Describe a typical cardiac cycle Flashcards
For the purposes of my notes the, cardiac cycle will start just after ventricular systole has ENDED. But in theory, you can start it anywhere.
The stages are:
- Ventricular filling (diastole) + Artial contraction
- Isovolumetric contraction (Systole)
- Ventricular ejection (Systole)
- Isovolumetric relaxation
Describe stage 1 - including state of valves, what chambers are involved
- Ventricles just finished contraction (are in diastole)
- As the ventricles relax, blood flows back against semilunar valves - closing them
- Blood flows into the relaxed atria - causing pressure to RISE in the atria - thus causing the AV valves to be pushed open and blood to fill the ventricles
- During the last moments of diastole - the atria contract and give an additional thrust to inflow of blood
For the purposes of my notes the, cardiac cycle will start just after ventricular systole has ENDED. But in theory, you can start it anywhere.
The stages are:
Ventricular filling (diastole) + Artial contraction
Isovolumetric contraction (Systole)
Ventricular ejection (Systole)
Isovolumetric relaxation
Describe stage 2 - including state of valves, what chambers are involved
- The ventricles start to contract, but semi-lunar valves do not open yet
- So the pressure in the ventricles is now increasing - pushing the AV valves SHUT
- this is called ISOVOLUMETRIC CONTRACTION
- This means the volume stays the same, but contraction is occuring causing the pressure to rise
For the purposes of my notes the, cardiac cycle will start just after ventricular systole has ENDED. But in theory, you can start it anywhere.
The stages are:
Ventricular filling (diastole) + Artial contraction
Isovolumetric contraction (Systole)
Ventricular ejection (Systole)
Isovolumetric relaxation
Describe stage 3 - including state of valves, what chambers are involved
- The ventricular pressure exceeds the aortic pressure - causing the semilunar valves to OPEN
- Blood is ejected at high pressure from the ventricles into the arteries
- Some of the blood will remain in the ventricles - END SYSTOLIC VOLUME
For the purposes of my notes the, cardiac cycle will start just after ventricular systole has ENDED. But in theory, you can start it anywhere.
The stages are:
Ventricular filling (diastole) + Artial contraction
Isovolumetric contraction (Systole)
Ventricular ejection (Systole)
Isovolumetric relaxation
Describe stage 4 - including state of valves, what chambers are involved
- ventricles relax, intravenrticular pressure drops
- Blood flows back against cusps of semilunar valves and forces them closed
- AV valves remain closed
Define the end diastolic volume
- The maximum amount of blood the ventricles will contain
- This is just after atrial systole (after the atria have contracted)
What is a typical EDV?
130ml
What is the typical ESV?
50ml - normally 40 percent of EDV
Define stroke volume, and give the calculation used to work it out
- The amount of blood pumped out of each ventricle during a single beat
- End Diastolic Volume MINUS End systolic volume
Define ejection fraction
- % of End diastolic volume represented by the SV
- In other words, how much of the end diastolic volume which actually pumped out of the heart, as a percentage
Unlike skeletal muscle, cardiac tissue contracts on it’s own, without neural or hormonal stimulation.
Unlike skeletal muscle, cardiac tissue contracts on it’s own, without neural or hormonal stimulation.
What is the feature of cells called in the heart that can contract without neural or hormonal stimulation?
Autorhytmicity
Label the areas of the heart conduction system
Alternative name for AV bundle = Bundle of his
What is the name of the conduction pathway that connects the SA and AV nodes?
Inter-nodal pathways
The two types of cardiac muscle cells involved in a normal heartbeat are what? Very briefly explain the roles of each
- Conduction cardiac cells - these control and coordinate the heartbeat contractions
- Contractile cardiac cells - produce the actual physical contraction
Where are the pacemaker cells conducting cells found in the heart?
SA and AV node
Explain the histologiical features of contractice cardiomyocytes
- mono nucleated
- central nucleus
- numerous mitochondria
- intercalacted discs (image below)
- sarcomeres
What are the main components of intercalated discs?
- Desmosomes
- Gap Junctions
- Fascia adherens
What is the function of gap junctions in contractile myocardiocytes?
- permit transmission of action potentials from one cell to another - creates pathways for ions to flow - allows the heart to contract in synchrony
What is the role of fascia adherens and desmosomes in intercalacted discs?
Anchoring proteins that hold the myofibrils and cardiomyocite cytoskeleton in place
Explain the main differences in conductive myocytes compared to contracticle cells?
- fewer myofibrils
- leaky ion channels - reduced potential resistance
What are the main places conductive cardiomyocytes are found?
- SA node
- AV node
- Purkinje fibres
What special type of conductive myocytes are found in the SA and AV nodes?
Pacemaker cells
Pacemaker cells are weird in that they do not have a stable resting membrane potentia. They have leaky ion channels which cause them to depolarise without stimulation. What is this special membrane potential called?
Pacemaker potential
Pacemaker cells in the SA Node depolarise spontaneously, but the rate at which they depolarise can be affected.
Describe the SA node action potenital, describe how the rate of depolarisation can be affected
- Phases 0, 3 and 4
- Phase 4 - you are getting spontanoeus polarisation due influx of sodium through HCN Funny channels, which is bringing the SA cells towards THRESHOLD
- Phase 0 - threshold has been reached, meaning depolairsation occurs due to influx of calcium via T-type calcium channels
- Phase 3 - repolarisation occurs due to rectifier Potassium channels
So this is how it would normally occur, but there is also imput from the AUTONOMIC nervous system.
SYMPATHETIC
- The sympathetic nervous system can cause adrenaline and noradrenaline production by the adrenal gland
- These both stimulate the production of cAMP, which has a key role in activiting more HCN funny channels
- Thus, the time to reach threshold decreases, giving you increased Heart rate
PARASYMPATHETIC
- Alternatively, ACh from the vagus nerve, then Potassium permability OUT increases, taking LONGER to reach threshold, thus slowing the heart rate
What is the resting membrane potential of a contractie cardiac cell
-90mV
Describe the action potential of contractile cardiac cells
- Phase 4 is the RESTING phase - cardiac cell is at it’s resting membrane potential
- AN ACTION POTENTIAL IS RECEIVED FROM A NEIGHBOURING CELL
- Phase 0 now occurs, whihc is marked by rapid depolarisation due to inward SODIUM channels, which are VOLTAGE GATED
- Phase 1, there ia partial repolarisation, which causes a small dip, this because the voltage gated sodium channels close
- Phase 2, calcium channels are open, so calcium can enter the cytoplasm, whilst there is also outward transport of Potassium - hence the relatively stability of the memrbane potential
- Phase 3 - true repolarisation - the inward calcium current inactivates, and more potassium channels begin sending potassium outrwad, thus making the cell more negative and bringing it back to it’s resting membrane potential.
WHhat produces the first Lubb sound of the heart?
Closeure of AV valves
What produces the second sound of the heart beat?
Closure of the semi-lunar valves.
Draw this
Describe what is meant by excitation contraction coupling (with regards to the cardiac muscle contraction)
The process by which generation of an action potential leads to the contraction of the heart muscle.
