Session 6 - Control of CVS Flashcards
If TPR is decreased and CO remains constant what happens to the arterial and venous pressures
Arterial pressure will decrease and venous pressure will increase
If CO is decreased and the TPR remains constant what will happen to the arterial and venous pressure
Arterial pressure will decrease and the venous pressure will increase
How does the CVS respond to eating a meal?
TPR falls as there is an increase in the production of local metabolites and therefore vasodilation, fall in arterial pressure and an increase in venous pressure. Starlings law means there is an increase in CO
Fall in arterial pressure triggers increase in HR and therefore CO
The increase in HR means there is a decrease in the venous volume and increase in arterial volume
In exercise how is overfilling of the ventricles prevented and why does this need to occur
By increasing the HR, which is driven by the brain
As otherwise at the top of Starlings curve and the system would become overloaded as massive fall in TPR and vasodilation of vessels in muscle therefore and very large increase in venous pressure
Why is there a risk of pulmonary oedema in exercise?
As the outputs of both sides of the heart need to be matched therefore is large pressure in RA from venous return then there is an increase in the pressure in the lungs –> fluid entering the tissues of the lung, results in poor gas exchange
How does the CVS respond to standing up?
The blood ‘pools’ in the superficial veins of the leg when standing due to gravity –> fall in CVP
CO then falls due to decrease in venous pressure
–> decrease in arterial pressure which is detected by baroreceptors –> increase in HR (via sympathetic activity)
However venous pressure is still low so TPR is increased (via skin and gut)
What reflex is impaired in postural hypotension? Who is it common in?
Baroreceptor reflex
The elderly
Where do you find baroreceptors?
Carotid sinus and the aorta
What is the Bainbridge Reflex
An increase in HR due to increased venous pressure sensed in the RA which leads to a decrease in parasympathetic activity
What happens during haemorrhage
Loss of blood volume, decrease in venous pressure –> fall in CO (reduced filling) –> fall in arterial pressure
Baroreceptor reflex –> increase HR and TPR
Increase HR makes venous pressure lower further (bad!!)
How is venous pressure increased in haemorrhage
By veno-constriction and ‘auto-transfusion’ (increase in volume of blood by moving fluid out of tissues and into the blood)
Eventually replace blood lost
How does the CVS cope with long term increase in blood volume
Controlled by the kidney (e.g. Epo)
Volume increased for days –> increase in venous pressure –> increase in CO and increase in arterial pressure
More blood perfuses tissues, which auto regulate and increase TPR –> further rise in arterial pressure which then stays up
What is long term blood pressure controlled by?
Blood volume therefore important in hypertension which is why diuretics are important
Define pre-load
End diastolic stretch of myocardium
Determined by venous pressure
Define after-load
the force necessary to expel blood into the arteries
