32Control of the cardiac performance. Intrinsic (self-control) regulation. Energetics of the heart. Extracardiac neural regulation of the cardiac performance – characteristics of the sympathetic and parasympathetic effects. Humoral factors affecting cardiac performance.

Intrinsic regulation

1. Preload – the volume of venous blood flow into the heart, accompanied by a corresponding change in the length of the myocardial fibers.
=The higher the preload the higher the stroke volume and the higher the cardiac output
2. Afterload – the level of resistance to the blood flow, which depends on the blood pressure in the aorta during systole
=The higher the afterload the lower the stroke volume and the lower the cardiac output
3. Contractility of the heart
=The higher the contractility the higher the stroke volume and the higher the cardiac output
4. The higher the heart rate the higher the cardiac output
5. Venous return- the higher the venous return the higher the preload

=The intrinsic ability of the heart to adapt to changing loads of inflowing blood is called the Frank- Starling law
The Frank- Starling law states – more the heart is filled during diastole, the higher the contractility of the heart and therefore the higher the quantity of blood pumped

Extrinsic regulation (Extracardial neural regulation

àReflex control (by ANS)
-Sympathetic NS - Noradrenaline work on B1 receptors – increases heart rate
=Stimulation of chromotropic, tonotropic, dromotropic, ionotropic, and batmotropic effects

-Parasympathetic NS - Ach bonds M2 receptors, increases K+ and decreases Ca2+ causing hyperpolarization – decreases heart rate
=Decreasing of chromotropic, tonotropic, dromotropic, ionotropic, and batmotropic effects

1. Chemoreceptors detect the CO2 and O2 levels in the blood
2. Baroreceptors detect the changes in arterial blood pressureàeither activate S or PS
3. Proprioceptors detect the muscle movements

humoral control

àHumoral control (by hormones and ions):
1. Hormones and metabolites:
-Adrenaline, noradrenalin – stimulates the SNS
-Thyroxine increases the number of B1 receptors and their sensitivity for SNS and catecholamines -Metabolites -as lactic acid – increases strength of cardiac muscle contraction

2. Ions:
-Increased potassium – heart becomes extremely dilated and flaccid and slows heart rate.

Tonotropic effect- tonus of the heart

-Increased calcium – spastic contraction -Increased sodium – depresses cardiac function

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