Blood circulation system work regulation.

Heart-vascular regulative center – is a rather complicated structure in which dominant importance has its “working” part, located in medulla oblongata. It was there where neurons are located from which excitement are transmitted on effector ways (parasympathetic and sympathetic) while reaching heart and vessels. That’s why their reflectory regulation is always performed simultaneously. When sympathetic nervous system tone is dominant (hypersympaticotony) than heart activity is increased:

· its contraction freaquency is rised up – positive chronotropic effect;

· contraction force is increased – positive inotropic effect;

· excitability is increased – positive bathmotropic effect;

· conductance is rised up- positive dromotropic effect;

· tone is increased – positive tonotropic effect.

At hyperparasympatheticotony – on the contrary, all mentioned effects will be negative.

Vascular tone will be changed too: in the first case – to increase, in the second – to decrease. It will influence on size of their filling with blood and arterial pressure.

“Working” part of heart-vascular regulation center consists of 2 parts:

· pressor – its irritation causes vasoconstriction;

· depressor – its irritation causes vasodilatation.

These parts of “working” center receives the information from different receptor groups located in heart, vessels and out of blood circulation system.

That’s why while characterizing blood circulation system reflectory regulative mechanism one can differentiate 2 reflexes types: proper and conjugated.

Proper reflexes – are such acts occuring in the structures of a given system and realizing in it. Such receptive zones in blood circulation system are vascular presso- and chemoreceptive zones. Special place in this reflectory group has sino-carotid zone. Reflectory act from carotid zone pressoreceptors is called as sino-carotid reflex (Chermak’s reflex). This reflectory act is performed at blood pressure increasing in a given zone. Pressoreceptors irritation leads to nervous impuls occurence, further coming through sino-carotid nerve in medulla oblongata where it passes on vessel-motor depressor part. From depressor part information is switched to sympathetic nervous system through inhibiting reticular neurons and through exciting reticular neuron – to parasympathetic part of this system and through efferent fibres - to heart and vessels smooth muscles. As the result of parasympathetic nervous system tone predominance both heart and vessels work is decreased (heart contractions freaquency and force, systolic volume size, blood pressure are decreased).

Another blood circulation system proper reflex type are chemoreflexes from same vessels zones. They answer to blood chemical content change, for example, CO₂ excess in blood. Reflectory arch of such reflex is a very similar to sino-carotid reflex reflectory arch but information comes to pressor part of heart-vascular regulation center. Then information through exciting reticular neurons come to synaptic, through inhibiting – to parasympathetic part of autonomic nervous system. Result: hypersympatheticotony and further heart activity enforcement and vascular tone increasing (heart contractions freaquency and force, systolic volume size, blood pressure are increased). CO₂ is more effectively removed from organism due to such mechanism.

Conjugated reflexes – reflectory acts that are originated from different receptive groups located out of blood system boundaries. As it is known, there are many such zones in organism but according to receptors classification one can differentiate 3 types of such reflexes:

1) Proprioreceptive – are originated from supporting-moving apparatus receptors for instance in course of physical activity. From theses receptors (they are localized in muscles, tendons, ligaments) the information occuring in them comes to heart-vascular regulation center pressor part that leads to heart and vessels activity enforcement (see above the mechanism). Pulse freaquency and blood pressure increasing in course of physical training is explained by this (probe with physical activity).

Reflexes of localization are too closely to these reflexes. One of them is known as orthostatic probe: one determine puls freaquency and blood pressure in investigated person while his lying on the bed. Then the investigated person must be gradually putted into vertical state and the measurements are repeated. Under norma these indexes are increased in course of orthostatic probe. The explanation: information flow from proprioreceptors (while someone’s staying muscles, joints, ligaments are tensed) is increased in spine. Then information goes to medulla oblongata, to pressor part of heart-vascular regulation center. Clinosthatic probe is the directly opposing to the previous probe: the investigated person is gradually putted from vertical to horizontal status. The information from proprioreceptors is significantly decreased and depressor part of regulative center became dominant that leads to puls and pressure reducing.

2) Interoreceptive – are connected with different inner organs activity. Everyone knows very well that heart and vessels activity is always changed in course of respiration, digestion, excretion changings. For example, if one presses on epigastrial region (epigastrial reflex) it’s accompanied by vessels hypotony, blood pressure and heart freaquency reducing. Mechanism: at peritoneum receptors irritation (that occurs at pressure to epigastral region) information finally reaches depressor center and then heart, vessels leading to their function decreasing or even stoppage. That’s why fights are so dangerous because they may be accompanied by shocks to epigastrial region and in the most horrible cases even to instant (moment) death.

3) Extero-receptive conjugated reflexes are multiple nervous acts group occuring at the irritation of body surface and mucosae separate receptive fields. Example: ocular-heart reflex (Danini-Ashner’s reflex): at pressure to eyeballs information comes to depressor centre. Result: heart contraction freaquency and blood pressure decreasing.

4) One knows very well vascular reactions to warmth (dilatation), colness (constriction), pain (moderate pain leads to vasodilatation, strong – to constriction), touching (especially of lovely person). Due to separate points irritation (acupuncture points) on skin surface one can achieve definite success in heart activity and vessels tone regulation that is widely used in clinical practice particularly in facial-maxillary region (at neurites, myosites, myalgias et al.).

Humoral-chemical regulation

of heart and vessels activity is determined by hormones, mediators and different chemical substances (metabolites) action.

Substances increasing heart and vessels activity:

Hormones:

· adrenaline;

· noradrenaline;

· vasopressine;

· thyroxine;

· insuline;

· renine et al.

Mediators:

· noradrenaline;

· serotonine and others.

Metabolites:

· calcium excess;

· oxygen excess.

Substances decreasing heart and vessels activity:

· acethylcholine;

· hystamine;

· many prostaglandines (f.ex. prostacycline);

· acids (lactic et al.);

· CO₂ surplus (excess).

Acid products (lactic acid, CO₂) accumulating in course of physical activity decrease tone of working muscles blood vessels increasing blood supply to them. At this time magistral vessels are in increased tone due to adrenaline and noradrenaline concentration increasing in answer to load. Such tone redistribution in different vessels of blood circulation system provides high reliability of a given system functionning.

Thus, we see that heart-vascular activity regulation is a complicated process in what both reflectory (conditioned and unconditioned) and humoral-chemical mechanisms take part.

How and in what sequence these mechanisms are switched on under physiological conditions for instance in course of physical work? At this activity type increased oxygen consumption and enforced carbon dioxide releasing occurs. It may be achieved due to increased activity not only of respiration system but also blood circulation apparatus. Describe the consequence of switching of all these regulatory mechanisms on. At the early beginning, in the period of preparation to work the blood circulation system activity is increased by means of 2 mechanisms: conditioned-reflectory and humoral. Conditioned-reflectory – the situation itself before physical activity (sportsmen before running) is conditioned stimuli complex (in example with sportsman these are running way, stadium, spectators, referees and so on) which will cause the changes from the side of heart and vessels. Emotional load at this is a reason of enforced adrenaline releasing from suprarenal glands. The result of this is more expressed increasing of heart and vessels activity. Organism prepares given (cardiac-vascular) system to future wok in such a way.

In course of performing of physical activity itself conjugated reflexes from proprioreceptors, proper reflexes from chemoreceptors (metabolism products accumulation and first of all CO₂) are involved into regulation and hormones (adrenaline, vasopressine et al.) continue to be released. All these factors encourage further heart and vessels activity increasing. At the same time in working organs (muscles) acid products are accumulated, decreasing vessels tone in these organs and blood fills them in more extent providing feeding and removal of metabolism exchange.

After physical activity performing everything came ito its initial level due to involvement ito the work proper receptors from pressoreceptors directed to heart and vessels activity restriction (restoration).