Tissue is a collection of cells and intercellular substance that have the same structure, function and origin.
In the body of mammals and humans, 4 types of tissues are distinguished: epithelial, connective, in which bone, cartilage and adipose tissues can be distinguished; muscular and nervous.
Tissue - location in the body, types, functions, structure
Tissues are a system of cells and intercellular substance that have the same structure, origin and functions.
The intercellular substance is a product of the vital activity of cells. It provides communication between cells and creates a favorable environment for them. It may be liquid, such as blood plasma; amorphous - cartilage; structured - muscle fibers; solid - bone tissue (in the form of salt).
Tissue cells have a different shape that determines their function. Fabrics are divided into four types:
- epithelial - border tissues: skin, mucous membrane;
- connective - the internal environment of our body;
- muscle;
- nervous tissue.
epithelial tissue
Epithelial (boundary) tissues - line the surface of the body, mucous membranes of all internal organs and cavities of the body, serous membranes, and also form the glands of external and internal secretion. The epithelium lining the mucous membrane is located on the basement membrane, and the inner surface is directly facing the external environment. Its nutrition is accomplished by the diffusion of substances and oxygen from the blood vessels through the basement membrane.
Features: there are many cells, there is little intercellular substance and it is represented by a basement membrane.
Epithelial tissues perform the following functions:
- protective;
- excretory;
- suction.
Classification of epithelium. According to the number of layers, single-layer and multi-layer are distinguished. The shape is distinguished: flat, cubic, cylindrical.
If all epithelial cells reach the basement membrane, this is a single-layer epithelium, and if only cells of one row are connected to the basement membrane, while others are free, it is multilayered. A single-layer epithelium can be single-row and multi-row, depending on the level of location of the nuclei. Sometimes mononuclear or multinuclear epithelium has ciliated cilia facing the external environment.
Stratified epithelium Epithelial (integumentary) tissue, or epithelium, is a boundary layer of cells that lines the integument of the body, the mucous membranes of all internal organs and cavities, and also forms the basis of many glands.
Glandular epithelium The epithelium separates the organism (internal environment) from the external environment, but at the same time serves as an intermediary in the interaction of the organism with the environment. Epithelial cells are tightly connected to each other and form a mechanical barrier that prevents the penetration of microorganisms and foreign substances into the body. Epithelial tissue cells live for a short time and are quickly replaced by new ones (this process is called regeneration).
Epithelial tissue is also involved in many other functions: secretion (external and internal secretion glands), absorption (intestinal epithelium), gas exchange (lung epithelium).
The main feature of the epithelium is that it consists of a continuous layer of densely packed cells. The epithelium can be in the form of a layer of cells lining all surfaces of the body, and in the form of large clusters of cells - glands: liver, pancreas, thyroid, salivary glands, etc. In the first case, it lies on the basement membrane, which separates the epithelium from the underlying connective tissue . However, there are exceptions: epithelial cells in the lymphatic tissue alternate with elements of connective tissue, such an epithelium is called atypical.
Epithelial cells located in a layer can lie in many layers (stratified epithelium) or in one layer (single layer epithelium). According to the height of the cells, the epithelium is divided into flat, cubic, prismatic, cylindrical.
Single-layer squamous epithelium - lines the surface of the serous membranes: pleura, lungs, peritoneum, pericardium of the heart.
Single-layer cubic epithelium - forms the walls of the tubules of the kidneys and the excretory ducts of the glands.
Single-layer cylindrical epithelium - forms the gastric mucosa.
The bordered epithelium - a single-layer cylindrical epithelium, on the outer surface of the cells of which there is a border formed by microvilli that provide absorption of nutrients - lines the mucous membrane of the small intestine.
Ciliated epithelium (ciliated epithelium) - a pseudo-stratified epithelium, consisting of cylindrical cells, the inner edge of which, i.e. facing the cavity or channel, is equipped with constantly fluctuating hair-like formations (cilia) - cilia ensure the movement of the egg in the tubes; in the respiratory tract removes germs and dust.
Stratified epithelium is located on the border of the organism and the external environment. If keratinization processes occur in the epithelium, i.e., the upper layers of cells turn into horny scales, then such a multilayer epithelium is called keratinizing (skin surface). Stratified epithelium lines the mucous membrane of the mouth, food cavity, horny eye.
Transitional epithelium lines the walls of the bladder, renal pelvis, and ureter. When filling these organs, the transitional epithelium is stretched, and cells can move from one row to another.
Glandular epithelium - forms glands and performs a secretory function (releasing substances - secrets that are either excreted into the external environment or enter the blood and lymph (hormones)). The ability of cells to produce and secrete substances necessary for the vital activity of the body is called secretion. In this regard, such an epithelium is also called the secretory epithelium.
Connective tissue
Connective tissue Consists of cells, intercellular substance and connective tissue fibers. It consists of bones, cartilage, tendons, ligaments, blood, fat, it is in all organs (loose connective tissue) in the form of the so-called stroma (skeleton) of organs.
In contrast to epithelial tissue, in all types of connective tissue (except adipose tissue), the intercellular substance predominates over the cells in volume, i.e., the intercellular substance is very well expressed. The chemical composition and physical properties of the intercellular substance are very diverse in different types of connective tissue. For example, blood - the cells in it “float” and move freely, since the intercellular substance is well developed.
In general, connective tissue makes up what is called the internal environment of the body. It is very diverse and is represented by various types - from dense and loose forms to blood and lymph, the cells of which are in the liquid. The fundamental differences between the types of connective tissue are determined by the ratio of cellular components and the nature of the intercellular substance.
In dense fibrous connective tissue (tendons of muscles, ligaments of joints), fibrous structures predominate, it experiences significant mechanical loads.
Loose fibrous connective tissue is extremely common in the body. It is very rich, on the contrary, in cellular forms of different types. Some of them are involved in the formation of tissue fibers (fibroblasts), others, which is especially important, primarily provide protective and regulatory processes, including through immune mechanisms (macrophages, lymphocytes, tissue basophils, plasma cells).
Bone
Bone tissue The bone tissue that forms the bones of the skeleton is very strong. It maintains the shape of the body (constitution) and protects the organs located in the cranium, chest and pelvic cavities, participates in mineral metabolism. The tissue consists of cells (osteocytes) and an intercellular substance in which nutrient channels with vessels are located. The intercellular substance contains up to 70% of mineral salts (calcium, phosphorus and magnesium).
In its development, bone tissue goes through fibrous and lamellar stages. In various parts of the bone, it is organized in the form of a compact or spongy bone substance.
cartilage tissue
Cartilage tissue consists of cells (chondrocytes) and intercellular substance (cartilaginous matrix), which is characterized by increased elasticity. It performs a supporting function, as it forms the bulk of the cartilage.
There are three types of cartilage tissue: hyaline, which is part of the cartilage of the trachea, bronchi, ends of the ribs, articular surfaces of bones; elastic, forming the auricle and epiglottis; fibrous, located in the intervertebral discs and joints of the pubic bones.
Adipose tissue
Adipose tissue is similar to loose connective tissue. The cells are large and filled with fat. Adipose tissue performs nutritional, shaping and thermoregulatory functions. Adipose tissue is divided into two types: white and brown. In humans, white adipose tissue predominates, part of it surrounds the organs, maintaining their position in the human body and other functions. The amount of brown adipose tissue in humans is small (it is present mainly in a newborn child). The main function of brown adipose tissue is heat production. Brown adipose tissue maintains the body temperature of animals during hibernation and the temperature of newborns.
Muscle
Muscle cells are called muscle fibers because they are constantly elongated in one direction.
The classification of muscle tissues is carried out on the basis of the structure of the tissue (histologically): by the presence or absence of transverse striation, and on the basis of the contraction mechanism - voluntary (as in skeletal muscle) or involuntary (smooth or cardiac muscle).
Muscle tissue has excitability and the ability to actively contract under the influence of the nervous system and certain substances. Microscopic differences make it possible to distinguish two types of this tissue - smooth (non-striated) and striated (striated).
Smooth muscle tissue has a cellular structure. It forms the muscular membranes of the walls of internal organs (intestines, uterus, bladder, etc.), blood and lymphatic vessels; its contraction occurs involuntarily.
Striated muscle tissue consists of muscle fibers, each of which is represented by many thousands of cells, merged, in addition to their nuclei, into one structure. It forms skeletal muscles. We can shorten them as we wish.
A variety of striated muscle tissue is the heart muscle, which has unique abilities. During life (about 70 years), the heart muscle contracts more than 2.5 million times. No other fabric has such strength potential. Cardiac muscle tissue has a transverse striation. However, unlike skeletal muscle, there are special areas where the muscle fibers meet. Due to this structure, the contraction of one fiber is quickly transmitted to neighboring ones. This ensures the simultaneous contraction of large sections of the heart muscle.
Also, the structural features of muscle tissue are that its cells contain bundles of myofibrils formed by two proteins - actin and myosin.
nervous tissue
Nervous tissue consists of two types of cells: nervous (neurons) and glial. Glial cells are closely adjacent to the neuron, performing supporting, nutritional, secretory and protective functions.
The neuron is the basic structural and functional unit of the nervous tissue. Its main feature is the ability to generate nerve impulses and transmit excitation to other neurons or muscle and glandular cells of the working organs. Neurons may consist of a body and processes. Nerve cells are designed to conduct nerve impulses. Having received information on one part of the surface, the neuron very quickly transmits it to another part of its surface. Since the processes of a neuron are very long, information is transmitted over long distances. Most neurons have processes of two types: short, thick, branching near the body - dendrites and long (up to 1.5 m), thin and branching only at the very end - axons. Axons form nerve fibers.
A nerve impulse is an electrical wave traveling at high speed along a nerve fiber.
Depending on the functions performed and structural features, all nerve cells are divided into three types: sensory, motor (executive) and intercalary. The motor fibers that go as part of the nerves transmit signals to the muscles and glands, the sensory fibers transmit information about the state of the organs to the central nervous system.
Now we can combine all the information received into a table.
Types of fabrics (table)
|
Fabric group |
Types of fabrics |
Fabric structure |
Location |
|
| Epithelium | Flat | The cell surface is smooth. Cells are tightly packed together | Skin surface, oral cavity, esophagus, alveoli, nephron capsules | Integumentary, protective, excretory (gas exchange, urine excretion) |
| Glandular | Glandular cells secrete | Skin glands, stomach, intestines, endocrine glands, salivary glands | Excretory (sweat, tears), secretory (formation of saliva, gastric and intestinal juice, hormones) | |
| Shimmery (ciliated) | Composed of cells with numerous hairs (cilia) | Airways | Protective (cilia trap and remove dust particles) | |
| Connective | dense fibrous | Groups of fibrous, densely packed cells without intercellular substance | Skin proper, tendons, ligaments, membranes of blood vessels, cornea of the eye | Integumentary, protective, motor |
| loose fibrous | Loosely arranged fibrous cells intertwined with each other. Intercellular substance structureless | Subcutaneous adipose tissue, pericardial sac, pathways of the nervous system | Connects the skin to the muscles, supports the organs in the body, fills the gaps between the organs. Carries out thermoregulation of the body | |
| cartilaginous | Living round or oval cells lying in capsules, the intercellular substance is dense, elastic, transparent | Intervertebral discs, cartilage of the larynx, trachea, auricle, surface of the joints | Smoothing rubbing surfaces of bones. Protection against deformation of the respiratory tract, auricles | |
| Bone | Living cells with long processes, interconnected, intercellular substance - inorganic salts and ossein protein | Skeleton bones | Support, movement, protection | |
| Blood and lymph | Liquid connective tissue, consists of formed elements (cells) and plasma (liquid with organic and mineral substances dissolved in it - serum and fibrinogen protein) | The circulatory system of the whole body | Carries O 2 and nutrients throughout the body. Collects CO 2 and dissimilation products. It ensures the constancy of the internal environment, the chemical and gas composition of the body. Protective (immunity). Regulatory (humoral) | |
| muscular | striated | Multinucleated cylindrical cells up to 10 cm long, striated with transverse stripes | Skeletal muscles, cardiac muscle | Arbitrary movements of the body and its parts, facial expressions, speech. Involuntary contractions (automatic) of the heart muscle to push blood through the chambers of the heart. Has properties of excitability and contractility |
| Smooth | Mononuclear cells up to 0.5 mm long with pointed ends | The walls of the digestive tract, blood and lymph vessels, skin muscles | Involuntary contractions of the walls of internal hollow organs. Raising hair on the skin | |
| nervous | Nerve cells (neurons) | The bodies of nerve cells, various in shape and size, up to 0.1 mm in diameter | Forms the gray matter of the brain and spinal cord | Higher nervous activity. The connection of the organism with the external environment. Centers of conditioned and unconditioned reflexes. Nervous tissue has the properties of excitability and conductivity |
| Short processes of neurons - tree-branching dendrites | Connect with processes of neighboring cells | Transfer the excitation of one neuron to another, establishing a connection between all organs of the body | ||
| Nerve fibers - axons (neurites) - long outgrowths of neurons up to 1.5 m in length. In organs, they end with branched nerve endings. | Nerves of the peripheral nervous system that innervate all organs of the body | Pathways of the nervous system. They transmit excitation from the nerve cell to the periphery along the centrifugal neurons; from receptors (innervated organs) - to the nerve cell along centripetal neurons. Intercalary neurons transmit excitation from centripetal (sensitive) neurons to centrifugal (motor) |
Tissue as a collection of cells and intercellular substance. Types and types of fabrics, their properties. Intercellular interactions.
There are about 200 types of cells in the adult human body. Groups of cells that have the same or similar structure, connected by a unity of origin and adapted to perform certain functions, form fabrics . This is the next level of the hierarchical structure of the human body - the transition from the cellular level to the tissue level (see Figure 1.3.2).
Any tissue is a collection of cells and intercellular substance , which can be a lot (blood, lymph, loose connective tissue) or little (integumentary epithelium).
The cells of each tissue (and some organs) have their own name: the cells of the nervous tissue are called neurons , bone cells osteocytes , liver - hepatocytes and so on.
intercellular substance chemically is a system consisting of biopolymers in high concentration and water molecules. It contains structural elements: collagen, elastin fibers, blood and lymphatic capillaries, nerve fibers and sensory endings (pain, temperature and other receptors). This provides the necessary conditions for the normal functioning of tissues and the performance of their functions.
There are four types of fabrics: epithelial , connecting (including blood and lymph), muscular and nervous (see figure 1.5.1).
epithelial tissue , or epithelium , covers the body, lines the internal surfaces of organs (stomach, intestines, bladder, and others) and cavities (abdominal, pleural), and also forms most of the glands. In accordance with this, integumentary and glandular epithelium are distinguished.
Integumentary epithelium (view A in figure 1.5.1) forms layers of cells (1), closely - practically without intercellular substance - adjacent to each other. He happens single layer or multilayered . The integumentary epithelium is a border tissue and performs the main functions: protection from external influences and participation in the metabolism of the body with the environment - absorption of food components and excretion of metabolic products ( excretion ). The integumentary epithelium is flexible, providing the mobility of internal organs (for example, contractions of the heart, distension of the stomach, intestinal motility, expansion of the lungs, and so on).
glandular epithelium consists of cells, inside of which there are granules with a secret (from the Latin secretio- branch). These cells carry out the synthesis and release of many substances important for the body. By secretion, saliva, gastric and intestinal juice, bile, milk, hormones and other biologically active compounds are formed. The glandular epithelium can form independent organs - glands (for example, the pancreas, thyroid gland, endocrine glands, or endocrine glands , secreting hormones directly into the blood, performing regulatory functions in the body, etc.), and may be part of other organs (for example, the glands of the stomach).
Connective tissue (types B and C in Figure 1.5.1) is distinguished by a large variety of cells (1) and an abundance of intercellular substrate consisting of fibers (2) and amorphous matter (3). Fibrous connective tissue can be loose and dense. Loose connective tissue (view B) is present in all organs, it surrounds the blood and lymphatic vessels. Dense connective tissue performs mechanical, supporting, shaping and protective functions. In addition, there is still a very dense connective tissue (type B), which consists of tendons and fibrous membranes (dura mater, periosteum, and others). Connective tissue not only performs mechanical functions, but also actively participates in metabolism, the production of immune bodies, the processes of regeneration and wound healing, and ensures adaptation to changing living conditions.
Connective tissue includes adipose tissue (view D in Figure 1.5.1). Fats are deposited (deposited) in it, during the decay of which a large amount of energy is released.
play an important role in the body skeletal (cartilaginous and bone) connective tissues . They perform mainly supporting, mechanical and protective functions.
cartilage tissue (type D) consists of cells (1) and a large amount of elastic intercellular substance (2), it forms intervertebral discs, some components of the joints, trachea, bronchi. Cartilage tissue does not have blood vessels and receives the necessary substances by absorbing them from surrounding tissues.
Bone (view E) consists of their bone plates, inside which cells lie. Cells are connected to each other by numerous processes. Bone tissue is hard and the bones of the skeleton are built from this tissue.
A type of connective tissue is blood . In our view, blood is something very important for the body and, at the same time, difficult to understand. Blood (view G in Figure 1.5.1) consists of an intercellular substance - plasma (1) and suspended in it shaped elements (2) - erythrocytes, leukocytes, platelets (Figure 1.5.2 shows their photographs obtained using an electron microscope). All shaped elements develop from a common precursor cell. The properties and functions of blood are discussed in more detail in section 1.5.2.3.
Cells muscle tissue (Figure 1.3.1 and views Z and I in Figure 1.5.1) have the ability to contract. Since a lot of energy is required for contraction, muscle tissue cells are characterized by a high content of mitochondria .
There are two main types of muscle tissue - smooth (view H in Figure 1.5.1), which is present in the walls of many, and usually hollow, internal organs (vessels, intestines, gland ducts, and others), and striated (view And in Figure 1.5.1), which includes cardiac and skeletal muscle tissue. Bundles of muscle tissue form muscles. They are surrounded by layers of connective tissue and permeated with nerves, blood and lymph vessels (see Figure 1.3.1).
General information on tissues is given in Table 1.5.1.
Table 1.5.1. Tissues, their structure and functions
| Fabric name | Specific cell names | intercellular substance | Where is this tissue found? | Functions | Picture |
|---|---|---|---|---|---|
| EPITHELIAL TISSUES | |||||
| Integumentary epithelium (single layer and multilayer) | Cells ( epitheliocytes ) closely adjoin each other, forming layers. The cells of the ciliated epithelium have cilia, the intestinal cells have villi. | Little, does not contain blood vessels; The basement membrane separates the epithelium from the underlying connective tissue. | The inner surfaces of all hollow organs (stomach, intestines, bladder, bronchi, blood vessels, etc.), cavities (abdominal, pleural, articular), the surface layer of the skin ( epidermis ). | Protection from external influences (epidermis, ciliated epithelium), absorption of food components (gastrointestinal tract), excretion of metabolic products (urinary system); provides organ mobility. | Fig.1.5.1, view A |
| Glandular epithelium |
Glandulocytes contain secretory granules with biologically active substances. They can be located singly or form independent organs (glands). | The intercellular substance of the gland tissue contains blood, lymphatic vessels, nerve endings. | Glands of internal (thyroid, adrenal glands) or external (salivary, sweat) secretion. Cells can be located singly in the integumentary epithelium (respiratory system, gastrointestinal tract). | Working out hormones (section 1.5.2.9), digestive enzymes (bile, gastric, intestinal, pancreatic juice, etc.), milk, saliva, sweat and lacrimal fluid, bronchial secretions, etc. | Rice. 1.5.10 "Skin structure" - sweat and sebaceous glands |
| Connective tissues | |||||
| Loose connective | The cellular composition is characterized by great diversity: fibroblasts , fibrocytes , macrophages , lymphocytes , single adipocytes and etc. | A large number of; consists of an amorphous substance and fibers (elastin, collagen, etc.) | Present in all organs, including muscles, surrounds blood and lymphatic vessels, nerves; main component dermis . | Mechanical (sheath of a vessel, nerve, organ); participation in metabolism trophism ), production of immune bodies, processes regeneration . | Fig.1.5.1, view B |
| Dense connective | Fibers predominate over amorphous matter. | Framework of internal organs, dura mater, periosteum, tendons and ligaments. | Mechanical, shaping, supporting, protective. | Fig.1.5.1, view B | |
| fatty | Almost all of the cytoplasm adipocytes occupies the fat vacuole. | There is more intercellular substance than cells. | Subcutaneous fatty tissue, perirenal tissue, abdominal omentums, etc. | Deposition of fats; energy supply due to the breakdown of fats; mechanical. | Fig.1.5.1, view D |
| cartilaginous | Chondrocytes , chondroblasts (from lat. chondron- cartilage) | Differs in elasticity, including due to the chemical composition. | Cartilage of the nose, ears, larynx; articular surfaces of bones; anterior ribs; bronchi, trachea, etc. | Supporting, protective, mechanical. Participates in mineral metabolism ("salt deposition"). Bones contain calcium and phosphorus (almost 98% of the total amount of calcium!). | Fig.1.5.1, view D |
| Bone | osteoblasts , osteocytes , osteoclasts (from lat. os- bone) | Strength is due to mineral "impregnation". | Skeleton bones; auditory ossicles in the tympanic cavity (hammer, anvil and stirrup) | Fig.1.5.1, view E | |
| Blood | red blood cells (including youth forms), leukocytes , lymphocytes , platelets and etc. | Plasma 90-93% consists of water, 7-10% - proteins, salts, glucose, etc. | The internal contents of the cavities of the heart and blood vessels. In violation of their integrity - bleeding and hemorrhage. | Gas exchange, participation in humoral regulation, metabolism, thermoregulation, immune defense; coagulation as a defensive reaction. | Fig.1.5.1, view G; fig.1.5.2 |
| Lymph | Mostly lymphocytes | Plasma (lymphoplasm) | The contents of the lymphatic system | Participation in immune defense, metabolism, etc. | Rice. 1.3.4 "Cell Shapes" |
| MUSCLE TISSUE | |||||
| Smooth muscle tissue | Orderly arranged myocytes spindle-shaped | There is little intercellular substance; contains blood and lymphatic vessels, nerve fibers and endings. | In the walls of hollow organs (vessels, stomach, intestines, urinary and gallbladder, etc.) | Peristalsis of the gastrointestinal tract, contraction of the bladder, maintenance of blood pressure due to vascular tone, etc. | Fig.1.5.1, view H |
| striated | Muscle fibers can contain over 100 cores! | Skeletal muscles; cardiac muscle tissue has automatism (chapter 2.6) | Pumping function of the heart; voluntary muscle activity; participation in the thermoregulation of the functions of organs and systems. | Fig.1.5.1 (view I) | |
| NERVE TISSUE | |||||
| nervous | Neurons ; neuroglial cells perform auxiliary functions | neuroglia rich in lipids (fats) | Brain and spinal cord, ganglia (glands), nerves (nerve bundles, plexuses, etc.) | Perception of irritation, development and conduction of an impulse, excitability; regulation of the functions of organs and systems. | Fig.1.5.1, view K |
Preservation of the form and performance of specific functions by the tissue is genetically programmed: the ability to perform specific functions and differentiation is transferred to daughter cells through DNA. The regulation of gene expression, as the basis of differentiation, was discussed in section 1.3.4.
Differentiation is a biochemical process in which relatively homogeneous cells that have arisen from a common progenitor cell are transformed into increasingly specialized, specific cell types that form tissues or organs. Most differentiated cells usually retain their specific features even in a new environment.
In 1952, scientists at the University of Chicago separated chick embryo cells by growing (incubating) them in an enzyme solution with gentle agitation. However, the cells did not remain separated, but began to combine into new colonies. Moreover, when hepatic cells were mixed with retinal cells, the formation of cell aggregates occurred in such a way that retinal cells always moved to the inner part of the cell mass.
Cell interactions . What allows fabrics not to crumble at the slightest external impact? And what ensures the coordinated work of cells and the performance of specific functions by them?
Many observations prove the ability of cells to recognize each other and respond accordingly. Interaction is not only the ability to transmit signals from one cell to another, but also the ability to act jointly, that is, synchronously. On the surface of each cell are receptors (see section 1.3.2), thanks to which each cell recognizes another similar to itself. And these "detector devices" function according to the "key - lock" rule - this mechanism is repeatedly mentioned in the book.
Let's talk a little about how cells interact with each other. There are two main ways of intercellular interaction: diffusion and adhesive . Diffusion is an interaction based on intercellular channels, pores in the membranes of neighboring cells, located strictly opposite each other. Adhesive (from Latin adhaesio- sticking, sticking) - mechanical connection of cells, long-term and stable retention of them at a close distance from each other. In the chapter on the structure of the cell, various types of intercellular connections (desmosomes, synapses, and others) are described. This is the basis for organizing cells into various multicellular structures (tissues, organs).
Each tissue cell not only connects with neighboring cells, but also interacts with the intercellular substance, using it to receive nutrients, signal molecules (hormones, mediators), and so on. Through chemicals delivered to all tissues and organs of the body, humoral type of regulation (from Latin humor- liquid).
Another way of regulation, as mentioned above, is carried out with the help of the nervous system. Nerve impulses always reach their target hundreds or thousands of times faster than delivery of chemicals to organs or tissues. The nervous and humoral ways of regulating the functions of organs and systems are closely interconnected. However, the very formation of most chemicals and their release into the blood are under constant control of the nervous system.
Cell, fabric - these are the first levels of organization of living organisms , but even at these stages it is possible to identify general mechanisms of regulation that ensure the vital activity of organs, organ systems and the body as a whole.
The human body is a complex holistic self-regulating and self-renewing system, consisting of a huge number of cells. At the level of cells, all the most important processes take place; metabolism, growth, development and reproduction. Cells and non-cellular structures combine to form tissues, organs, organ systems and the whole organism.
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 are borderline, as they cover the body from the outside and line the inside of the hollow organs and walls of the body cavities. A special type of epithelial tissue - glandular epithelium - forms the majority of glands (thyroid, sweat, liver, etc.), the cells of which produce one or another secret. 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 recover (regenerate).
epithelial cells in form can be flat, cylindrical, cubic. In count epithelial layers are single-layered and multi-layered. Examples of epithelium: a single-layered squamous lining the thoracic 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; protective, secretory, absorption.
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 due to 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.
There are three types of muscle tissue: striated, smooth and cardiac (Fig. 12.1). Striated (skeletal) muscle tissue is built from many multinucleated fiber-like cells 1-12 cm long. The presence of myofibrils with light and dark areas that refract light differently (when viewed under a microscope) gives the cell a characteristic transverse striation, which determined the name of this type of tissue. All skeletal muscles, muscles of the tongue, walls of the oral cavity, pharynx, larynx, upper esophagus, mimic, and diaphragm are built from it. Features of striated muscle tissue: speed and arbitrariness (i.e., the dependence of contraction on the will, desire of a person), consumption of a large amount of energy and oxygen, fatigue.
Rice. 12.1 . Types of muscle tissue: a - striated; 6 - cardiac; in - smooth.
heart tissue consists of transversely striated mononuclear muscle cells, but has other 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 a pumping function.
Cells smooth muscle tissue do not have transverse striation, they are fusiform, single-core, 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: involuntariness and low strength of contractions, the ability to long-term tonic contraction, less fatigue, a small need for energy and oxygen.
Connective tissues (tissues of the internal environment) unite groups of tissues of mesodermal origin, very different in structure and functions. Types of connective tissue: bone, cartilage, subcutaneous fat, ligaments, tendons, blood, lymph and others. A common characteristic feature of the structure of these tissues is the 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.
Each type of connective tissue has a special structure of the intercellular substance, and, consequently, different functions due to it. For example, in the intercellular substance of the bone tissue there are salt crystals (mainly calcium salts), which give the bone tissue special strength. Therefore, bone tissue performs protective and supporting functions.
Blood- 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 is 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.
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.
formations coming both from the environment and from the organs of the organism 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.
The main properties of nerve cells - neurons, forming nervous tissue are excitability and conductivity. Excitability- this is the ability of the nervous tissue in response to irritation to come into a state of excitation, and 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.
Nerve cell, or neuron, consists of a body and processes of two types (Fig. 12.2). Body The 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, i.e. in the central nervous system (CNS), where their clusters form gray matter of the brain. Clusters of nerve cell bodies outside the CNS form ganglia, or ganglia.
Short, tree-like processes extending from the body of a neuron are called dendrites. They perform the functions of perceiving irritation and transmitting excitation to the body of the neuron.
Rice. 12.2 . Structure of a neuron: 1 - dendrites; 2 - cell body; 3 - nucleus; 4 - axon; 5 - myelin sheath; b - axon branches; 7 - interception; eight - neurolemma.
The most powerful and longest (up to 1 m) non-branching process is called axon, or nerve fibre. Its function is to conduct excitation from the body of the nerve cell to the end of the axon. It is covered with a special white lipid sheath (myelin), which plays the role of protecting, nourishing and isolating nerve fibers from each other. Accumulations of axons in the CNS form white matter of the brain. Hundreds and thousands of nerve fibers that extend beyond the CNS are combined into bundles with the help of connective tissue - nerves, giving numerous branches to all organs.
Lateral branches depart from the ends of the axons, ending in extensions - axopian endings, or terminals. This is the zone of contact with other nerve, muscle or glandular marks. It is called synapse whose function is broadcast arousal. One neuron can connect to hundreds of other cells through its synapses.
There are three types of neurons according to their functions. Sensitive (centripetal) neurons perceive stimulation from receptors that are excited under the influence of stimuli from the external environment or from the human body itself, and in the form of a nerve impulse transmit excitation from the periphery to the central nervous system. Propulsion (centrifugal) neurons send a nerve signal from the central nervous system to the muscles, glands, i.e., to the periphery. Nerve cells that perceive excitation from other neurons and transmit it to nerve cells are also intercalary neurons, or interneurons. They are located in the CNS. Nerves that contain both sensory and motor fibers are called mixed.
abstract
Topic: "Physiological characteristics of human tissues"
Completed:
Student S-105
Sitnikov N.M
Checked:
Polskaya S.V.
Voronezh 2012
Plan:
2. Epithelial tissue
2.1 simple epithelium
2.2 Stratified epithelium
3. Connective tissue
3.1 Loose and fatty.
3.2 Fibrous and elastic.
3.3 Cartilaginous.
3.4 Bone.
4. Muscle tissue
5. Nervous tissue
6. Literature used:
The structure and functions of human tissues.
In a multicellular human body, there are cells that differ in their structure and functions, which is associated with their differentiation (with lat. - different, distinctive) and specialization in the performance of certain functions. Cell differentiation and specialization are genetically programmed. A nerve cell, for example, will never perform the function of an erythrocyte. Individual groups of cells form a specific tissue.
Textile- an evolutionarily established system of cells and intercellular substance, which has a common structure, development and performs certain functions.
In the human body, there are 4 types of tissues that form human organs: Epithelial, Connective, Muscular, Nervous.
epithelial tissue covers the surface of the body and cavities of various tracts and ducts, with the exception of the heart, blood vessels and some cavities. In addition, almost all glandular cells are of epithelial origin. Layers of epithelial cells on the surface of the skin protect the body from infection and external damage. The cells that line the digestive tract from the mouth to the anus have several functions: they secrete digestive enzymes, mucus, and hormones; absorb water and food products.
single layer
1) Flat (endothelium and mesothelium) (Lines the inside of blood, lymphatic vessels, heart cavities)
2) Cubic (Lines the small excretory ducts of the pancreas, bile ducts and renal tubules)
3) Cylindrical (Lines the organs of the middle part of the digestive canal. It is found in the digestive glands, kidneys, sex glands and genital tract.)
4) Kamchaty (Lines the renal tubules and intestinal mucosa)
5) Multi-row ciliated (Lines the airways)
multilayer
1) Flat non-keratinized (Lines the cornea, anterior alimentary canal, anal alimentary canal, vagina.)
2) Flat keratinizing (epidermis) (Lines the skin)
3) Cubic and cylindrical (They are rare - in the region of the conjunctiva of the eye and the junction of the rectum.)
4) Transitional (uroepithelium) (Lines the urinary tract allantois)
5) Glandular (Lines the glands of the skin, intestines, endocrine glands, salivary glands)
Connective tissue, or tissues of the internal environment, is represented by a group of tissues that are diverse in structure and functions, which are located inside the body and do not border on either the external environment or organ cavities. Connective tissue protects, insulates and supports parts of the body, and also performs a transport function within the body (blood). For example, the ribs protect the organs of the chest, the fat is an excellent insulator, the spine supports the head and torso, and the blood carries nutrients, gases, hormones, and waste products. In all cases, the connective tissue is characterized by a large amount of intercellular substance.
1) Loose and fatty. Loose connective tissue has a network of elastic and elastic (collagen) fibers located in a viscous intercellular substance. This tissue surrounds all blood vessels and most organs, and also underlies the epithelium of the skin. Loose connective tissue containing a large number of fat cells is called adipose tissue; it serves as a place for storing fat and a source of water formation. Loose tissue also contains other cells - macrophages and fibroblasts. Macrophages phagocytize and digest microorganisms, destroyed tissue cells, foreign proteins and old blood cells; their function can be called sanitary. Fibroblasts are mainly responsible for the formation of fibers in the connective tissue.
2) Fibrous and elastic.(densely formed fibrous) Where a resilient, elastic and durable material is needed (for example, to attach a muscle to a bone or to hold two bones in contact together). Muscle tendons and ligaments of joints are built from this tissue, and it is represented almost exclusively by collagen fibers and fibroblasts. However, where soft, but elastic and strong material is needed, for example, in the so-called. yellow ligaments - dense membranes between the arches of adjacent vertebrae, we find elastic connective tissue, consisting mainly of elastic fibers with the addition of collagen fibers and fibroblasts.
3) cartilaginous. Connective tissue with a dense intercellular substance is represented by either cartilage or bone. Cartilage provides the strong yet flexible backbone of organs. The outer ear, nose and nasal septum, larynx and trachea have a cartilaginous skeleton. The main function of these cartilages is to maintain the shape of various structures. The cartilage between the vertebrae makes them mobile relative to each other.
4) Bone. Bone is a connective tissue, an intercellular substance that consists of organic material and inorganic salts, mainly calcium and magnesium phosphates. It always contains specialized bone cells - osteocytes scattered in the intercellular substance. Unlike cartilage, bone is permeated with a large number of blood vessels and a certain number of nerves. From the outside, it is covered with periosteum. The growth of limb bones in length in childhood and adolescence occurs in the so-called. epiphyseal (located at the articular ends of the bone) plates. These plates disappear when the growth of the bone in length stops. The rate of growth in the epiphyseal plates and bone as a whole is controlled by pituitary growth hormone.
5) Blood is a connective tissue with a liquid intercellular substance, plasma, which makes up a little more than half of the total blood volume. Plasma contains various proteins (including antibodies), metabolic products, nutrients (glucose, amino acids, fats), gases (oxygen, carbon dioxide and nitrogen), various salts and hormones. Red blood cells (erythrocytes) contain hemoglobin, an iron-containing compound with a high affinity for oxygen. Most of the oxygen is carried by mature erythrocytes.
Muscle. Muscles provide movement of the body in space, its posture and contractile activity of internal organs. The ability to contract, to some extent inherent in all cells, is most strongly developed in muscle cells.
There are three types of muscles: skeletal(striated, or arbitrary), smooth(visceral, or involuntary) and cardiac. Skeletal muscles.
1) Skeletal muscle cells are long tubular structures, the number of nuclei in them can reach several hundred. Their main structural and functional elements are muscle fibers (myofibrils), which have a transverse striation.
2) Smooth muscles consist of spindle-shaped mononuclear cells with fibrils devoid of transverse bands. These muscles act slowly and contract involuntarily. They line the walls of internal organs (except the heart). Thanks to their synchronous action, food is pushed through the digestive system, urine is excreted from the body, blood flow and blood pressure are regulated, and the egg and sperm move through the appropriate channels.
3) The cardiac muscle forms the muscle tissue of the myocardium (middle layer of the heart) and is built from cells whose contractile fibrils have a transverse striation. It contracts automatically and involuntarily, like smooth muscle.
nervous tissue- tissue of ectodermal origin, is a system of specialized structures that form the basis of the nervous system and create conditions for the implementation of its functions. Nervous tissue communicates the body with the environment, perceives and converts stimuli into a nerve impulse and transmits it to the effector. Nervous tissue provides the interaction of tissues, organs and systems of the body and their regulation. Nervous tissues form the nervous system, are part of the nerve nodes, spinal cord and brain. They consist of nerve cells - neurons, whose bodies have a stellate shape, long and short processes. Neurons perceive irritation and transmit excitation to muscles, skin, other tissues, organs. Nervous tissues ensure the coordinated work of the body. nervous tissue characterized by the maximum development of such properties as irritability and conductivity. Irritability - the ability to respond to physical (heat, cold, light, sound, touch) and chemical (taste, smell) stimuli (irritants). Conductivity - the ability to transmit an impulse resulting from irritation (nerve impulse).
The element that perceives irritation and conducts a nerve impulse is a nerve cell (neuron). A neuron consists of a cell body containing a nucleus, and processes - dendrites and an axon. Each neuron can have many dendrites, but only one axon, which, however, has several branches. Dendrites, perceiving a stimulus from different parts of the brain or from the periphery, transmit a nerve impulse to the body of the neuron. From the cell body, a nerve impulse is conducted along a single process - an axon - to other neurons or effector organs. The axon of one cell can contact either dendrites, or the axon or bodies of other neurons, or muscle or glandular cells; these specialized contacts are called synapses. The axon extending from the cell body is covered with a sheath formed by specialized (Schwann) cells; the sheathed axon is called a nerve fiber. Bundles of nerve fibers make up nerves. They are covered with a common connective tissue sheath, in which elastic and non-elastic fibers and fibroblasts (loose connective tissue) are interspersed along the entire length.
Used Books:
1) Biology: study guide / A.G. Lebedev. M.: AST: Astrel. 2009.
2) The Great Encyclopedia of Cyril and Methodius. Moscow. 2009. Electronic edition
Used Internet resources:
1) http://www.egeteka.ru
2) http://www.dimassage.ru
3) http://ru.wikipedia.org
The structure and biological role of the tissues of the human body:
General instructions: Textile- a collection of cells that have a similar origin, structure and function.
Each tissue is characterized by development in ontogeny from a certain embryonic germ and its typical relationships with other tissues and position in the body (N.A. Shevchenko)
tissue fluid- an integral part of the internal environment of the body. is a liquid with dissolved nutrients, end products of metabolism, oxygen and carbon dioxide. It is located in the spaces between the cells of tissues and organs in vertebrates. It acts as an intermediary between the circulatory system and the cells of the body. From the tissue fluid, carbon dioxide enters the circulatory system, and water and end products of metabolism are absorbed into the lymphatic capillaries. Its volume is 26.5% of body weight.
epithelial tissue:
Epithelial (integumentary) tissue, or epithelium, is a boundary layer of cells that lines the integument of the body, the mucous membranes of all internal organs and cavities, and also forms the basis of many glands.
The epithelium separates the organism from the external environment, but at the same time serves as an intermediary in the interaction of the organism with the environment. Epithelial cells are tightly connected to each other and form a mechanical barrier that prevents the penetration of microorganisms and foreign substances into the body. Epithelial tissue cells live for a short time and are quickly replaced by new ones (this process is called regeneration).
Epithelial tissue is also involved in many other functions: secretion (external and internal secretion glands), absorption (intestinal epithelium), gas exchange (lung epithelium).
The main feature of the epithelium is that it consists of a continuous layer of densely packed cells. The epithelium can be in the form of a layer of cells lining all surfaces of the body, and in the form of large clusters of cells - glands: liver, pancreas, thyroid, salivary glands, etc. In the first case, it lies on the basement membrane, which separates the epithelium from the underlying connective tissue . However, there are exceptions: epithelial cells in the lymphatic tissue alternate with elements of connective tissue, such an epithelium is called atypical.
Epithelial cells located in a layer can lie in many layers (stratified epithelium) or in one layer (single layer epithelium). According to the height of the cells, the epithelium is divided into flat, cubic, prismatic, cylindrical.
Connective tissue:
Connective tissueconsists of cells, intercellular substance and connective tissue fibers. It consists of bones, cartilage, tendons, ligaments, blood, fat, it is in all organs (loose connective tissue) in the form of the so-called stroma (skeleton) of organs.
In contrast to epithelial tissue, in all types of connective tissue (except adipose tissue), the intercellular substance predominates over the cells in volume, i.e., the intercellular substance is very well expressed. The chemical composition and physical properties of the intercellular substance are very diverse in different types of connective tissue. For example, blood - the cells in it “float” and move freely, since the intercellular substance is well developed.
Generally, connective tissueconstitutes what is called the internal environment of the organism. It is very diverse and is represented by various types - from dense and loose forms to blood and lymph, the cells of which are in the liquid. The fundamental differences between the types of connective tissue are determined by the ratio of cellular components and the nature of the intercellular substance.
In dense fibrous connective tissue (muscle tendons, ligaments of joints), fibrous structures predominate, it experiences significant mechanical stress.
Loose fibrous connective tissue is extremely common in the body. It is very rich, on the contrary, in cellular forms of different types. Some of them are involved in the formation of tissue fibers (fibroblasts), others, which is especially important, primarily provide protective and regulatory processes, including through immune mechanisms (macrophages, lymphocytes, tissue basophils, plasma cells).
Bone, forming the bones of the skeleton, is very durable. It maintains the shape of the body (constitution) and protects the organs located in the cranium, chest and pelvic cavities, participates in mineral metabolism. The tissue consists of cells (osteocytes) and an intercellular substance in which nutrient channels with vessels are located. The intercellular substance contains up to 70% of mineral salts (calcium, phosphorus and magnesium).
In its development, bone tissue goes through fibrous and lamellar stages. In various parts of the bone, it is organized in the form of a compact or spongy bone substance.
cartilage tissue made up of cells (chondrocytes) and intercellular substance cartilage matrix), characterized by increased elasticity. It performs a supporting function, as it forms the bulk of the cartilage.
nervous tissue:
nervous tissue consists of two types of cells: nerve (neurons) and glial. Glial cells closely adjacent to the neuron, performing supporting, nutritional, secretory and protective functions.
Neuron- the main structural and functional unit of the nervous tissue. Its main feature is the ability to generate nerve impulses and transmit excitation to other neurons or muscle and glandular cells of the working organs. Neurons may consist of a body and processes. Nerve cells are designed to conduct nerve impulses. Having received information on one part of the surface, the neuron very quickly transmits it to another part of its surface. Since the processes of a neuron are very long, information is transmitted over long distances. Most neurons have processes of two types: short, thick, branching near the body - dendrites and long (up to 1.5 m), thin and branching only at the very end - axons. Axons form nerve fibers.
nerve impulse is an electrical wave traveling at high speed along a nerve fiber.
Depending on the functions performed and structural features, all nerve cells are divided into three types: sensory, motor (executive) and intercalary. The motor fibers that go as part of the nerves transmit signals to the muscles and glands, the sensory fibers transmit information about the state of the organs to the central nervous system.
Muscle
Muscle cells are called muscle fibers because they are constantly elongated in one direction.
The classification of muscle tissues is carried out on the basis of the structure of the tissue (histologically): by the presence or absence of transverse striation, and on the basis of the mechanism of contraction - voluntary (as in skeletal muscle) or involuntary (smooth or cardiac muscle).
Muscle has excitability and the ability to actively contract under the influence of the nervous system and certain substances. Microscopic differences make it possible to distinguish two types of this fabric – smooth(unstreaked) and striated(striated).
Smooth muscle tissue has a cellular structure. It forms the muscular membranes of the walls of internal organs (intestines, uterus, bladder, etc.), blood and lymphatic vessels; its contraction occurs involuntarily.
Striated muscle tissue consists of muscle fibers, each of which is represented by many thousands of cells, merged, in addition to their nuclei, into one structure. It forms skeletal muscles. We can shorten them as we wish.
A variety of striated muscle tissue is the heart muscle, which has unique abilities. During life (about 70 years), the heart muscle contracts more than 2.5 million times. No other fabric has such strength potential. Cardiac muscle tissue has a transverse striation. However, unlike skeletal muscle, there are special areas where the muscle fibers meet. Due to this structure, the contraction of one fiber is quickly transmitted to neighboring ones. This ensures the simultaneous contraction of large sections of the heart muscle.
Fabric types
Fabric group | Types of fabrics | Fabric structure | Location | Functions |
Epithelium | Flat | The cell surface is smooth. Cells are tightly packed together | Skin surface, oral cavity, esophagus, alveoli, nephron capsules | Integumentary, protective, excretory (gas exchange, urine excretion) |
Glandular | Glandular cells secrete | Skin glands, stomach, intestines, endocrine glands, salivary glands | Excretory (sweat, tears), secretory (formation of saliva, gastric and intestinal juice, hormones) |
|
Ciliary (ciliated) | Composed of cells with numerous hairs (cilia) | Airways | Protective (cilia trap and remove dust particles) |
|
Connective | dense fibrous | Groups of fibrous, densely packed cells without intercellular substance | Skin proper, tendons, ligaments, membranes of blood vessels, cornea of the eye | Integumentary, protective, motor |
loose fibrous | Loosely arranged fibrous cells intertwined with each other. Intercellular substance structureless | Subcutaneous adipose tissue, pericardial sac, pathways of the nervous system | Connects the skin to the muscles, supports the organs in the body, fills the gaps between the organs. Carries out thermoregulation of the body |
|
Cartilaginous (hyalinous, elastic, fibrous) | Living round or oval cells lying in capsules, the intercellular substance is dense, elastic, transparent | Intervertebral discs, cartilage of the larynx, trachea, auricle, surface of the joints | Smoothing rubbing surfaces of bones. Protection against deformation of the respiratory tract, auricles |
|
Bone compact and spongy | Living cells with long processes, interconnected, intercellular substance - inorganic salts and ossein protein | Skeleton bones | Support, movement, protection |
|
Blood and lymph | Liquid connective tissue, consists of formed elements (cells) and plasma (liquid with organic and mineral substances dissolved in it - serum and fibrinogen protein) | The circulatory system of the whole body | Carries O2 and nutrients throughout the body. Collects CO2 and dissimilation products. It ensures the constancy of the internal environment, the chemical and gas composition of the body. Protective (immunity). Regulatory (humoral) |
|
muscular | Cross-striped | Multinucleated cylindrical cells up to 10 cm long, striated with transverse stripes | Skeletal muscles, cardiac muscle | Arbitrary movements of the body and its parts, facial expressions, speech. Involuntary contractions (automatic) of the heart muscle to push blood through the chambers of the heart. It has the properties of excitability and contractility |
Smooth | Mononuclear cells up to 0.5 mm long with pointed ends | The walls of the digestive tract, blood and lymph vessels, skin muscles | Involuntary contractions of the walls of internal hollow organs. Raising hair on the skin |
|
nervous | Nerve cells (neurons) | The bodies of nerve cells, various in shape and size, up to 0.1 mm in diameter | Forms the gray matter of the brain and spinal cord | Higher nervous activity. The connection of the organism with the external environment. Centers of conditioned and unconditioned reflexes. Nervous tissue has the properties of excitability and conductivity |
Short processes of neurons - tree-branching dendrites | Connect with processes of neighboring cells | Transfer the excitation of one neuron to another, establishing a connection between all organs of the body |
||
Nerve fibers - axons (neurites) - long outgrowths of neurons up to 1.5 m in length. In organs, they end with branched nerve endings. | Nerves of the peripheral nervous system that innervate all organs of the body | Pathways of the nervous system. They transmit excitation from the nerve cell to the periphery along the centrifugal neurons; from receptors (innervated organs) - to the nerve cell along centripetal neurons. Intercalary neurons transmit excitation from centripetal (sensitive) neurons to centrifugal (motor) |
||
neuroglia | Neuroglia is made up of neurocytes. | Found between neurons | Support, nutrition, protection of neurons |
