Circulation regulation peculiarities in separate organs 


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Circulation regulation peculiarities in separate organs



There are both blood circulation and its regulation several distinguishing features in different organs. It is connected with different organs innervation and their various sensitivity to hormones, mediators and different chemicals which can influence on vascular vessels activity.

Circulation in heart

It is performed by coronary arteries, big capillaries amount. Circulative conditions in coronary arteries differ greatly from circulation in other organs. In course of ventricules systole myocardium presses vessels in it. That’s why blood circulation is weakened, oxygen supply is decreased to the tissues. Right after systole heart blood circulation is increased. Main regulative role of sympathetic and parasympathetic influencings interrelations is in rapid and adequate coronary circulation adaptation to current organism organism needs. Vagus excitement leads to coronars dilation. Cardiac sympathetic rami (branches) excitement results in coronarodilation and blood stream activation in them. Oxygen myocardial consumption sufficiency is important for coronary circulation regulation. Cardiac muscle hypoxy results in myocardial chemoreceptors excitement which leads to reflectory arterioles dilations and blood stream activation. Carbonic dioxide accumulation in blood causes the same effect (that’s why coronary circulation is increased at respiration lack).

Circulation in brain

It is more intensive in this region comparatively to all others. About 15 per cent of blood from every cardiac discharge in large circle comes into brain vessels. Brain vessels are muscular, with excessive adrenergic innervation that allows them to change their cavity in wide limits. Circulation distribution in brain is rather unequal: its maximal level is in hypothalamus and cortex.

Brain circulation independence from general (systemic) circulation is its important feature. It is explained by skull rigidity and brain disability to be pressed. That’s why all liquids volume in intracranial vessels is practically constant. Even small increasing of this volume caused by significant arterioles dilation that leads to circulation increasing is compensed easily with insufficient veins constriction the volume of which is rather more.

Under norma, vasonstricting nervous fibres influence on brain blood stream insignificantly. Such weak brain innervation with vasoconstricting nerves is favourable for it. When blood pressure decreases for instance after strong bleeding (at which peripheral vessels are constricted), brain vessels are dilated. Brain circulation remains constant even under such conditions due to autoregulation (but only if blood pressure is not less as 50-60 mm merc col.) At further blood pressure decreasing blood circulation will be reduced in brain too that may leads to unconscious state.

In brain vessels tone regulation local factors are of great importance too. Merabolism intensivity activation in brain, blood content change (CO2 level increasing) causes brain vessels dilation. H+-ions role, oxygen tension are very important in these reactions too (at oxygen low tension – brain vessels are dilated, at high tension – are constricted, on the contrary). At oxygen content increasing in air brain vessels are constricted.

Blood circulation in lungs

Lung circulation peculiarity: circulation small circle vessels are relatively short, resistance in them is less; that’s why pressure in them is in 5-6 times lower comparatively to aortal. Lung vessels capacity may be increased or decreased. Thus, due to this mechanism, lung filling with blood may varies in the limits of 10-25 per cent from common blood amount in organism. It provides blood depot creation. Lung net vessels big ability to stretching creates favourable conditions for easy blood stream and volume change. Inspiration leads to blood regional content increasing and to regional resistance decreasing to blood in course of usual breathing or even in course of hyperventillation.

At hypertony in reflexogenic zones vessels with parallel reflectory heart activity weakening and large circle vessels dilation lung circle reflectory filling takes place. Due to this blood pressure is leveled and blood distribution between circulation big and small circles occurs. At pulmonal arteries pressure increasing, when small circle is overfilled with blood, reflexes from pulmonal artery receptors occurs on large circle vessels. As the result of this blood amount is increased in large and is decreased - in small circle. It prevents blood stagnation in lungs and provides heart activity and blood circulation as a whole.

 

 

Lecture 14



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