lecture 8 - the heart as a pump Flashcards
What are the 2 circuits that the 2 ‘pumps’ of the heart flow into?
Pulmonary, Systemic
What are the components of the pulmonary circuit?
Heart and lungs
What are the components of the systemic circuit?
Heart and body
What is the relative flow through the pulmonary and systemic circuits?
The flow is equal
Do the left and right ventricles contract at the same time or in sequence?
The same time
What is the name for the contractile units of cardiomyocytes?
sarcomeres
What is the thin filament of a cardiomyocyte sarcomere?
Actin
What is the thick filament of a cardiomyocyte sarcomere?
Myosin
What must be released into a muscle cell to facilitate sarcomere cross bridging and contraction?
Ca2+
What is the basic process of cardiomyocyte contraction?
Ca2+ released into cell by sarcoplasmic reticulum, myosin binds to actin forming cross bridges that pull on sarcomeres to shorten them and generate force.
How does cardiomyocyte recruitment increase the force of cardiac contraction?
It doesn’t - all cardiomyocytes are activated during every heart beat, so there are no more to be recruited
How is the force of cardiac contraction increased?
Increased cytosol Ca2+ release in cardiomyocytes facilitates the formation of more cross bridges, allowing individual cells to contract more strongly.
What is the cellular mechanism of cardiac relaxation?
Ca2+ pumped into sarcoplasmic reticulum, cross bridges released as ATP binds to myosin,
What are the 2 states that the heart alternates between?
Diastole and systole
Is diastole associated with relaxation or contraction of the heart?
relaxation
Is systole associated with relaxation or contraction of the heart?
Contraction
Is diastole associated with falling or rising pressure in the heart?
Falling pressure
Is systole associated with falling or rising pressure in the heart?
Rising pressure
Does ventricular systole precede or succeed atrial systole?
Succeed
What are 5 main phases of the cardiac cycle?
Atrial systole, isovolumetric ventricular contraction, ventricular ejection, isovolumetric ventricular relaxation, passive filling
What occurs during the atrial systole phase of the cardiac cycle?
Atria contract, AV valves open, semi-lunar valves closed
What occurs during the isovolumetric ventricular contraction phase of the cardiac cycle?
Ventricles start to contract. All valves are shut. Thus, pressure in the ventricles rapidly increases.
What occurs during the ventricular ejection phase of the cardiac cycle?
Semilunar valves open, ventricles contract to pump blood into pulmonary and systemic circuits.
What occurs during the isovolumetric ventricular relaxation phase of the cardiac cycle?
All valves are closed, atria fill, and the ventricles are mostly empty.
What occurs during the passive filling phase of the cardiac cycle?
All valves open, atria and ventricles are passively filled with blood to prepare for the cycle to begin again
Why is there a pulsatile change in blood pressure in major arteries?
Due to the ejection of blood with each heart beat
How does arterial blood pressure change during systole?
Increases
How does arterial blood pressure change during diastole?
Decreases
Which is higher, systemic arterial pressure, or pulmonary arterial pressure?
Systemic
Is the highest point on a blood pressure trace systolic or diastolic?
Systolic
Is the lowest point on a blood pressure tract systolic or diastolic?
Diastolic
What is the pulse pressure?
The difference between the highest and lowest point on a blood pressure trace, which correlates directly to the pressure in the heart
What is the mean pressure of a blood pressure trace?
The average pressure (systolic and diastolic) across a blood pressure cycle - not the average of the highest and lowest
Is mean pressure usually higher or lower than the average of systolic and diastolic pressure?
Lower - the heart is in diastole for longer
What mechanical event occurs in the heart immediately after the QRS complex on an ECG?
Ventricular contraction
