The Cardiac Cycle Flashcards
What is convection?
The mass movement of fluid caused by pressure difference
Why is diffusion not used for whole body transport?
Diffusion is a very slow process for distances > 1 mm which is why it’s useless for whole body transport
What is the Sino Atrial Node?
Group of cells located in the right atrium wall
What is the function of the SAN?
The SAN has the ability to spontaneously produce an action potential that travels through the heart via the electrical conduction system
SAN sets rhythm of the heart - natural pacemaker
What is the AV node?
Part of the electrical conduction system of the heart, coordinating the top of the heart
What is the role of the AV node?
The AV node electrically connects the right atrium and right ventricle, delaying impulses, so that the atria have time to empty their blood into ventricles, before ventricular contractions.
How is the resting potential maintained?
The cell interior has a negative resting potential compared to the exterior. Normally there’s a high [K+] inside and high [Na+] and {Cl-] outside
The Na+/K+ ATP pump transports 3 Na+ out for every 2 K+ in
Outline how SAN pacemaker potential occurs?
- Resting membrane potential
- Funny channel - If threshold
- membrane repolarises below If threshold - unstable
- At -50 mV Na+ channel activated causing slow Na+
influx
- Rapid depolarisation
- Cell depolarises, reaching threshold which activates
Ca2+ channels causing rapid depolarisation
- Cell depolarises, reaching threshold which activates
- Repolarisation
- Ca2+ channels are switched off and Voltage K+
channels are opened causing an efflux of K+
- Ca2+ channels are switched off and Voltage K+
Describe how atrial & ventricle muscle action potentials occur
- Rapid depolarisation
- Depolarisation signal received from SAN, opening
Na+ channels leading to Na+ influx - Voltage gated Ca2+ channels open slowly
- Depolarisation signal received from SAN, opening
- Early repolarisation
- Na+ channels close
- Cells begin repolarising
- Plateau phase
- VGCC fully open causing an influx of Ca2+
- Halts repolarisation and voltage gated K+ channels
slowly open
- Rapid depolarisation
- Ca2+ channels close and K+ channels fully open
causing an efflux of K+
- Ca2+ channels close and K+ channels fully open
- Resting membrane potential
- Stable Na+/K+ ATP pump in 3:2 ratio
Outline how electrical conduction occurs in the heart
- Electrical activity generated in SAN spreads out via gap
junctions into atria - At AV node, conduction is delayed to allow correct
filling of ventricles - Conduction occurs rapidly through Bundle of HIs into
the ventricles - Conduction through Purkinje fibres spreads quickly
throughout ventricles
Where is electrical activity generated in the heart?
Electrical activity is generated at the SAN node and conducted throughout the heart
Electrical activity is converted to myocardial contraction, creating pressure changes within chambers
Which direction does blood flow in the heart?
Blood flows from areas of high to low pressures, unless blocked by a valve
How do valves function?
Valves open and close depending on chamber pressure changes
How do the events in the heart differ between the right & left sides?
Cardiac events are the same on the right & left sides, but the right has a lower pressure than the left
Outline the route of blood flow through the heart
Systemic circulation
vena cava -> right atrium -> tricupsid valve (AV) -> right ventricle -> pulmonary valves (SL) -> pulmonary arteries
Lung circulation
pulmonary veins -> left atrium -> bicupsid (mitral AV) valve -> left ventricle -> aortic (SL) valve -> aorta
Describe the events that take place during the cardiac cycle
- Ventricular filling / atrial contraction - diastole
Blood enters atria then into ventricles
pressure in atria > ventricles
mitral / tricupsid valves open aided by atrial contraction - Isovolumetric contraction - systole
Pressure in full ventricles > atria
mitral / tricupsid valves close
Closed ventricle contracts increasing pressure - Ejection - systole
Pressure in ventricles > aorta / pulmonary artery
valves open and blood is ejected into atria - Isovolumetric relaxation
aorta / pulmonary artery pressure > ventricles
aortic / pulmonary valves close
closed ventricle relaxes ready to receive blood
Describe the left ventricular pressure changes that occur during the cardiac cycle
- Ventricular diastole (left atrium contraction)
slight rise in ventricular pressure
mitral valves close
ventral pressure > atrial pressure - Isovolumetric contraction causes pressure rise
- Ejection occurs when ventricle pressure > aorta as
aortic valves open - Isovolumetric relaxation causes large pressure drops
Ventricles empties as ventricular pressure > atria
aortic valves close and mitral valves open
Outline the left ventricular volume changes
- filling of ventricles due to atrial contraction
EDV = 120 ml - Full ventricles have higher pressure so mitral valves
close initiating systole but no change in volume yet - Ventricular pressure > aortic valve pressure causing
ejection of blood - Isovolumetric relaxation occurs when ventricular
pressure falls as aortic valves close due to high aortic
pressure
How is Stroke volume calculated using Ventricular volumes?
SV = EDV - ESV
SV - stroke volume
EDV - end diastolic volume
ESV - end systolic volume
Summarise the cardiac cycle using the Ventricular pressure - volume loop
Mitral valves open
Mitral valves close
Aortic valves open
Aortic valves close
The ventricle pressure - volume loop relates to the amount of energy consumed during the cardiac cycle
Outline the equation used to calculate Work Done by the heart
Work = Change in ventricle pressure x Change in volume
area inside the ventricle pressure - volume loop is the amount of stroke work done
Describe the cardiac events occurring in the right atria and jugular veins
a wave
- atrium contract
- blood moves out of atrium into ventricles
x descent
- atrium releasing blood
- tricupsid valves closed, refilling of atria begins
v wave
- atrium full and tense
- tricupsid valves closed and atria start to empty
y descent
- atrium emptying and tricupsid valves opened
What are the noises heard from the heart?
The noises heard from the heart are vibrations induced by the closure of cardiac valves, ventricular chamber vibrations and turbulent blood flow through valves
Describe the noises occurring during cardiac cycle
S1 - ‘lub’
closure of tricupsid / mitral valves at beginning of ventricular systole
S2 - ‘dub’
closure of aortic / pulmonary valves (SL) at end of ventricular systole
S3 - occasional
turbulent blood flow into ventricles, detected near end of first 1/3 diastole, especially in older people
S4 - pathological in adults
Forceful atrial contraction against a stiff ventricle - less prominent in young people
