hearts

• Structure of cardiac muscle cells allows propagation of stimuli through the heart wall
• Signals from the sinoatrial node that cause contraction cannot pass directly from atria to ventricles
• There is a delay between the arrival and passing on of a stimulus at the atrioventricular node
• This delay allows time for atrial systole before the atrioventricular valves close
• Conducting fibres ensure coordinated contraction of the entire ventricle wall
• Normal heart sounds are caused by the atrioventricular valves and semilunar valves closing causing changes in blood flow
• Use of artificial pacemakers to regulate the heart rate
• Use of defibrillation to treat life-threatening cardiac conditions
• Causes and consequences of hypertension and thrombosis
• Measurement and interpretation of the heart rate under different conditions
• Interpretation of systolic and diastolic blood pressure measurements
• Mapping of the cardiac cycle to a normal ECG trace
• Analysis of epidemiological data relating to the incidence of coronary heart disease
• Cardiac muscle cells contract without stimulation by the central nervous system (contraction is myogenic)
• Cardiac muscle cells are branched, allowing for faster signal propagation and contraction in three dimensions
• Cardiac muscles cells are not fused together, but are connected by gap junctions at intercalated discs
• Cardiac muscle cells have more mitochondria, as they are more reliant on aerobic respiration than skeletal muscle
• Cardiac muscle has a longer period of contraction and refraction, needed to maintain a viable heart beat
• The heart tissue does not become fatigued, allowing for continuous, lifelong contractions
• The interconnected network of cells is separated between atria and ventricles, allowing them to contract separately
• Atrial Contraction is directed by the sinoatrial node, acting as a primary pacemaker
• The atria and ventricles of the heart are separated by a fibrous cardiac skeleton composed of connective tissue
• The AV node propagates electrical signals more slowly than the SA node, creating a delay in the passing on of the signal
• Features of AV node:

  • AV node cells have a smaller diameter and do not conduct as quickly
  • Relatively reduced number of Na+ channels in the membranes of AV node cells, a more negative resting potential and a prolonged refractory period within the cells of the AV node
  • Fewer gap junctions between the cells of the AV node
  • Relatively more non-conductive tissues in the node
• Conducting fibres ensure coordinated contraction of the entire ventricular wall
• Ventricular contraction occurs following excitation of the atrioventricular node
• Features of Purkinje fibres:

  • Fewer myofibrils
  • Bigger diameter
  • Higher densities of voltage-gated sodium channels
  • High number of mitochondria and high glycogen stores
• After every contraction of the heart, there is a period of insensitivity to stimulation (refractory period)
• Heart sounds are caused by the AV valves and semilunar valves closing causing changes in blood flow
• The heart contains atrioventricular valves (tricuspid and bicuspid) and semilunar valves (pulmonary and aortic)
• Electrocardiography maps the series of events in the heart over a single heartbeat
• Each normal heart beat should follow the same sequence of electrical events represented in an ECG trace
• Data generated via electrocardiography can be used to identify heart conditions like tachycardia, bradycardia, arrhythmias, and fibrillations
• Heart rate is the number of times the heart contracts in one minute, and can be affected by various factors
• Blood pressure is affected by stroke volume, volume of blood, contractility of the heart, and resistance from blood vessels
• Blood pressure measurements include systolic and diastolic readings
• Hypertension is defined as abnormally high blood pressure and can have various causes
• Thrombosis is the formation of a clot within a blood vessel and can lead to serious consequences
• Coronary heart disease is caused by the build-up of plaque within the coronary arteries and has several risk factors
• Artificial pacemakers regulate heart rate and are used for bradycardia and arrhythmias