Histology (from Greek ίστίομ - tissue and Greek Λόγος - knowledge, word, science) is a branch of biology that studies the structure of tissues of living organisms. This is usually done by dissecting tissue into thin layers and using a microtome. Unlike anatomy, histology studies the structure of the body at the tissue level. Human histology is a branch of medicine that studies the structure of human tissues. Histopathology, the branch of microscopic examination of diseased tissue, is an important tool in pathomorphology (pathological anatomy), since an accurate diagnosis of cancer and other diseases usually requires histopathological examination of specimens. Forensic histology is a branch of forensic medicine that studies the features of damage at the tissue level.
Histology was born long before the invention of the microscope. The first descriptions of fabrics are found in the works of Aristotle, Galen, Avicenna, Vesalius. In 1665, R. Hooke introduced the concept of a cell and observed the cellular structure of some tissues under a microscope. Histological studies were carried out by M. Malpighi, A. Leeuwenhoek, J. Swammerdam, N. Gru and others. A new stage in the development of science is associated with the names of K. Wolf and K. Baer, the founders of embryology.
In the 19th century, histology was a full-fledged academic discipline. In the middle of the 19th century, A. Kölliker, Leiding, and others created the foundations of the modern theory of fabrics. R. Virchow initiated the development of cellular and tissue pathology. Discoveries in cytology and the creation of cell theory stimulated the development of histology. The works of I. I. Mechnikov and L. Pasteur, who formulated the basic ideas about the immune system, had a great influence on the development of science.
The 1906 Nobel Prize in Physiology or Medicine was awarded to two histologists, Camillo Golgi and Santiago Ramón y Cajal. They had mutually opposite views on the nervous structure of the brain in various examinations of identical images.
In the 20th century, the improvement of methodology continued, which led to the formation of histology in its current form. Modern histology is closely connected with cytology, embryology, medicine and other sciences. Histology develops such issues as the patterns of development and differentiation of cells and tissues, adaptation at the cellular and tissue levels, problems of tissue and organ regeneration, etc. Achievements in pathological histology are widely used in medicine, making it possible to understand the mechanism of development of diseases and suggest ways to treat them.
Research methods in histology include the preparation of histological preparations with their subsequent study using a light or electron microscope. Histological preparations are smears, prints of organs, thin sections of pieces of organs, possibly stained with a special dye, placed on a microscope slide, enclosed in a preservative medium and covered with a coverslip.
Tissue histology
A tissue is a phylogenetically formed system of cells and non-cellular structures that have a common structure, often origin, and are specialized in performing specific specific functions. The tissue is laid in embryogenesis from the germ layers. From the ectoderm, the epithelium of the skin (epidermis), the epithelium of the anterior and posterior alimentary canal (including the epithelium of the respiratory tract), the epithelium of the vagina and urinary tract, the parenchyma of the large salivary glands, the outer epithelium of the cornea and nervous tissue are formed.
From the mesoderm, mesenchyme and its derivatives are formed. These are all types of connective tissue, including blood, lymph, smooth muscle tissue, as well as skeletal and cardiac muscle tissue, nephrogenic tissue and mesothelium (serous membranes). From the endoderm - the epithelium of the middle part of the digestive canal and the parenchyma of the digestive glands (liver and pancreas). Tissues contain cells and intercellular substance. At the beginning, stem cells are formed - these are poorly differentiated cells capable of dividing (proliferation), they gradually differentiate, i.e. acquire the features of mature cells, lose the ability to divide and become differentiated and specialized, i.e. capable of performing specific functions.
The direction of development (differentiation of cells) is genetically determined - determination. This orientation is provided by the microenvironment, the function of which is performed by the stroma of organs. A set of cells that are formed from one type of stem cells - differon. Tissues form organs. In the organs, the stroma formed by connective tissues and the parenchyma are isolated. All tissues regenerate. A distinction is made between physiological regeneration, which constantly proceeds under normal conditions, and reparative regeneration, which occurs in response to irritation of tissue cells. The mechanisms of regeneration are the same, only reparative regeneration is several times faster. Regeneration is at the heart of recovery.
Regeneration mechanisms:
By cell division. It is especially developed in the earliest tissues: epithelial and connective, they contain many stem cells, the proliferation of which ensures regeneration.
Intracellular regeneration - it is inherent in all cells, but is the leading mechanism of regeneration in highly specialized cells. This mechanism is based on the enhancement of intracellular metabolic processes, which lead to the restoration of the cell structure, and with further enhancement of individual processes
hypertrophy and hyperplasia of intracellular organelles occurs. which leads to compensatory hypertrophy of cells capable of performing a greater function.
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 the nervous system.
Fabrics have evolved. There are 4 groups of tissues. The classification is based on two principles: histogenetic, based on origin, and morphofunctional. According to this classification, the structure is determined by the function of the tissue. The first to appear were epithelial or integumentary tissues, the most important functions being protective and trophic. They are rich in stem cells and regenerate through proliferation and differentiation.
Then appeared connective tissues or musculoskeletal, tissues of the internal environment. Leading functions: trophic, supporting, protective and homeostatic - maintaining the constancy of the internal environment. They are characterized by a high content of stem cells and regenerate through proliferation and differentiation. In this tissue, an independent subgroup is distinguished - blood and lymph - liquid tissues.
The following are muscle (contractile) tissues. The main property - contractile - determines the motor activity of organs and the body. Allocate smooth muscle tissue - a moderate ability to regenerate by proliferation and differentiation of stem cells, and striated (striated) muscle tissue. These include cardiac tissue - intracellular regeneration, and skeletal tissue - regenerates due to the proliferation and differentiation of stem cells. The main recovery mechanism is intracellular regeneration.
Then came the nervous tissue. Contains glial cells, they are able to proliferate. but the nerve cells themselves (neurons) are highly differentiated cells. They react to stimuli, form a nerve impulse and transmit this impulse through the processes. Nerve cells have intracellular regeneration. As the tissue differentiates, the leading method of regeneration changes - from cellular to intracellular.
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 one another 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 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.
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.
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Ministry of Agriculture and Food of the Republic of Belarus
Educational Establishment "Vitebsk Order of the Badge of Honor"
State Academy of Veterinary Medicine”
Department of Pathological Anatomy and Histology
DIPLOMAWORK
on the topic: "The study of issues of cytology, histology and embryology"
Vitebsk 2011
1. Histology as a science, its relationship with other disciplines, the role in the formation and practical work of a veterinarian
2. Definition of the concept of "cell". Its structural organization
3. Composition and purpose of the cytoplasm
4. Cell organelles (definition, classification, characterization of the structure and functions of mitochondria, lamellar complex, lysosomes, endoplasmic reticulum)
5. Structure and functions of the nucleus
6. Types of cell division
8. The structure of spermatozoa and their biological properties
9. Spermatogenesis
10. Structure and classification of eggs
11. Stages of development of the embryo
12. Features of the embryonic development of mammals (formation of trophoblast and fetal membranes)
13. Placenta (structure, functions, classifications)
14. Morphological classification and brief description of the main types of epithelium
15. General characteristics of blood as a tissue of the internal environment of the body
16. Structure and functional significance of granulocytes
17. Structure and functional significance of agranulocytes
18. Morphofunctional characteristics of loose connective tissue
19. General characteristics of the nervous tissue (composition, classification of neurocytes and neuroglia)
20. The structure and functions of the thymus
21. Structure and functions of lymph nodes
22. Structure and functions
23. The structure and functions of a single-chamber stomach. Characteristics of his sinewy apparatus
24. Structure and functions of the small intestine
25. Structure and functions of the liver
26. The structure and functions of the lung
27. Structure and functions of the kidney
28. The structure and functions of the testes
29. The structure and functions of the uterus
30. Composition and purpose of the endocrine system
31. Cellular structure of the cerebral cortex
1. G histology as a science, its relationship with other disciplines, the role in the formation and practical work of a veterinary medicine doctor
Histology (histos - tissue, logos - teaching, science) is the science of the microscopic structure, development and vital activity of cells, tissues and organs of animals and humans. The body is a single holistic system built from many parts. These parts are closely interconnected, and the organism itself constantly interacts with the external environment. In the process of evolution, the animal organism acquired a multi-level nature of its organization:
Molecular.
Subcellular.
Cellular.
Tissue.
Organ.
System.
Organismic.
This allows, when studying the structure of animals, to divide their organisms into separate parts, apply various research methods and single out the following sections in histology as separate branches of knowledge:
1. Cytology - studies the structure and functions of body cells;
2. Embryology - explores the patterns of the embryonic development of the body:
a) General embryology - the science of the earliest stages of development of the embryo, including the period of the emergence of organs that characterize the belonging of individuals to a certain type and class of the animal kingdom;
b) Private embryology - a system of knowledge about the development of all organs and tissues of the embryo;
3. General histology - the study of the structure and functional properties of body tissues;
4. Private histology - the most extensive and important section of the discipline, including the fullness of knowledge about the structural features and functional functions of the organs that form certain body systems.
Histology belongs to the morphological sciences and is one of the fundamental biological disciplines. It is closely related to other general biological (biochemistry, anatomy, genetics, physiology, immunomorphology, molecular biology), animal husbandry and veterinary disciplines (pathanatomy, veterinary medical examination, obstetrics, therapy, etc.). Together they form the theoretical basis for the study of veterinary medicine. Histology is also of great practical importance: many histological research methods are widely used in medical practice.
Tasks and significance of histology.
1. Together with other sciences, it forms medical thinking.
2. Histology creates the biological basis for the development of veterinary medicine and animal husbandry.
3. Histological methods are widely used in the diagnosis of animal diseases.
4. Histology provides control over the quality and effectiveness of the use of feed additives and prophylactic agents.
5. With the help of histological research methods, the therapeutic efficacy of veterinary preparations is monitored.
6. Provides an assessment of the quality of breeding work with animals and the reproduction of the herd.
7. Any targeted intervention in the body of animals can be controlled by histological methods.
2. Definition of the term "cell". Its structural organization
A cell is the basic structural and functional unit that underlies the structure, development and life of animal and plant organisms. It consists of 2 inextricably linked parts: the cytoplasm and the nucleus. The cytoplasm includes 4 components:
cell wall (plasmolemma).
Hyaloplasm
Organelles (organelles)
Cell inclusions
The core also consists of 4 parts:
Nuclear membrane, or karyolemma
Nuclear sap, or karyoplasm
Chromatin
The plasmalemma is the outer shell of the cell. It is built from a biological membrane, a supra-membrane complex and a sub-membrane apparatus. Holds cellular contents, protects the cell and ensures its interaction with the pericellular environment, other cells and tissue elements.
Hyaloplasm is a colloidal environment of the cytoplasm. Serves for placement of organelles, inclusions, implementation of their interaction.
Organelles are permanent structures of the cytoplasm that perform certain functions in it.
Inclusions - substances that enter the cell for nutrition purposes or are formed in it as a result of vital processes.
The nuclear membrane consists of two biological membranes, delimits the contents of the nucleus from the cytoplasm and at the same time ensures their close interaction.
Nuclear juice is a colloidal environment of the nucleus.
Chromatin is a form of existence of chromosomes. Consists of DNA, histone and non-histone proteins, RNA.
The nucleolus is a complex of DNA of nucleolar organizers, ribosomal RNA, proteins and subunits of ribosomes that are formed here.
3. Composition and purpose of the cytoplasm
The cytoplasm is one of the two main parts of the cell, which provides its basic life processes.
The cytoplasm includes 4 components:
The cell membrane (plasmolemma).
Hyaloplasm.
Organelles (organelles).
Cell inclusions.
Hyaloplasm is a colloidal matrix of the cytoplasm, in which the main life processes of the cell take place, organelles and inclusions are located and function.
The cell membrane (plasmolemma) is built from a biological membrane, a supra-membrane complex and a sub-membrane apparatus. It retains cellular contents, maintains the shape of cells, carries out their motor reactions, performs barrier and receptor functions, provides the processes of intake and excretion of substances, as well as interaction with the pericellular environment, other cells and tissue elements.
The biological membrane as the basis of the plasmolemma is built from a bimolecular lipid layer, in which protein molecules are mosaically included. The hydrophobic poles of lipid molecules are turned inward, forming a kind of hydraulic lock, and their hydrophilic heads provide active interaction with the external and intracellular environment.
Proteins are located superficially (peripheral), enter the hydrophobic layer (semi-integral), or penetrate the membrane through (integral). Functionally, they form structural, enzymatic, receptor and transport proteins.
The supra-membrane complex - glycocalyx - membranes is formed by glycosaminoglycans. Performs protective and regulatory functions.
The submembrane apparatus is formed by microtubules and microfilaments. Acts as a musculoskeletal system.
Organelles are permanent structures of the cytoplasm that perform certain functions in it. There are general purpose organelles (Golgi apparatus, mitochondria, cell center, ribosomes, lysosomes, peroxisomes, cytoplasmic reticulum, microtubules and microfilaments) and special (myofibrils - in muscle cells; neurofibrils, synaptic vesicles and tigroid substance - in neurocytes; tonofibrils, microvilli, cilia and flagella - in epithelial cells).
Inclusions - substances that enter the cell for nutrition purposes or are formed in it as a result of vital processes. There are trophic, secretory, pigment and excretory inclusions.
4. Cell organelles (definition, classification, characterization of the structure and functions of mitochondria, lamellar complex, lysosomes, endoplasmic reticulum)
Organelles (organelles) are permanent structures of the cytoplasm that perform certain functions in it.
The classification of organelles takes into account the peculiarities of their structure and physiological functions.
Based on the nature of the functions performed, all organelles are divided into two large groups:
1. Organelles of general purpose, expressed in all cells of the body, provide the most common functions that support their structure and life processes (mitochondria, centrosome, ribosomes, lysosomes, peroxisomes, microtubules, cytoplasmic reticulum, Golgi complex)
2. Special - found only in cells that perform specific functions (myofibrils, tonofibrils, neurofibrils, synaptic vesicles, tigroid substance, microvilli, cilia, flagella).
According to the structural feature, we distinguish organelles of a membrane and non-membrane structure.
Membrane organelles basically have one or two biological membranes (mitochondria, lamellar complex, lysosomes, peroxisomes, endoplasmic reticulum).
Non-membrane organelles are formed by microtubules, globules from a complex of molecules and their bundles (centrosome, microtubules, microfilaments and ribosomes).
By size, we single out a group of organelles visible under a light microscope (Golgi apparatus, mitochondria, cell center), and ultramicroscopic organelles visible only under an electron microscope (lysosomes, peroxisomes, ribosomes, endoplasmic reticulum, microtubules and microfilaments).
The Golgi complex (lamellar complex) is visible under light microscopy in the form of short and long filaments (up to 15 µm long). With electron microscopy, each such thread (dictyosome) is a complex of flat cisterns layered on top of each other, tubules and vesicles. The lamellar complex ensures the accumulation and excretion of secrets, synthesizes some lipids and carbohydrates, and forms primary lysosomes.
Mitochondria under light microscopy are found in the cytoplasm of cells in the form of small grains and short filaments (up to 10 microns long), from the names of which the very name of the organoid is formed. With electron microscopy, each of them appears in the form of round or oblong bodies, consisting of two membranes and a matrix. The inner membrane has ridge-like protrusions - cristae. The matrix contains mitochondrial DNA and ribosomes that synthesize some structural proteins. Enzymes localized on mitochondrial membranes provide the processes of oxidation of organic substances (cellular respiration) and the storage of ATP (energy function).
Lysosomes are represented by small bubble-like formations, the wall of which is formed by a biological membrane, inside which a wide range of hydrolytic enzymes (about 70) is enclosed.
They play the role of the digestive system of cells, neutralize harmful agents and foreign particles, and utilize their own outdated and damaged structures.
There are primary lysosomes, secondary (phagolysosomes, autophagolysosomes) and tertiary telolisosomes (residual bodies).
The endoplasmic reticulum is a system of tiny tanks and tubules that anastomose with each other and penetrate the cytoplasm. Their walls are formed by single membranes, on which enzymes for the synthesis of lipids and carbohydrates are ordered - a smooth endoplasmic reticulum (agranular) or ribosomes are fixed - a rough (granular) network. The latter is intended for the accelerated synthesis of protein molecules for the general needs of the body (for export). Both types of EPS also provide circulation and transport of various substances.
veterinary medicine histology cell organism
5. The structure and functions of the kernel
The cell nucleus is its second most important component.
Most cells have one nucleus, but some liver cells and cardiomyocytes have 2 nuclei. In macrophages of bone tissue, there are from 3 to several tens of them, and in striated muscle fiber, from 100 to 3 thousand nuclei are found. Conversely, mammalian erythrocytes are non-nuclear.
The shape of the nucleus is often rounded, but in prismatic cells of the epithelium it is oval, in flat cells it is flattened, in mature granular leukocytes it is segmented, in smooth myocytes it lengthens to rod-shaped. The nucleus is located, as a rule, in the center of the cell. In plasma cells, it lies eccentrically, and in prismatic epithelial cells it shifts to the basal pole.
Chemical composition of the core:
Proteins - 70%, nucleic acids - 25%, carbohydrates, lipids and inorganic substances make up about 5%.
Structurally, the core is built from:
1. nuclear membrane (karyolemma),
2. nuclear juice (karyoplasm),
3. nucleolus,
4. chromatin. The nuclear membrane - the karyolemma consists of 2 elementary biological membranes. Perinuclear space is expressed between them. In some areas, two membranes are interconnected and form pores of the karyolemma, up to 90 nm in diameter. They have structures that form the so-called pore complex of three plates. There are 8 granules along the edges of each plate, and one in their center. The thinnest fibrils (threads) go to it from peripheral granules. As a result, peculiar diaphragms are formed to regulate the movement of organic molecules and their complexes through the shell.
Karyolemma functions:
1. delimiting,
2. regulatory.
Nuclear juice (karyoplasm) is a colloidal solution of carbohydrates, proteins, nucleotides and minerals. It is a microenvironment for providing metabolic reactions and the movement of messenger and transport RNA to nuclear pores.
Chromatin is a form of existence of chromosomes. It is represented by a complex of DNA, RNA molecules, packaging proteins and enzymes (histones and non-histone proteins). Histones are directly attached to the chromosome. They ensure the spiralization of the DNA molecule in the chromosome. Non-histone proteins are enzymes: DNA - nucleases that destroy complementary bonds, causing its despiralization;
DNA and RNA - polymerases that ensure the construction of RNA molecules on embroidered DNA, as well as self-duplication of chromosomes before division.
Chromatin is present in the nucleus in two forms:
1. dispersed euchromatin, which is expressed as fine grains and threads. In this case, sections of the DNA molecules are in the untwisted state. RNA molecules are easily synthesized on them, reading information about the structure of the protein, and transfer RNAs are built. The resulting and - RNA moves into the cytoplasm and is introduced into the ribosomes, where the processes of protein synthesis are carried out. Euchromatin is the functionally active form of chromatin. Its predominance indicates a high level of cell vital processes.
2. Condensed heterochromatin. Under light microscopy, it looks like large granules and clumps. At the same time, histone proteins tightly coil and pack DNA molecules, on which it is therefore impossible to build i-RNA, which is why heterochromatin is a functionally inactive, unclaimed part of the chromosome set.
Nucleus. It has a rounded shape, up to 5 microns in diameter. From 1 to 3 nucleoli can be expressed in cells, depending on its functional state. Represents a set of terminal sections of several chromosomes, which are called nucleolar organizers. On the DNA of nucleolar organizers, ribosomal RNAs are formed, which, when combined with the corresponding proteins, form ribosome subunits.
Kernel functions:
1. Preservation of hereditary information received from the mother cell unchanged.
2. Coordination of vital processes and implementation of hereditary information through the synthesis of structural and regulatory proteins.
3. Transfer of hereditary information to daughter cells during division.
6. Types of cell division
Division is a way of self-reproduction of cells. It provides:
a) the continuity of the existence of cells of a certain type;
b) tissue homeostasis;
c) physiological and reparative regeneration of tissues and organs;
d) reproduction of individuals and conservation of animal species.
There are 3 ways of cell division:
1. amitosis - cell division without visible changes in the chromosomal apparatus. It occurs by a simple constriction of the nucleus and cytoplasm. Chromosomes are not detected, the spindle of division is not formed. It is characteristic of some embryonic and damaged tissues.
2. mitosis - a method of division of somatic and germ cells at the stage of reproduction. At the same time, two daughter cells with a complete, or diploid, set of chromosomes are formed from one mother cell.
3. meiosis is a method of division of germ cells at the stage of maturation, in which 4 daughter cells with a half, haploid, set of chromosomes are formed from one mother cell.
7. Mitosis
Mitosis is preceded by interphase, during which the cell prepares for future division. This training includes
cell growth;
Energy storage in the form of ATP and nutrients;
Self-doubling of DNA molecules and chromosome set. As a result of doubling, each chromosome consists of 2 sister chromatids;
Doubling of the centrioles of the cell center;
Synthesis of special proteins such as tubulin to build fission spindle filaments.
Mitosis itself consists of 4 phases:
prophase,
metaphase,
anaphase,
Telophase.
In prophase, chromosomes coil, condense, and shorten. They are now visible under light microscopy. The centrioles of the cell center begin to diverge towards the poles. Between them, a division spindle is built. At the end of prophase, the nucleolus disappears and fragmentation of the nuclear envelope occurs.
In metaphase, the construction of the division spindle is completed. Short spindle filaments are attached to the centromeres of chromosomes. All chromosomes are located at the equator of the cell. Each of them is held in the equatorial plate with the help of 2 chromatin filaments that go to the poles of the cell, and its central zone is filled with long achromatin fibrils.
In anaphase, due to the contraction of the chromatin filaments, the spindles of division of the chromatids break away from each other in the region of centromeres, after which each of them slides along the central filaments to the upper or lower pole of the cell. From this point on, the chromatid is called a chromosome. Thus, at the poles of the cell there is an equal number of identical chromosomes, i.e. one complete, diploid, set of them.
In telophase, a new nuclear envelope forms around each group of chromosomes. The condensed chromatin begins to loosen. Nucleoli appear. In the central part of the cell, the plasmolemma protrudes inwards, the tubules of the endoplasmic reticulum are connected to it, which leads to cytotomy and the division of the mother cell into two daughter cells.
Meiosis (reduction division).
It is also preceded by interphase, in which the same processes are distinguished as before mitosis. Meiosis itself includes two divisions: reduction, in which haploid cells with doubled chromosomes are formed, and equational, leading by mitosis to the formation of cells with single chromosomes.
The leading phenomenon that ensures a decrease in the chromosome set is the conjugation of paternal and maternal chromosomes in each pair, which takes place in the prophase of the first division. When homologous chromosomes consisting of two chromatids approach each other, tetrads are formed, which already include 4 chromatids.
In the metaphase of meiosis, tetrads are preserved and located at the equator of the cell. In anaphase, therefore, whole doubled chromosomes depart to the poles. As a result, two daughter cells are formed with a half set of doubled chromosomes. Such cells, after a very short interphase, divide again by normal mitosis, which leads to the appearance of haploid cells with single chromosomes.
The phenomenon of conjugation of homologous chromosomes simultaneously solves another important problem - the creation of prerequisites for individual genetic variability due to the processes of crossing over and gene exchange and multivariance in the polar orientation of tetrads in the metaphase of the first division.
8. The structure of spermatozoa and their biological properties
Spermatozoa (male sex cells) are flagellar cells of a flagellate shape. The sequential arrangement of organelles in the spermatozoon makes it possible to distinguish the head, neck, body and tail in the cell.
The head of the spermatozoon of representatives of agricultural mammals is asymmetric - bucket-shaped, which ensures its rectilinear, translational-rotational movement. Most of the head is occupied by the nucleus, and the most anterior part forms the head cap with acrosome. Enzymes (hyaluronidase, proteases) accumulate in the acrosome (a modified Golgi complex), which allow spermatozoa to destroy the secondary membranes of the egg during fertilization.
Behind the nucleus, in the neck of the cell, two centrioles are located one after the other - proximal and distal. The proximal centriole lies freely in the cytoplasm and is introduced into the egg during fertilization. An axial thread grows from the distal centriole - this is a special cell organelle that ensures the beating of the tail in only one plane.
In the body of the sperm around the axial thread, mitochondria are located one after another, forming a spiral thread - the energy center of the cell.
In the region of the tail, the cytoplasm gradually decreases, so that in its final part the axial filament is dressed only by the plasmolemma.
Biological properties of spermatozoa:
1. Carrying hereditary information about the paternal organism.
2. Spermatozoa are not capable of division, their nucleus contains a half (haploid) set of chromosomes.
3. The size of the cells does not correlate with the weight of the animals, and therefore, in representatives of agricultural mammals, it varies within narrow limits (from 35 to 63 microns).
4. The movement speed is 2-5mm per minute.
5. Spermatozoa are characterized by the phenomenon of rheotaxis, i.e. movement against a weak current of mucus in the female genital tract, as well as the phenomenon of chemotaxis - the movement of spermatozoa to chemicals (gynogamons) produced by the egg.
6. In the epididymis, spermatozoa acquire an additional lipoprotein coat, which allows them to hide their antigens, since for the body of the female, the male gametes act as foreign cells.
7. Spermatozoa have a negative charge, which makes it possible for them to repel each other and thereby prevent gluing and mechanical damage to cells (there are up to several billion cells in one ejaculate).
8. Spermatozoa of animals with internal fertilization cannot stand the impact of environmental factors, in which they die almost immediately.
9. High temperature, ultraviolet radiation, acidic environment, salts of heavy metals have a detrimental effect on spermatozoa.
10. Adverse effects are manifested when exposed to radiation, alcohol, nicotine, narcotic substances, antibiotics and a number of other drugs.
11. At the temperature of the animal's body, the processes of spermatogenesis are disrupted.
12. Under conditions of low temperature, male gametes are able to retain their vital properties for a long time, which made it possible to develop the technology of artificial insemination of animals.
13. In a favorable environment of the female genital tract, spermatozoa retain their fertilizing capacity for 10-30 hours.
9. spermatogenesis
It is carried out in the convoluted tubules of the testis in 4 stages:
1. stage of reproduction;
2. growth stage;
3. maturation stage;
4. stage of formation.
During the first stage of reproduction, stem cells lying on the basement membrane (with a complete set of chromosomes) repeatedly divide by mitosis, forming many spermatogonia. With each round of division, one of the daughter cells remains in this extreme row as a stem cell, the other is forced out into the next row and enters the growth stage.
In the growth stage, germ cells are called spermatocytes of the 1st order. They grow and prepare for the third stage of development. Thus, the second stage is simultaneously an interphase before future meiosis.
In the third stage of maturation, germ cells sequentially undergo two divisions of meiosis. At the same time, from spermatocytes of the 1st order, spermatocytes of the 2nd order are formed with a half set of doubled chromosomes. These cells, after a short interphase, enter the second division of meiosis, which results in the formation of spermatids. Spermatocytes of the 2nd order make up the third row in the spermatogenic epithelium. Due to the short duration of the interphase, spermatocytes of the 2nd order are not found along the entire length of the convoluted tubules. Spermatids are the smallest cells in the tubules. They form 2-3 cell rows at their inner edges.
During the fourth stage of formation, small round spermatid cells gradually turn into spermatozoa that have a flagellum shape. To ensure these processes, spermatids come into contact with trophic Sertoli cells, penetrating into niches between the processes of their cytoplasm. The arrangement of the nucleus, lamellar complex, centrioles is ordered. An axial filament grows from the distal centriole, followed by the displacement of the cytoplasm with the plasmolemma, forming the tail of the spermatozoon. The lamellar complex is located in front of the nucleus and is converted into an acrosome. Mitochondria descend into the cell body, forming around the axial spiral thread. The heads of the formed spermatozoa still remain in the niches of the supporting cells, and their tails hang down into the lumen of the convoluted tubule.
10. The structure and classification of eggs
The egg is a motionless, round-shaped cell with a certain supply of yolk inclusions (nutrients of a carbohydrate, protein and lipid nature). In mature eggs, there are no centrosomes (they are lost at the end of the maturation stage).
Mammalian eggs, in addition to the plasmolemma (ovolemma), which is the primary membrane, also have secondary membranes with protective and trophic functions: a shiny, or transparent, membrane consisting of glycosaminoglycans, proteins, and a radiant crown formed by one layer of prismatic follicular cells glued between is hyaluronic acid.
In birds, the secondary membranes are weakly expressed, but the tertiary membranes are significantly developed: albumen, subshell, shell and suprashell. They act as protective and trophic formations during the development of embryos in land conditions.
Oocytes are classified according to the number and distribution in the cytoplasm of the yolk:
1. Oligolecithal - small-yolk eggs. They are characteristic of primitive chordate animals (lancelet) living in the aquatic environment, and female mammals in connection with the transition to the intrauterine development of the embryos.
2. Mesolecithal oocytes with moderate accumulation of yolk. Inherent in most fish and amphibians.
3. Polylecital - multi-yolk eggs are characteristic of reptiles and birds in connection with terrestrial conditions for the development of embryos.
Classification of eggs according to the distribution of yolk:
1. Isolecithal eggs, in which yolk inclusions are relatively evenly distributed throughout the cytoplasm (oligolecital eggs of the lancelet and mammals);
2. Telolecithal eggs. Their yolk is displaced to the lower vegetative pole of the cell, while free organelles and the nucleus move to the upper animal pole (in animals with meso- and telolecital types of eggs).
11. Stages of development of the embryo
Embryonic development is a chain of interrelated transformations, as a result of which a multicellular organism is formed from a single-celled zygote, capable of existing in the external environment. In embryogenesis, as part of ontogenesis, the processes of phylogenesis are also reflected. Phylogeny is the historical development of a species from simple to complex forms. Ontogenesis is the individual development of a particular organism. According to the biogenetic law, ontogenesis is a short form of phylogenesis, and therefore representatives of different classes of animals have common stages of embryonic development:
1. Fertilization and zygote formation;
2. Cleavage of the zygote and formation of the blastula;
3. Gastrulation and the appearance of two germ layers (ectoderm and endoderm);
4. Differentiation of ecto- and endoderm with the appearance of the third germ layer - mesoderm, axial organs (chord, neural tube and primary intestine) and further processes of organogenesis and histogenesis (development of organs and tissues).
Fertilization is the process of mutual assimilation of the egg and sperm, in which a single-celled organism arises - a zygote that combines two hereditary information.
Cleavage of the zygote is the repeated division of the zygote by mitosis without the growth of the resulting blastomeres. This is how the simplest multicellular organism, the blastula, is formed. We distinguish:
Complete, or holoblastic, crushing, in which the entire zygote is crushed into blastomeres (lancelet, amphibians, mammals);
Incomplete, or meroblastic, if only part of the zygote (animal pole) undergoes cleavage (birds).
Complete crushing, in turn, happens:
Uniform - blastomeres of relatively equal size (lancelet) are formed with their synchronous division;
Uneven - with asynchronous division with the formation of blastomeres of different sizes and shapes (amphibians, mammals, birds).
Gastrulation is the stage of formation of a two-layer embryo. Its superficial cell layer is called the outer germ layer - ectoderm, and the deep cell layer - the inner germ layer - endoderm.
Types of gastrulation:
1. invagination - invagination of the blastomeres of the bottom of the blastula in the direction of the roof (lancelet);
2. epiboly - fouling with rapidly dividing small blastomeres of the roof of the blastula of its marginal zones and bottom (amphibians);
3. delamination - stratification of blastomeres and migration - movement of cells (birds, mammals).
Differentiation of the germ layers leads to the appearance of cells of different quality, giving the rudiments of various tissues and organs. In all classes of animals, axial organs first appear - the neural tube, the notochord, the primary intestine - and the third (middle position) germ layer - the mesoderm.
12. Peculiarities of embryonic development of mammals (formation of trophoblast and fetal membranes)
Features of mammalian embryogenesis are determined by the intrauterine nature of development, as a result of which:
1. The egg does not accumulate large reserves of yolk (oligolecital type).
2. Fertilization is internal.
3. At the stage of complete uneven fragmentation of the zygote, early differentiation of blastomeres occurs. Some of them divide faster, are characterized by a light color and small size, others are dark in color and large in size, since these blastomeres are late in dividing and split less often. Light blastomeres gradually envelop slowly dividing dark ones, due to which a spherical blastula without a cavity (morula) is formed. In the morula, dark blastomeres make up its internal contents in the form of a dense knot of cells, which are later used to build the body of the embryo - this is the embryoblast.
Light blastomeres are located around the embryoblast in one layer. Their task is to absorb the secretion of the uterine glands (royal jelly) to ensure the nutritional processes of the embryo before the formation of a placental connection with the mother's body. Therefore, they form a trophoblast.
4. The accumulation of royal jelly in the blastula pushes the embryoblast upward and makes it look like a bird's discoblastula. Now the embryo represents the germinal vesicle, or blastocyst. As a result, all further developmental processes in mammals repeat the already known paths characteristic of avian embryogenesis: gastrulation is carried out by delamination and migration; the formation of axial organs and mesoderm occurs with the participation of the primary strip and nodule, and the isolation of the body and the formation of fetal membranes - the trunk and amniotic folds.
The trunk fold is formed as a result of active reproduction of the cells of all three germ layers in the zones bordering the germinal shield. The rapid growth of cells forces them to move inward and bend the leaves. As the trunk fold deepens, its diameter decreases, it separates and rounds the embryo more and more, simultaneously forming the primary intestine and the yolk sac with royal jelly contained in it from the endoderm and visceral mesoderm.
The peripheral parts of the ectoderm and the parietal sheet of the mesoderm form an amniotic circular fold, the edges of which gradually move over the detached body and completely close over it. The fusion of the inner sheets of the fold forms an internal aqueous membrane - the amnion, the cavity of which is filled with amniotic fluid. The fusion of the outer sheets of the amniotic fold ensures the formation of the outermost membrane of the fetus - the chorion (villous membrane).
Due to the blind protrusion through the umbilical canal of the ventral wall of the primary intestine, a middle membrane is formed - allantois, in which a system of blood vessels (vascular membrane) develops.
5. The outer shell - the chorion has a particularly complex structure and forms multiple protrusions in the form of villi, with the help of which a close relationship is established with the mucous membrane of the uterus. The composition of the villi includes areas of allantois fused with the chorion with blood vessels and the trophoblast, whose cells produce hormones to maintain the normal course of pregnancy.
6. The totality of allantochorion villi and endometrial structures with which they interact form a special embryonic organ in mammals - the placenta. The placenta provides nutrition to the embryo, its gas exchange, removal of metabolic products, reliable protection against adverse factors of any etiology, and hormonal regulation of development.
13. Placenta (structure, functions, classifications)
The placenta is a temporary organ that is formed during the embryonic development of mammals. Distinguish between baby and maternal placenta. The baby placenta is formed by a collection of allanto-chorionic villi. The maternal is represented by areas of the uterine mucosa, with which these villi interact.
The placenta provides the embryo with nutrients (trophic function) and oxygen (respiratory), the release of the blood of the fetus from carbon dioxide and unnecessary metabolic products (excretory), the formation of hormones that support the normal course of pregnancy (endocrine), and the formation of the placental barrier (protective function) .
The anatomical classification of the placenta takes into account the number and location of the villi on the surface of the allantochorion.
1. Diffuse placenta is expressed in pigs and horses (short, unbranched villi are evenly distributed over the entire surface of the chorion).
2. Multiple, or cotyledon, placenta is characteristic of ruminants. Allantochorion villi are located in islets - cotyledons.
3. The girdled placenta in carnivores is a zone of accumulation of villi located in the form of a wide belt surrounding the fetal bladder.
4. In the discoidal placenta of primates and rodents, the zone of chorionic villi has the shape of a disc.
The histological classification of the placenta takes into account the degree of interaction of the allantochorion villi with the structures of the uterine mucosa. Moreover, as the number of villi decreases, they become more branched in shape and penetrate deeper into the mucous membrane of the uterus, shortening the path of movement of nutrients.
1. Epitheliochorial placenta is characteristic of pigs, horses. Chorionic villi penetrate the uterine glands without destroying the epithelial layer. During childbirth, the villi easily protrude from the glands of the uterus, usually without bleeding, so this type of placenta is also called a semi-placenta.
2. Desmochorial placenta is expressed in ruminants. The allanto-chorionic villi penetrate into the endometrial lamina propria, in the area of its thickenings, caruncles.
3. Endotheliochorial placenta is characteristic of carnivorous animals. The villi of the baby placenta are in contact with the endothelium of the blood vessels.
4. The hemochorial placenta is found in primates. The chorionic villi sink into blood-filled lacunae and are bathed in maternal blood. However, the mother's blood does not mix with the fetal blood.
14. Morphological classification and brief description of the main types of epithelium
The morphological classification of epithelial tissues is based on two features:
1. the number of layers of epithelial cells;
2. cell shape. At the same time, in varieties of stratified epithelium, only the shape of epitheliocytes of the surface (integumentary) layer is taken into account.
A single-layer epithelium, in addition, can be built from cells of the same shape and height, then their nuclei lie on the same level - a single-row epithelium, and from significantly different epitheliocytes.
In such cases, in low cells, the nuclei will form the lower row, in medium-sized epithelial cells - the next one, located above the first, and in the highest ones, one or two more rows of nuclei, which ultimately translates the single-layered tissue into a pseudo-multilayered form - multi-row epithelium.
Given the above, the morphological classification of the epithelium can be represented as follows:
Epithelium
Single layer Multilayer
Single Row Multi Row Flat: Transitional Cubic
Flat Prismatic keratinizing
Cubic ciliated non-keratinizing
Prismatic- (ciliated) Prismatic
In any type of single-layer epithelium, each of its cells has a connection with the basement membrane. Stem cells are located mosaically among the integumentary.
In the stratified epithelium, we distinguish three zones of epitheliocytes that differ in shape and degree of differentiation. Only the lowest layer of prismatic or tall cuboidal cells is associated with the basement membrane. It is called basal and consists of stem, repeatedly dividing epitheliocytes. The next, intermediate, zone is represented by differentiating (maturing) cells of various shapes, which can lie in one or more rows. On the surface are mature differentiated epitheliocytes of a certain shape and properties. Stratified epithelium provides protective functions.
The single-layer squamous epithelium is formed by flattened cells with irregular contours and a large surface. Covers the serous membranes (mesothelium); forms the vascular lining (endothelium) and alveoli (respiratory epithelium) of the lungs.
The single-layered cuboidal epithelium is built from epithelial cells having approximately the same base width and height. The nucleus is rounded, characterized by a central position. Forms the secretory sections of the glands, the walls of the urinary renal tubules (nephrons).
A single-layer prismatic epithelium forms the walls of the excretory ducts in the exocrine glands, the uterine glands, covers the mucous membrane of the stomach of the intestinal type, small and large intestine. The cells are characterized by high height, narrow base and longitudinally oval shape of the nucleus displaced to the basal pole. The intestinal epithelium is bordered by microvilli at the apical poles of the enterocytes.
A single-layer multi-row prismatic ciliated (ciliated) epithelium covers mainly the mucous membrane of the airways. The lowest wedge-shaped cells (basal) are constantly dividing, the middle ones in height are growing, not yet reaching the free surface, and the high ones are the main type of mature epithelial cells, bearing up to 300 cilia at the apical poles, which, contracting, move mucus with adsorbed foreign particles for coughing . Mucus is produced by ciliated goblet cells.
Stratified squamous non-keratinized epithelium covers the conjunctiva and cornea of the eyes, the initial sections of the digestive tube, transitional zones in the organs of reproduction and urinary excretion.
Stratified squamous keratinized epithelium consists of 5 layers of gradually keratinizing and desquamating cells (keratinocytes) - basal, layer of spiny cells, granular, shiny, horny. It forms the epidermis of the skin, covers the external genital organs, the mucous membrane of the mammary canals in the mammary glands, and the mechanical papillae of the oral cavity.
Stratified transitional epithelium lines the mucous membranes of the urinary tract. The cells of the integumentary zone are large, longitudinally oval, secrete mucus, have a well-developed glycocalyx in the plasmolemma to prevent the reabsorption of substances from the urine.
Stratified prismatic epithelium is expressed in the mouths of the main ducts of the parietal salivary glands, in males - in the mucous membrane of the pelvic part of the urogenital canal and in the canals of the testicular appendages, in females - in the lobar ducts of the mammary glands, in secondary and tertiary ovarian follicles.
The stratified cubic forms the secretory sections of the sebaceous glands of the skin, and in males, the spermatogenic epithelium of the convoluted tubules of the testes.
15. General characteristics of blood as a tissue of the internal environment of the body
Blood belongs to the tissues of the support-trophic group. Together with the reticular and loose connective tissues, it plays a decisive role in the formation of the internal environment of the body. It has a liquid consistency and is a system consisting of two components - intercellular substance (plasma) and cells suspended in it - formed elements: erythrocytes, leukocytes and platelets (blood platelets in mammals).
Plasma makes up about 60% of the mass of blood and contains 90-93% water and 7-10% solids. About 7% of it falls on proteins (4% - albumins, 2.8% - globulins and 0.4% - fibrinogen), 1% - for minerals, the same percentage remains for carbohydrates.
Functions of blood plasma proteins:
Albumins: - regulation of acid-base balance;
Transport;
Maintaining a certain level of osmotic pressure.
Globulins are immune proteins (antibodies) that perform a protective function, and a variety of enzyme systems.
Fibrinogen - takes part in the processes of blood coagulation.
The pH of the blood is 7.36 and is fairly stable at this level by a number of buffer systems.
The main functions of the blood:
1. Continuously circulating through the blood vessels, it carries out the transfer of oxygen from the lungs to the tissues, and carbon dioxide from the tissues to the lungs (gas exchange function); delivers nutrients absorbed in the digestive system to all organs of the body, and metabolic products to the excretory organs (trophic); transports hormones, enzymes and other biologically active substances to the places of their active influence.
All these aspects of the functional functions of blood can be reduced to one common transport and trophic function.
2. Homeostatic - maintaining the constancy of the internal environment of the body (creates optimal conditions for metabolic reactions);
3. Protective - providing cellular and humoral immunity, various forms of non-specific protection, especially phagocytosis of foreign particles, blood coagulation processes.
4. Regulatory function associated with maintaining a constant body temperature and a number of other processes provided by hormones and other biologically active substances.
Platelets - in mammals, non-nuclear cells, 3-5 microns in size, are involved in blood coagulation processes.
Leukocytes are divided into granulocytes (basophils, neutrophils and eosinophils) and agranulocytes (monocytes and lymphocytes). They perform various protective functions.
Erythrocytes in mammals are non-nuclear cells, they are in the form of biconcave discs with an average diameter of 6-8 microns.
Part of the blood plasma through the vessels of the microvasculature constantly goes into the tissues of organs and becomes tissue fluid. Giving nutrients, perceiving metabolic products, being enriched in the hematopoietic organs with lymphocytes, the latter enters the vessels of the lymphatic system in the form of lymph and returns to the bloodstream.
Formed elements in the blood are in certain quantitative ratios and make up its hemogram.
The number of formed elements is calculated in 1 µl of blood or a liter:
Erythrocytes - 5-10 million per µl (x 1012 per l);
Leukocytes - 4.5-14 thousand per μl (x109 per l);
Blood platelets - 250-350 thousand per µl (x109 per l).
16. The structure and functional significance of granulocytes
Leukocytes in vertebrates are nucleated cells capable of active movement in body tissues. The classification is based on taking into account the structural features of their cytoplasm.
Leukocytes, the cytoplasm of which contains a specific granularity, are called granular, or granulocytes. Mature granular leukocytes have a segmented nucleus - segmented cells, in young it is unsegmented. Therefore, it is customary to divide them into young forms (bean-shaped nucleus), stab-nuclear (curved rod-shaped nucleus) and segmented - fully differentiated leukocytes, the nucleus of which contains from 2 to 5-7 segments. In accordance with the difference in staining of cytoplasmic granularity, 3 types of cells are distinguished in the group of granulocytes:
Basophils - granularity is stained with basic dyes in purple;
Eosinophils - granularity is stained with acid dyes in various shades of red;
Neutrophils - granularity is stained with both acidic and basic dyes in a pink-violet color.
Neutrophils are small cells (9-12 microns), the cytoplasm of which contains 2 types of granules: primary (basophilic), which are lysosomes, and secondary oxyphilic (contain cationic proteins and alkaline phosphatase). Neutrophils are characterized by the finest (dust-like) granularity and the most segmented nucleus. They are microphages and carry out the phagocytic function of small foreign particles of any nature, the utilization of antigen-antibody complexes. In addition, substances are released that stimulate the regeneration of damaged tissues.
Eosinophils often contain a two-segment nucleus and large oxyphilic granules in the cytoplasm. Their diameter is 12-18 microns. The granules contain hydrolytic enzymes (microphages in function). They show antihistamine reactivity, stimulate the phagocytic activity of connective tissue macrophages and the formation of lysosomes in them, utilize antigen-antibody complexes. But their main task is to neutralize toxic substances, so the number of eosinophils increases dramatically with helminthic invasions.
Basophils, 12-16 microns in size, contain medium-sized basophilic granules, which include heparin (prevents blood clotting) and histamine (regulates vascular and tissue permeability). They are also involved in the development of allergic reactions.
The percentage ratio between individual types of leukocytes is called the leukocyte formula, or leukogram. For granulocytes, it looks like this:
Neutrophils - 25-40% - in pigs and ruminants; 50-70% - in horses and carnivores;
Eosinophils - 2-4%, in ruminants - 6-8%;
Basophils - 0.1-2%.
17. The structure and functional significance of agranulocytes
Non-granular leukocytes (agranulocytes) are characterized by the absence of specific granularity in the cytoplasm and large non-segmented nuclei. In the group of agranulocytes, 2 types of cells are distinguished: lymphocytes and monocytes.
Lymphocytes are characterized by a predominantly round shape of the nucleus with compact chromatin. In small lymphocytes, the nucleus occupies almost the entire cell (its diameter is 4.5-6 microns), in medium-sized lymphocytes the rim of the cytoplasm is wider, and their diameter increases to 7-10 microns. Large lymphocytes (10-13 microns) in the peripheral blood are extremely rare. The cytoplasm of lymphocytes is stained basophilically, in various shades of blue.
Lymphocytes provide the formation of cellular and humoral immunity. They are classified into T- and B-lymphocytes.
T-lymphocytes (thymus-dependent) undergo primary antigen-independent differentiation in the thymus. In the peripheral organs of the immune system, after contact with antigens, they turn into blast forms, multiply, and now undergo secondary antigen-dependent differentiation, as a result of which effector types of T cells appear:
T-killers that destroy foreign cells and their own with defective phenocopies (cellular immunity);
T-helpers - stimulating the transformation of B-lymphocytes into plasma cells;
T-suppressors that suppress the activity of B-lymphocytes;
Memory T-lymphocytes (long-lived cells) that store information about antigens.
B-lymphocytes (bursodependent). In birds, they primarily differentiate in the bursa of Fabricius, and in mammals, in the red bone marrow. During secondary differentiation, they turn into plasma cells, which produce large amounts of antibodies that enter the blood and other body fluids, which ensures the neutralization of antigens and the formation of humoral immunity.
Monocytes are the largest blood cells (18-25 microns). The nucleus is sometimes bean-shaped, but more often irregular. The cytoplasm is significantly expressed, its share can reach half the volume of the cell, it stains basophilically - in a smoky blue color. It has well developed lysosomes. Monocytes circulating in the blood are the precursors of tissue and organ macrophages that form a protective macrophage system in the body - the system of mononuclear phagocytes (MPS). After a short stay in the vascular blood (12-36 hours), monocytes migrate through the endothelium of capillaries and venules into tissues and turn into fixed and free macrophages.
Macrophages primarily utilize dying and damaged cellular and tissue elements. But they play a more responsible role in immune reactions:
They convert antigens into a molecular form and present them to lymphocytes (antigen-presenting function).
They produce cytokines to stimulate T and B cells.
Utilize complexes of antigens with antibodies.
The percentage of agranulocytes in the leukogram:
Monocytes - 1-8%;
Lymphocytes - 20-40% in predatory animals and horses, 45-56% in pigs, 45-65% in cattle.
18. Morphofunctional characteristics of loose connective tissue
Loose connective tissue is present in all organs and tissues, forming the basis for the placement of the epithelium, glands, connecting the functional structures of organs into a single system. Accompanies blood vessels and nerves. It performs shaping, supporting, protective and trophic functions. The tissue consists of cells and intercellular substance. This is a polydifferential fabric, because. her cells came from various stem cells.
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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 the nervous system.see also EMBRYOLOGY. 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 one another 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.see also BLOOD. nervous tissue. Nervous tissue consists of highly specialized cells - neurons, 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, the restoration of a rather significant area of the liver tissue can be observed.see also REGENERATION.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 a shiny layer (in which keratinization begins, and its cells become transparent), below it is a 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.
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 connect.. 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 specimen. 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 different chemical composition, which kill cells very quickly without distorting the details of their structure and ensuring the preservation of the tissue 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 for a certain distance corresponding to the desired cut thickness. The thickness of the sections can reach 20 microns (0.02 mm) or be as small as 1-2 microns (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 soluble in water, is used to fill the tissue.
After all these procedures, the preparation is ready for staining - a very important stage 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 time-consuming 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.see also PLANT ANATOMY.LITERATURE Ham A, Cormac D. Histology, tt. 1-5. M., 1982-1983
Tissues are a collection of cells and non-cellular structures (non-cellular substances) that are similar in origin, structure and functions. There are four main groups of tissues: epithelial, muscle, connective and nervous.
… Epithelial tissues cover the body from the outside and line the hollow organs and walls of the body cavities from the inside. A special type of epithelial tissue - glandular epithelium - forms most of the glands (thyroid, sweat, liver, etc.).
… Epithelial tissues have the following features: - their cells are closely adjacent to each other, forming a layer, - there is very little intercellular substance; - cells have the ability to restore (regenerate).
… Epithelial cells in shape can be flat, cylindrical, cubic. According to the number of layers of the epithelium, there are single-layer and multilayer.
... Examples of epithelium: single-layer flat lines the chest and abdominal cavities of the body; multilayer flat forms the outer layer of the skin (epidermis); single-layer cylindrical lines most of the intestinal tract; multilayer cylindrical - the cavity of the upper respiratory tract); a single-layer cubic forms the tubules of the nephrons of the kidneys. Functions of epithelial tissues; borderline, protective, secretory, absorption.
CONNECTIVE TISSUE PROPERLY CONNECTIVE SKELETAL Fibrous Cartilaginous 1. loose 1. hyaline cartilage 2. dense 2. elastic cartilage 3. formed 3. fibrous cartilage 4. unformed With special properties Bone 1. reticular 1. coarse fibrous 2. fatty 2. lamellar: 3. mucosa compact substance 4. pigmented spongy substance
... Connective tissues (tissues of the internal environment) combine groups of tissues of mesodermal origin, very different in structure and functions. Types of connective tissue: bone, cartilage, subcutaneous fat, ligaments, tendons, blood, lymph, etc.
... Connective tissues A common characteristic feature of the structure of these tissues is a loose arrangement of cells separated from each other by a well-defined intercellular substance, which is formed by various fibers of protein nature (collagen, elastic) and the main amorphous substance.
... Blood is a type of connective tissue in which the intercellular substance is liquid (plasma), due to which one of the main functions of blood is transport (carries gases, nutrients, hormones, end products of cell life, etc.).
... The intercellular substance of loose fibrous connective tissue, located in the layers between organs, as well as connecting the skin with muscles, consists of an amorphous substance and elastic fibers freely located in different directions. Due to this structure of the intercellular substance, the skin is mobile. This tissue performs supporting, protective and nourishing functions.
... Muscle tissues determine all types of motor processes within the body, as well as the movement of the body and its parts in space.
... This is ensured by the special properties of muscle cells - excitability and contractility. All muscle tissue cells contain the thinnest contractile fibers - myofibrils, formed by linear protein molecules - actin and myosin. When they slide relative to each other, the length of the muscle cells changes.
... Striated (skeletal) muscle tissue is built from many multinuclear fiber-like cells 1-12 cm long. All skeletal muscles, muscles of the tongue, walls of the oral cavity, pharynx, larynx, upper esophagus, mimic, diaphragm are built from it. Figure 1. Fibers of striated muscle tissue: a) appearance of the fibers; b) cross section of fibers
... Features of striated muscle tissue: speed and arbitrariness (i.e., dependence of contraction on the will, desire of a person), consumption of a large amount of energy and oxygen, fatigue. Figure 1. Fibers of striated muscle tissue: a) appearance of the fibers; b) cross section of fibers
… Cardiac tissue consists of transversely striated mononuclear muscle cells, but has different properties. The cells are not arranged in a parallel bundle, like skeletal cells, but branch, forming a single network. Due to the many cellular contacts, the incoming nerve impulse is transmitted from one cell to another, providing simultaneous contraction and then relaxation of the heart muscle, which allows it to perform its pumping function.
... Cells of smooth muscle tissue do not have transverse striation, they are fusiform, single-nuclear, their length is about 0.1 mm. This type of tissue is involved in the formation of the walls of tube-shaped internal organs and vessels (digestive tract, uterus, bladder, blood and lymphatic vessels).
... Features of smooth muscle tissue: - involuntary and small force of contractions, - the ability to long-term tonic contraction, - less fatigue, - a small need for energy and oxygen.
… Nervous tissue, from which the brain and spinal cord, nerve nodes and plexuses, peripheral nerves are built, performs the functions of perception, processing, storage and transmission of information coming from both the environment and the organs of the body itself. The activity of the nervous system provides the body's reactions to various stimuli, regulation and coordination of the work of all its organs.
... Neuron - consists of a body and processes of two types. The body of a neuron is represented by the nucleus and the cytoplasm surrounding it. It is the metabolic center of the nerve cell; when it is destroyed, she dies. The bodies of neurons are located mainly in the brain and spinal cord, that is, in the central nervous system (CNS), where their accumulations form the gray matter of the brain. Accumulations of nerve cell bodies outside the CNS form ganglia, or ganglia.
Figure 2. Various shapes of neurons. a - a nerve cell with one process; b - nerve cell with two processes; c - a nerve cell with a large number of processes. 1 - cell body; 2, 3 - processes. Figure 3. Scheme of the structure of a neuron and nerve fiber 1 - body of a neuron; 2 - dendrites; 3 - axon; 4 - axon collaterals; 5 - myelin sheath of the nerve fiber; 6 - terminal branches of the nerve fiber. The arrows show the direction of propagation of nerve impulses (according to Polyakov).
... The main properties of nerve cells are excitability and conductivity. Excitability is the ability of the nervous tissue in response to irritation to come into a state of excitation.
... conductivity - the ability to transmit excitation in the form of a nerve impulse to another cell (nerve, muscle, glandular). Due to these properties of the nervous tissue, the perception, conduction and formation of the body's response to the action of external and internal stimuli is carried out.
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 become more familiar with such a section of biology as histology.
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.
- organism. This is a biologically integral system, which is formed in the process of ontogenesis.
- Organs. This is a complex of tissues that interact with each other, performing their main functions and ensuring that the organs perform basic functions.
- 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.
- Cells. This level represents the main structural and functional unit of the tissue - the cell, as well as its derivatives.
- Subcellular level. At this level, the components of the cell are studied - the nucleus, organelles, plasmolemma, cytosol, and so on.
- 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 today). 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 (border), 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.
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