The Cardiovascular System

The Cardiovascular System

1. The Conduction System

   • 6 Steps of system
     • 1) Cardiac Impulses initiate from the SA (Sinoatrial) node in the right atrium
       • 2) Impulses pass through right and left atrium walls to the AV node, causing both atria to contract, this is known as 'atrial systole'
         • 3+4) The AV node conducts impulse down through bundle of HIS...
     • 5) ... down through the left and right bundle branches to the apex of the heart
       • 6) Impulses travel up around ventricle walls via purkinje fibres, causing both ventricles to contracts; this in know as 'ventricular systole'
   • The heart is myogenic - it generates its own electrical impulses called the cardiac cycle

2. Links between Conduction System and The Cardiac Cycle

   • The heart has a dual pump action with 2 separate pumps that work simultaneously to pump blood to two different destinations
   • The right side of the heart pumps de-oxygenated blood towards the lungs
   • The left side of the heart oxygenated blood towards the rest of the body

3. The Cardiac Cycle

   • Represents the mechanical events of one hartbeat. One complete cycle last approx. 0.8 seconds and consists of 2 phases that represent the contraction and relaxation of the heart muscle
   • Diastole (0.5s)
     • 1) Both avia fill with blood. AV valves closed
       • 2) Atria blood pressure rises above ventricular pressure
         • 3) Rising blood pressure forces AV valves open and blood passively passes into both ventricles. Semilunar valves close
   • Systole (0.3s)
     • 4) Both atria and actively forcing the remaining blood into ventricles
       • 5) Semilunar valves remain closed
         • 6) Both ventricles contract increasing ventricular pressure
           • 7) Aortic and pulmonary forces open. AV valve closed
       • 8) Blood forced out into: aorta to blood tissue/muscles = stroke volume; pulmonary arteries to lungs. N.B. only 40% is ejected at rest during ventricular systole
         • 9) Diastole of the next cardiac cycles begins. Semilunar valves close preventing backflow of blood from aorta and pulmonary arteries

4. Cardiac Output , Stroke Volume and Heart Rate

   • Heart Rate (HR)
     • The number of times the heart ventricles beat in one minute.
     • Average resting heart rate is 70-72 bpm
     • Max heart rate is calculate using 220 - age
   • Cardiac Output (Q)
     • The volume of blood ejected by heart ventricles in one minute
     • Average = 5litres (Q) = 70ml (SV) x 72 (HR
   • Stroke Volume (SV)
     • The volume of blood ejected by heart ventricles per beat
     • Average Resting Stroke Volume is 70ml

5. Changes in heart rate

   • Resting heart rate
     • 1) Average is 72, but a young, fit aerobic athlete may have have a resting HR of 60
   • Anticipatory Rise
     • 2) Heart rate increases even before exercise due to release of adrenalin
   • Rapid increase in HR at start of exercise due to receptors
     • 3) -Continues use of adrenalin (hormonal, -Propioreceptors (muscle/joint) relating to inc. motor activity (neural control), -Chemoreceptors relating to inc. CO2/lactic acid (decreased ph) and decreased O2 levels (neural control)
   • Continued but slower inc. in HR
     • 4) -Continued effect of Chemoreceptors and Propiorecptors (neural control) -Increase in blood temperature (intrinsic control) -Increase in Venous Return (intrinsic control)