Cardiac Cycle Flashcards
What does the ‘lub’ and ‘dub’ sounds come from?
Lub= Atrioventricular valve closes (S1)
Dub= Semi lunar valves close (S2)
What happens in the aorta and LV when the pressure starts falling in both?
Aorta= Elastic fibres in walls of aorta recoil
LV= Muscular walls start relaxing so heart volume increases
What is a dicrotic notch?
This is an increase in pressure in the aorta when the aortic valve shuts and there is recoil of the elastic fibres in the walls of the aorta which increases the pressure so blood can be pumped all around the body.
What is the a wave?
This is the bump on the cardiac cycle diagram where the atrium contracts which increases the pressure in the atrium
What is the role of chordae tendinae?
They are attached to the atrioventricular valves are prevent the AV valves from buckling back into the atria under the very high pressure of the ventricles
What is the c wave?
This is the increase in pressure in the atria as a result of the snapping shut of the AV valves causing a slight recoil of the blood. (This is similar to the dicrotic notch).
What does EDV mean?
End diastolic volume- Volume in the ventricle at the end of diastole. About 130ml
What does ESV mean?
End systolic volume- the volume in the the ventricle at the end of systole. About 60ml
What is Stroke Volume?
The volume ejected per beat from each ventricle, about 70ml
What does Inotropy mean?
Relates to the force of muscle contraction
What does Chronotropy mean?
Relates to the change of rate
What does Lusitropy mean?
Relates to the rate of relaxation
When does blood enter the atria?
There are no valves into the atria so blood is always passing into the atria continuously.
How do calcium ions affect the force of the muscular contraction?
The more calcium ions that bind to troponin molecules, the more cross bridges that form, and therefore the stronger the muscular contraction.
How many phases of the Cardiac Cycle are there?
7
What is pre-load?
This is the volume of blood in the ventricle at the end of diastole.
What is Isovolumetric contraction?
This is when the ventricles contract with the valves closed in order to create high enough pressure for it to be greater than that of the aorta so blood can flow out of the ventricles.
The ventricular volume does not change because all valves are closed during this phase. Individual myocyte contraction is not necessarily isometric because individual myocytes are undergoing length changes.
What is the c wave in a heart chamber pressure graph?
This is due to the bulging of mitral valve leaflets back into the left atrium when the left ventricle contracts and creates a very high pressure in the left ventricle.
Why does the atrial pressure rise gradually?
As the blood is continuously flowing into the atria resulting in a gradual increase in pressure.
When ventricular pressure falls slightly below that of the tract pressure, why does outward flow still occur?
This is due to the kinetic energy of the blood.
What is the S4 sound?
This is ‘a stiff wall’. It is caused by vibration of the ventricular wall during atrial contraction.
What is the S3 sound?
May represent tensing of the chordae tendineae and AV ring during ventricular relaxation and filling. (slosh-ing in)
Why does the SA node have the highest rate of intrinsic rhythmicity?
It has the shortest action potential and refractory period.
Explain the pacemaker action potential curve in the heart?
Starting at around -60mv there is a gradual rise to the threshold potential of -40mv. This is due to an influx of Na+ ions coming into the cell.
At the threshold potential, Calcium ion channels open (and diffuse into the cell) resulting in depolarisation and a steep increase to around +5mv.
At the peak, Calcium ion channels close and Potassium ion channel open resulting (and diffuse out of the cell) resulting in repolarisation of the membrane.
The cycle is then repeated at a constant rate resulting in a continuous heart beat.
How does sympathetic stimulation affect the pacemaker potential?
Increases the number of HCN channels in the membrane so the membrane is more leaky to sodium ions so there is more frequent action potentials.
What is vagal withdrawal?
This results in withdrawal of the parasympathetic nervous system so the sympathetic activity increases causing SA node to increase to about 100bpm.
Why is there a plateau in the membrane potential of the ventricles?
This is due to both calcium ion and potassium ion channels being open so they cancel each other out resulting in a stable membrane potential. This allows for a longer cardiac muscle contraction time and gives time for cardiac muscle cells to depolarize fully.
