electron microscopy contributes to the rapid expansion of our knowledge of cell biology, as well as increasing the accuracy of medical diagnoses.

"Optical Staining".

Traditional histological staining methods involve fixation that kills tissue. Optical staining methods are based on the fact that cells and tissues that differ in thickness and chemical composition also have different optical properties. As a result, using polarized light, dispersion, interference, or phase contrast, it is possible to obtain images in which individual structural details are clearly visible due to differences in brightness and (or) color, while such details are hardly distinguishable in a conventional light microscope. These methods make it possible to study both living and fixed tissues and eliminate the appearance of artifacts that are possible when using conventional histological methods.

Teaching about tissues

The study of tissues - histology. epithelial tissue. glands. Connective tissue. nervous tissue. General physiology of excitable tissues. Bioelectric phenomena. Conduction of excitation along the nerve. Laws of conduction of excitation along the nerve.

Topic for self-study: Fundamentals of human embryology. Sex cells and fertilization. Embryo development. Organs and organ systems. Anatomical terminology. Axes and planes. Sex cells and fertilization. Embryo development. Anatomical terminology. Axes and planes. (2 hours).

The body of animals and humans is made up of tissues.

HISTOLOGY (from the Greek. histos - tissue and logy), a branch of morphology that studies the tissues of multicellular animals.

The formation of G as an independent science in the 20s. 19th century associated with the development of microscopy. The cellular theory formed the methodological basis of genetics.

A tissue is a historically established system of cells and non-cellular structures (intercellular substance) that have a common structure and are specialized to perform certain functions.

According to the structure, function and development, the following types of tissues are distinguished:

• 1) epithelial tissue (epithelium);
• 2) blood and lymph;
• 3) connective tissue;
• 4) muscle tissue;
• 5) nervous tissue.

Each organ consists of various tissues that are closely related to each other. Throughout the life of the organism, cellular and non-cellular elements wear out and die (physiological degeneration) and their restoration (physiological regeneration). These processes in different tissues proceed differently. In the process of life, slowly ongoing age-related changes occur in all tissues. It has now been established that tissues regenerate when damaged. Epithelial, connective, non-striated (smooth) muscle tissues regenerate well and quickly, striated (striated) muscle tissue is restored only under certain conditions, and only nerve fibers are restored in the nervous tissue. Restoration of tissues in case of damage is called reparative regeneration. histology epithelial tissue

The tasks of modern G. - elucidation of the evolution of tissues, the study of the course and causes of their development in the body (histogenesis), the structure and functions of the specialist. cells, interstitial media, interaction of cells within the same tissue and between cells of different tissues, regeneration of tissue structures and regulatory mechanisms that ensure the integrity and joint activity of tissues. Modern G. pays much attention to experiments. study of tissue mechanisms of development. Modeling of tissue and organ processes is also characteristic, for example, in the culture of tissues (and organs), during their transplantations, etc.

G. is usually divided into general G., exploring the main. the principles of development, structure, and functions of tissues, and the particular G., which elucidates the properties of tissue complexes in the composition of specific organs of multicellular animals.

HISTOGENESIS (from the Greek histos - tissue and genesis), the set of processes that has developed in phylogeny, which ensures the formation, existence and restoration of tissues with their inherent organ-specific characteristics in the ontogenesis of multicellular organisms. features. In the body, tissues develop from certain embryonic rudiments (derivative germ layers) formed as a result of proliferation, movement (morphogenetic movements) and adhesion of embryonic cells at the early stages of its development in the process of organogenesis.

Scheme of the histogenetic series of renewing tissues. L - stem cells; Bi -- B4 -- progenitor cells; B - mature differentiated cells. Vertical arrows reflect the comparative ability of cells to proliferate.

EPITHELIUM (from epi and Greek thele - nipple), epithelial tissue, in multicellular animals - the tissue covering the body and lining its cavities in the form of a layer, is also the main. funkt. component of most glands. In embryogenesis, E. is formed earlier than other tissues from all three germ layers and participates in the formation of covers, their derivatives, and many others. glands. For him characterized by a high ability to regenerate , because E., due to its position, wears out quickly. E. is underlain by a basal membrane, does not contain blood vessels, and receives nutrition from the underlying tissue.

E. performs the following functions: restrictive, protective, metabolism (absorption, excretion), secretory.

Allocate E. integumentary --single layer (all its cells are connected to the basement membrane, e.g. E. of the gastrointestinal tract, mesothelium), multilayer (only its lower layer is connected to the basement membrane, and the remaining layers of this connection are devoid of, for example, E. skin), transition (two-layer, its external appearance varies depending on the degree of stretching of the wall of the organ, for example, E. of the urinary bladder of the urinary tract) and secreting - glandular.

Scheme of the structure of various types of epithelium:

A, B, C - single-layer single-row (A - cylindrical, B - cubic, C - flat.); G - single-layer multi-row; D, E - multilayer flat (D - non-keratinized, E - keratinized.); F and Fg - transitional (F - with a stretched wall of the organ, Fg - with a collapsed.); / - epithelium, 2 - basement membrane; 3 - underlying connective tissue.

Due to the diversity of the structure of dec. forms E. some scientists propose to consider otd. its varieties are independent. tissues.

The structure of E.'s cells corresponds to their functions. specialization and depends on the variety of E.

According to the shape of the cells distinguish flat, cubic and cylindrical . E. For the cells of the suction E., a brush border is characteristic, for the ciliated epithelium - the presence of cilia, for the protective - the ability to keratinize, for the glandular - the development of a granular endoplasmic reticulum and the Golgi complex.

GLANDS (glandlae), organs of animals and humans that produce and secrete specific. the substances participating in fiziol. departures of the body.

exocrine J., or J. external secretion (sweat, salivary, milk fats, wax fats of insects, etc.), secrete their products - secrets - onto the surface of the body or mucous membranes through the excretory ducts.

Endocrine glands, or J. internal secretion, do not have excretory ducts and the products produced by them (Secrets, or hormones) are released into the blood or lymph. Some zh. (kidneys, sweat zh., partly lacrimal zh.) selectively absorb the end products of metabolism from the blood, concentrate them and release them to the outside , thereby preventing poisoning of the body; the substances they secrete. excreta .

Types of simple glands: a - tubular; 6 - tubular with a branched adenomer; in - tubular glomerular; g - alveolar; e - alveolar with a branched adenomer.

Often referred to as secrets. products of all. irrespective of their fiziol. values. secrets pl. Zh. (eg, parotid, pancreas) in its chemical. nature belong to proteins; dissolving in water, they are released in the form serous fluids . Such Zh. are often called. proteinaceous, or serous. Dr. the group is mucous G. (eg, Zh. esophagus, uterus), producing mucins and mucoids (substances from the group of glycoproteins). Some Zh., so-called. heterocrine, produce both protein and mucous secretions simultaneously. Zh., cells to-rykh at the end of the secretory cycle are destroyed, called. holocrine; Zh., functioning repeatedly, - merocrine. Exocrine glands and most endocrine glands develop as derivatives of epithelial tissues.

By shape (elongated or rounded) terminal (secretory) section - adenomer - G. is divided into tubular and alveolar . Zh., consisting of one adenomer (including sometimes branched) and a non-branching excretory duct, called. simple (tubular or alveolar), for example, fundic and pyloric. G. stomach. Zh., consisting of many adenomers, the secret of which is numerous. branches merges into a common excretory duct, called. complex.

Types of complex glands: a - tubular; b - alveolar; in - tubular-alveolar; g - mesh.

According to the shape of the adenomers, complex glands can be tubular (eg, salivary sublingual gland) and alveolar (eg, pancreatic gland, parotid gland). Sometimes in the same complex gland there are adenomeres of tubular and alvelar forms (for example, salivary submandibular gland). Occasionally, tubular adenomeres, branching out, connect between them into a loose network, and the gland becomes folded mesh (eg, liver, anterior pituitary gland).

CONNECTIVE TISSUE (textus conjunctivus), tissue of an animal organism that develops from the mesenchyme and performs basic, trophic and protective functions.

Peculiarity buildings S. t. - the presence of well-developed intercellular structures: collagen, elastic and reticular fibers and structureless main. substance containing a large number of mucopolysaccharides. Depending on the function in the body, cell composition, type and properties of intercellular structures, fiber orientation, etc. allocate actually S. t., bone and cartilage tissue , as well as reticular, adipose and pigment-rich tissue , to-rye, together with blood and lymph, are combined into an internal tissue system. environment. Actually S. t. is divided into issued, or oriented (fibers are regularly oriented - tendons, fascia, ligaments, sclera of the eye, etc.), and unformed, or diffuse (fibers are connected in bundles arranged randomly), in which a swarm is isolated dense (e.g. connective tissue base of the skin) and loose (eg, subcutaneous tissue, tissue that fills the gaps between internal organs and accompanies blood vessels). In loose S. t. there are histiocytes, obese, fatty, pigmented, plasmatic. cells, dec. Types of blood leukocytes, it creates ext. Wednesday, through which the delivery of nourishment takes place. substances to cells and removal of products of their metabolism, i.e. participates practically in all fiziol. and pathological. body reactions. In S. t. support type (bone, cartilaginous tissues) intercellular structures prevail, and cells are presented by hl. arr. fibroblasts and similar chondroblasts and osteoblasts. For S. t. with pronounced trophic. and protective functions (tissues of the internal environment) are characterized by a relatively large number and variety of free cells.

NERVOUS SYSTEM (systema nervo-sum), morphofunctional. set of departments neurons and other structures of the nervous tissue of animals and humans

N. s. perceives external and int. stimuli, analyzes and processes incoming information, stores traces of past activity (mechanisms of memory) and, accordingly, regulates and coordinates body functions. At the heart of N.'s activity with. lies reflex, associated with the spread of excitation along reflex arcs and the process of inhibition.

N. s. formed Ch. arr. nervous tissue, structural and functional. the unit of which is a neuron. During evolution of animals there was a gradual complication of N. of page. (centralization and cephalization) and at the same time their behavior became more complicated. As multicellular organisms develop, a specialization is formed. tissue capable of reproducing active reactions, i.e., to excitation.

NERVOUS TISSUE (textus nervosus), complexes of nerve and glial cells specific to animal organisms. It appears (evolutionarily) in coelenterates and reaches the most complex development in the cerebral cortex of the mammalian cerebral hemispheres. N. t. - the main structural and functional. element of the nervous system. Neurons (derivatives of the ectoderm) do not divide, have special (compared with muscle cells and fibers) excitability and conductivity, and are able to form stable contacts with other cells. Glial cells (collectively, neuroglia) are the trophic, supporting, and protective apparatus of N. t. In vertebrates, blood vessels pass through N. t., and in insects, the trachea. Usually, N. t. is surrounded by layers that will connect, tissues (meninges in vertebrates). N.'s cells of t. closely adjoin each other. In N. t. are often special. receptor and secretory cells. N. t. carries out the relationship of tissues and organs in the body.

NERVE FIBER (neurofibra), a process of a neuron (axon), covered with membranes and conducting nerve impulses from the perikaryon. Diam. N. in. ranges from 0.5 to 1700 microns, dl. may exceed 1 m. Flesh (myelinated) N. century. covered with Schwann and myelin sheaths, and amyelinated (non-myelinated) - only Schwann. Depending on the speed of the excitation, the duration of the phases of the action potential and the diameter, warm-blooded animals are divided into 3 main. groups N. century, designated A (subgroups a, P, y, 6), B and C. Diam. engine and feels. N. in. gr. A 1--22 microns, speed 5--120 m / s, gr. In (primarily preganglionic N. century), respectively, 1--3.5 microns and 3--18 m / s, gr. C (predominantly postganglionic N. century) 0.5 - 2 microns and 0.5 - 3 m / s. The speed of propagation of nerve impulses in N. century. is directly proportional to its diameter: with thickening of axons, it increases and is always higher in myelinated N. century. In them, the impulse does not propagate continuously, as in the non-fleshy ones, but in jumps, from one interception of Ranvier to another (saltatory conduction). N. in. make up the periphery. nervous system and pathways to the CNS. Bunches of N. in. form nerves.

NERVE ENDING (terminatio nervi), a specialized formation in the terminal branching of the processes of a neuron, devoid of a myelin sheath; used to receive or transmit signals.

Sensitive, or sensory, neurons that receive signals (reception) are similar in structure and function to dendrites and, like them, have a receptor membrane. They are free or form a complex with special. feels. cells. Effector N. about. (telodendria, terminals, presynaptic endings), which transmit nerve impulses, are formed by axon branches, which enter synaptic. contact with nerve, muscle or glandular cells. Axon terminals contain mitochondria and clusters of synapses. bubbles (vesicles), contents to-rykh at N.'s activation of the lake. thrown into the synaptic. gap and leads to a change in the ion permeability of postsynaptic. membranes (see Synapses).

NERVE IMPULSE, a wave of excitation that propagates along the nerve fiber and manifests itself in electric. (action potential), ionic, mechanical, thermal. and other changes. Provides information transfer from peripherals. receptor endings to nerve centers within the CNS and from them to effectors. It is characterized by a short-term decrease in the potential difference (in relation to the initial one), resulting from a local shift in the ion permeability of the excitable membrane. The energy necessary for N.'s transfer and., is released in the nerve. N. and. arises according to the “all or nothing” law, that is, it does not depend on the strength and quality of the stimulus, and is capable of spasmodically propagating along the nerve fiber at a speed of 0.2 to 180 m / s. At the time of N.'s distribution and. internal part of the nerve fiber is positively charged and the potential difference between the axoplasm and ext. medium can reach 40--50 mV. Reducing the potential difference (depolarization) at the time of N. and. depends on the concentration of Ca2+ and Mg2+ ions in the environment. N.'s duration and. and the speed of its conduction depend on the temperature, diameter and structure of the nerve fiber.

An important property of excitable tissue is refractoriness. The duration of the refractory period limits the ability of the nerve cell to reproduce rhythmic. impulses, that is, determines its lability. In nature. conditions, a series of N. and continuously run along the nerve fibers. The frequency of these rhythmic discharges depends on the strength of the stimulus that caused them. Yes, engine. neurons can conduct without distortion approx. 500 N. and. per second, intermediate - up to 1000. After the refractory period, long trace changes in excitability follow, that is, aftereffects, to-rye in the body of the nerve cell are expressed almost 10 times stronger than in the axon. N. and. capable of self-propagation due to those electric. currents, to-rye it creates; in this way, undistorted information is carried along the nerve fibers, encoded either by the frequency of action potentials or by a “discharge pattern, that is, by a certain sequence of N. and. within the overall response time of the cell. About N.'s transition and. from neuron to neuron or to performer, organs, see Synapses.

NERVE CENTER, set of neurons, b. or m. strictly localized in the nervous system and participating in the implementation of the reflex, in the regulation of one or another function of the body or one of the sides of this function. In the simplest cases, N. c. consists of several neurons that form a separate node (ganglion). So, in some crustaceans, the cardiac ganglion, consisting of 9 neurons, controls the heartbeats. In highly organized animals N. c. are part of the central nervous system and can consist of thousands and even millions of neurons.

In each N. c. the nerve fibers receive information in the form of nerve impulses from the sense organs or from other N. c.; here it is processed by N.'s neurons of c., processes (axons) to-rykh do not go beyond its limits. Dr. neurons, processes to-rykh leave N. of c., deliver its command impulses to peripheral. bodies or other N. c. The neurons that make up the N. c. are interconnected through excitatory and inhibitory synapses and form complex complexes, the so-called. neural networks. Along with neurons, to-rye are excited only in response to incoming nerve signals or the action of a variety of chemicals. irritants contained in the blood, in the composition of N. c. may include pacemaker neurons (English pacemaker neurones), which have their own. automatism; they have the ability to periodically generate nerve impulses.

From representation about N. of c. it follows that the various functions of the body are regulated by decomp. parts of the CNS. This idea of ​​the localization of functions in the nervous system is not shared by some physiologists or is accepted with reservations. They refer to experiments proving:

1) plasticity of certain parts of the nervous system, its ability to function. restructuring, compensating, for example, loss of brain matter; 2) that structures located in different parts of the nervous system are interconnected and can affect the performance of the same function. This gave some physiologists a reason to completely deny the localization of functions, and others to expand the concept of N. c., including in it all the structures that affect the performance of a given function. Modern neurophysiology uses the idea of ​​funkts. hierarchy of N. c., according to Krom otd. sides of the same body function are controlled by N. c., located at different levels of the nervous

NERVES (Latin singular nervus, from Greek neuron - vein, nerve), strands of nervous tissue that connect the brain and nerve ganglions with other tissues and organs of the body. N. are formed by bundles of nerve fibers. Each bundle is surrounded by a connective tissue membrane (perineurium), from which thin layers (endoneurium) go inside the bundle. All N. is covered with a common membrane (epineurium). Usually N. consists of 103-104 fibers, but in humans there are more than 1 million of them in the visual N. In invertebrates, N. are known, consisting of several fibers. For each N. fiber, the impulse propagates in isolation, without passing to other fibers. Distinguish sensitive (afferent, centripetal), motor (efferent, centrifugal) and mixed N. In vertebrates, cranial nerves depart from the brain, and spinal nerves from the spinal cord. Several neighboring N. can form nerve plexuses. According to the nature of the innervated organs, N. is classified into vegetative and somatic, the totality of which forms peripheral. nervous system.

EXCITABILITY, the ability of living cells, organs and whole organisms (from protozoa to humans) to perceive the effects of stimuli and respond to them with an excitation reaction. Measure V. - the threshold of irritation. V. is connected with specific. sensitivity of cell membranes, with their ability to respond to the action of adequate stimuli (eg, chemical, mechanical) specific. changes in ion permeability and membrane potential. The intensity, duration and speed of reactions in response to irritation are not the same for decomp. fabrics. V. as one of the forms of irritability arose in the process of evolution in connection with the development of specific. tissues and, above all, is inherent in the nervous system. The term is "B." It is also used to assess the state of the nervous system, neuro-psychic. tension.

EXCITATION, the reaction of a living cell to irritation, characterized by a combination of physical, physico-chemical. and functional changes in it. During V. the live system passes from a state carries, fiziol. dormancy to the activity characteristic of a given cell or tissue. M Natural V. is characteristic of sections of the cell membrane specialized for the perception of stimuli coming from outside (the receptor membrane) or from other nerve cells (the postsynaptic membrane). It increases as the strength of the stimulus increases and occurs immediately after irritation. Local V. is associated with an increase in elect. membrane permeability to extra- and intracellular ions and manifests itself in the form of negative. fluctuations in the surface (membrane) potential (see Depolarization). At local V. important funkts. Receptor and generator potentials in the area of ​​contact (synapse) of one nerve or muscle cell with the axons of another nerve cell are of importance. Local V. has no threshold, varies in amplitude and duration depending on the strength and duration of the stimulus, the rate of its rise and fall. When local V. reaches a threshold value (an irritation threshold), a spreading V. arises, which immediately acquires a max, amplitude and therefore obeys the all-or-nothing law. In nerve and muscle cells, V. is accompanied by the appearance of an action potential (AP), which can propagate without attenuation along the entire cell membrane, which ensures the rapid transmission of information along nerve fibers over long distances. PD in muscle cells leads to the activation of contractions, the apparatus of myofibrils (see Muscle contraction), and in nerve cells it causes the secretion of chemicals in the endings of axons, substances - mediators that have an excitatory or inhibitory effect on the innervated tissues. During PD, the cell is completely immune to stimuli, excitability is restored gradually after the end of PD (see Refractoriness).

In the reaction of V. beings, the role is played by electrical, structural, chemical. (including enzymatic), physical. (temperature) and other processes. The penetration of Na + and (or) Ca2 + ions into the cytoplasm during V. activates enzymatic processes that restore the initial inequality in the concentrations of Na +, K +, Ca2 + ions on both sides of the membrane and are aimed at the synthesis of proteins and phospholipids to renew the membrane itself and cytoplasm. If the local V. is able to more accurately reflect the characteristics of the stimulus, then the propagating V. encodes these characteristics with the frequency of nerve impulses, the change in this frequency over time and the entire duration of the impulse burst, and is also capable of transmitting this information through the nerve conductors. V. and the inhibition associated with it is the basis of all types of nervous activity.

EMBRYOLOGY (from embryo and...logy), in the narrow sense - the science of embryonic development, in the broadest sense - the science of the individual development of organisms (ontogenesis). E. of animals and humans studies preembryonic development (oogenesis and spermatogenesis), fertilization, embryonic development, and the larval and postembryonic (or postnatal) periods of individual development. Embryol. studies in India, China, Egypt, Greece are known until the 5th century. BC e. Hippocrates (with followers) and Aristotle studied the development of many embryos. animals, especially chickens, as well as humans.

A significant shift in the development of E. came in the middle. 17th century with the advent of the work of W. Harvey "Research on the origin of animals" (1651). Of great importance for the development of E. was the work of K. F. Wolf "The Theory of Origin" (1759), the ideas of which were developed in the works of X. I. Pander (the concept of germ layers), K. M. Baer (discovery and description eggs of humans and mammals, a detailed description of the main stages of embryogenesis in a number of vertebrates, elucidation of the subsequent fate of germ layers, etc.), etc. Fundament of evolution. compare. E., based on the theory of Ch. Darwin and substantiating, in turn, the relationship of animals of different taxa, was laid by A. O. Kovalevsky and I. I. Mechnikov. Experiment. E. (originally - the mechanics of development) owes its development to the works of V. Ru, H. Driesch, H. Shpeman, D. P. Filatov. In the history of E. for a long time, the struggle between supporters epigenesis (W. Harvey, K. F. Wolf, X. Driesch and others) and preformism (M. Malpighi, A. Leeuwenhoek, S. Bonnet and others). Depending on the tasks and methods of research, there are general, comparative, experimental, population, ecological E. On the data will compare. E. in means, the degree of nature is built. animal system, especially in its higher sections. Experiment. E., using the removal, transplantation, and cultivation of the rudiments of organs and tissues outside the body, studies the causal mechanisms of their emergence and development in ontogeny. Data E. are of great importance for medicine and page. x-va. In recent decades, at the junction of E. with cytology, genetics and pier. biology originated developmental biology. EMBRIBN (Greek embryon - embryo), an animal organism in the early period of development, the same as the embryo.

Lecture plan:

Histology as a science, the subject of study of histology

Cell - structural unit of tissues

Fabrics: concept, characteristics. Fabric classification

Histology as a science, the subject of study of histology

Histology and cytology are traditionally classified as morphological sciences (from the Greek morphe - form), in previous years they were largely descriptive. In recent decades, the possibilities of histology and cytology are not limited to the study of the features of the microscopic or ultramicroscopic structure of tissues, these sciences analyze their functional characteristics. Histology and cytology are an important part of medical education. They form the basis for the study of other fundamental biomedical and clinical disciplines.

Cytology- (from the Greek kytos - cell and logos - teaching) or cell biology. General cytology studies the most common structural and functional properties inherent in all cells of the body: their vital activity and morphology, function and death.

Histology- the science of tissues (from the Greek gistos - tissue and the Greek logos - teaching) the science of the structure, development and vital activity of tissues of animal organisms. Histology as a science traditionally combines two sections: general and private histology.

General histology studies the basic fundamental properties of the most important groups of tissues, being, in fact, the biology of tissues.

Private histology studies the features of the structural and functional organization and interaction of tissues in the composition of specific organs, closely interlocking with microscopic anatomy, thus. the main object of study of general and particular histology of a person is his tissues.

An independent section of histology is the study of tissue in the dynamics of its development - embryology.

Embryology(Greek embryon - fetal fetus, embryo and Greek logos - teaching) - the science of the intrauterine development of a new organism from a unicellular to a highly organized multicellular organism. It is necessary for the doctor, as it reveals the patterns of development, key stages and critical periods in the life of the organism.

Cell - structural unit of tissues

A cell is a living system of structured biopolymers, delimited by a biologically active membrane, capable of self-regulation of metabolic processes, self-replenishment of energy, self-reproduction and adaptation.

In eukaryotic cells, they secrete 3 main parts: cell membrane - plasmolemm or cytolemma, nucleus and cytoplasm.

In addition to the cell, other structural units are created in the human and animal body:

Symplast- supracellular multinuclear structure containing a large amount of undivided cytoplasm. An example of a symplast is a muscle fiber, which can be several centimeters in size.

Postcellular structures- derived cells, as a rule, which have lost the nucleus in the process of development and are not capable of dividing. An example of a post-cellular structure is an erythrocyte.

The intercellular substance waste product of the cell . In some tissues, its structure determines the properties, for example, bone and cartilage tissues have a high mechanical density due to the special structure of the intercellular substance.

Fabrics: concept, characteristics. Fabric classification

The human and animal organism is an integral system in which a number of hierarchical levels of organization of living matter can be distinguished:

cells - tissues - structural and functional units of organs - organs - organ systems - the body as a whole.

Outstanding scientists from Aristotle and Galen drew attention to the homogeneity of living matter in various organs in humans and animals. But for the first time the term tissue was used by the French anatomist and surgeon M. Xavier. This scientist described 21 fabrics, but his classification reflected the era of idealism and metaphysics. So he singled out the nervous tissue of animal life and the nervous tissue of organic (plant) life. And only in 1854, I. Keliker and F. Leydig simultaneously created a new classification, highlighting only 4 types of fabrics. This classification has not lost its significance to this day.

Tissue is a historically established system consisting of cells and non-cellular structures similar in origin (genesis), structure (morphology), metabolism and functioning.

So, histologically, the body consists of 4 types of tissues:

1. Epithelial tissues

2. Tissues of the internal environment - connective tissues

3. Muscle tissue

4. Nervous tissue

epithelial tissues develop from all three germ layers, therefore, epithelia of ectodermal, mesodermal and endodermal origin are distinguished. They are combined into one group based on the similarity of structure and functioning:

All epithelial tissues are layers(less often strands) of cells - epitheliocytes, between which there are almost no intercellular substance, and the cells are closely connected to each other through various contacts.

Epithelial tissue (if it is multilayered, then the very first one is its inner layer) is located on the basement membrane separating epithelial cells from the underlying connective tissue.

Epithelium does not contain blood vessels. Nutrition of epitheliocytes is carried out diffusely through the basement membrane from the side of the underlying connective tissue. An exception is the vascular strip of the cochlear canal of the inner ear.

Epithelial cells have a polarity: secrete basal(underlying) and apical(apical) poles of cells that have a different structure.

All epithelia have a high capacity for regeneration.

Distinguish two groups of epithelial tissues:

surface epithelium(integumentary and lining), which, in turn, are single-layered (squamous, cubic, cylindrical epithelium) and multi-layered (keratinizing, non-keratinizing, transitional epithelium).

glandular epithelium, forming glands that synthesize and secrete specific products - secrets.

The most complex and diverse in morphology tissues of the internal environment or connective tissues. All of them are united in one group. have a number of common features:

Common genesis - develop from mesenchyme.

The general principle of the structure - they all consist of two structural units - cells and intercellular substance.

All these tissues do not border on the external environment and body cavities, form the internal environment of the body and maintain its homeostasis

The cells of the tissues of the internal environment, as a rule, are apolar and are not connected with each other.

Classification of tissues of the internal environment (connective tissues)

Tissues of the internal environment with protective and trophic function Key words: blood, lymph, hematopoietic tissues - myeloid, lymphoid.

Actually connective tissues: RVST (unformed), PVST (formed and unformed).

Tissues of the internal environment with special properties: adipose, reticular, pigment, mucous tissue.

Tissues of the internal environment with support function- skeletal connective tissues: bone, cartilage.

Muscle tissues have a different origin, but are united in one group, as they are capable of contraction and provide various kinds of motor reactions of the body.

All muscle tissues are divided into:

Smooth

a. Visceral type (actually smooth muscle tissue)

b. myoneural muscle tissue

in. Myoepithelial tissue or myoid cell complexes

2. Cross-striped

a. Somatic type (skeletal muscle tissue).

b. Coelomic type (cardiac muscle tissue).

nervous tissue is the basis of the structure of the organs of the nervous system and sensory organs, consists of interconnected nerve cells and neuroglia, which provide specific functions for the perception of stimuli, excitation, and transmission of a nerve impulse.

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