Cardiovascular system. Heart.

Structure, functions of system of a circulation.

The circulation system consists of heart and pots: vascular and lymphatic.

The major importance of system of a circulation consists in supply by blood of organs and tissues. Heart at the expense of the delivery activity provides blood locomotion on the closed system of pots.

Blood continuously moves on pots that gives the chance to it to carry out all vital functions, namely transport (transmission oxygen and nutrients), protective (contains antibodies), regulatory (contains enzymes, hormones and other biologically active materials).

Heart

Anatomical constitution of heart. A cardial cycle. Value of the valval apparatus.

Human heart - a hollow muscular organ. Heart shares a continuous erect septum on two half: left and right. The second septum going in a horizontal direction, forms four lumens in heart: the top lumens - auricles, inferior - ventricles. The mass of heart of newborns is on the average peer 20 gm. The mass of heart of the adult human compounds 0,425-0,570 kg. The length of heart at the adult human reaches 12-15sm, the cross-section dimension 8-10 sm, anteroposterior 5-8 sm. The mass and the heart dimensions are enlarged at some diseases (heart diseases), and also at humans, long time engaged in intense physical work or sports.

The heart side consists of three layers: intrinsic, average and outside. The inside layer is presented by an endothelial cover (endocardium) which covers an intrinsic surface of heart. The centre (myocardium) consists from cross-section - a striatal muscle. The musculation of auricles is unbound from a musculation of ventricles a connective tissue septum which consists of dense fibrous fibers - the fibrous ring. The muscular layer of auricles is educed much more weakly, than a muscular layer of ventricles that is bound to features of functions which are carried out by each department of heart. The outside surface of heart is covered by a serous cover (epicardium) which is an intrinsic leaf of a pericardiac ascus - a pericardium. Under a serous cover the largest coronary arteries and veins which provide blood supply of tissues of heart, and also the big clump of the excitatory cells and nerve fibrils, innervating heart are located.

Pericardium and its value. The pericardium (a warm shirt) surrounds heart as the pouch and provides its free locomotion. The pericardium consists of two leaves: intrinsic (epicardium) and outside, turned towards thorax organs. Between pericardium leaves there is the cleft filled with serous fluid. Fluid reduces a friction of leaves of a pericardium. The pericardium confines a distention of heart to blood filling it and is a leg for coronary pots.

In heart distinguish two kinds of valves - atrioventricular (auricular - ventricular) and semilunar. Atrioventricular valves settle down between auricles and the conforming ventricles. The left auricle from a left ventricle abjoints the bicuspid valve. On border between the right auricle and a right ventricle there is a three-cuspidate valve. Edges of valves are bridged to papillary muscles of ventricles thin and strong tendinous strands which sag in their lumen.

Semilunar valves abjoint an aorta from a left ventricle and a pulmonary fulcrum from a right ventricle. Each semilunar valve consists of three cusps (pockets) in which centre there are thickenings - nodules. These nodules, adjoining, to each other, provide full hermetic sealing at closure of semilunar valves.

Cardial cycle and its phases. In heart activity it is possible to secure two phases: a systole (reduction) and a diastole (release phenomenon). The Auricular systole is more weak and shorter than a ventricular systole: in heart of the human it lasts 0,1 sec, and the ventricular systole - 0,3 sec an auricular diastole occupies 0,7sec, and ventricles - 0,5 sec. The general pause (a simultaneous auricular diastole and ventricles) hearts lasts 0,4 sec. All cardial cycle proceeds 0,8sec. Duration of various phases of a cardial cycle depends on frequency of warm reductions. At more frequent warm reductions activity of each phase decreases, especially diastoles.

Value of the valval apparatus in blood locomotion through heart chambers. During an auricular diastole atrioventricular valves are open also the blood arriving from the conforming pots, fills not only their lumens, but also ventricles. During an auricular systole ventricles are completely filled with blood. Anatropic locomotion of blood in hollow and pulmonary veins is thus excluded. It is bound by that the musculation of auricles forming of a mouth of veins first of all is reduced. In process of filling of lumens of ventricles by blood of a cusp of atrioventricular valves are densely closed and abjoint a lumen of auricles from ventricles. As a result of reduction of papillary muscles of ventricles at the moment of their systole tendinous strands of cusps of atrioventricular valves stretch and do not allow to them to be turned out towards auricles. To the extremity of a ventricular systole pressure in them becomes more pressure in an aorta and pulmonary a fulcrum.

It promotes discovering of semilunar valves, and blood from ventricles arrives in the conforming pots. During a diastole of ventricles pressure in them sharply drops, that frames conditions for anatropic locomotion of blood towards ventricles. Thus blood fills pockets of semilunar valves and causes their articulation.

Thus, discovering and closure of valves of heart is bound to change of size of pressure in cardial cavities.

Basic physiological properties of a cardiac muscle

The cardiac muscle, as well as sceletal, possesses excitability, ability to spend excitation and contractility.

Excitability of a cardiac muscle. The cardiac muscle is less erethitic, than sceletal. For excitation occurrence in a cardiac muscle it is necessary to apply stronger stimulus, than to the sceletal. It is established, that the size of reaction of a cardiac muscle does not depend on force of put borings (electrical, mechanical, chemical etc.). The cardiac muscle is as much as possible reduced both on threshold, and to stronger on size a boring.

Conductivity. Excitation waves are spent on fibers of a cardiac muscle and a so-called special tissue of heart with unequal rate. Excitation on fibers of muscles of auricles extends with rate 0,8-1,0 met/sec, on fibers of muscles of ventricles - 0,8-0,9 met/sec, on a special tissue of heart-2,0-4,2 met/sec.

Contractility. Contractility of a cardiac muscle has the features. The first reduce muscles an auricle, then - papillary muscles and subendocardial a layer of muscles of ventricles. Further reduction covers also an inside layer of ventricles, providing with that locomotion of blood from lumens of ventricles in an aorta and a pulmonary fulcrum.

Physiological features of a cardiac muscle is the extended refractory season and the automaticity.

The refractory season. In heart unlike other erethitic tissues there is considerably expressed and extended refractory season. It is characterised by sharp depression of excitability of a tissue during its activity. Excrete the absolute and relative refractory season. During the absolute refractory season of what force would not put a boring on a cardiac muscle, she does not answer it with excitation and reduction. It corresponds on time to a systole and the beginning of an auricular diastole and ventricles. During the relative refractory season excitability of a cardiac muscle gradually comes back to initial level. In this season the muscle can answer a stimulus more strongly the threshold. It is found during an auricular diastole and ventricles.

Myocardium reduction proceeds nearby 0.3 sec, on time approximately coincides with a refractory phase. Hence, in reduction heart is incapable to react to stimuluses. Thanks to the expressed river of the item which lasts more than the systole season, a cardiac muscle it is incapable of tetanic (long) reduction and makes the work as the solitary muscular contraction.

The heart automaticity. Out of an organism under certain conditions heart is capable to be reduced and relaxed, keeping a correct rhythm. Hence, the cause of reductions of an isolated heart lays in him. Ability of heart rhythmicallies to be reduced under the influence of the impulses arising in him, wears the automaticity name.

In heart distinguish the working musculation presented by a transversely striated muscle, and atypical, or special, the tissue in which arises and is spent excitation.

At the human the atypical tissue consists from:

• the sinuauricular knot which is settling down on a back side of the right auricle at a place of a confluence of venas cava;
• atrioventricular (atrial ventricular) knot being in the right auricle near to a septum between auricles and ventricles;

bundle of His (atrial ventricular fascicle), departing from atrioventricular knot one fulcrum. Bundle of His, having passed through a septum between auricles and ventricles, shares on two legs going to the right and left ventricles. Comes to an end bundle of His in a depth of muscles Purkinje fibres. Bundle of His-it the unique muscular ponticulus bridging auricles with ventricles.

The sinuauricular knot is the leader in activity hearts (pacemaker), in it there are the impulses defining frequency of reductions of heart. In norm atrioventricular knot and bundle of His are only transmitters of excitation from leading knot to a cardiac muscle. However ability to the automaticity is inherent in them, it only is expressed to a lesser degree, than at sinuauricular knot, and shows only in the conditions of a pathology.

The atypical tissue consists of the few-differentiated muscular fibers. In the field of sinuauricular knot the significant amount of the excitatory cells, nerve fibrils and their terminals which here form the excitatory network is revealed. Nerve fibrils approach to knots of an atypical tissue from wandering and sympathetic nerves.

Heart rhythm. Indicators of warm activity.

Heart rhythm and the factors influencing it. The Heart rhythm, i.e. The quantity of reductions in 1 min, depends mainly on a functional state wandering and sympathetic nerves. At excitation of sympathetic nerves frequency of warm reductions increases. This phenomenon wears the tachycardia name. At excitation of vagus nerves frequency of warm reductions decreases - a bradycardia.

The heart rhythm is influenced also by a state of a cortex of a brain: at intensifying of inhibition the heart rhythm is slowed down, at intensifying of excitative process is suscitated.

The heart rhythm can variate under the influence of humoral influences, in particular temperatures of blood, afferent to heart. In experiences it has been shown, that the aboriginal boring heat of range of the right auricle (localisation of leading knot) conducts to heart rhythm increase at refrigerating of this range of heart the inverse effect is observed. The aboriginal boring is not reflected by heat or a cold of other fields of heart in frequency of warm reductions. However it can variate rate of carrying out of exaltations on conductive system of heart and to be reflected in force of warm reductions.

Frequency of warm reductions at the healthy human is in dependence from age. These data are presented in the table.

Indicators of warm activity. Cardiac performance indicators are systolic and minute volume of heart.

Systolic, or shock, the quantity of the blood, which heart throws out volume of heart-it in the conforming pots at each reduction. The size of systolic volume depends on the dimensions of heart, a myocardium and organism state. At the adult healthy human at relative rest the systolic volume of each ventricle compounds approximately 70-80 ml. Thus, at reduction of ventricles in arterial system 120-160 ml of blood arrive.

The minute volume of heart-it quantity of the blood, which heart throws out in a pulmonary fulcrum and an aorta for 1 minute Minute volume of heart is a product of size of systolic volume on frequency of warm reductions 1 minute On the average minute volume compounds 3-5 l.

The systolic and minute volume of heart characterises activity of all apparatus of a circulation.

Choronomic implications of activity of heart

How it is possible to define a cardiac performance without special equipment?

There are data on which doctor judges a cardiac performance on choronomic implications of its activity which concern an apical beat, warm tints. More in detail about these data:

Apical beat. Heart during a ventricular systole makes gyral locomotion, turning from left to right. The heart apex rises and presses on a thorax in the field of the fifth intercostal space. During a systole heart becomes very dense, therefore on an intercostal space it is possible to see pressing of an apex of heart (a protrusion, a diverticulum), especially at thin subjects. The apical beat can be palpated to (palpate) and by that to define its border and force.

Warm tints are the sound phenomena arising in working heart. Distinguish two tints: 1-systolic and 2-diastolic.

Systolic tint. Atrioventricular valves take part in a parentage of this tint mainly. During a ventricular systole atrioventricular valves are occluded, and fluctuations of their cusps and the tendinous strands attached to them cause 1 tint. Besides, the sound phenomena which arise at reduction of muscles of ventricles take part in a parentage of 1 tint. On the sound features 1 tint lingering and low.

The second sound arises in the beginning of a diastole of ventricles during a protodiastolic phase when there is a closure of semilunar valves. Fluctuation of cusps of valves thus is a source of the sound phenomena. Under the sound characteristic 2 tint short and high.

Also it is possible to judge a cardiac performance on the electrical phenomena arising in it. Them name biological potentials of heart and receive by means of the electrocardiograph. They wear the electrocardiogram name.

Regulation of warm activity

Any activity of an organ, tissue, cell is regulated by is excitatory-humoral pathes.

Nervous control of activity of heart

Influence of the excitatory system on heart activity is carried out at the expense of wandering and sympathetic nerves. These nerves concern vegetative excitatory system. Vagus nerves go to heart from the kernels located in myelencephalon at the bottom of IV ventricle. Sympathetic nerves approach to heart from the kernels localised in lateral horns of a spinal cord (I-V thoracal segments). Wandering and sympathetic nerves terminate in sinuauricular and atrioventricular knots, also in a heart musculation. As a result at excitation of these nerves changes in the automaticity of sinuauricular knot, rate of carrying out of excitation on conductive system of heart, in intensity of warm reductions are observed.

Weak borings of vagus nerves lead to heart rhythm retardation, strong - cause a stopping of warm reductions. After the termination of a boring of vagus nerves heart activity can be recovered again.

At a boring of sympathetic nerves there is an increase of a heart rhythm and force of warm reductions is enlarged, excitability and a cardiac muscle tonus, and also rate of carrying out of excitation raises.

Tonus of the centres of cardiac nerves. The centres of warm activity presented by kernels wandering and sympathetic nerves, always are in a state of a tonus which can be enhanced or relaxed depending on conditions of existence of an organism.

The tonus of the centres of cardiac nerves depends on the eisodic influences going from mehano - and chemoceptors of heart and pots, an internals, receptors of a skin and mucosas. The tonus of the centres of cardiac nerves is affected also by humoral factors.

There are also certain features in work of cardiac nerves. One of a bottom shows that at rising of excitability of neurones of vagus nerves excitability of kernels of sympathetic nerves decreases. Such functionally interconnected attitudes centre to centre cardiac nerves promote the best adaptation of activity of heart to conditions of existence of an organism.

Reflex influences on heart activity:

Reflex influences on heart activity are carried out from the heart. Intracardiac reflex influences show in changes of force of warm reductions. So, it is established, that the distention of a myocardium of one of heart departments leads to change of force of reduction of a myocardium of its other department, hemodynamically with it separated. For example, at a distention of a myocardium of the right auricle intensifying of work of a left ventricle is observed. This effect can be result only reflex intracardiac influences.

Extensive communications of heart with various departments of the excitatory system frame conditions for various reflex influences on activity of the heart, carried out through vegetative excitatory system.

In sides of pots the numerous receptors possessing ability to provoke at change of size of a blood pressure and a chemical compound of blood settle down. Especially many receptors are available in the field of an aortic arch and carotid sine (small dilating, a vascular wall diverticulum on an intrinsic carotid artery). They still name vascular reflexogenic regions.

At reduction of arterial pressure there is an excitation of these receptors, and impulses from them arrive in myelencephalon to kernels of vagus nerves. Under the influence of nervous impulses excitability of neurones of kernels of vagus nerves that enhances influence of sympathetic nerves on heart (about this feature I already decreases spoke above). As a result of influence of sympathetic nerves the heart rhythm and force of warm reductions are enlarged, pots are narrowed, that is one of the causes of normalisation of arterial pressure.

At augmentation of arterial pressure the nervous impulses which have arisen in receptors of range of an aortic arch and carotid sine, enhance activity of neurones of kernels of vagus nerves. Influence of vagus nerves on heart is found, the heart rhythm is slowed down, warm reductions are relaxed, pots extend, that also is one of the causes of restoration of initial level of arterial pressure.

Thus, the hearts which are carried out from receptors of range of an aortic arch and carotid sine, it is necessary to carry reflex influences on activity to the mechanisms of self-control showing in reply to change of size of arterial pressure.

Excitation of receptors of an internals if it strong enough, can variate heart activity.

It is naturally necessary to note influence of a cortex of a brain on a cardiac performance. Influence of a cortex of a brain on heart activity. The brain cortex regulates and корригирует heart activity through wandering and sympathetic nerves. The proof of influence of a cortex of a brain on heart activity is possibility of formation of conditioned reflexes. Conditioned reflexes on heart are easily enough formed at the human, and also at animals.

It is possible to give an example experience with a dog. At a dog formed a conditioned reflex on heart, using as a prearranged signal flash of light or a sound boring. An unconditional stimulus were pharmacological materials (for example, Morphinum), hearts typically changing activity. Alterations in a cardiac performance supervised by electrocardiogram registration. It has appeared, that after 20-30 injections of Morphinum a complex of the boring, bound to introduction of this preparation (light flash, a laboratory situation etc.), led to a conditioned-reflex bradycardia. Heart rhythm retardation was observed and when to an animal instead of Morphinum introduced isotonic solution of Sodium chloridum.

At the human various emotional states (excitement, pavor, anger, a rage, pleasure) are accompanied by respective alterations in heart activity. It also testifies to influence of a cortex of a brain on a cardiac performance.

Humoral influences on heart activity

Humoral influences on heart activity are realised by the hormones, some electrolytes and other highly active materials which are arriving in blood and being products of vital activity of many organs and tissues of an organism.

Acetylcholinum and Noradrenalinum - mediators of the excitatory system - make the expressed impact on a cardiac performance. Acetylcholinum action inseparably from functions of parasympathetic nerves as it is synthesised in their terminals. Acetylcholinum reduces excitability of a cardiac muscle and force of its reductions.

For regulation of activity of heart catecholamins which Noradrenalinum (mediator) and adrenaline (hormone) concern have great value. Catecholamins make on heart the impact similar to influence of sympathetic nerves. Catecholamins suscitate metabolic processes in heart, raise a power consumption and by that enlarge requirement of a myocardium for oxygen. Adrenaline simultaneously causes dilating of coronary pots that promotes enriching of a food of heart.

In regulation of activity of heart especially important role is played by adrenal hormones and a thyroid gland. Adrenal hormones - mineralocorticoids - enlarge force of warm reductions of a myocardium. The thyroid gland hormone - a thyroxine - raises metabolic processes in heart and enlarges its sensitivity to influence of sympathetic nerves.

Veins

Phylums of veins, features of their constitution

In vascular system distinguish some kinds of pots: the main, resistive, true capillars, capacitor and shunting.

The main pots-it the largest arteries to which rhythmicallies the pulsing, changeable blood stream turns in more uniform and smooth. Blood moves to them from heart. Sides of these pots contain a little smoothly - muscular elements and many elastic fibers.

Resistive pots (resistance pots) include precapillary (fine arteries, arterioles) and postcapillary (venules and fine veins) resistance pots.

True capillars (metabolic pots) - the major department warmly - vascular system. Through thin sides of capillars there is an exchange between blood and tissues (a transcapillary exchange). Sides of capillars do not contain is smooth-muscular elements, they are formed by one layer of cells outside of which there is a thin is connective - a woven membrane.

Capacitor pots-venous department of warmly vascular system. Their sides are more thin and is softer than sides of arteries, also have in a lumen of pots valves. Blood moves to them from organs and tissues to heart. Capacitor these pots name because they contain approximately 70-80 % of all blood.

Shunting pots - the arteriovenous anastomosises providing a direct communication between fine arteries and veins bypassing a capillary bed.

Pressure of blood in various departments of a vascular bed

Blood locomotion on pots.

Pressure of blood in various departments of a vascular bed is unequal: in arterial system it above, in venous more low.

Bloody pressure-pressure of blood upon sides of veins. The normal blood pressure is necessary for blood circulation and appropriate supply by blood of organs and tissues, for intercellular lymph formation in capillars, and also for realisation of processes of secretion and an egestion.

The blood pressure size depends on three major factors: frequencies and forces of warm reductions; peripheric resistance sizes, i.e. A tonus of sides of pots, mainly arterioles and capillars; volume of circulating blood.

Distinguish arterial, venous and a blood capillary pressure.

Arterial blood pressure. The size of arterial pressure at the healthy human is enough constant, However it always is exposed to small fluctuations depending on phases of activity of heart and breath.

Distinguish systolic, diastolic, sphygmic and average arterial pressure.

Systolic (maximum) pressure reflects a state of a myocardium of a left ventricle of heart. Its size of 100-120 mm hg

Diastolic (minimum) pressure characterises degree of a tonus of arterial sides. It is equaled 60-80 mm hg

Pulse pressure is a difference between systolic and a diastolic pressure. Pulse pressure is necessary for discovering of semilunar valves during a ventricular systole. In norm pulse pressure compounds 35-55 mm hg If the systolic pressure becomes peer diastolic - blood locomotion will be impossible and there will come mors.

Average arterial pressure is equaled to the sum diastolic and 1/3 pulse pressure.

The size of arterial pressure is influenced by various factors: age, time of days, a state of an organism, the central excitatory system etc.

With the years the maximal pressure is enlarged in larger degree, than minimum.

Within days fluctuation of size of pressure is observed: in the afternoon it above, than at night.

Substantial increase of the maximum arterial pressure can be observed at a serious exercise stress, during sports meets, etc. After cessation of work or the terminal of competitions arterial pressure quickly comes back to initial indicators.

Rising of arterial pressure is called as a hypertonia. Dropping of arterial pressure is called as a hypotension. The hypotension can come at a venenating with narcotics, at strong traumas, extensive combustions, the big hemorrhages.

Arterial sphygmus. These are periodic dilatings and elongations of sides of the arteries, the bloods caused by entering in an aorta at a left ventricle systole. Sphygmus is characterised by a number of qualities which are defined by a palpation more often a radial artery in the inferior third of forearm where it is located most superficially;

Palpation define following qualities of sphygmus: frequency - quantity of impacts in 1 mines, rhythmicity - correct alternating of sphygmic impacts, filling - degree of change of volume of the artery, established on force of sphygmic impact, naprjazhenie-is characterised by force, which should be put to squeeze an artery before full disappearance of sphygmus.

Circulation in capillars. These pots lie in intercellular spaces, closely adjoining to cells of organs and organism tissues. Total of capillars hugely. The total length of all capillars of the human compounds about 100 000 km, i.e. A strand to which could surround 3 times globe on equator.

Rate of a blood flow in capillars is insignificant and compounds 0,5-1 mmet/sec. Thus, each particle of blood is in a capillar approximately 1 with. A small thickness of this layer and its close contact to cells of organs and tissues, and also continuous change of blood in capillars provide metabolism possibility between blood and intercellular fluid.

Distinguish two kinds of functioning capillars. One of them form the shortest path between arterioles and venules (the main capillars). Others represent side branches from the first; they depart from the arterial extremity of the main capillars and run into their venous extremity. These side branches form capillary networks. The main capillars play the important role in blood allocation in capillary networks.

In each organ blood streams only in capillars "on duty". The part of capillars is switched off from a circulation. In concentrated activities of organs (for example, at reduction of muscles or secretory activity of glands) when the metabolism in them strengthens, the quantity of functioning capillars considerably increases. At the same time in capillars the blood rich with erythrocytes - oxygen carriers starts to circulate.

Adjustment of a microcirculation by the excitatory system, influence on it of physiologically active materials - hormones and metabolites are carried out by means of influence on arteries and arterioles. Their narrowing or dilating variates quantity of functioning capillars, blood allocation in a branching capillary network, variates structure of the blood proceeding on capillars, i.e. An interrelation of erythrocytes and plasma.

The pressure size in capillars is closely bound to an organ state (rest and activity) and those functions which it carries out.

Arteriovenous anastomosises. In some fields of a body, for example in a skin, lungs and nephroses, there are immediate bonds of arterioles and veins - arteriovenous anastomosises. It is the shortest path between arterioles and veins. In usual conditions anastomoses are occluded, and blood passes through a capillary network. If anastomoses are discovered, the blood part can arrive in veins, passing capillars.

Thus, arteriovenous anastomosises play a role of the shunts regulating a microcirculation. An example to it is change of a microcirculation in a skin at rising (from above 35 °C) or dropping (more low 15 °C) choronomic temperature. Anastomoses in a skin the blood flow from arterioles immediately in veins that plays the big role in thermoregulation processes is discovered and established.

Blood locomotion in veins. Blood from a microcirculatory bed (a venule, fine veins) arrives in venous system. In veins pressure of blood the low. If pressure of blood is peer the beginning of an arterial bed 140 mm hg in venules it compounds, 10-15 mm hg In a final part of a venous bed pressure of blood come nearer to zero and even can be below atmospheric pressure.

Blood locomotion on veins is promoted by a number of factors. Namely: a cardiac performance, the valval apparatus of veins, reduction of the skeletal muscles, sticking function of a thorax.

The cardiac performance frames a difference of pressure of blood in arterial system and the right auricle. It provides venous return of blood to heart. Presence in veins of valves promotes blood locomotion in one direction - to heart. Alternating of reductions and a release phenomenon of muscles is the important factor promoting locomotion of blood on veins. At reduction of muscles thin sides of veins are compressed, and blood moves ahead on a direction to heart. The release phenomenon of skeletal muscles promotes entering of blood from arterial system in veins. Such forcing action of muscles has received the name of the muscular pompe which is the assistant to the basic pompe - hearts. It is quite clear, that blood locomotion on veins is facilitated during walking when rhythmicallies the muscular pompe of the inferior extremities works.

Negative intrathoracic pressure, especially in an inspiratory phase, promotes venous return of blood to heart. Intrathoracic negative pressure causes dilating of venous pots of range of a neck and the thoracal lumen, possessing thin and pliable sides. Pressure in veins goes down, that facilitates blood locomotion on a direction to heart.

In fine and average veins there are no sphygmic fluctuations of pressure of blood. In large veins near to heart sphygmic fluctuations - a venous pulse having other parentage, than arterial sphygmus become perceptible. It is caused by difficulty of inflow of blood from veins in heart during an auricular systole and ventricles. At a systole of these departments of heart pressure in veins raises and there are fluctuations of their sides.

Regulation of a vascular tonus

Nervous control of a vascular tonus

Modern data testify that sympathetic nerves for pots are vasoconstrictors (narrow pots). Vasohypertonic influence of sympathetic nerves does not extend on pots of a brain, lungs, heart and working muscles. At excitation of sympathetic nerves pots of the specified organs and tissues extend.

Vasodilator nerves (vasodilators) have some sources. They are a part of some parasympathetic nerves. Also vasohypotonic nerve fibrils are found as a part of sympathetic nerves and back roots of a spinal cord.

Vasomotor centre. Is in myelencephalon and is in a state of tonic activity, i.e. Long constant excitation. Elimination of its influence causes a vasodilatation and falling of arterial pressure.

The myelencephalon vasomotor centre is located at the bottom of IV ventricle and consists of two departments - pressor and depressor. The boring of the first causes narrowing of arteries and lifting of arterial pressure, and a boring of the second - an arteriectasia and pressure drop.

The influences going from the vasohypertonic centre of myelencephalon, come to nerve centres of a sympathetic part of the vegetative excitatory system, located in lateral horns of thoracal segments of a spinal cord where the vasohypertonic centres regulating a tonus of pots of separate fields of a body are formed.

Except a vasomotor centre prolate and a spinal cord, on a state of pots nerve centres of a diencephalon and the big hemispheres influence.

Reflex regulation of a vascular tonus. The vasomotor centre tonus depends on the eisodic signals coming from peripheric receptors, located in some vascular ranges and on a body surface, and also from influence of the humoral stimuluses reacting immediately on nerve centre. Hence, the vasomotor centre tonus has both reflex, and a humoral parentage.

Reflex changes of a tonus of arteries - vascular jerks - can be parted on two bunches: own and interfaced jerks. Own vascular jerks cause signals from receptors of pots. Morphological researches the big number of such receptors is revealed. The receptors concentrated in an aortic arch and in the field of a bifurcation of a carotid artery on intrinsic and outside have especially important physiological value. Receptors of vascular reflexogenic regions provoke at change of pressure of blood in pots. Therefore them name pressoreceptors, or baroreceptors.

Vascular jerks can be caused, stimulating receptors not only an aortic arch or a carotid sine, but also pots of some other ranges of a body. So, at pressure rising in pots of a lung, an intestine, a lien reflex changes of arterial pressure and other vascular ranges are observed.

The reflex regulation of pressure of blood is carried out with the help not only mechanioreceptors, but also the chemoceptors sensitive to changes of a chemical compound of blood. Such chemoceptors are concentrated in aortal and carotid little bodies, i.e. In places of localisation of pressoreceptors.

Chemoceptors are sensitive to dioxide of oxygen and an oxygen and blood disadvantage; they stimulate also Carboneum oxide, Cyanidums, nicotine. From these receptors excitation on centripetal nerve fibrils is transferred to a vasomotor centre and causes rising of its tonus. As a result pots are narrowed also pressure raises. Simultaneously there is a respiratory centre excitation.

Chemoceptors are found also in pots of a lien, adrenals, nephroses, an osteal brain. They are sensitive to the various chemical compounds circulating in blood, for example, to Acetylcholinum, adrenaline, etc.

The interfaced vascular jerks, i.e. The jerks arising in other systems and organs, show mainly rising of arterial pressure. They can be caused, for example, a body surface boring. So, at pain stimulations pots, especially organs of an abdominal lumen are reflex narrowed, and arterial pressure raises. The boring of a skin a cold also causes a reflex vasoconstriction, mainly dermal arterioles.

Influence of a cortex of a brain on a vascular tonus. Influence of a cortex of hemicerebrums on pots has been proved for the first time by a boring of certain fields of a cortex.

Cortical vascular reactions at the human are studied by a method of conditioned reflexes. If repeatedly to combine any boring, for example, warming, refrigerating or a pain stimulation of a field of a skin with any indifferent stimulus (sound, light etc.) through some number similar a combination one indifferent stimulus can cause the same vascular reaction, as well as applied simultaneously with it unconditional thermal or a pain stimulation.

Vascular reaction to earlier indifferent stimulus is carried out is conditional reflex by, i.e. with the assistance of a cortex of the big hemispheres. The human thus has also conforming sensations (colds, heat or a pain) though no boring of a skin existed.

Humoral regulation of a tonus of pots

Some humoral agents narrow, and others dilate a lumen of arterial pots. Hormones of marrow of adrenals concern vasohypertonic materials - adrenaline and Noradrenalinum, and also a back lobe of a pituitary body - a vasopressin.

Adrenaline and Noradrenalinum narrow arteries and arterioles of a skin, organs of an abdominal lumen and lungs, and the vasopressin reacts mainly on arterioles and capillars.

The serotonin produced in a mucosa of an intestine and some fields of a brain concerns number of humoral vasohypertonic factors. The serotonin is formed also at disintegration of platelets. Physiological value of a serotonin in this case consists that it narrows pots and interferes with a bleeding from the amazed field.

Acetylcholinum which is formed in the terminals of parasympathetic nerves and sympathetic vasodilators concerns vasohypertonic materials. It is quickly blasted in bloods, therefore its action on pots in physiological conditions purely aboriginal.

Vasohypotonic material is also Histaminum - the material formed in a side of a stomach and an intestine, and also in many other things organs, in particular in a skin at its boring and in a sceletal musculation in an operating time. Histaminum dilates arterioles and enlarges a blood filling of capillars.