Download The Structure and Function of the Heart

The Structure and
Function of the Heart
Higher Human Physiology and Health
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What do you know now?
• 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
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superior vena cava
pulmonary veins
AV valve
mitral
AV valve
tricuspid
inferior vena cava
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The Heart - external
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The Heart - internal
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Cardiac cycle
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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
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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
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Cardiac output
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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
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Heart sounds
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Cardiac cycle
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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
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Cardiac conducting system
• Heart beat originates in the heart
• But it is regulated by nervous and hormonal control
Sinoatrial node
Atrioventricular node
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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)
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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
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Abnormal ECGs
CPR
Defibrillator
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Regulation and control of heart beat
• Nervous
• Control centre located in medulla
• Autonomic nervous system
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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
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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
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Digital syphgmomanometer
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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
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What you should know
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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
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