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Higher Human Biology Subtopic 14 The Heart
Physiology and Health Higher Human Biology Subtopic 14 The Heart
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Learning Intentions To discuss the structure of the heart
To calculate cardiac output To describe the nervous control of the heart To describe how to measure blood pressure
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blockbusters
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The Heart
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Structure of the heart 4 chambers Right and left atria
Right and left ventricle Valves Atrioventricular valves (tricuspid and bicuspid) Semilunar valves The valves prevent backflow
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Right semi-lunar valve
Left atrio-ventricular valve Right atrio-ventricular valve Left semi-lunar valve
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Right AV valve Left AV valve
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Calculating Cardiac Output
Heart Rate (HR) Number of beats per minute Stroke Volume (SV) Volume of blood expelled by each ventricle when contracting Cardiac Output (CO) Volume of blood pumped out of a ventricle per minute
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Calculating Cardiac Output
Heart rate (bpm) CO = HR × SV Cardiac output (litres) Stroke volume (ml / min)
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What is the CO of this individual? CO = 72 x 70 = 5040 ml/min
a) At rest: HR = 72bpm SV = 70ml What is the CO of this individual? CO = 72 x 70 = 5040 ml/min = 5 litres/min b) During exercise: HR = 200bpm SV = 150ml CO = 200 x 150 = ml/min = 30 litres/min
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Factors Affecting Cardiac Output
CO can very depending on level of exercise and level of fitness More intense exercise = higher cardiac output Increased physical fitness level improves cardiac output
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Cardiac cycle Systole – contraction Diastole – relaxation
The atria contract first – 0.1s Then the ventricles contract –0.3s Then the heart rests – diastole - 0.4s
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Cardiac Cycle - 3 stages ATRIAL SYSTOLE
VENTRICULAR SYSTOLE AND ATRIAL DIASTOLE VENTRICULAR DIASTOLE
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ATRIAL SYSTOLE 2 Atria contract simultaneously
Sends blood through open AV Valves into the ventricles SL valves closed, ventricles fill up First 0.1 seconds
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At this point the ventricles are relaxed and in a state of diastole
VENTRICULAR DIASTOLE At this point the ventricles are relaxed and in a state of diastole
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VENTRICULAR SYSTOLE AND ATRIAL DIASTOLE
ATRIAL SYSTOLE VENTRICULAR SYSTOLE AND ATRIAL DIASTOLE VENTRICULAR DIASTOLE 18
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VENTRICULAR SYSTOLE AV valves close, ventricles contract
Pressure inside ventricles > arteries Forces SL valves open and blood leaves heart Takes 0.3 seconds
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VENTRICULAR SYSTOLE AND ATRIAL DIASTOLE
ATRIAL SYSTOLE VENTRICULAR SYSTOLE AND ATRIAL DIASTOLE VENTRICULAR DIASTOLE 20
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ATRIAL AND VENTRICULAR DIASTOLE
Blood returns from Vena Cava and Pulmonary Vein Blood pressure in the atria increases Begins to force AV valves open, next ATRIAL SYSTOLE begins Takes 0.4 seconds
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State of Ventricular Wall
Summary Table Atrial Systole Ventricular Systole State of Atrial Wall State of Ventricular Wall State of AV Valves State of SL Valves Contracted Relaxed Relaxed Contracted Open Closed Closed Open
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Heart Sounds Start of v diastole (closing of SL) Start of v systole
(closing of AV)
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Conduction of the Heart
Heart beat is regulated by the nervous system and hormones
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Sino-atrial (SA) node Atrio-ventricular (AV) node Bundle of His Right & left bundle branches Purkinje fibres
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The Pacemaker Called the sinoatrial node Found in right atrial wall
Initiates the heartbeat Exhibits spontaneous excitation Causes atria to contract
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The steps in contraction……
Waves from SA node pass across the atria causes contraction Signal passes to AV node Down bundle of His Divides into left and right bundles Is conducted up through the pirkinje fibres Ventricles contract (from bottom up)
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Nervous Control The heart is controlled by the autonomic nervous system. There are 2 pathways that are antagonistic to one another (work in opposites).
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Control Centre CAC - cardioaccelaratory centre
Medulla of the brain contains 2 groups of neurones which control heart rate CAC - cardioaccelaratory centre CIC - cardioinhibitory centre CAC has sympathetic fibres which when stimulated increase heart rate CIC has parasympathetic fibres that innervate the heart, stimulation of these nerves slow heart rate
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Control Centre
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Cardiac accelerator nerves – sympathetic fibres
CAC in medulla Cardiac accelerator nerves – sympathetic fibres Noradrenaline released Innervates SA node/AV node/Myocardium Increased Heart rate and strength of contraction
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CIC in medulla Parasympathetic fibres Acetylcholine released This innervates SA node/AV node Decreased Heart rate and strength of contraction
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Hormonal Regulation of the Heart
Stress / exercise causes the adrenal glands to produce adrenaline This travels in the blood to the SA node and causes an increase in HR
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Electrocardiogram (ECG)
ECG’s measure the electrical activity of the heart 3 waves: P QRS T
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Electrocardiogram (ECG)
P wave – electrical excitation over the atria QRS wave - electrical excitation over the ventricles T wave – electrical recovery at end of ventricular systole
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ABNORMAL ECG’S Atrial flutter Rapid contraction of the atria
Atria contract 3 times for every ventricular contraction
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ABNORMAL ECG Ventricular tachycardia
Ventricles beat rapidly and independently of the atria SOLUTION – artificial pacemaker
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ABNORMAL ECG’S Ventricular fibrillation
Unco-ordinated electrical activity Pumping cannot take place Fatal if not corrected Defibrillation
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Blood Pressure Blood pressure is the pressure exerted on the wall of a blood vessel Measured in mmHg Highest in large elastic arteries
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How do we measure BP? Using a sphygmomanometer Systolic pressure
Maximum pressure during ventricular contraction - 120mmHg Diastolic pressure Minimum pressure during ventricular relaxation - 80mmHg
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Pressure decreases as blood flows round the body
Narrow vessels cause friction and resistance that decrease pressure
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Measuring Blood Pressure
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Hypertension Hypertension – prolonged elevation of blood pressure
Major risk factor for many diseases including coronary heart disease.
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Hypertension Factors Overwieght Lack of exercise Fatty diet
High salt diet Excess alcohol Stress
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Learning Intentions To discuss the structure of the heart
To calculate cardiac output To describe the nervous control of the heart To describe how to measure blood pressure
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