Physiology Flashcards
During which phase of the cardiac cycle does ventricular filling occur?
Diastole
If a persons heart rate is 60 bpm, how long is systole and how long is diastole?
60 bpm = 1 beat/sec
In 1 second, 0.66 s is diastole, 0.34 s is systole
Which valves are
a) open
b) closed
during atrial systole?
During atrial systole;
a) Mitral and tricuspid valves are open
b) aortic and pulmonary valves are closed
Approximately what % of ventricular filling does atrial systole account for? How does this change when a patient is tachycardia and why?
At rest - approximately 20%.
Tachycardia - 40% - when patients are tachycardia due to reduced passive diastolic filling
on the cardiac cycle diagram, what is the a wave and x descent (with reference to atrial systolic pressures)
Atrial systole causes small increase in pressure (a wave). Once complete, the pressures fall (x descent), the AV valves float upwards and close .
Are the valves open or closed during isovolumeric contraction?
All valves are closed
What is isovolumetric contraction?
Time interval between the mitral and tricuspid (AV) valves closing and the semilunar (aortic and pulmonary) valves opening. These changes occur as during this phase, there is ventricular depolarisation and a rapid increase in ventricular pressure. During this phase, there is an increase in pressure but no increase in the volume of the heart.
What causes the first heart sound? Why is it split?
The closing of the mitral and tricuspid valves secondary to ventricular depolarisation and contraction. The increase in pressure forces the valves to close. It is split because the mitral valve closes slightly before the tricuspid.
Why does atrial pressure increase during isovolumetric contraction? What is the name of the wave in the cardiac cycle?
The closure of the AV valves increases atrial pressure during isovolumetric contraction. This is shown as the “c wave”
What is the name of the phase after isovolumetric contraction?
Rapid ejection
What happens to the atria’s blood flow and pressure during rapid ejection?
Blood flows into the atria during rapid ejection from both the lungs and systemic circulation.
The pressure will decrease as the AV valves get pulled downwards and the size of the atria increases.
Why does ventricular emptying continue during the reduced ejection phase of the cardiac cycle?
The kinetic energy generates continues to propel blood forward
What is the normal flow velocity of the aortic valve?
0.7 - 1.2 m/sec
This is a doppler ultrasound of blood flow across a stenosed aortic valve. What does the bright yellow area and dull yellow area represent?
the bright yellow area represents the low velocity/large area of the LVOT, and the peak of 4 m/s represents the large velocity/small area through a stenosed aortic valve.
Which equation can demonstrate the pressure gradient over an aortic valve from the flow velocity ?
Bernoulli equation ΔP ≃ 4 x V2
What are the valves doing during isometric relaxation?
They are all closed.
What does the dicrotic notch represent?
Increased aortic and pulmonary pressure during isometric relaxation that occurs due to the closure of the semilunar valves, brief reversal of blood flow and the subsequent elastic recoil of the vessel walls e.g. the sinus of valsalva will bulge (sinus just above aortic root)
What makes the AV valves close during IMR?
Continued relaxation of the ventricles results in a continued decrease in intraventricular pressures which reverses the pressure gradient across the semilunar valves causing them to close.
What is represented by the v wave in IMR?
The back flow of blood against the closed AV valves during IMR creates the v wave of the jugular pulse.
What creates the second heart sound? Why is it split?
The closure of the aortic and pulmonary valves. Split because the aortic valve closes slightly before the pulmonary valve.
Are the valves open or closed during the rapid filling phase of the cardiac cycle?
Mitral and tricuspid are open and the aortic and pulmonary valves are closed.
What stage occurs after isovolumetric relaxation in the cardiac cycle? Why is it called this?
Rapid (ventricular) filling.
It’s called rapid filling because during IVR, the ventricular pressure falls. When the ventricular pressure is lower than atrial pressure, the AV valves open and there is rapid filling as the atrial are at maximal pressure (high volume) AND there is diastolic suction of the ventricles as it actively relaxes.
What is the name of the part of the jugular pulse waveform which represents the fall in atrial volume and pressure ?
y descent
What causes a third heart sound?
Occurs at the end of diastole, after the rapid filling phase. Caused by the tensing of the chord tendinae and the atrioventricular ring supporting the valve leaflets - always pathological.
Why does ventricular filling have a reduced filling stage?
As the ventricles become more full, the pressure gradient between the atria and the ventricles decreases causing them to fill more slowly.
What happens in the a wave, c wave and x descent ?
a wave. Atrial contraction causes a reflux of blood into the venae cavae, which briefly increases the pressure to the maximun central venous pressure of 3-5 mmHg. No a wave is seen in atrial fibrillation
c wave. Occurs as the cusps of the AV valves bulge back into the atria during isovolumetric contraction and the transmitted pulsation from carotid arteries forms the c wave
x descent. Following the c wave, the atrial pressure drops rapidly as the atria relax and the atrioventricular ring and base of the ventricle are pulled down during the early rapid ejection phase
What happens during the v waves and y descent?
v wave. In ventricular systole, the pressure rises due to filling of the atria from the continued venous return of blood to the heart and closed AV valves
y descent. This pressure drop represents the AV valves opening and blood rapidly leaving the atria into the relaxed ventricle in diastole
When can a 4th heart sound occur?
Atrial systole
What does the 4th heart sound represent?
Vibration of the ventricular walls during atrial contraction and occur in conditions associated with stiff ventricles.
When does the aortic valve open?
When the ventricular pressure exceeds the aortic pressure
What is systolic pressure? Why is this not reached immediately after rapid ejection?
The maximal aortic pressure. After rapid ejection, the volume of blood in the aorta exceeds the amount that can be distributed to the peripheral circulation causing bulging of the aorta as it reaches its maximal systolic pressure
Why does the aortic valve not close at the start of the rapid ejection?
Although the aortic pressure is higher than the ventricular pressure, the aortic valve stays open during rapid ejection due to the kinetic energy of blood flowing past the valve and propelling it open.
What causes the aortic valve to close? What phase does this occur in?
When approximately 5% of blood has flowed back into the left ventricle, the aortic valve closes. This occurs during the reduced (ventricular) ejection phase. There is back flow of blood during the rapid ejection phase as the valve remains open.
What does the dicrotic notch represent?
Increase in aorta pressure when the aortic valve closes and there is bulging at the aortic root (the sinus of valsalva).
Do heart sounds result from valves opening or closing?
Closing
What is stroke volume?
End diastolic volume (EDV) - End systolic volume (ESV)
What is a syncytium ?
A network of myocytes connected by gap junctions that allows coordinated contraction of the ventricles.
What is the definition of depolarisation?
depolarisation or hypopolarization is a change within a cell, during which the cell undergoes a shift in electric charge distribution, resulting in less negative charge inside the cell compared to the outside.
What phases are there is the cardiac conduction system action potential?
Phase 0, Phase 1, Phase 2, Phase 3 and Phase 4
Why is the plateau phase not completely flat?
The influx of calcium ions slows depolarisation but it is not halted altogether
What is normal cardiac axis?
Between -30 and +90 degrees
What is shown here?
Pacemaker action potential
This is a sarcomere i.e. a basic contractile unit of muscle. Note where the Z-disc is, surrounded by the I-band followed by the A-band, H-zone and thin M - disc.
ZIAHM
What is the function of the cardiomyocyte’s T tubules ?
Short and broad invaginations of the sarcolemma. Allow the depolarisation of the sarcolemma to rapidly penetrate the myocyte
Where are T tubules located on the cardiomyocyte?
At Z-lines and close to a terminal sarcoplasmic reticulum cisterns to form a diad
What does a desmosome junctional complex contain?
Intercellular adhesion plaques and cadherins. Cadherins are transmembrane glycoproteins spanning that gap between myocytes.
6 connexINS form 1 connesON which forms a gap junction. What makes up a singular connexIN?
4 transmembrane domains (M1-M4)
2 extracellular loops (E1, E2)
Cystoplastic loop (CL), cytoplasmic C-terminals and N terminals
What is the LMM region of a thick filament composed of?
Light meromysin (LMM) and heavy meromysin (HMM) arranged in an alpha helix with a flexible hinge region
What is the HMM region of myosin composed of
2 globular heads each with three segments. ›
What is the name of the structure where the adjacent, bare thick filaments join? How it this part of the filament stabilised?
M disc
Stabilised with creatinine kinase, M-protein and myosin to form a stable lattice
How many tropomyosins wind around the actin polyfilament? What is their function?
- Block the myosin binding site.
Where are troponin found? What are the three types?
Found in clusters spaced out along the tropomyosin.
TnI - inhibitory actin binding
TnC - calcium binding
TnT - tropomyosin binding
With reference to actin, myosin and troponin describe the stages of muscle contraction?
- At rest, tropomyosin is bound to actin by TnI and TnT, blocking its binding sites.
- Muscle contraction requires the release of calcium from the sarcoplasmic reticulum. Calcium ions bind to TnC which causes the unbinding of the myosin heads to actin.
- Myosin binding to 1 actin subunit causes full displacement of tropomyosin and allows additional heads to bind.
- Calcium is sequestered (separated) and tropomyosin rebinds to actin preventing further cross links
What is desmin?
52 kD intermediate filament protein that encircles the z-disc and connects to the z-disc of adjacent sarcomeres, intracellular surface of sarcolemma, nucleus, mitochondria and other organelles. Involved in force transmission and longitudinal load bearing. Plays an important role in the integrity of cardiac myocytes.
