Regulation of Cardiac output

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Regulation of Cardiac Output
Blood is pumped around the body to supply oxygen and remove CO2 from respiring tissues.
CARDIAC OUTPUT: The volume of blood pumped by the heart in one minute.
Cardiac output = Stroke volume X Heart rate
The stroke volume is the volume of blood pumped out of the left ventricle each time the ventricle contracts.
During exercise there is greater muscle action therefore more blood returns to the heart ­ the venous return. The heart is stretched to a
greater extent, causing it to contract with a greater force, and so more blood is expelled. This increases stroke volume and cardiac output.
Differences in resting heart rate are caused by many factors:
Our hearts differ in size due to different body sizes and genetic factors. A larger heart will have a lower resting heart rate.
Endurance training produces a lower resting heart rate, due to an increase in the size of the heart, resulting from thickening of the
heart muscle walls.
Nervous control of heart rate:
Heart rate is under the control of the cardiovascular control centre located in the medulla of the brain.
Nerves forming part of the AUTONOMIC NERVOUS SYSTEM lead from the cardiovascular control centre to the heart. There are two such
nerves going from the cardiovascular control centre to the heart:
A sympathetic nerve ­ an accelerator. Stimulation of the SAN by this nerve increases the heart rate.
The vagus nerve ­ a parasympathetic nerve (decelerator) ­ slowing the heart rate (when the demand for oxygen and removal of CO2
reduces.)
The cardiovascular control centre detects:
Accumulation of CO2
Lactate in the blood
Reduction of oxygen

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Increased temperature
Mechanical activity in muscles and joints is detected by sensory receptors in muscles, and impulses are sent to the control centre.
All these changes result in a higher rate.
There are also HORMONAL effects on the heart ­ the release of adrenaline into the bloodstream from the adrenal glands located above the
kidneys has a direct effect on the sinoatrial node, increasing the heart rate.
Blood pressure rises with higher cardiac output.…read more

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