CVS - control of cardiac output Flashcards
What determines arterial pressure?
Cardiac output and TPR
What determines venous pressure?
Rate blood enters the veins and rate the heart pumps it out. As volume increases in veins, venous pressure increases.
What happens to arterial and venous pressure if TPR falls but cardiac output remains constant?
Arterial pressure falls and Venous pressure rises. The volume in the venous system increases.
What happens to arterial and venous pressure if TPR rises but cardiac output remains constant?
Arterial pressure rises and venous pressure falls. The volume in the venous decreases.
What happens to arterial and venous pressure if cardiac output rises and total peripheral resistance remains constant?
Arterial pressure increases and venous pressure decreases. Decreased volume of blood in veins.
What happens to arterial and venous pressure if cardiac output falls and total peripheral resistance remains constant?
Arterial pressure falls and venous pressure rises. Increased volume of blood in veins.
What is the relationship between total peripheral resistance and the body’s demand for blood?
TPR is inversely proportionally for the body’s demand for blood. As demand for blood increases TPR decreases.
What is meant by ‘demand-led pumping’?
If the body needs more blood the heart pumps more to meet the ‘demand’. This ‘demand’ is expressed as changes in arterial and venous pressure (due to changes in TPR).
How can a big meal affect the cardiac output?
- After a meal the gut needs more blood
- Local vasodilators dilate arterioles
- TPR falls
- Cardiac output increases in order to compensate for a transient fall in arterial pressure and increase in venous pressure.
- Arterial and venous pressures return to normal
What is stroke volume?
End diastolic volume - end systolic volume
What is end diastolic volume?
The volume of blood in the right or left ventricle after it has filled during diastole.
What is end systolic volume?
The volume of blood that remains in the left or right ventricle after ejection in systole.
What affects ventricular filling?
There is no hormonal or neuronal involvement in ventricular filling. In diastole the ventricles are isolated from the arteries and connected to the veins. The ventricles passively fill until the ventricle walls stretch enough to produce an intra-ventricular pressure equal to venous pressure. Therefore the larger the venous pressure the more the ventricles will fill.
What does the ventricular compliance graph show?
The relationship between venous pressure and ventricular volume.
What is the effect of end diastolic volume on systole?
A higher end diastolic volume stretches the ventricular muscle more and therefore their sarcomeres which increases the force they can generate enabling them to eject the increased volume = Starling’s law of the heart.
What controls the Frank-Starling mechanism?
It is intrinsic to the heart and is not controlled by any neuronal or hormonal factors. If the ventricle muscle is stretched more it intrinsically contracts harder.
Explain one mechanism for the increase in contraction seen when cardiomyocytes are stretched:
Increasing the sarcomere length increases troponin C sensitivity, which increases the rate of cross-bridge detachment and reattachment and the amount of tension developed by the muscle fibre. Other mechanisms are probably involved.
