cardiac cycle 1 Flashcards
- The heart is composed of a unique type of muscle - cardiac muscle
- Key features of cardiomyocytes are:
– myogenically – ( — )
– have — , — shaped fibres
– mostly — , — (can be —)
– — in appearance
– connected to each other by — ( — junctions)
active
involuntary
regular , Y
single , nucleated ( binucleate )
straighten
intercelated discs
gap junctions
- The intercalated discs mean that the myocardium is a — (from the Greek syn kytos: — cell)
– strictly speaking two syncytia as – AND – - Once one cell – , current will flow to the adjacent cell via—
- This is how — flows through the heart
– it is not — dependent, that is set by the —
functional syncytium
one cell
atria and ventricle
depolarises
intercalated discs
depolarisation
directionally
refractory period
membrane potential:
* All cells are relative — charged
– due to DNA, fixed — and—
* Excitable cells ( — & — ) can rapidly change their —
– via changes in – to various —
* Therefore excitable cells can transport — via — ( —- )
-ve
anions and Na/K ATPase
neurons and msucles
membrane potenial
membrane permeability
ions
messages
electrical signals
action potential
- SA node is the — as it is — due to a — membrane
– it is “leaky” to — so “resting” potential is around — mV - At rest Na+ (and some K+) leak — cell slowly — it
– via the — channels, down it’s concentration and electrical gradient - Around — mV, slow L-type Ca2+ channels — and the cell —
– —- channel - This is — dependent, so after ~ — ms the — channels close and— channels open leading to —
– cell — and process starts again - This sloping resting phase in the SAN gives rise to the —
– the rate of this is ~ — bpm but slowed in the body by — - The —- affects heart rate via this slow automatic depolarisation
– increasing the gradient of the slope increases rate (—)
– decreasing the gradient of the slope decreases rate (—)
pacemaker
unstable
leaky
cations
-55
into
depolarising
funny HCN
-40mv
open
depolarises
voltage gated
time
200
ca+2
k+
k+ efflux
repolarises
(check pic slide 7)
automaticity
100
PNS
autonomic nervous system (ANS)
SNS
PNS
ventricular action potential:
* In ventricular cells, resting potential is around – mV
* Action potential is triggered by — spreading from adjecent cells via —
* Voltage gated — channels open and cell depolarises
* Voltage gated — channels open AND — type Ca2+ channels too
– K+ efflux and Ca2+ influx cancel out and cause a —
* — channels close, K+ efflux leads to –
Phase 0: — , — influx
Phase 1: Initial — (— )
Phase 2: — (— and —)
Phase 3: — (—)
Phase 4: —
AP = -70
RP = -90
-90 mv
depolarisation
intercalated discs
na+
k+ and L type
ca+2
repolarisation
k+ efflux
repolarisation
fast na+
repolarisation (k+)
platue ( k+ + ca+2)
repolarisation ( k+)
resting potential
( pls check slide 10 )
- The plateau is due to the – of — alongside the — of —
- It allows the ventricle to fully — and —, — the next action potential arrives
- This prevents cardiac muscle from entering — contraction
– because the twitch is over — the cell can depolarise again - The length of this action potential sets the upper limit of —
– heart rate cannot exceed ~ — bpm
check slide 12
influx of ca+2
efflux of k+
contract and relax
before
titanic
before
heart limit
200
conduction pathway:
* Depolarisation starts in — at the — node
– — gives this is the fastest depolarisation rate
* Via —- , depolarisation spreads through the right and left atria
* The depolarisation reaches the — node and is —
– allowing for — ventricular filling
* From the AV node it spreads down the — , onto the — and on to —
– from — to —
right atrium
SA
funny current
intercalated disc
AV
slowed
increased
bundle of HIS
purkinjie fibbers
ventricular muscle
endocardium to epicardium
- The speed of conduction depends on the — and the number of—
– the more gap junction the — the spread
– the larger the diameter the – the spread (just as in nerves) - Approximate Conduction velocities
– Atria 0.3 m/sec
– internodal pathway 1.0 m/sec
– AV node 0.03 m/sec (small diameter)
– Purkinje 3.0 m/sec (large diameter)
– Ventricles 0.3 m/sec - summary:
- The action potential in the SA node and ventricular myocytes are
similar to — - Once a threshold is reached voltage-gated channels —
- Reaching the threshold is due to — or — of adjacent cells
diameter
gap junctions
quicker
quicker
nerves
open
leakiness or depolarisation
cardiac valves:
* Pressure in the atria, ventricles and arteries changes with respect to
each other over the cycle
* There are four valves in the heart that prevent — and keep blood moving —
* AV valves between the — and the —
– on the left is the — valve, on the right is the — valve
* semi lunar valves between — and the —
– on the left is the — valve and right is the — valve
backflow
forward
atria and venctirucles
mitral valve
tricuspid valve
ventricles and arteries
aortic valce
pulmonary valve
PLS check slide 5 so important !
heart sound:
* 1st heart sound: — of the– valves as the ventricles — causes —
– – pitch and relatively– , — sound“—”
* 2nd heart sound: — snap — of the— and — valves again causing –
– — than first“—”
* These are what you hear with the a—, but other sounds can be detected by—.
closing
AV
contracts
vibration
low
long
loudest
lubb
rapid
closing
aortic and pulmonary valves
vibration
shorter (dub)
stethoscope
phonocardiogram
- The phonocardiogram will pick up a — and — heart sound
- 3rd heart sound: the transition between— filling and — filling of
the —
– more common in —/— , may be pathological elsewhere - 4th heart sound: known as — it is the — filling of a – ventricle.
– always — but can be more common in — - Murmurs also occur due to — flow
– flow through produced by— or— valves as described above
– — in the cycle is important for identifying the problem
3rd and fourth
rapid and slow
ventricles
young/healthy
arterial systole
rapid
stiff ventricles
pathological
elderly
tubelant
stenosed or leaky
timing
summary:
* The cardiac cycle is the — contraction and relaxation of the heart
– it is how it can act as a—
* It is triggered by— in the — node
* The — of the chambers, lead to— changes that drive — through the heart (and circulation)
* These changes also open and close valves that can be heard on—
rhythmical
pump
depolarisation
SA
contraction
pressure
blood flow
auscultation
- The — is a complete cycle of heart activity
– from the start of – beat to the start of the next - Each cycle consists of a period of contraction ( — ) and a period of
relaxation (—) - Heart rate at rest is ~– bpm so the duration of a cycle is approximately -= ms
– of which ~ – is systole (— ms) and ~ — diastole (— ms) - During exercise heart rate can increase to— bpm
– this is a cycle of about — ms
– (200 ms – , 100 ms— )
cardiac cycle
one beat
systole
diastole
70
850
2/5 ( 330)
3/5 (520)
200
300
systole
diastole
- During diastole, ventricular pressure drops to — mmHg
- Due to the — pressure, blood flows in from the – so ventricular
pressure —
– the atria have filled during — - Towards the end of diastolic, contraction of the atria (—)
expels — blood into ventricle and pressure and volume—
– a — in the jugular venous pulse - The jugular venous pressure (JVP) is an — measure of the — pressure
- The pulmonary capillary wedge
pressure is an – measure of the
— pressure - Most blood entering the atria flows directly into the – (~—%)
– contraction of the atria only adds ~—%
info:
a wave: atrial systole 5-7 mmHg increase in pressure
c wave: AV valves close and cusps bulge into atria
x descent: atria relax, valves no longer bulge
v wave: ventricular systole, atria fill with venous return
y descent: blood enters the ventricles (atria pressure
drops)
0
low
atria
rises
ventricular systole
arterial systole
more
increases
wave
indirect
right atrial
indirect
left atrial
ventricles (75%)
25%
ventricular pressure - systole:
* Ventricle — , – valves – and pressure starts to—. This is–
– no – until — valves —
* Once pressure exceeds — pressure there is the period of ejection as blood is —
– ~80 mmHg on the— , ~25 mmHg on the —
* As ventricle — , pressure — and there is —
– pressure – until – valves — and the next cycle begins
- ventricular volume:
* Ventricle fills during —
– — adds another ~25% (up to ~120 ml)
* — until pressure exceeds aortic (or pulmonary) pressure then ejection phase
– — ejection first, slowing towards the end of —
* Ejection fraction is approximately —% of the end-diastolic volume
– approx 70 ml of the 120 ml, 50 ml remain
* As pressure —, filling from the— begins again
contract
AV
closes
rise
isovulmetric contraction
ejection
semi linar
open
atrial pressure
expelled
left
right
relaxes
drop
isovulmetric relaxation
drops
av
opens
diastole
arterial contraction
isovulmetric contraction
rapid
systole
60%
drops
atria
aortic pressure:
* From — , as ventricular pressure exceeds aortic pressure, aortic pressure rises along with it from ~ — mmHg to — pressure (~ –mmHg)
* During — , ventricular pressure drops but backflow is prevented by —
* Elastic recoil of the large elastic arteries drives blood flow—
toward tissues
* As blood flows out towards tissues, aortic pressure — to diastolic
pressure (~– mmHg)
summary:
* The cardiac cycle is the rhythmical contraction and relaxation (of the
ventricles)
* It is triggered by depolarisation (viewed by ECG)
* The contraction of the chambers, lead to pressure changes and so
blood flow through the heart
* These changes also open and close valves that can be heard on
auscultation
mid-systole
80
peak systolic
120
diastole
aortic valve
forward
drops
80
