First chemical substances classified at the end of the 9th century by the Arab scholar Abu Bakr ar-Razi. Based on the origin of the substances, he divided them into three groups. In the first group he assigned a place to mineral substances, in the second to plant substances and in the third to animal substances.

This classification was destined to last for almost a millennium. Only in the 19th century two of those groups were formed - organic and inorganic substances. Chemical substances of both types are built thanks to the ninety elements included in D.I. Mendeleev’s table.

Group of inorganic substances

Among inorganic compounds, simple and complex substances are distinguished. Group simple substances combines metals, non-metals and noble gases. Complex substances represented by oxides, hydroxides, acids and salts. All inorganic substances can be built from any chemical elements.

Group of organic substances

The composition of all organic compounds necessarily includes carbon and hydrogen (this is their fundamental difference from minerals). Substances formed by C and H are called hydrocarbons - the simplest organic compounds. Hydrocarbon derivatives contain nitrogen and oxygen. They, in turn, are classified into oxygen- and nitrogen-containing compounds.

The group of oxygen-containing substances is represented by alcohols and ethers, aldehydes and ketones, carboxylic acids, fats, waxes and carbohydrates. Nitrogen-containing compounds include amines, amino acids, nitro compounds and proteins. For heterocyclic substances, the position is twofold - they, depending on their structure, can belong to both types of hydrocarbons.

Cell chemicals

The existence of cells is possible if they contain organic and inorganic substances. They die when they lack water and mineral salts. Cells die if they are severely depleted of nucleic acids, fats, carbohydrates and proteins.

They are capable of normal life if they contain several thousand compounds of organic and inorganic nature, capable of entering into many different chemical reactions. The biochemical processes occurring in the cell are the basis of its vital activity, normal development and functioning.

Chemical elements that saturate the cell

Cells of living systems contain groups of chemical elements. They are enriched with macro-, micro- and ultra-microelements.

• Macroelements are primarily represented by carbon, hydrogen, oxygen and nitrogen. These inorganic substances of the cell form almost all of its organic compounds. They also include vital elements. A cell is not able to live and develop without calcium, phosphorus, sulfur, potassium, chlorine, sodium, magnesium and iron.
• The group of microelements is formed by zinc, chromium, cobalt and copper.
• Ultramicroelements are another group representing the most important inorganic substances of the cell. The group is formed by gold and silver, which have a bactericidal effect, and mercury, which prevents the reabsorption of water that fills the kidney tubules and affects enzymes. It also includes platinum and cesium. Selenium plays a certain role in it, the deficiency of which leads to various types cancer.

Water in the cell

The importance of water, a common substance on earth for cell life, is undeniable. Many organic and inorganic substances dissolve in it. Water is a fertile environment where an incredible number of chemical reactions take place. It is capable of dissolving decay and metabolic products. Thanks to it, waste and toxins leave the cell.

This liquid has high thermal conductivity. This allows heat to spread evenly throughout the body tissues. It has a significant heat capacity (the ability to absorb heat when its own temperature changes minimally). This ability prevents sudden temperature changes from occurring in the cell.

Water has exceptionally high surface tension. Thanks to it, dissolved inorganic substances, like organic ones, easily move through tissues. Many small organisms, using the property of surface tension, stay on the water surface and slide freely along it.

Turgor of plant cells depends on water. In certain species of animals, it is water that copes with the support function, and not any other inorganic substances. Biology has identified and studied animals with hydrostatic skeletons. These include representatives of echinoderms, round and annelids, jellyfish and sea anemones.

Saturation of cells with water

Working cells are filled with water by 80% of their total volume. The liquid remains free and related form. Protein molecules bind tightly to bound water. They are surrounded water shell, are isolated from each other.

Water molecules are polar. They form hydrogen bonds. Thanks to hydrogen bridges, water has high thermal conductivity. Bound water allows cells to withstand cold temperatures. Free water accounts for 95%. It promotes the dissolution of substances involved in cellular metabolism.

Highly active cells in brain tissue contain up to 85% water. Muscle cells are 70% saturated with water. Less active cells that form adipose tissue need 40% water. It not only dissolves inorganic chemicals in living cells, it is a key participant in the hydrolysis of organic compounds. Under its influence, organic substances, breaking down, turn into intermediate and final substances.

The importance of mineral salts for the cell

Mineral salts are represented in cells by cations of potassium, sodium, calcium, magnesium and anions HPO 4 2-, H 2 PO 4 -, Cl -, HCO 3 -. The correct proportions of anions and cations create the acidity necessary for cell life. Many cells maintain a slightly alkaline environment, which remains virtually unchanged and ensures their stable functioning.

The concentration of cations and anions in cells is different from their ratio in the intercellular space. The reason for this is active regulation aimed at transporting chemical compounds. This course of processes determines the constancy of chemical compositions in living cells. After cell death, the concentration of chemical compounds in the intercellular space and cytoplasm reaches equilibrium.

Inorganic substances in the chemical organization of the cell

The chemical composition of living cells does not contain any special elements that are unique to them. This determines the unity of the chemical compositions of living and nonliving objects. Inorganic substances in the composition of the cell play a huge role.

Sulfur and nitrogen help proteins form. Phosphorus is involved in the synthesis of DNA and RNA. Magnesium is an important component of enzymes and chlorophyll molecules. Copper is necessary for oxidative enzymes. Iron is the center of the hemoglobin molecule, zinc is part of the hormones produced by the pancreas.

Importance of inorganic compounds for cells

Nitrogen compounds convert proteins, amino acids, DNA, RNA and ATP. In plant cells, ammonium ions and nitrates are converted into NH 2 during redox reactions and become involved in the synthesis of amino acids. Living organisms use amino acids to form their own proteins needed to build their bodies. After the death of organisms, proteins flow into the cycle of substances; during their decay, nitrogen is released in free form.

Inorganic substances that contain potassium play the role of a “pump”. Thanks to the “potassium pump,” substances that they urgently need penetrate into the cells through the membrane. Potassium compounds lead to the activation of cell activity, thanks to which excitations and impulses are carried out. The concentration of potassium ions in cells is very high, in contrast to environment. After the death of living organisms, potassium ions easily pass into the natural environment.

Substances containing phosphorus contribute to the formation of membrane structures and tissues. In their presence, enzymes and nucleic acids are formed. Various layers of soil are saturated to varying degrees with phosphorus salts. Root secretions of plants, dissolving phosphates, absorb them. Following the death of organisms, the remaining phosphates undergo mineralization, turning into salts.

Inorganic substances containing calcium contribute to the formation of intercellular substance and crystals in plant cells. Calcium from them penetrates into the blood, regulating the process of blood clotting. Thanks to it, bones, shells, calcareous skeletons, and coral polyps are formed in living organisms. Cells contain calcium ions and crystals of its salts.

Substances such as sand, clay, various minerals, water, carbon oxides, carbonic acid, its salts and others found in “ inanimate nature", are called inorganic or mineral substances.

Of the approximately one hundred chemical elements found in earth's crust, only sixteen are necessary for life, and four of them - hydrogen (H), carbon (C), oxygen (O) and nitrogen (N) are most common in living organisms and make up 99% of the mass of living things. The biological significance of these elements is associated with their valency (1, 2, 3, 4) and the ability to form strong covalent bonds, which are stronger than the bonds formed by other elements of the same valence. The next most important are phosphorus (P), sulfur (S), sodium, magnesium, chlorine, potassium and calcium ions (Na, Mg, Cl, K, Ca). Iron (Fe), cobalt (Co), copper (Cu), zinc (Zn), boron (B), aluminum (Al), silicon (Si), vanadium (V), molybdenum ( Mo), iodine (I), manganese (Mn).

All chemical elements in the form of ions or as part of certain compounds participate in the construction of the body. For example, carbon, hydrogen and oxygen are found in carbohydrates and fats. In the composition of proteins, nitrogen and sulfur are added to them, in the composition of nucleic acids - nitrogen, phosphorus, iron, which are involved in the construction of the hemoglobin molecule; magnesium is found in chlorophyll; copper is found in some oxidative enzymes; iodine is contained in the thyroxine molecule (thyroid hormone); sodium and potassium provide electrical charge on the membranes of nerve cells and nerve fibers; zinc is included in the molecule of the pancreatic hormone - insulin; Cobalt is found in vitamin B12.

Compounds of nitrogen, phosphorus, calcium and other inorganic substances serve as a source of building material for the synthesis of organic molecules (amino acids, proteins, nucleic acids, etc.) and are part of a number of supporting structures of the cell and organism. Some inorganic ions (for example, calcium and magnesium ions) are activators and components of many enzymes, hormones and vitamins. With a lack of these ions, vital processes in the cell are disrupted.

Important functions in living organisms are performed by inorganic acids and their salts. Hydrochloric acid is part of the gastric juice of animals and humans, accelerating the process of digesting food proteins. Residues of sulfuric acid, joining foreign substances insoluble in water, give them solubility, facilitating their removal from the body. Inorganic sodium and potassium salts of nitrous and phosphoric acids serve as important components of the mineral nutrition of plants; they are added to the soil as fertilizers. Calcium and phosphorus salts are part of animal bone tissue. Carbon dioxide (CO2) is constantly formed in nature during oxidation organic matter(rotting of plant and animal remains, respiration, combustion of fuel) it is released in large quantities from volcanic fissures and from the waters of mineral springs.

Water is a very common substance on Earth. Almost the surface of the globe is covered with water, forming oceans and seas. Rivers, lakes. Much water exists as a gaseous vapor in the atmosphere; it lies in the form of huge masses of snow and ice all year round on the peaks high mountains and in the polar countries, in the bowels of the Earth there is also water that permeates the soil and rocks.

Water has a very great importance in the life of plants, animals and humans. According to modern ideas, the very origin of life is connected with the sea. In any organism, water is the medium in which chemical processes take place that ensure the life of the organism; in addition, it itself takes part in a number of biochemical reactions.

The chemical and physical properties of water are quite unusual and are associated mainly with the small size of its molecules, with the polarity of its molecules and with their ability to connect with each other through hydrogen bonds.

Let's consider the biological significance of water. Water - excellent solvent for polar substances. These include ionic compounds, such as salts, in which charged particles (ions) dissociate (separate from each other) in water when the substance is dissolved, as well as some non-ionic compounds, such as sugars and simple alcohols, which contain charged molecules. (polar) groups (in sugars and alcohols these are OH groups). When a substance goes into solution, its molecules or ions are able to move more freely and, accordingly, its reactivity increases. For this reason, most chemical reactions in a cell occur in aqueous solutions. Non-polar substances, such as lipids, do not mix with water and therefore can separate aqueous solutions into separate compartments, just as membranes separate them. The non-polar parts of the molecules are repelled by water and, in its presence, are attracted to each other, as happens, for example, when oil droplets merge into larger droplets; in other words, nonpolar molecules are hydrophobic. Such hydrophobic interactions play an important role in ensuring the stability of membranes, as well as many protein molecules and nucleic acids. The inherent properties of water as a solvent also mean that water serves as a medium for the transport of various substances. It performs this role in the blood, in the lymphatic and excretory systems, in the digestive tract and in the phloem and xylem of plants.

Water has great heat capacity. This means that a significant increase in thermal energy causes only a relatively small increase in its temperature. This phenomenon is explained by the fact that a significant part of this energy is spent on breaking hydrogen bonds that limit the mobility of water molecules, i.e., on overcoming its stickiness. The high heat capacity of water minimizes the temperature changes occurring in it. Due to this, biochemical processes occur in a smaller temperature range, with more constant speed, and the danger of disruption of these processes from sudden temperature deviations does not threaten them so much. Water serves as a habitat for many cells and organisms, which is characterized by a fairly significant constancy of conditions.

Water is characterized by large heat of vaporization. The latent heat of evaporation (or relative latent heat of evaporation) is a measure of the amount of thermal energy that must be imparted to a liquid in order for it to transform into vapor, that is, to overcome the forces of molecular cohesion in the liquid. Evaporation of water requires quite significant amounts of energy. This is explained by the existence of hydrogen bonds between water molecules. It is because of this that the boiling point of water, a substance with such small molecules, is unusually high.

The energy required for water molecules to evaporate comes from their environment. Thus, evaporation is accompanied by cooling. This phenomenon is used in animals during sweating, during thermal dyspnea in mammals or in some reptiles (for example, crocodiles), which sit in the sun with their mouths open; it may also play a significant role in cooling transpiring leaves. The latent heat of fusion (or relative latent heat of fusion) is a measure of the thermal energy required to melt a solid (ice). Water needs a relatively large amount of energy to melt (melt). The opposite is also true: when water freezes, it must release a large amount of thermal energy. This reduces the likelihood of the cell contents and surrounding fluid freezing. Ice crystals are especially harmful to living things when they form inside cells.

Water is the only substance that has liquid state greater density, than in solid. Since ice floats in water, it forms when it freezes first on its surface and only finally in the bottom layers. If the freezing of ponds occurred in the reverse order, from bottom to top, then in areas with a temperate or cold climate, life in freshwater bodies could not exist at all. Ice covers the water column like a blanket, which increases the chances of survival for the organisms living in it. This is important in cold climates and during the cold season, but undoubtedly it played a particularly important role during the Ice Age. Being on the surface, ice melts faster. The fact that layers of water whose temperature has fallen below 4 degrees rise upward causes their movement in large bodies of water. The nutrients contained in it circulate along with the water, due to which water bodies are populated by living organisms to great depths.

The water has a big surface tension and cohesion. Cohesion- this is the cohesion of molecules physical body with each other under the influence of attractive forces. There is surface tension on the surface of a liquid - the result of cohesive forces acting between molecules, directed inward. Due to surface tension, the liquid tends to take a shape such that its surface area is minimal (ideally, a spherical shape). Of all liquids, water has the highest surface tension. The significant cohesion characteristic of water molecules plays an important role in living cells, as well as in the movement of water through xylem vessels in plants. Many small organisms benefit from surface tension: it allows them to float on water or glide across its surface.

The biological significance of water is also determined by the fact that it is one of the necessary metabolites, i.e., it participates in metabolic reactions. Water is used, for example, as a source of hydrogen in the process of photosynthesis, and also participates in hydrolysis reactions.

The role of water for living organisms is reflected, in particular, in the fact that one of the main factors natural selection influencing speciation is a lack of water (limitation of the distribution of some plants with motile gametes). All terrestrial organisms are adapted to obtain and conserve water; in their extreme manifestations - in xerophytes, in desert-dwelling animals, etc. This kind of adaptation seems to be a true miracle of nature’s ingenuity.

Biological functions of water:

In all organisms:

1) ensures the maintenance of structure (high water content in protoplasm); 2) serves as a solvent and medium for diffusion; 3) participates in hydrolysis reactions; 4) serves as a medium in which fertilization occurs;

5) ensures the dispersal of seeds, gametes and larval stages of aquatic organisms, as well as the seeds of some terrestrial plants, such as the coconut palm.

In plants:

1) determines osmosis and turgidity (on which many things depend: growth (enlargement of cells), maintenance of structure, movement of stomata, etc.); 2) participates in photosynthesis; 3) provides transport of inorganic ions and organic molecules; 4) ensures seed germination - swelling, rupture of the seed coat and further development.

In animals:

1) provides transport of substances;

2) determines osmoregulation;

3) promotes body cooling (sweating, thermal shortness of breath);

4) serves as one of the components of lubrication, for example in joints;

5) has supporting functions (hydrostatic skeleton);

6) performs a protective function, for example in tear fluid and mucus;

7) promotes migration (sea currents).



Chemical composition of the cell

Mineral salts

water.
good solvent

Hydrophilic(from Greek hydro- water and filleo

Hydrophobic(from Greek hydro- water and Phobos

elasticity

Water. Water- universal solvent hydrophilic. 2- hydrophobic. .3- heat capacity. 4- Water is characterized 5- 6- Water provides movement of substances 7- In plants, water determines turgor support functions, 8- Water - component lubricating fluids slime

Mineral salts. action potential ,

Physico-chemical properties of water as the main medium in the human body.

Of the inorganic substances that make up the cell, the most important is water. Its amount ranges from 60 to 95% of the total cell mass. Water plays a vital role in the life of cells and living organisms in general. In addition to the fact that it is part of their composition, for many organisms it is also a habitat. The role of water in a cell is determined by its unique chemical and physical properties, associated mainly with the small size of molecules, with the polarity of its molecules and with their ability to form hydrogen bonds with each other.

Lipids. Functions of lipids in the human body.

Lipids are a large group of substances of biological origin, highly soluble in organic solvents such as methanol, acetone, chloroform and benzene. At the same time, these substances are insoluble or slightly soluble in water. Weak solubility is associated with the insufficient content of atoms with polarizable properties in lipid molecules. electronic shell, such as O, N, S or P.

The system of humoral regulation of physiological functions. Principles of hum..

Humoral physiological regulation uses body fluids (blood, lymph, cerebrospinal fluid, etc.) to transmit information. Signals are transmitted through chemicals: hormones, mediators, biologically active substances (BAS), electrolytes, etc.

Features of humoral regulation: does not have an exact addressee - with the flow of biological fluids, substances can be delivered to any cells of the body; the speed of information delivery is low - determined by the speed of flow of biological fluids - 0.5-5 m/s; duration of action.

The transmission of humoral regulation is carried out by the blood flow, lymph, by diffusion, nervous regulation is carried out by nerve fibers. The humoral signal travels more slowly (with the blood flow through the capillary at a speed of 0.05 mm/s) than the nervous signal (nerve transmission speed is 130 m/s). A humoral signal does not have such a precise addressee (it works on the principle of “everyone, everyone, everyone”) as a nervous one (for example, a nerve impulse is transmitted by the contracting muscles of a finger). But this difference is not significant, since cells have different sensitivity to chemicals. Therefore, chemicals act on strictly defined cells, that is, on those that are able to perceive this information. Cells that have such a high sensitivity to any humoral factor are called target cells.
Among humoral factors, substances with a narrow
spectrum of action, that is, directed action on a limited number of target cells (for example, oxytocin), and wider (for example, adrenaline), for which there is a significant number of target cells.
Humoral regulation is used to ensure reactions that do not require high speed and accuracy of execution.
Humoral regulation, like nervous regulation, is always carried out
a closed regulatory loop in which all elements are interconnected by channels.
As for the monitoring element of the device circuit (SP), it is absent as an independent structure in the humoral regulation circuit. The function of this link is usually performed by the endocrine system.
cell.
Humoral substances that enter the blood or lymph diffuse into the intercellular fluid and are quickly destroyed. In this regard, their effect can only extend to nearby organ cells, that is, their influence is local in nature. In contrast to local effects, distant effects of humoral substances extend to target cells at a distance.

HYPOTHALAMUS HORMONES

hormone effect

Corticoliberin - Stimulates the formation of corticotropin and lipotropin

Gonadotropin-releasing hormone - Stimulates the formation of lutropin and follitropin

Prolactoliberin - Promotes the release of prolactin

Prolactostatin - Inhibits the release of prolactin

Somatoliberin Stimulates the secretion of growth hormone

Somatostatin - Inhibits the secretion of growth hormone and thyrotropin

Thyroliberin - Stimulates the secretion of thyrotropin and prolactin

Melanoliberin - Stimulates the secretion of melanocyte-stimulating hormone

Melanostatin - Inhibits the secretion of melanocyte-stimulating hormone

ADENOGYPOPHYSIC HORMONES

STH (somatotropin, growth hormone) - Stimulates body growth, protein synthesis in cells, glucose formation and lipid breakdown

Prolactin - Regulates lactation in mammals, the instinct to nurse offspring, differentiation of various tissues

TSH (thyrotropin) - Regulates the biosynthesis and secretion of thyroid hormones

Corticotropin - Regulates the secretion of hormones from the adrenal cortex

FSH (follitropin) and LH (luteinizing hormone) - LH regulates the synthesis of female and male sex hormones, stimulates the growth and maturation of follicles, ovulation, the formation and functioning of the corpus luteum in the ovaries FSH has a sensitizing effect on follicles and Leydig cells to the action of LH, stimulates spermatogenesis

THYROID HORMONES The release of thyroid hormones is controlled by two “superior” endocrine glands. The area of ​​the brain that connects the nervous and endocrine systems is called the hypothalamus. The hypothalamus receives information about the level of thyroid hormones and secretes substances that affect the pituitary gland. Pituitary also located in the brain in the area of ​​a special depression - the sella turcica. It secretes several dozen hormones that are complex in structure and action, but only one of them acts on the thyroid gland - thyroid-stimulating hormone or TSH. The level of thyroid hormones in the blood and signals from the hypothalamus stimulate or inhibit the release of TSH. For example, if the amount of thyroxine in the blood is small, then both the pituitary gland and hypothalamus will know about it. The pituitary gland will immediately release TSH, which activates the release of hormones from the thyroid gland.

Humoral regulation is the coordination of the physiological functions of the human body through blood, lymph, and tissue fluid. Humoral regulation is carried out by biologically active substances - hormones that regulate body functions at the subcellular, cellular, tissue, organ and system levels and mediators that transmit nerve impulses. Hormones are produced by the endocrine glands (endocrine), as well as by the external secretion glands (tissue - the walls of the stomach, intestines, and others). Hormones affect the metabolism and activity of various organs, entering them through the blood. Hormones have the following properties: High biological activity; Specificity – effects on certain organs, tissues, cells; They are quickly destroyed in tissues; The molecules are small in size and penetrate easily through the walls of capillaries into tissues.

Adrenal glands - paired endocrine glands of vertebrates animals and person. The zona glomerulosa produces hormones called mineralcorticoids. These include :Aldosterone (basic mineralocorticosteroid hormone adrenal cortex) Corticosterone (insignificant and relatively inactive glucocorticoid hormone). Mineralcorticoids increase reabsorption Na + and K + excretion in the kidneys. In the beam zone there are formed glucocorticoids, which include: Cortisol. Glucocorticoids have an important effect on almost all metabolic processes. They stimulate education glucose from fat And amino acids(gluconeogenesis), oppress inflammatory, immune And allergic reactions, reduce proliferation connective tissue and also increase sensitivity sense organs And excitability nervous system . Produced in the mesh zone sex hormones (androgens, which are precursor substances estrogen). These sex hormones play a slightly different role than the hormones secreted gonads. Adrenal medulla cells produce catecholamines - adrenalin And norepinephrine . These hormones increase blood pressure, increase heart function, dilate the bronchial tubes, and increase blood sugar levels. When at rest, they constantly release small amounts of catecholamines. Influenced stressful situation the secretion of adrenaline and norepinephrine by the cells of the adrenal medulla increases sharply.

The resting membrane potential is a deficiency of positive electric charges inside the cell, arising due to the leakage of positive potassium ions from it and the electrogenic action of the sodium-potassium pump.

Action potential (AP). All stimuli acting on the cell primarily cause a decrease in PP; when it reaches a critical value (threshold), an active propagating response—PD—occurs. AP amplitude approximately = 110-120 mv. A characteristic feature of AP, which distinguishes it from other forms of cell response to stimulation, is that it obeys the “all or nothing” rule, i.e., it occurs only when the stimulus reaches a certain threshold value, and a further increase in the intensity of the stimulus no longer affects amplitude, nor on the duration of AP. The action potential is one of the most important components of the excitation process. In nerve fibers it ensures the conduction of excitation from sensory endings ( receptors) to the body nerve cell and from it - to synaptic endings located on various nerve, muscle or glandular cells. The conduction of PD along nerve and muscle fibers is carried out by the so-called. local currents, or currents of action that arise between the excited (depolarized) and the resting sections of the membrane adjacent to it.

Postsynaptic potentials (PSPs) arise in areas of the membrane of nerve or muscle cells directly adjacent to synaptic terminals. They have an amplitude of the order of several mv and duration 10-15 msec. PSPs are divided into excitatory (EPSP) and inhibitory (IPSP).

Generator potentials arise in the membrane of sensitive nerve endings - receptors. Their amplitude is on the order of several mv and depends on the strength of stimulation applied to the receptor. The ionic mechanism of generator potentials has not yet been sufficiently studied.

Action potential

An action potential is a rapid change membrane potential, which occurs when nerve, muscle and some glandular cells are excited. Its occurrence is based on changes in the ionic permeability of the membrane. In the development of an action potential, four successive periods are distinguished: local response, depolarization, repolarization and trace potentials.

Irritability is the ability of a living organism to respond to external influence changes in their physicochemical and physiological properties. Irritability manifests itself in changes in the current values ​​of physiological parameters that exceed their shifts at rest. Irritability is a universal manifestation of the vital activity of all biosystems. These environmental changes causing a reaction organism, can include a wide repertoire of reactions, ranging from diffuse protoplasmic reactions in protozoa to complex, highly specialized reactions in humans. In the human body, irritability is often associated with the property of nervous, muscle and glandular tissues to respond in the form of producing a nerve impulse, muscle contraction or secretion of substances (saliva, hormones, etc.). In living organisms that lack a nervous system, irritability can manifest itself in movements. Thus, amoebas and other protozoa leave unfavorable solutions with high salt concentrations. And plants change the position of the shoots to maximize light absorption (stretch towards the light). Irritability is a fundamental property of living systems: its presence is a classic criterion by which living things are distinguished from nonliving things. The minimum magnitude of the stimulus sufficient for the manifestation of irritability is called the perception threshold. The phenomena of irritability in plants and animals have much in common, although their manifestations in plants differ sharply from the usual forms of motor and nervous activity animals

Laws of irritation of excitable tissues: 1) law of force– excitability is inversely proportional to the threshold force: the greater the threshold force, the less excitability. However, for excitation to occur, the force of stimulation alone is not enough. It is necessary that this irritation last for some time; 2) law of time action of the stimulus. When the same force is applied to different tissues, different durations of irritation will be required, which depends on the ability of a given tissue to manifest its specific activity, that is, excitability: the least time will be required for tissue with high excitability and the longest time for tissue with low excitability. Thus, excitability is inversely proportional to the duration of the stimulus: the shorter the duration of the stimulus, the greater the excitability. The excitability of tissue is determined not only by the strength and duration of irritation, but also by the rate (speed) of increase in the strength of irritation, which is determined by the third law - law of the rate of increase in the strength of irritation(the ratio of the strength of the stimulus to the time of its action): the greater the rate of increase in the strength of stimulation, the less excitability. Each tissue has its own threshold rate of increase in the strength of irritation.

The ability of a tissue to change its specific activity in response to irritation (excitability) is inversely dependent on the magnitude of the threshold force, the duration of the stimulus and the speed (speed) of increase in the strength of irritation.

The critical level of depolarization is the value of the membrane potential, upon reaching which an action potential occurs. The critical level of depolarization (CLD) is such a level electric potential membranes of an excitable cell, from which the local potential passes into the action potential.

A local response occurs to subthreshold stimuli; spreads over 1-2 mm with attenuation; increases with increasing stimulus strength, i.e. obeys the law of “force”; sums up - increases with repeated frequent subthreshold stimulation 10 - 40 mV increases.

The chemical mechanism of synaptic transmission, compared to the electrical one, more effectively provides the basic functions of the synapse: 1) one-way signal transmission; 2) signal amplification; 3) convergence of many signals on one postsynaptic cell, plasticity of signal transmission.

Chemical synapses transmit two types of signals - excitatory and inhibitory. In excitatory synapses, the neurotransmitter released from presynaptic nerve endings causes an excitatory post-synaptic potential in the postsynaptic membrane - local depolarization, and in inhibitory synapses - inhibitory postsynaptic potential, as a rule, hyperpolarization. The decrease in membrane resistance that occurs during an inhibitory postsynaptic potential short-circuits the excitatory postsynaptic current, thereby weakening or blocking the transmission of excitation.

Chemical composition of the cell

Organisms are made up of cells. Cells different organisms have similar chemical composition. About 90 elements are found in the cells of living organisms, and about 25 of them are found in almost all cells. According to their content in the cell, chemical elements are divided into three large groups: macroelements (99%), microelements (1%), ultramicroelements (less than 0.001%).

Macroelements include oxygen, carbon, hydrogen, phosphorus, potassium, sulfur, chlorine, calcium, magnesium, sodium, iron. Microelements include manganese, copper, zinc, iodine, fluorine. Ultramicroelements include silver, gold, bromine, selenium.

A deficiency of any element can lead to illness and even death of the body, since each element plays a specific role. Macroelements of the first group form the basis of biopolymers - proteins, carbohydrates, nucleic acids, as well as lipids, without which life is impossible. Sulfur is part of some proteins, phosphorus is part of nucleic acids, iron is part of hemoglobin, and magnesium is part of chlorophyll. Calcium plays an important role in metabolism. Some of the chemical elements contained in the cell are part of inorganic substances - mineral salts and water.

Mineral salts are found in the cell, as a rule, in the form of cations (K +, Na +, Ca 2+, Mg 2+) and anions (HPO 2-/4, H 2 PO -/4, CI -, HCO 3), the ratio of which determines the acidity of the environment, which is important for the life of cells.

Of the inorganic substances in living nature, plays a huge role water.
It makes up a significant mass of most cells. A lot of water is contained in the cells of the brain and human embryos: more than 80% water; in adipose tissue cells - only 40.% By old age, the water content in cells decreases. A person who has lost 20% of water dies. The unique properties of water determine its role in the body. It is involved in thermoregulation, which is caused by the high heat capacity of water - consumption large quantity energy when heated. Water - good solvent. Due to their polarity, its molecules interact with positively and negatively charged ions, thereby promoting the dissolution of the substance. In relation to water, all cell substances are divided into hydrophilic and hydrophobic.

Hydrophilic(from Greek hydro- water and filleo- love) are called substances that dissolve in water. These include ionic compounds (for example, salts) and some non-ionic compounds (for example, sugars).

Hydrophobic(from Greek hydro- water and Phobos- fear) are substances that are insoluble in water. These include, for example, lipids.

Water plays a big role in chemical reactions, occurring in the cell in aqueous solutions. It dissolves metabolic products that the body does not need and thereby promotes their removal from the body. The high water content in the cell gives it elasticity. Water facilitates the movement of various substances within a cell or from cell to cell.

Inorganic compounds in the human body.

Water. Of the inorganic substances that make up the cell, the most important is water. Its amount ranges from 60 to 95% of the total cell mass. Water plays a vital role in the life of cells and living organisms in general. In addition to the fact that it is part of their composition, for many organisms it is also a habitat. The role of water in a cell is determined by its unique chemical and physical properties, associated mainly with the small size of its molecules, the polarity of its molecules and their ability to form hydrogen bonds with each other. Water as a component of biological systems performs the following essential functions: 1- Water- universal solvent for polar substances, such as salts, sugars, alcohols, acids, etc. Substances that are highly soluble in water are called hydrophilic. 2- Water does not dissolve non-polar substances and does not mix with them, since it cannot form hydrogen bonds with them. Substances that are insoluble in water are called hydrophobic. Hydrophobic molecules or parts of them are repelled by water, and in its presence they are attracted to each other. Such interactions play an important role in ensuring the stability of membranes, as well as many protein molecules, nucleic acids, and a number of subcellular structures. .3- Water has a high specific heat capacity. 4- Water is characterized high heat of vaporization, i.e. e. the ability of molecules to carry away a significant amount of heat while simultaneously cooling the body. 5- It is exclusively characteristic of water high surface tension. 6- Water provides movement of substances in the cell and body, absorption of substances and excretion of metabolic products. 7- In plants, water determines turgor cells, and in some animals performs support functions, being a hydrostatic skeleton (round and annelids, echinoderms). 8- Water is an integral part lubricating fluids(synovial - in the joints of vertebrates, pleural - in pleural cavity, pericardial - in the pericardial sac) and slime(facilitate the movement of substances through the intestines, create a moist environment on the mucous membranes of the respiratory tract). It is part of saliva, bile, tears, sperm, etc.

Mineral salts. In living organisms modern methods chemical analysis 80 elements detected periodic table. By quantitative composition they are divided into three main groups. Macroelements make up the bulk of organic and inorganic compounds, their concentration ranges from 60% to 0.001% of body weight (oxygen, hydrogen, carbon, nitrogen, sulfur, magnesium, potassium, sodium, iron, etc.). Microelements - predominantly ions heavy metals. Contained in organisms in the amount of 0.001% - 0.000001% (manganese, boron, copper, molybdenum, zinc, iodine, bromine). The concentration of ultramicroelements does not exceed 0.000001%. Their physiological role in organisms has not yet been fully elucidated. This group includes uranium, radium, gold, mercury, cesium, selenium and many other rare elements. Not only the content, but also the ratio of ions in the cell is significant. The difference between the amounts of cations and anions on the surface and inside the cell ensures the occurrence action potential , what underlies the occurrence of nervous and muscle excitation.

The bulk of the tissues of living organisms inhabiting the Earth are made up of organogenic elements: oxygen, carbon, hydrogen and nitrogen, from which organic compounds are mainly built - proteins, fats, carbohydrates.

Excretory functions are carried out by the gastrointestinal tract; external respiratory organs; sweat, sebaceous, lacrimal, mammary and other glands, as well as kidneys (Fig. 1.14), with the help of which decay products are removed from the body.

Rice. 1.14.

An important organ of the excretory system is the kidneys, which are directly involved in the regulation of water and mineral metabolism, ensure acid-base balance (balance) in the body, and form biologically active substances, such as renin, which affects blood pressure levels.

Chemical structure of the human body

The human body contains organic and inorganic substances. Water makes up 60% of body weight, and minerals average 4%. Organic substances are represented mainly by proteins (18%), fats (15%), carbohydrates (2-3%). All substances of the body, as well as inanimate nature, are built from atoms of various chemical elements.

Of the 110 known chemical elements, the human body contains mainly 24 (Table 1.2). Depending on their quantity in the body, chemical elements are divided into basic, macro-, micro- and ultramicroelements.

Note that individual chemical elements accumulate unevenly in various organs and tissues of the human body. For example, bone tissue accumulates calcium and phosphorus, blood - iron, thyroid gland - iodine, liver - copper, skin - strontium, etc.

The quantitative and qualitative composition of the chemical elements of the body depends both on external environmental factors (nutrition, ecology, etc.) and on the functions of individual organs.

Macronutrients and their significance in the body is determined by the fact that they are necessary for the implementation of many biological

Table 1.2

Chemical elements that make up the human body

(according to N.I. Volkov)

	Chemical element
Basic	Oxygen (O)		Total 99.9%
elements	Carbon (C)
	Hydrogen (H) Nitrogen (N)
Macronutrients	Calcium (Ca)
	Phosphorus (P)
	Sodium (Na)
	Magnesium (Mg)
Micro and ultra
microelements	Fluorine (F) Silicon (Si) Vanadium (V) Chromium (Cr) Manganese (Mn) Iron (Fe) Cobalt (Co) Copper (Cu) Zinc (Zn) Selenium (Se)
	Molybdenum (Mo) Iodine (J)

chemical processes. They are essential nutritional factors, as they are not produced in the body. The mineral content is relatively low (4-10% of dry body weight) and depends on the functional state of the body, its age, nutritional status and environmental conditions.

Calcium in the human body makes up 40% of the total amount of all minerals. It is part of teeth and bones, giving them strength. A decrease in the flow of calcium into the body’s tissues leads to its release from the bones, which causes a decrease in their strength (osteoporosis), as well as dysfunction of the nervous system, blood circulation, including muscle activity.

Phosphorus makes up 22% of the amount of all minerals. About 80% of its amount is found in tissues in the form of calcium phosphate. Phosphorus plays an important role in the processes of energy formation, since in the form of phosphoric acid residues it is included in the composition of energy sources - ATP, ADP, CrP, various nucleotides, as well as in the composition of hydrogen carriers and some metabolic products.

Sodium and potassium found in all tissues and fluids of the body. Potassium is predominantly inside cells, sodium - in the extracellular space. Both are involved in the conduction of nerve impulses, tissue stimulation, creation of osmotic blood pressure (osmotic active ions), maintaining acid-base balance, and also affect the activity of the enzymes Naf, Kf, ATPase. These elements regulate water exchange in the body: sodium ions retain water in tissues and cause swelling of proteins (formation of colloids), which leads to edema; Potassium ions, on the contrary, enhance the excretion of sodium and water from the body. Insufficiency of sodium and potassium in the body causes disruption of the central nervous system, muscle contractile apparatus, cardiovascular and digestive systems, which leads to a decrease in physical performance.

Magnesium in the tissues of the body is in a certain ratio with calcium. It affects energy metabolism, protein synthesis, since it is an activator of many enzymes, which are called kinases and perform the function of transferring a phosphate group from an ATP molecule to various substrates. Magnesium also affects muscle excitability and helps remove cholesterol from the body.

Its deficiency leads to increased neuromuscular excitability, the appearance of cramps and muscle weakness.

Chlorine refers to osmotic active substances and is involved in the regulation of osmotic pressure and water metabolism of body cells, used for the formation of hydrochloric acid(HC1) - an obligatory component of gastric juice. Lack of chlorine in the body can lead to a decrease in blood pressure, contributes to myocardial infarction, and causes fatigue, irritability, and drowsiness.

Micro- and ultra-microelements. Iron plays a very important role in the processes of aerobic energy formation in the body. It is part of the proteins hemoglobin and myoglobin, which transport 0 2 and CO 2 in the body, as well as cytochromes - components of the respiratory chain in which the processes of biological oxidation and formation of LTP occur. Iron deficiency in the body leads to impaired formation of hemoglobin and a decrease in its concentration in the blood. This can lead to the development of iron deficiency anemia, a decrease in the oxygen capacity of the blood and a sharp decrease in physical performance.

Zinc is part of many energy metabolism enzymes, as well as carbonic anhydrase enzymes, which catalyze the exchange of H 2 CO 3 and lactate dehydrogenase, which regulate the oxidative breakdown of lactic acid. It participates in the creation of the active structure of the insulin protein - the pancreatic hormone, and enhances the effect of pituitary (gonadotropic) and gonadal hormones (testosterone, estrogen) on the processes of protein synthesis. Zinc deficiency can lead to weakened immunity, loss of appetite, and slower growth processes.

Copper promotes body growth, enhances hematopoietic processes, affects the rate of glucose oxidation and glycogen breakdown. It is part of the enzymes of the respiratory chain, increases the activity of lipase, pepsin and other enzymes.

Manganese, cobalt, chromium are used by the body as activators of many enzymes that take part in the metabolism of carbohydrates, proteins, lipids, cholesterol synthesis, affect hematopoietic processes, and increase the body's defenses. Chromium also enhances protein synthesis, exhibiting an anabolic effect. Manganese is involved in the synthesis of vitamin C, which is very important for athletes.

Iodine necessary for the construction of thyroid hormones - thyroxine and its derivatives. Its deficiency in the body leads to diseases of the thyroid gland (endemic goiter): 150 mcg satisfies the body's daily need for iodine.

Fluorine is part of tooth enamel and dentin. Excess of it suppresses processes tissue respiration and fatty acid oxidation. Insufficient fluoride causes dental disease (caries), and excess causes enamel staining (fluorosis).

Selenium has an antioxidant effect, i.e. protects cells from excessive lipid peroxidation, which leads to the accumulation of harmful hydrogen peroxides in tissues. The latest research suggests that selenium strengthens the immune system and prevents the occurrence of cancer cells, and is involved in the transfer of genetic information.

Remember the substances that organisms need for their life. What role do aqueous solutions play in nature and in human life? What type chemical bond exists in a water molecule? What are ions and how are they formed?

Chemical elements of living organisms

Plant and animal cells contain more than 70 chemical elements. But the cell does not contain any special elements characteristic only of living nature. The same elements are found in inanimate nature.

All chemical elements, according to their content in a living cell, are divided into three groups: macroelements, microelements and ultramicroelements.

The elements O, C, H, N are sometimes considered as a separate group of organogenic elements due to the fact that they are part of all organic substances and make up up to 98% of the mass of a living cell.

Inorganic substances of living organisms

While studying chemistry, you learned about such groups of substances as acids, salts, oxides, etc. All of them are common in inanimate nature, outside living organisms. That's why they are called inorganic substances. But this does not mean that they do not exist in living organisms at all. They exist and play a very important role in life processes.

Inorganic substances usually enter living organisms from the external environment with food (in animals) or with a water solution through the surface of the body (in plants, fungi and bacteria). But in some cases, living organisms can synthesize them on their own. For example, stomach cells in vertebrates synthesize chloride acid. This allows you to digest food more efficiently, as many digestive enzymes work in an acidic environment. Many predatory mollusks also independently produce sulfate acid in their salivary glands. This acid can destroy the shells and outer coverings of their victims.

Functions of inorganic substances in the cell

Inorganic substances	Functions in the cell
Hydrogen cations (H+)	Provide acid-base balance (maintain the constancy of the intracellular environment)
Cations and anions of soluble salts (Na+, K+, Cl)	Create a potential difference between the contents of the cell and the extracellular environment, ensuring the conduction of a nerve impulse
Slightly soluble calcium and phosphorus salts	Form supporting structures (for example, in the bones of vertebrates)
Metal element ions	They are components of many hormones, enzymes and vitamins or participate in their activation
Complex inorganic compounds of Nitrogen, Calcium and Phosphorus	Participate in the synthesis of organic molecules

Inorganic compounds can be found in living organisms both in dissolved (in the form of ions) and in undissolved form. Many salts are present in dissolved forms.

Insoluble inorganic compounds are also important for living organisms. For example, calcium and phosphorus salts are part of the animal skeleton and provide its strength (Fig. 2.1, p. 10). Without such substances, it is impossible for a person to form healthy teeth.

Various structures of animal organisms can also be formed from inorganic substances (Fig. 2.2).

Properties of water

The properties of water are determined by the structural features of its molecule, as well as the bonds of molecules with each other.

As you already know, in a water molecule ( chemical formula- H 2 O) there is a covalent polar bond between the Hydrogen and Oxygen atoms (Fig. 2.3). This means that a partial negative charge (S -) is formed on the Oxygen atom, and a positive charge (S+) is formed on the Hydrogen atoms. The positively charged Hydrogen atom of one water molecule is attracted to the negatively charged Oxygen atom of another water molecule. This bond is called a hydrogen bond.

A hydrogen bond is approximately 15-20 times weaker than a covalent bond. Therefore, the hydrogen bond is relatively easily broken, which happens, for example, when water evaporates. In the liquid state, hydrogen bonds between water molecules are constantly breaking and forming anew.

Biological role of water

In living organisms, water performs many functions: solvent medium, transport, metabolic, thermoregulatory, structural.

Water is a universal solvent. Substances involved in most biological reactions are found in an aqueous solution in the body.

The transport role of water is very important for cells and organisms in general. Dissolved substances, along with water, can be transferred from one part of the cell to another. And between various parts In multicellular organisms, they are transported as part of special fluids (for example, in the blood). The evaporation of water by plant leaves causes it to move upward from the roots. At the same time, substances dissolved in water also move.

Water molecules perform a metabolic function when they participate in metabolic reactions (they are called biochemical reactions). The thermoregulatory function of water is extremely important for maintaining the body temperature of organisms. When, for example, a person sweats, water evaporates, lowering his body temperature.

The structural function of water is clearly visible in plants and some invertebrate animals. Plants maintain the shape of their leaves and herbaceous stems due to increased pressure in the cells filled with water. And many worms maintain their body shape high blood pressure water in body cavities.

Living organisms contain both organic and inorganic substances. Inorganic substances are water, salts, acids and other compounds. They play an important role in the life of living organisms. Water creates the environment in which metabolic reactions occur. Other inorganic substances are involved in the formation of the skeleton, the functioning of the nervous, digestive and other systems of the body.

Test your knowledge

1. What inorganic substances are found in living organisms? 2. Prove with examples that the properties of water are of great importance for living cells. 3. What functions can acids perform in living organisms? 4*. What consequences can the loss of Na salts lead to for the human body?

This is textbook material