By Sophia Mahfooz 7.3 PEAK PERFORMANCE

Points covered A myogenic heart- the Cardiac cycle The control of heart rate- the function and role of SAN and AVN Role of ECG Aerobic capacity Role of Cardiovascular centre and Ventilation Cardiac output the nervous and hormonal control of the heart The control of ventilation rate

The heart The heart is a muscular organ It pumps oxygen depleted blood to the lungs and pumps oxygenated blood around the body. To do this effectively the heart is divided into four chambers . Two on the right and two on the left side of the heart. The chambers / compartments are separated by valves.

Position of the valves The Right Atrium and Ventricle are separated by the tricuspid valve . The Left Atrium and Ventricle are separated by the Mitral valve

A myogenic Heart The heart will beat without input from the nervous system and will continue to beat, even outside the body, as long as its cells are alive. A change in polarity causes the cells to contract. This cycle of the heart pumping blood to the lungs and to the body is called the Cardiac Cycle  One complete sequence of filling and pumping blood is called a cardiac cycle, or heartbeat

Cardiac cycle Atrial systole Ventricular systole Diastole The Cardiac cycle can be simplified into three phases, atrial systole, ventricular systole and diastole. Atrial systole Blood fills into the atria- pushes the atrioventricular valves open- the atria contract forcing blood into the ventricle Ventricular systole The ventricles contract from the base of the heart upwards. This pushes blood up and out through the arteries. Atrioventricular valves close-preventing backflow Diastole Elastic recoil of the relaxing heart walls lower pressure in the atria and ventricles-Blood under high pressure is drawn into the heart closing the semilunar valves Atria- ventricular

Cardiac conducting system

Role of ECG Measuring electrical impulses The Electrocardiogram (ECG) can record the electrical activity of the heart during the cardiac cycle. How is an ECG carried out 12 electrodes are used to give 12 views of the Heart. Using the different combinations of electrodes the ECG can detect electrical currents during the cardiac cycle as they spread in different directions across the heart. When there a change in polarisation of the cardiac muscle a small electrical current can be detected at the skin surface- this is what the ECG measures. ECG can be used to measure heart rate- doc’s can find out if you have heart problems

What does the ECG trace show?

1In the heart, an action potential originates in the 1In the heart, an action potential originates in the... A)Purkinje fibres B)bundle branches C)atrioventricular bundle D)atrioventricular node E)sinoatrial node. 2The sequence of travel by an action potential through the heart is... A)sinoatrial node, atrioventricular node, atrioventricular bundle, bundle branches, Purkinjefibres. B)atrioventricular node, sinoatrial node, atrioventricular bundle, bundle branches, Purkinje fibres. C)atrioventricular bundle, atrioventricular node, sinoatrial node, bundle branches, Purkinje fibres. D)Purkinje fibres, atrioventricular bundle, atrioventricular node, sinoatrial node, bundlebranches. E)atrioventricular node, sinoatrial bundle, atrioventricular node, bundle branches, Purkinje fibres. 3Which of the following is true concerning the heart conduction system? A)action potentials pass slowly through the atrioventricular node. B)action potentials pass slowly through the atrioventricular bundle. C)action potentials pass slowly through the Purkinje fibers. D)action potentials pass slowly through the ventricle wall. E)action potentials pass slowly through the bundle branches.

4In the ventricles, the action potential travels along the interventricular septum to the apex of the heart, where it then spreads superiorly along the ventricle walls. A)True B)False 5Action potentials are carried by the Purkinje fibres from the bundle branches to the ventricular walls. A)True B)False 6) If there is a blockage between the AV node and AV bundle, how will this affect the appearance of the ECG a) P-R interval would be smaller b) QRS interval would be longer c) there would be more P waves than QRS complexes d) there would be more QRS complexes than P waves e) the T wave would not be present 7) The T wave on an ECG represents: a) ventricular depolarization b) ventricular repolarisation c) atrial depolarization d) atrial repolarisation e) ventricular systole

Aerobic capacity Endurance exercise depends on the ability to maintain a continuous supply of ATP for muscle contractions. This in turn depends on aerobic capacity- the ability to take in, transport and use oxygen. VO₂- Volume of O₂ per minute. The VO₂ is the volume of which we take up at rest. This is 0.2-0.3 litres. VO₂ (max)- Maximum Volume of This is 3-6 litres per minute. It’s units are ml min⁻ᶦ kg⁻ᶦ VO₂ (max) is dependent on the efficiency of uptake and delivery of oxygen by the lungs and the cardiovascular system. O₂ O₂ taken up by the body

Cardiovascular centre & Ventilation Centre The Cardiovascular system and the Ventilation system adjust to meet the demands of exercise. They ensure that enough oxygen and fuel reaches the muscles and removes excess Carbon dioxide and lactate. The major changes are to : Cardiac output Ventilation rate Depth of breathing . When running adequate supply of oxygen is maintained by increasing the cardiac output, increasing rate of ventilation and deeper breaths are taken.

Cardiac output Cardiac output (CO)- Volume of blood pumped by the heart per minute. At rest CO is 5dmᵌ in both trained and untrained people. During exercise for athletes this can raise up to 30dmᵌ min⁻ᶦ. CO depends on volume of blood ejected from the left ventricle called the Stroke volume(SV) and the heart rate (HR) Cardiac Output(CO)= Stroke Volume (SV) x Heart rate (HR)

Stroke Volume & Heart Rate This is the volume of blood pumped out of the left ventricle each time the ventricle contracts. Heart draws blood into the atria as it relaxes How much blood is pumped out is determined by how much blood is returned to the heart- the Venous return At rest there is some residual blood in the heart- not all of the blood in the heart gets pumped out. To increase cardiac output during exercise more of the residual blood is ejected. Heart rate With each beat of your heart a pulse of blood is ejected. This can be felt along the arteries. The average heart rate for males is 70bpm and for females 75bpm. Differences in heart rate depend on many factors mainly our genetics. Some differences are Heart size – a larger heart has a lower resting rate- it will expel more blood with each beat The size of the heart is due to the thickening of cardiac muscle endurance athletes have lower heart rates because the size of their heart is larger so the stroke volume is greater and the heart doesnt need to beat as much.

1) Cardiac output is equal to: a) diastolic BP + 1/3(systolic BP-diastolic BP) b) SV x HR c) EDV-ESV d) HR x BP 2)What is the average heart rate of a resting male adult a)55bpm b)75bpm c)80bpm d)70bpm 3) If the heart rate is 75 beats per minute and the stroke volume is 70 ml per beat, then what is the cardiac output? Answer............................................................................................................................................. 4) What's the relationship between cardiac muscle stretch and force of contraction? What effect does this have on stroke volume? Answer............................................................................................................................................... 5) What effect does a fast heart rate have on stroke volume?

nervous system control of the heart 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 types of nerves going from the cardiovascular control centre to the heart A sympathetic nerve (accelerator nerve) A vagus nerve which is a parasympathetic nerve ( decelerator nerve) Stimulation of the SAN by the sympathetic nerve causes an increase in the heart rate Impulses from the vagus nerve slow down the rate. The cardiovascular control centre detects build up of CO₂ and Lactate in the blood, also detect reduction of oxygen and increase in temperature. The muscle activity is detected by sensory receptors which send impulses to the cardiovascular control centre. This causes an increase in heart rate there is an increase in venous return – leads to rise in stroke volume = higher cardiac output Thus transferring fuels and oxygen to the muscles quickly.

Hormonal effect on heart rate Fear , excitement and shock cause the realise of the hormone adrenaline into the blood stream from the adrenal glands Adrenaline has an effect on the heart rate similar to stimulation by the sympathetic nerve. It has a direct effect on the SAN- increasing the heart rate to prepare the blood for any physical activity. Adrenaline can also cause dilation of the arterioles supplying the skeletal muscles This maximises blood flow to the active muscles It also increases heart rate before the start of physical activity Adrenaline effecting SA node directly via the blood

The ventilation rate Lung volumes The volume of air we breathe in and out at each breath is the tidal volume At rest this is about 0.5dmᵌ The maximum volume of air we can inhale and exhale is the vital capacity In most people this is 3-4 dmᵌ but in fit people it can be 5 dmᵌ Lung volumes including tidal volume and vital capacity can be measured using a spirometer The Minute ventilation is the volume of air taken into the lungs per minute. Minute ventilation= Tidal Volume x breaths per minute

The spirometer trace

The control of breathing The ventilation centre in the medulla oblongata of the brain controls breathing Inhalation Ventilation centre sends nerve impulses every 2-3 seconds to the external intercostals muscles and diaphragm muscles – these muscles contract causing inhalation Exhalation As the lung inflates, stretch receptors in the bronchioles are stimulated. The stretch receptors send inhibitory impulses back to the ventilation centre. So the impulses to the muscles stop and the muscles relax- allowing exhalation. Exhalation is caused by elastic recoil. Not all the air is exhaled from the lungs there is some residual air. Ventilation centre in the medulla Impulse to Impulse during exercise to Chemoreceptor's in the medulla, aorta and carotid artery Detected by Changes in CO₂ , pH and temperature of the blood Motor cortex and medulla in brain Impulse from stretch receptor Impulse to diaphragm

Controlling ventilation rate and depth At rest- the main stimulus controlling the breathing rate and depth is the concentration of dissolved carbon dioxide in the arterial blood and its effect on pH. A small increase in carbon dioxide concentration causes a large increase in in ventilation . This is achieved through : Carbon dioxide dissolving in the blood plasma- making carbonic acid Carbonic acid detach into hydrogen ions and hydrogen carbonate ions – thus lowering the pH of the blood Chemoreceptor's sensitive to hydrogen ions are located in the ventilation centre of the medulla oblongata- they detect the rise in hydrogen ion concentration Impulses are sent from the ventilation centre to stimulate the muscles involved in breathing Alveoli air pO₂ 13.3 kPa pCO₂ 5.3 kPa Blood flowing into lung capillaries Blood flow out of lung capillaries Equilibrium Diffusion pO₂ 13.3 kPa pCO₂ 5.3 kPa pO₂ 13.3 kPa pCO₂ 5.3 kPa There are also chemoreceptor's in the walls of the carotid artery and aorta. These are stimulated by the change in pH. These receptors monitor the blood before it reaches the brain and sends impulses to the ventilation centre The increase in Carbon dioxide and fall in pH causes an increase in rate and depth of breathing.

Controlling breathing during exercise The motor cortex of the brain is the region that controls movement When exercise begins, impulses from the motor cortex have a direct effect on the ventilation centre in the medulla It increases ventilation rapidly. Ventilation is also increased in response to impulses reaching the ventilation centre from stretch receptors in tendons and muscles involved in movement. The chemoreceptor's sensitive to Carbon dioxide levels and temperature increase depth and rate of breathing via the ventilation centre.

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