The Structure and Function of the Heart Higher Human Physiology and Health

What do you know now? What you are learning? From your previous N5 or maybe S1/2 work label the diagram of the heart and write any facts you know. What you are learning? Revising the heart structure and function The cardiac cycle and output Cardiac conduction and heart beat Cardiac pressures

superior vena cava pulmonary veins AV valve mitral AV valve tricuspid inferior vena cava

The Heart - external

The Heart - internal

Cardiac cycle

Systole / Diastole Systole – when part of the heart is contracting either atria or ventricles Diastole – when part of the heart is relaxing either atria or ventricles Both atria contract or relax at the same time Both ventricles contract or relax at the same time Atria and ventricles can be relaxed at same time Atrio-ventricular valves (AV) and semi-lunar valves (SL) are forced open or kept closed depending on systole or diastole of atria or ventricles Valves allow flow of blood in one direction through the heart

Measuring cardiac output Cardiac output = heart rate x stroke volume CO HR SV Cardiac output is the volume of blood pumped through each ventricle per minute Heart rate is the number of times the heart beats per minute Stroke volume is the volume of blood pumped through a ventricle at each beat Each ventricle pumps the same volume of blood to aorta or pulmonary artery respectively

Cardiac output

Valves and heart sounds Heart sounds come from the closing of valves and sounds like LUB/DUB AV valve closes and gives the ‘LUB’ sound SL valve closes and gives the ‘DUB’ sound Heart murmurs can be heard and are defective valves

Heart sounds

Cardiac cycle

Cardiac cycle and pressure changes Atria contract (systole) pushing blood into ventricle via AV valve, SL valve is closed Ventricles contract (systole) closing the AV valve. Blood is pumped out into aorta or pulmonary artery via SL valve All relax (diastole) SL valves closed

Cardiac conducting system Heart beat originates in the heart But it is regulated by nervous and hormonal control Sinoatrial node Atrioventricular node

Cardiac conducting system Sinoatrial node (SAN) ii right atrium controls contractions and timing of beat Impulses from SAN radiate across atria Impulses from SAN transmitted to atrioventricular node (AVN) at base of atria Conducting fibres pass down centrally and branch left and right across ventricles Impulses sent to ventricular muscle fibres starting at apex (bottom) moving upwards Atrial systole first then ventricular systole next (coordinated)

Measuring heart impulses Impulses are electrical so can be measured by electrocardiogram (ECG) Electrodes placed on skin 3 distinct phases P wave – atrial excitation from SAN QRS complex – ventricle excitation T wave – electrical recovery of ventricles

Abnormal ECGs CPR Defibrillator

Regulation and control of heart beat Nervous Control centre located in medulla Autonomic nervous system Cardio accelerator centre – sympathetic nerve increases heart rate Cardio inhibitor centre – parasympathetic nerve decreases heart rate Impulses sent to SAN Relative number of impulses determines heart beat Hormonal Sympathetic nerve acts on adrenal gland It releases norepinephrine (noradrenaline) speeding up heart rate Parasympathetic nerve releases acetylcholine slowing heart rate

Measuring blood pressure Blood pressure is the force put on walls of blood vessels Measured in the aorta Systolic pressure as left ventricle pushes blood out into aorta (pulse detected) Diastolic pressure as left ventricular contraction has stopped (pulse not detected) Measured in mm of mercury (Hg) Typically 120 mm Hg for systolic 70 mm Hg for diastolic in young adult (120 over 70) Mercury manometer

Digital syphgmomanometer

Hypertension High blood pressure Caused by many factors: being overweight, lack of exercise, diet of fatty foods, too much salt, excessive alcohol, high levels of stress Measurements of 140 over 90 mm Hg for extended periods when resting Hypertension increases risks of coronary heart disease and strokes

What you should know Know the heart structure and function Know what cardiac output is how to calculate it Know what the cardiac cycle is and describe it Know how the cardiac cycle is controlled Know how the cardiac cycle can be measured Know what blood pressure is and how it can be measured Consolidate your learning Read appropriate pages from textbook, complete questions in textbook, complete summary, make own notes, complete scholar work