Session 6 Flashcards
What determines arterial pressure?
Cardiac output and total peripheral resistance
What happens to arterial and venous pressures at a given cardiac output if total peripheral resistance changes?
TPR falls - arterial pressure will fall and venous pressure will rise
TPR rises - arterial pressure will rise and venous pressure will fall
What happens to arterial and venous pressures at a given total peripheral resistance if cardiac output changes?
CO falls - arterial pressure falls and venous pressure rises
CO rises - arterial pressure rises and venous pressure falls
What factors determine how much the ventricles fill during diastole?
During diastole the ventricles are isolated from the arteries and connected to the veins. Th ventricle fills until the walls stretch enough to produce an Intraventricular pressure equal to venous pressure. The higher the venous pressure, the more the heart fills in diastole.
Define preload and afterload
Preload = volume of blood in ventricles at the end of diastole. Determined by venous pressure. Afterload = the resistance the left ventricle must overcome to circulate blood
What is Starling’s law of the heart?
The more the heart fills the harder it contracts and the bigger the stroke volume (up to a limit)
What is the bodies response to a fall in arterial pressure?
Detected by baroreceptors in coronoid sinus and aorta.
Heart rate is increased by increased sympathetic and decreased parasympathetic stimulation.
Stroke volume is increased by increasing the contractility (sympathetic activity) due to the mechanical effect of reduced afterload.
What is the bodies response to an increase in venous pressure?
Detected by the right atrium.
Rise in heart rate due to reduced parasympathetic activity - Bainbridge reflex, minor effect.
Rise in stroke volume due to Starling’s law
What are the consequences of a low mean arterial blood pressure?
Inadequate tissue perfusion and a negative central venous pressure.
What is the response of the CVS to standing up?
On standing blood pools in the superficial veins in the leg (~500ml per leg).
Central venous pressure falls, reducing right atrial filling
Stroke volume drops
Mean arterial pressure falls, which is signalled by baroreceptors.
The SNS responds to increase heart rate and increase vasomotor tone in the skin and gut.
Venous smooth muscle tone is increased to limit pooling and muscles contract to force venous blood upwards.
What is the response of the CVS after eating a meal?
Parasympathetic activity increases causing release of metabolites and local vasodilation.
Total peripheral resistance falls, causing arterial pressure to fall and venous pressure to rise.
Cardiac output increases and arterial and venous pressures are returned to normal.
Demand is met by increasing cardiac output.
What is the response of the CVS to exercise?
Muscle pumping forces extra blood back to the heart.
Overfilling of the ventricles is prevented by a rise in heart rate.
Supply to organs other than heart and brain drops.
What is the response of the CVS to haemorrhage?
Reduced blood volume lowers venous pressure
Cardiac output falls
Arterial pressure falls
Baroreceptors detect fall, increasing heart rate, total peripheral resistance and central venous pressure, hence stroke volume.
All systems but heart and brain experience decreases supply.
What is the contractility of the heart muscle?
The force of contraction at any given fibre length.
