Flashcards in Session 6 Deck (17):
What effect does changing cardiac output have on arterial and venous pressure at a constant TPR?
If cardiac output rises arterial pressure rises and venous pressure falls
What is end diastolic volume?
Volume of blood in the ventricle at the end of diastole
What is end systolic volume?
Volume of blood in the ventricle at the end of systole
What is stroke volume?
Difference between end diastolic and end systolic volume
What determines how much the ventricles fill during diastole?
Venous pressure: the higher venous pressure is, the more the heart fills in diastole
What is pre-load?
The end diastolic stretch of the myocardium
What determines pre-load?
What is after-load?
The force needed to expel blood into the arteries
How does end diastolic volume affect force of contraction of the heart?
The more the heart fills, the harder it will contract so the bigger stroke volume will become: Starlings Law of the heart
What happens if the heart fills above its upper limit of contractility?
The myocardium becomes overstretched so stroke volume begins to decrease because contractility decreases
What is contractility?
The stroke volume attained at a given venous pressure
What acts to increase contractility in the heart?
Increased sympathetic activity
How is autonomic outflow from the heart controlled?
Signals from baroreceptors in the aortic arch and carotid sinuses sense arterial pressure and send signals to the medulla to control the heart
What effect does increasing venous return have on cardiac output?
Increasing venous return, and therefore venous pressure, causes cardiac output to rise
What effect does increasing arterial pressure have on cardiac output?
If arterial pressure rises cardiac output falls
What causes postural hypotension?
Failure of the baroreceptor reflex to work when standing up, so blood pressure falls on standing