-there are two phases of a heart beat: contraction (systole) and relaxation (diastole).
-the direction of blood flow depends on pressure and valves.
-the direction of blood flow depends on pressure and valves.
Relaxation of the Heart (diastole)
-as the atria fill with blood from the pulmonary vein and the vena cava, the pressure increases.
-this means there is a higher pressure in the atria than there is in the ventricles and so blood is naturally forced through the AV valves into the ventricles. -all muscles are relaxed during this phase. -the semi lunar valves are closed at this point due to the ventricles having a lower pressure than the arteries as a result of ventrial diastole (dub). |
Contraction of Atria (atrial systole)
Contraction of the Ventricles (ventricular systole)
-after a short delay (to allow the ventricles to completely fill with blood) the ventricles contract.
-the pressure is increased so that it forces the AV closed (lub). -with AV valves shut, the pressure is even higher in ventricles and so blood is forced through semi lunar valves into the aorta and pulmonary artery. -the ventricles have thicker muscular walls than arteries as they must force blood a longer distance (round the body) -the left ventricle has a thicker muscular wall than the right as it must force blood around the whole body while the right one has to do it round the lungs. |
Cardiac Output
3 -1
-cardiac output: the volume of blood pumped by a ventricle per minute (measured in dm min
-it depends on: the stroke volume (volume of blood leaving the ventricle per beat) and the heart rate (number of beats per minute).
-the formula is: cardiac output = stroke volume x heart beat
-cardiac output: the volume of blood pumped by a ventricle per minute (measured in dm min
-it depends on: the stroke volume (volume of blood leaving the ventricle per beat) and the heart rate (number of beats per minute).
-the formula is: cardiac output = stroke volume x heart beat