Regulation of cardiac activity
During the life of a person repeatedly as the alternate periods of high physical and emotional stress, and periods of relative calm. Therefore, the parameters of the heart must vary greatly depending on the load on the body. Regulation of cardiac activity in two ways: neural and humoral.
The nervous regulation of the heart made of the autonomic nervous system, the structure and operation of which will be described in detail in a special section. The autonomic nervous system is divided into two divisions: sympathetic and parasympathetic. Sympathetic influence, ie the nerve impulses coming to the heart of sympathetic fibers, quickens the heartbeat, increase reduce atrial and ventricular walls, improve conduction of excitation in the heart. Under the influence of Sympathetic influences improved supply the heart muscle with oxygen and nutrients m. P. Sympathetic influence on heart are amplified with increased physical and emotional stress, under stress. The sympathetic effects on the heart are manifested not instantaneous, it takes a few seconds to the heart increased its activities. These effects continue long after the stimulation of the sympathetic nerve.
The parasympathetic influence, that is impulses coming to the heart of the main parasympathetic nerve fibers – the vagus, or vagal, lead to reactions of the opposite direction compared to the sympathetic effects. Parasympathetic effects cause slowing of heart rate, a decrease in the force of contraction of the myocardium, reducing the speed of conduction of excitation in the heart. An abnormally strong stimulation of the vagus nerve can even lead to cardiac arrest. It should be noted that the result of stimulation of the vagus nerves is also dependent on the degree of filling of the heart and blood vessels, if enough blood to the heart, and its walls are stretched slightly, the stimulation of the vagus nerve may cause rapid heart rate, and so on. D.
From the sympathetic nerve fibers in the heart of the neurotransmitter norepinephrine is released, stimulating the heart’s activity, and the endings of the vagus nerve – a neurotransmitter acetylcholine, inhibiting the heart.
Humoral effects on cardiac function have many physiologically active substances carried by the blood. These include certain hormones, peptides, salts, etc… The hormones adrenal medulla – adrenaline released from the gland into the blood at high load on the body, and increases the rate of contraction of the heart increases, interacting with specific receptors on cardiac myocytes. Stimulating effect on cardiac function also have a thyroid hormone – thyroxine pancreas – glucagon. Important factors are regulatory peptides – bradykinin, angiotensin, and others. In recent years, it proved that atrial cardiomyocytes themselves produce and secrete into the blood so-called atriopeptidy affecting the heart. Elevated levels of plasma K + salt weakens the heart’s activity, and Ca2 + salts have a stimulating effect on the heart.
The work of the heart is changing under the influence of different emotions – joy, fear, rage, anxiety, and so on. N. The material substrate of these and other emotional states are the old and new structure of the cerebral cortex. Therefore, cortical influences on heart activity are important.
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