The Heart As A Pump Flashcards
What is the difference between capacitance and resistance vessels?
Capacitance vessel enable the system to amount of blood pumped around the body. They usually work in low venous pressure.
Resistance vessels restrict blood flow to drive supply to hard to perfume areas of the body. They usually work in high arterial pressure.
How does the blood flow change in response to oxygen demand?
The supply of blood flow to various tissues must change to meet demand. For example, at rest and after eating, the gut receives the majority of the blood flow. Whereas during moderate exercise, the skeletal and cardiac muscle receive the majorit you of the blood flow.
The brain and kidneys receive a constant flow of blood.
Explain how the heart works as a pump.
Two pumps acting in series
Systemic circulation = High Pressure
Pulmonary circulation = Low pressure
Output of left and right sides over time
must be equal
Atria act as “priming pumps” for
ventricles
Right heart is receiving deoxygenated blood pumped through heart to pulmonary artery. This is the only artery that carries oxygenated blood. Arteries always carry blood away from the heart.
Left side of heart is working under much higher pressure than the right side.
Both sides of heart have equal outputs
Left ventricular walls are very thick compared to the thinner right ventricle
What is the difference between diastole and systole?
Systole = Contraction and ejection of blood from ventricles
Diastole = Relaxation and filling of ventricles
What is the typical pressure (mM Hg) in the:
A) Left atrium B) Left Ventricle C) Aorta D) Right Atrium E) Right Ventricle F) Pulmonary Artery
A) 8-10 B) 120 systole/ 10 diastole C) 120 systole/ 80 diastole D) 0-4 E) 25 systole / 4 diastole F) 25 systole / 10 diastole
What is the stroke volume?
The volume of blood (ml) pumped out of the heart per beat.
At rest each ventricle pumps ~ 70 ml blood per
beat
At a heart rate of 70 bpm = 4.9 litres blood pumped per minute (i.e. the approximate
volume of blood in the body)
Describe how the structure of the heart muscle is related to its function.
Specialised form of striated muscle
Skeletal are formed by synsitiam of fibres whereas smooth muscle are distinct individual cells
Cardiac - functional syncitiam of cells. What happens in one can influence what happens in another cell eg electrical impulses can pass easily because these cells are functionally working via gap junctions.
Discrete cells but interconnected
electrically
Cells contract in response to action
potential in membrane
Describe how a cardiac action potential is formed?
How is this different to a normal action potential?
Cardiac ap is unusual due to duration - it is a lot longer (280ms) needs to be long because one action potential is driving the action potential of another. Muscle of arranged in a figure of 8 - this is ejecting the blood
Action potential causes a rise in
intracellular calcium
Action potentials are triggered by spread of excitation from cell to cell
What are the names of the Four valves that determine pathway of blood flow through heart?
Where are they located and which way do they allow blood flow?
In - Tricuspid valve and Mitral valve
Out - Pulmonary valve and Aortic valve
Right - Tricuspid valve and pulmonary valve
Left - Pulmonary valve and mitral valve
How do the heart valves work?
Open or close depending on differential
blood pressure on each side.
The valves on the left and right side of the heart cannot e open at the same time. If one is open, another is closed.
Valve cusps are pushed open to allow blood flow and close together to seal and prevent backflow.
What happens if too much pressure is placed on the valves?
How do we prevent this?
Why is the left side of the heart more at risk?
There is a danger that valves could invert due to the high pressure placed on them by the blood.
To prevent that we have chordae tendineae to anchor the valve and prevent inversion Of valves during systole`.
There is a higher blood pressure in the left side of the heart.
The cusps of mitral and tricuspid valves attach to papillary muscles via chordae tendineae. This prevents inversion of valves on systole.
Give a brief overview of the heart’s conduction system.
The beating of the heart is driven by the generation of an action potential passing through the myocardium.
The AP is generated in the pacemaker cells in SAN - sinoatrial node.
Activity spreads over atria – atrial systole
Reaches the atrioventricular node and
delayed for ~ 120 ms. This prevents the ventricles from contracting at the same time as the atria.
From a-v node excitation spreads down septum between ventricles via purkinje fibres
The AP then spreads through ventricular myocardium from inner (endocardial) to outer (epicardial) surface
Ventricle contracts from the apex up
forcing blood through outflow valves
The cardiac cycle can be split into 7 phases. What are they?
Which phase is systole and which phase is diastole?
The cardiac cycle is the sequence of events that occur in the heart as it is beating.
1) Atrial Contraction
2) Isovolumetric Contraction
3) Rapid Ejection
4) Reduced Ejection
5) Isovolumetric Relaxation
6) Rapid Filling
7) Reduced Filling
2, 3 and 4 are systole and the rest are diastole.
What happens to the cardiac cycle if the heart rate increased from 67 beats per min to 97 beats per min?
The duration of the cycle will increase.
Although as heart rate increases, systole stays the same, diastole gets shorter
What’s the difference between a wiggers diagram for the left and right side of the heart?
Typically a Wiggers diagram is plotted for just the LEFT side of heart.
A diagram for the RIGHT side would be very similar but at lower pressures
What are the waves that are observed in a Wiggers diagram?
The first half of the diagram compare pressure and time per secs:
Aortic pressure
Left Atrial Pressure
Left Ventricular pressure
The second half compares volume per time in secs:
Left Ventricular volume
Electrocardiogram
Phonocardiogram
Describe what would be seen on a Wiggers diagram at Phase 1?
Phase 1 is Atrial Contraction
On an ECG machine, contraction of the atria is signified by p wave. This signifies onset of atrial depolarisation.
Contraction of atria can also be detected in the atrial pressure wave. This is because pressure in atria increases slightly rises due to atrial systole. This is called the “A wave”.
On the left ventricular volume wave we see that the atrial contraction accounts for final ~10% of ventricular filling. This value varies with age and exercise. The ventricles have already been filled to about 80% of its max volume from the previous cardiac cycle.
At the end of Phase 1 ventricular volumes are maximal: termed the End-Diastolic Volume (EDV) (Typically ~120 ml)
Which valves are opened and closed during phase 1 of the cardiac cycle?
Mitral/Tricuspid: Open Aortic/Pulmonary: Closed
Using your understanding of atrial contraction and ventricular filling, explain why an individual is able to survive with atrial fibrillation.
Because the ventricles do not solely rely on the atria’s contraction for filling. The contraction of the atria only accounts for 10-20% (depending on age and exercise) of ventricular filling.
Describe what would be seen on a Wiggers diagram at Phase 2?
Phase 2: Isovolumetric Contraction
Once atria have finished contracting, the ventricles are then signalled to start contracting.
Mitral valve closes as intraventricular pressure exceeds atrial pressure.
Rapid rise in ventricular pressure as ventricle contracts
Closing of mitral valve Can be detected by a “C wave” in the atrial pressure curve
Isovolumetric since there is no change in ventricular volume (all valves are closed)
QRS complex in ECG signifies onset of ventricular depolarisation.
Closure of the mitral and tricuspid valves results in the first heart sound (S1).
Describe what would be seen on a Wiggers diagram at Phase 3?
Rapid ejection Phase
Ejection begins when the intraventricular pressure exceeds the pressure within the aorta. This causes the aortic valve to open.
Atrial pressure initially decreases as the atrial base is pulled downward as ventricle contracts. This is called the “X descent”
Rapid decrease in ventricular volume as blood is ejected into aorta
Blood continues to flow into the atria from their respective venous inputs
Which valves are open and closed during phase 3?
Mitral/Tricuspid: Closed Aortic/Pulmonary: Open
Describe what would be seen on a Wiggers diagram at Phase 4?
Reduced ejection
Repolarization of ventricle leads to a decline in tension and the rate of ejection begins to fall
Ventricular repolarization depicted by T-wave of ECG
Left ventricular pressure continues to decrease and the volume decreases.
Atrial pressure gradually rises due to the continued venous return from the lungs. This is called the “V wave”
Describe what would be seen on a Wiggers diagram at Phase 5?
Isovolumetric Relaxation
When intraventricular pressure falls below aortic pressure, there is a brief backflow of blood which causes the aortic valve to close
( Mitral/Tricuspid: Closed Aortic/Pulmonary: Closed)
Closure of the aortic and pulmonary valves results in the second heart sound (S2).
Although rapid decline in ventricular pressure, volume remains constant since all valves are closed. Hence isovolumetric relaxation
Dicrotic notch” in aortic pressure curve caused by elastic recoiled of valve closure
End systolic Volume (ESV) EDV-ESV = Stroke volume (Typically ~80ml)
The ventricles have not ejected all the blood they contain
