Cardiovascular Sytem During Exercise and Recovery

• As we start to exercise, the demand for oxygen of the muscles increases rapidly. It is the role of the cardiovascular system to increase oxygenated blood flow to the muscles.
• HR increases in proportion to the intesnity of exercise until we reach HR max.
• SV increases in proportion to exercise intensity until a plateau is reached at approximately 40-60% of working capacity. This corresponds to sub-maximal intensity exercise.
• Sv is able to increase due to: increased venous return (due to skeletal muscle pump); and the Frank-Starling mechanism (Starling's Law).
• SV reaches a plateau during sub-maximal intensity because increased HR towards maximal intensities does not allow enough time for the ventricles to fill completely in the diastolic phase, limiting the Frank-Starling mechanism.
• Venous return is the return of the bloof to the right atria through the veins.
• Frank-Starling mechanism: increased venous return leads to increased SV, due to an increased stretch of the ventricular walls and therefore force of contraction.
• CO increases in line with exercise intensity and plateaus during maximal exercise.
• SV is maintained during the early stages of recovery, as HR rapidly reduces. This will maintain blood flow and the removal of waste products while lowering the stress and workload on the cardiac muscle.
• CO rapidly decreases in recovery followed by a slower decrease to resting levels.
• Heart rate is regulated by the sutomatic nervous sysem. There are three main sources of information that determine the action of the Cardiac Control Centre. These are known as control mechanism and they can work to increase heart rate during exercise and decrease heart rate suring recovery.
• Intrinsic Control:

  Body/ heart temperature changes will affect the speed of nerve impulse transmission to the SA node and the viscosity of the blood.
• Intrinsic Control:

  During exercise a higher body/heart temperature causes faster nerve transmission so the SA node fires quicker which increases Heart Rate, blood also needs to get to the skin faster to aid cooling.
• Intrinsic Control:

  Venous return changes will affect the stretch in the atria & ventricle walls, force of ventricular contraction and stroke volume.
• Intrinsic control:

  During exercise increased venous return causes increased atria and ventricular stretch causing increased force of contraction, which increases the stroke volume. The increased atrial and ventricular stretch also directly stimulates SA node faster to increase HR.
• Hormonal Control:

  During exercise adrenaline and noradrenaline is released from the adrenal glands which directly stimulates sino atrial node which increases heart rate. The sympathetic nervous system becomes stimulated. Adrenaline also increases the force of ventricular contraction and increases the speed of electrical activity through the heart.
• Neural Control:

  During exercise chemoreceptors detect and inform the CCC of increased levels of C02 and lactic acid, decreased 02 in the blood.
• Neural Control:

  During exercise proprioceptors inform the CCC of increased movement.
• Neural Control:

  During exercise Baroreceptors inform the CCC of increased blood pressure and increased stretch on the vessel walls.
• The Cardiac Control Centre (located in the medulla oblongata) responds by increasing in stimulation of the SA node by stimulating the sympathetic nervous system, releasing adrenaline and sending stimulation to increase the firing rate of the SA node via the accelerator nerve. This will increase heart rate.
• During recovery receptors in our muscles and blood vessels detect changes in the body sensing movement has stopped.
• During recovery the chemoreceptors detect an increase in 02 and a decrease in C02 and lactic acid.
• During recovery the proprioceptors detect a decrease in movement.
• During recovery the baroreceptors detect a decrease in blood pressure.
• This information is sent to the cardiac control centre which is located in the medulla oblongata in the brain, telling it that exercise has stopped. The cardiac control centre tells the parasympathetic nervous system to send commands down the vagus nerve to inhibit the stimulation from the SA node thus decreasing heart rate to its resting value.
• During recovery the release of adrenalin in inhibited by the parasympathetic nervous system therefore the sino atrial node is stimulated less as a result heart rate decreases.
• Intrinsic Control: Recovery

  Body and heart temperature decreases causing blood to be less thin and ttravel slower. Decreased body temperature makes nerve impulses travels slower so the SA node fires slower, decreasing the hart rate. As colder blood travels slower, venous return decreases, causing the atria and ventricles to stretch less. This decreases the force of contraction, decreasing stroke volume and heart rate.
• Arteries and arterioles transport blood away from the heart towards tissues/muscles and lungs.
• Arterioles also have a large layer of smooth muscle allowing both vessels to vasodilate and vasoconstrict to regulate blood flow and control blood pressure. Arterioles also have a ring of smooth muscle surrounding the entry of a capillary bed called pre-capillary sphincters. These dilate and constrict to control the blood flow through the capillary bed.
• Capillaries bring blood directly in contact with tissues where oxygen and C02 are actually exchanged.
• Veins and venules transport blood back towards the heart.
• Veins and venules have a small layer of smooth muscle allowing them to venodilate and venoconstrict to maintain the slow flow of blood towards the heart.
• Vasodilate: widening of arteries, arterioles and pre-capillary sphincters.
• Vasoconstrict: narrowing of arteries, arterioles and pre-capillary sphincters.
• Venodilate: the widening of the veins and venules.
• Venoconstrict: the narrowing of the veins and venules.
• Pocket valves: one way valves located in the veins which prevent the backflow of blood and direct it towards the heart.
• Pocket valves work at rest and during exercise.
• Muscle Pump: veins are situated between skeletal muscles, which when contracting and relaxing compress the veins and help push blood back to the heart.
• Muscle pump only worls during exercise.