D.3 The Heart

• Heart sounds:

  1. «heart sounds» produced by the closing of the valves
  2. First sound «lub» is due to «closure of» the atrioventricular valves
  3. Second sound «dup» is due to «closure of» the semilunar valves  
  4. sequence of sounds is lub dup
• Systolic pressure: measured when ventricle contracts; when blood is pumped out of the heart

  Diastolic pressure: measured when ventricles are filled with blood; heart is at rest/relaxed
• Unique properties of cardiac muscles:

  1. cells are myogenic/self-excitatory
  2. joined end to end/by intercalated discs (transverse cross-bands of attachement between adjacent cells) - allows for faster propagation of signals
  3. cells contract together for coordinated response
  4. contain many mitochondria
  5. contain many glycogen granules
  6. has gap junctions
  7. cells are branching/Y-shaped
  8. controlled by pacemaker/SA and AV nodes
• Use of defibrilators:

  1. defibrillator is electrodes/a metal paddle/pad that is placed on the patient’s chest
  2. the device determines whether fibrillation is happening
  3. a series of electrical shocks are delivered through the electrodes
  4. electrical impulse is used to depolarise the heart muscle
  5. to re-establish the function of the SA node/natural pacemaker/natural rhythm «of the heart»
• Effect of hypertension:

  1. stroke
  2. thrombosis
  3. blood clot
  4. heart attack
  5. heart failure
  6. aortic aneurysms
  7. coronary heart disease/CHD
  8. peripheral arterial disease
  9. atherosclerosis
• How to measure the following:

  Blood pressure: sphygomomanometer/blood pressure monitor

  Heart rate: taking pulse manually/using a blood rate monitor/stethoscope
• What happens during R wave of ECG:

  1. impulses initiated from the AV node spread across heart
  2. impulses travel along Purkinje fibres/across ventricles OR that triggers ventricular contraction
  3. causing depolarisation of the ventricles
• What happens at the QRS complex:

  1. arrival of signal at AV node
  2. transmission via bundle of His (heart muscle that aids electrical conduction)/Purkinje fibres (branched fibres that carry electrical impulses)
  3. ventricle depolarises
  4. AV valves close; semilunar valves open
  5. ventricular systole/contraction
  6. contraction begins at the apex/base
• How low blood pH causes hyperventilation:

  1. increased CO2 lowers blood pH
  2. chemoreceptors in carotid/aorta detect lower pH OR signal/impulses to respiratory centre
  3. signal/impulses to medulla «oblongata»
  4. «from medulla/respiratory centre» to intercostal muscles/diaphragm
  5. ventilation rate increase occurs to expel CO2
• Valves in the heart that prevent backflow: semilunar / sigmoid / pulmonary and aortic valve
• How does an artificial pacemaker work:

  1. a pacemaker contains a battery and pulse generator OR it is connected to the heart by wires/cables
  2. it detects that the heart’s natural rhythm is incorrect
  3. it sends electrical impulses to correct the heartbeat/it replaces sinoatrial node
  4. provide a regular impulse/constant rhythm
• Risk factors for coronary heart disease:

  1. increased triglycerides/cholesterol in blood
  2. presence of plaque/atherosclerosis
  3. hypertension
  4. sedentary lifestyle/lack of exercise
  5. hereditary factor
  6. smoking
  7. age
  8. diet
• What happens during the P wave of ECG:

  Atrial depolarisation/electrical impulse travels from the SA node to the AV node
• Explain why the amplitude of a QRS wave is greater than a P wave:

  1. atrium has a small contraction requiring low electrical charge
  2. the QRS complex shows the depolarization of the «right and left» ventriclesOR ventricle contraction needs more electricity than atrial contraction
  3. the ventricles have a large muscle mass compared to the atria, so the QRS complex has a larger amplitude than the P wave
• Describe how the structure of cardiac muscle cells allows them to carry out their function

  1. intercalated disk: form connections between cells/join cells together to resist mechanical stress
  2. cytoplasmic connections/gap junctions: allow for propagation of electrical stimuli/coordinated control
  3. striations: form mechanism for contraction
  4. abundance of mitochondria: produce energy for continuous contractions
  5. branched/Y-shaped cells: allow for rapid propagation/faster coordination
  6. ion channels: flow of ions allow rhythmic depolarisation/tigger action potentials without nervous input
• Function of AV node:

  1. relays signal from SAN to ventricles
  2. causes ventricular systole OR delays signal so the atria empty before ventricular systole
  3. delays signal enabling both ventricles to contract simultaneously
• Explain the reason for the delay between contractions of the atria and of the ventricles.

  1. impulses from atria do not pass directly to ventricles «due to layer of fibrous material»
  2. travel to ventricle via atrio-ventricular node/AVN in wall of right atrium
  3. impulses from AVN sent along Bundle of His /conducting fibres/Purkinje fibres
  4. ensures that the atria have ejected their blood into the ventricles first before the ventricles contract
• • The P wave represents depolarisation of the atria in response to signalling from the sinoatrial node (i.e. atrial contraction)
  • The QRS complex represents depolarisation of the ventricles (i.e. ventricular contraction), triggered by signals from the AV node
  • The T wave represents repolarisation of the ventricles (i.e. ventricular relaxation) and the completion of a standard heart beat
  • Between these periods of electrical activity are intervals allowing for blood flow (PR interval and ST segment)
• An individual’s heart rate is controlled by both nervous and hormonal signals:

  • Heart rate is increased by the sympathetic nervous system and decreased by parasympathetic stimulation (vagus nerve)
  • Heart rate can also be increased hormonally via the action of adrenaline / epinephrine
• • Thrombosis is the formation of a clot within a blood vessel that forms part of the circulatory system
  • Thrombosis occurs in arteries when the vessels are damaged as a result of the deposition of cholesterol (atherosclerosis)
  • Atheromas (fat deposits) develop in the arteries and significantly reduce the diameter of the vessel (leading to hypertension)
  • The high blood pressure damages the arterial wall, forming lesions known as atherosclerotic plaques
• • If atherosclerotic plaque ruptures, blood clotting is triggered, forming a thrombus that restricts blood flow
  • If the thrombus becomes dislodged it becomes an embolus and can cause blockage at another site
  • Thrombosis in the coronary arteries leads to heart attacks, while thrombosis in the brain causes strokes