Cardiovascular system at rest Learning Objectives To know the structure of the heart and relate it to the cardiac cycle. To understand the relationship between heart rate, stroke volume and cardiac output. To explain the cardiac cycle and the conduction system that is linked to this.

HR, SV & Q Heart rate is …………….. The number of times the heart beats per minute. Stroke volume is ……………. The amount of blood ejected by the ventricle at each contraction. Cardiac output is …………….. The amount of blood the heart pumps out per minute.

Calculation Knowing what you now know, how can you calculate Cardiac Output? Q = HR v SV Measurements HR = Beats per minute SV = ml of blood per beat Q = l/min

Resting values Using the following resting values, calculate Q at rest: HR = 72bpm SV = 70ml Q = 72 x 70 = 5,040ml = 5l/min

What can vary? Heart rate – the heart rate of an individual can vary greatly. If a person does a lot of aerobic work their resting pulse can drop to 60bpm,or even lower. But…. We still need a Q of 5l/min. Rearrange the equation to work out what the SV would need to be for this person. Q = SV x HR 5l = ? X 60(bpm) SV = Q/HR SV = 5l/60 SV = 83ml

Heart rate task Take the resting heart rate of everyone in the group. Work out their stroke volume. Is there a relationship between exercise and resting heart rate?

Stroke volume There are 4 factors that may affect stroke volume to vary, what do you think they are? How much blood is being returned to the heart (venous return). How far the ventricles will stretch. The contractility of the ventricles. The pressure in the main arteries leading from the heart.

Cardiac Cycle Trace the path of the blood around the heart on your diagram (0.8 seconds at rest). Blood fills right and left atrium (atrium relaxed) Ventricles relax and pressure drops so blood flows from atria into ventricles. Atria contract to ensure ventricles are completely filled. Ventricles contract and blood is pushed out of ventricles. Atrium relax and begin to fill again. Systole – the contraction phase of the heart. Usually lasts around 0.3 seconds (at rest). Diastole – the relaxation phase of the heart. Usually lasts around 0.5 seconds (at rest). Atria contract before ventricles – systole/ diastole refers to the ventricles. https://www.youtube.com/watch?v=jLTdgrhpDCg

Conduction system of the heart

Wave of contraction is initiated by specialist node in right atrium wall (SA node). Nerve impulse spreads through cardiac tissue causing the atria to contract, pushing blood into the ventricles. Impulse spreads over ventricles from the bottom of the heart through the next specialised node called the AV node. Impulse travels across the atria to the AV node and then down the specialised nerve tissue in the septum, known as the bundle of His. Nerve impulse is then carried to the apex of the heart, where specialised fibres branch out into smaller bundles called purkinje fibres. The purkinje fibres spread upwards and outwards across the ventricles causing them to contract and push blood up and out of the heart. Once the ventricles have completely relaxed another impulse is initiated at the SA node and the cycle is repeated.

HR SV Q At rest 60-72 70ml (average) 5l/min Submaximal exercise Resting – 60/80% max HR 170ml (trained) 120ml (untrained) Maximum SV is achieved during submaximal work 15-25l/min (trained) 10-15l/min (untrained) Maximal exercise 220-age Any increases in Q (after 40-60%) during maximal exercise are due to an increase in HR not SV. 20-40l/min (trained) 23-30l/min (average adult) Recovery Falls rapidly and then slows to gradually return to resting

End-Diastolic Volume (EDV) The amount of blood in the ventricles just before the contraction phase (systole). If heart rate is lower, then stroke volume needs to increase (increase in SV that reduces HR NOT the other way around). This means…. EDV of the ventricles increases (it can physically hold more blood as it is bigger and stronger).

Learning Objectives To know how cardiac output is redistributed during exercise. To understand mechanisms of venous return. To be able to explain how the vascular shunt mechanism changes cardiac output at different exercise intensities.

Cardiac Output at rest Skeleton Brain Heart Kidneys Liver Muscles Skin Other 5% 15% 25% How much is sent to each part of the body during rest? Extension – what volume of cardiac output goes to the muscles and organs at rest?

Cardiac Output redistribution

Vascular Shunt During exercise the demand for oxygen from the skeletal muscles increases dramatically and more oxygenated blood must flow to them to meet the demand. The increases in SV and HR and overall Q increases the oxygen supply but this is not enough on its own. Blood must be redistributed so that more goes to the skeletal muscles and less to other organs.

Vascular Shunt Mechanisms Vasodilation of the arterioles supplying the skeletal muscles – increasing blood flow to them. Vasoconstriction of the arterioles supplying the other organs, such as the kidneys and liver, reducing blood flow to the organs. Pre-capillary sphincters in the capillary network supplying the skeletal muscles, open. This increases blood flow to them. Pre-capillary sphincters in the capillary network supplying the organs, close. This decreases blood flow to them.

Vasomotor Centre Controls the vascular shunt mechanism. Controls blood pressure and redistribution of blood flow. Chemoreceptors Proprioceptors Baroreceptors Uses the sympathetic nervous system. Vasomotor nerves are linked to the PCS or muscular layer of arteriole walls. Sympathetic nervous system The sympathetic nervous system normally functions to produce localized adjustments (such as sweating as a response to an increase in temperature) and reflex adjustments of the cardiovascular system. Under conditions of stress, however, the entire sympathetic nervous system is activated, producing an immediate, widespread response called the fight-or-flight response. This response is characterized by the release of large quantities ofepinephrine from the adrenal gland, an increase in heart rate, an increase in cardiac output, skeletal muscle vasodilation, cutaneous and gastrointestinal vasoconstriction, pupillary dilation, bronchial dilation, and piloerection. The overall effect is to prepare the individual for imminent danger. Vasomotor nerve – a nerve affecting dilation

Put together the paragraph that describes venous return

Regulation of heart rate during exercise Proprioceptors – in the muscles, tendons and joints inform the CCC that movement has increased. Chemoreceptors – in the muscles and arteries inform the CCC that lactic acid and Carbon dioxide levels have increased and oxygen and pH levels have decreased. Baroreceptors – in the blood vessel walls inform the CCC that blood pressure has increased. Neural Control Hormonal Control Intrinsic Control Adrenalin is released from the adrenal glands into the blood. Adrenaline stimulates the SA node to increase both HR and the strength of contraction of the ventricles which increases SV. Temperature increases, which increases the speed of nerve impulses, which increases HR. VR increases, which increases EDV, increasing SV. Temperature decreases and HR decreases. VR decreases, which decreases SV.

Recovery

Task Increase well above resting values even before exercise is started. This is termed anticipatory rise and is a result of the early release of adrenaline which stimulates the SA node to increase HR. Increase as exercise intensity increases. Decrease as exercise intensity decreases Increase with intensity but slow down just prior to maximal HR values Increase with intensity, but reach a plateau during sub-maximal work and represent the optimal steady state HR for meeting the demand for oxygen at that specific intensity of work. Gradually and more slowly decreases, but still remains elevated, towards resting values, to allow the body to recover – termed oxygen debt Decrease rapidly, immediately after exercise stops due to a decrease in the demand for oxygen to the working muscles A much slower and longer recover towards resting values due to a greater oxygen debt Link to the numbers on the graph you have just drawn, the following statements:

Home Study Research the effects of altitude training and training in the heat can have on the cardiovascular system. Tomorrow’s lesson will be practical. You will need outdoor kit.