Week 6 - Control of Cardiac Output Flashcards
What determines venous pressure?
Rate at which blood flows into veins
Rate at which blood flows out of the veins
What determines arterial pressure?
TPR
Cardiac output
If TPR rises, but cardiac output is constant, what happens to arterial and venous pressures?
Arterial pressure rises
Venous pressure falls
If TPR is constant, but cardiac output rises, what happens to arterial and venous pressures?
Arterial pressure rises
Venous pressure falls
How does the body respond when arterial pressure falls?
Detected by baroreceptors in the carotid sinus
Sends signals to the medulla oblongata
This sends signals to heart
Results in rise in heart rate and force of contraction, in order to raise arterial pressure
What does cardiac output depend on?
Heart rate and stroke volume
What is stroke volume?
Stroke volume is the amount of blood pumped out of the heart at each systole. It is therefore the difference between end diastolic volume and end systolic volume.
How may stroke volume be increased?
Filling the heart more during diastole
Emptying the heart more during systole
What determines end diastolic volume?
Venous pressure
Ventricular compliance - how much the ventricles stretch
How do venous pressure and ventricular pressure relate?
As the ventricles fill, the walls stretch. This increases interventricular pressure.
At the point at which ventricular pressure = venous pressure, filling ceases.
Therefore, whatever venous pressure is, ventricular pressure rises to meet it.
How does venous pressure affect end diastolic volume?
Higher venous pressure means the ventricles have to fill with a larger volume of blood to match venous pressure.
Therefore higher venous pressure = higher end diastolic volume
What is Starling’s Law of the Heart?
Higher venous pressure = increased filling = higher stroke volume
Or “more in = more out”
What is preload?
How does it affect stroke volume?
Preload is the “end diastolic stretch”
Up to a point, higher preload = greater force of contraction = higher stroke volume
Why does the Starling curve show that at very high venous pressures, stroke volume begins to decrease?
At very high venous pressures, the ventricles must fill very full to match the venous pressure. However, the pericardium is not distensible, and thus prevents the heart from overfilling. Therefore, at very high venous pressures, the heart cannot fill enough to meet venous pressure, and therefore stroke volume decreases.
What is contractility?
How does it relate to the Starling curve?
Contractility is the extent by which stroke volume increases with venous pressure.
It is the slope of the curve
