The Heart

• Cardiac output

  Stroke volume x BPM
• Right atrium receives deoxygenated blood from vena cavae
• The lower the resting heart rate, the fitter the person is
• ECGs

  P - atria contract (atrial systole)

  Q - end of the delay

  R - ventricle contracts

  QRS - contraction through ventricles (ventricular systole)

  T - diastole - heart chambers are relaxed
• Atria have thinner walls and they receive blood coming into the heart
• Ventricles have thicker walls and forcefully have to pump blood to the lungs and the rest of the body
• Atrioventricular valves prevent blood flow back into the aorta
• Cardiac muscle contracts and relaxes without any signal from the nervous system
• The cardiac cycle is myogenic meaning that contractions start with the cardiac muscle
• A region called the sinoatrial node or SAN sets the pace - often referred to as the pacemaker
• The SA node is found in the wall of the right atrium where the vena cava enters
• Impulses spread rapidly throughout the walls of the atria causing them to contract in unison
• The heart is behind the sternum which provides some protection. It's enclosed in membrane made of inelastic tissue called pericardium
• The right and left coronary artery branches from ascending aorta and brings oxygenated blood to cardiac muscle
• The coronary veins feed back into the heart through the right atrium and blood can then be pumped to the lungs
• The capillaries spread throughout the myocardium and deliver oxygen and nutrients. They are essential to provide energy for contraction
• Myogenic means it originates in muscle tissue rather than from nerve impulses
• The atria begin to contract following depolarisation of the atria and pump blood into the ventricles
• The AV node receives the signal from the SA node
• The signal received by the SA node is sent to the atria via the AV node. The impulse is the delayed about 0.1s before spreading
• It is important that there is a delay between the atria and ventricles contracting as it ensures the atria are empty before the ventricles contract
• During the cardiac cycle, ventricle walls are relaxed and blood flows into them, a process known as ventricular diastole.
• Both atria are filled with blood from the vena cava and pulmonary arteries, a process known as atrial diastole.
• As pressure of blood in the ventricles rise, it forces the AV valves shut to prevent backflow into the atria.
• The SA node then generates an electrical impulse causing muscle in both atria to contract in unison which forces the AV valves open.
• The AV node receives the signal from the SA node and this is conducted through the bundle of his to the apex of the heart.
• Purkinje fibres conduct the impulse through each ventricular wall.
• The ventricle walls then contract from the bottom up which increases the pressure in each ventricle.
• This forces the semi-lunar valves in the aorta and pulmonary arteries to open, a process known as ventricular systole.
• Right side

  Receives deoxygenated blood from the vena cava

  Pumps deoxygenated blood to the lungs via pulmonary artery
• Left side

  Receives oxygenated blood from pulmonary veins

  Pumps oxygenated blood to the rest of the body via the aorta
• An ECG is where electrical sensors are attached to the skin and pick up activity in the heart
• Tachycardia is where the heart rate is over 100 beats per minute

  
• Brachycardia is where the heart rate is slower than normal (below 60)

  
• Ventricular fibrillation is a fast and chaotic heart rhythm

  
• Sinus arrhythmia is a variation in a beating heart