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The control and regulation of the heart

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John Falzon

on 25 October 2012

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Transcript of The control and regulation of the heart

The Heart is controlled by the Autonomic Nervous System (ANS). i.e. It is under our involuntary control. It is the ANS which determines the rate at which the SA node (pacemaker) sends out impulses. The Control and Regulation of the Heart Hormonal Factors There are 3 main factors that determine the action of the cardiac control centre (CCC) Intrinsic Factors Sympathetic
nervous system The ANS has two subdivisions which determine the actions of the Cardiac Control Centre (CCC) in the medulla oblongata of the brain. Adrenaline increases the strength of ventricular contraction - i.e. stroke volume. The sympathetic nervous system increases the heart rate by releasing adrenaline and noradrenaline from the adrenal medulla (located at the top of the kidneys). Parasympathetic nervous system They work antagonistically Noradrenaline aids the spread of the impulse throughout the heart, and therefore increases heart rate. The parasympathetic nervous system, on the other hand, releases acetylcholine, which slows the spread of impulses and therefore reduces heart rate, returning it to the normal resting level. In a nut shell: Neural Factors As the body starts to exercise proprioceptors and mechanoreceptors within the muscles and joints inform the cardiac centre that movement has increased and hence a greater supply of blood is needed.

Chemoreceptors located in the aorta and carotid arteries inform the CCC of changes to the chemical composition of the blood - increased levels of carbon dioxide. The CCC increased hr to remove carbon dioxide.

Baroreceptors, meanwhile respond to changes in blood pressure due to increased activity. Once stimulated the sympathetic nerves cause the release of adrenaline and noradrenaline. Increase in stroke volume and heart rate, together, will increase cardiac output. Moreover these hormones (adrenaline and noradrenaline) help to control blood pressure and assist in the redistribution of blood to the working muscles through vasoconstriction and vasodilation of arterioles. Exercise also increases body temperature. This helps increase the flow of blood round the body (as blood becomes less viscous) and helps raise the heart rate by increasing the speed of nerve impulse transmission. Regulation during exercise At rest parasympathetic system overrides sympathetic system.
So heart rate is kept down. When we begin to exercise sympathetic system and parasympathetic system .
So heart rate is allowed to increase.
metabolic activity causes an concentration of carbon dioxide and lactic acid in the blood. These changes are detected by the chemoreceptors sited in the aortic arch and carotid arteries. Chemoreceptors inform the Sympathetic centre (located in the upper thoracic area of the spinal cord) to increase heart rate in order to transport the carbon dioxide to the lungs. Messages from the sympathetic centre are sent to the SA node via accelerator nerves, which release adrenaline and noradrenaline on stimulation. Other factors which increase heart rate during exercise include:
increased body temperature - and therefore decreased blood viscosity (the 'thickness' of blood).
increased venous return ( a result of the increased action of the muscle pump.
Both factors will result in greater cardiac output. Adrenaline and noradrenaline generally have the same effect:
increase heart rate and strength of contraction.
They also help to increase metabolic activity, convert glycogen into glucose, make glucose and free fatty acids available to working muscles and redistribute blood to the working muscles. Venous return - the volume of blood returning to the right atrium. When exercise stops, sympathetic stimulation and parasympathetic takes over again. The Parasympathetic system responds to the baroreceptors - the body's inbuilt blood pressure recorders. When blood pressure is too high, messages are sent from the cardiac inhibitory centre to the SA node via the vagus nerve. The parsympathetic nerve then releases acetylcholine which decreases the heat rate. The continuous interaction of the sympathetic and parasympathetic systems ensure that the heart works as efficiently as possible and enables sufficient nutrients to reach the tissue cells to ensure effective muscle action. Chemoreceptors, Mechanoreceptors & Baroreceptors are
sensory cells.
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