Flashcards in Response to changes Deck (25)
What does a fall in arterial pressure do to certain tissues?
It will increase the flow resistance. Eg the skin and gut.
Also increases vaso constriction.
What happens to blood vessels after eating a meal?
There is local vaso dilatation due to increased activity in the gut.
What happens to pressure in the vessels after eating a meal?
The total peripheral resistance falls, venous pressure rises and atrial pressure falls.
How can venous pressure be reduced?
Extra pumping of the heart. So arterial pressure will rise.
If the total peripheral resistance is standard and the heart rate increases, what will happen to the cardiac output?
It will initially rise, but this will reduce the venous pressure so the stroke volume will fall and cardiac output will return to the original value.
In exercise, what mechanism forces extra blood back to the heart?
What will happen during exercise if there was no special coping mechanism?
The venous pressure would increase greatly and the arterial pressure would decrease greatly. This could be too large for the body to cope with.
What does a large increase in venous pressure do to the heart in respect to the Starling curve?
It tends to overfill the heart and push the ventricles onto the flat part of the curve.
If the left and right output do not match each other, what is there a risk of?
How can the left and right ventricles beat at the same rate?
By matching stroke volume. This relies on the Starling curve.
What happens in the heart if it is on the top of the Starling curve?
The left section cannot respond to the right section so blood will accumulate on the lungs.
How is overfilling of the ventricles prevented during exercise?
There is a rise in heart rate, driven by the brain as exercise begins.
How does the preventative action of a rise in heart rate at the beginning on exercise work?
It means that when the venous pressure rises, the heart rate is already high so it keeps the stroke volume down.
What situation cannot be corrected by the normal mechanisms of the heart?
When someone stands up after lying down.
Wen someone stands, their central venous pressure falls. According to Starlings law, what will happen?
Cardiac output will decrease, causing arterial and venous pressure to change in the same direction.
When someone stands, what is the mechanism that defends arterial pressure?
Extra point - what happens if this doesn't work?
Baroreceptors detect a fall in the arterial pressure, so they increase heart rate. This causes venous pressure to decrease and the total peripheral resistance increases. This defends arterial pressure.
Extra point - postural hypotension.
What happens to the venous pressure during a haemorrhage?
It decreases. This causes the cardiac output to decrease (due to Starlings law) and the arterial pressure also decreases.
How can the body worsen the effects of a haemorrhage?
The Baroreceptors detect the decrease in arterial pressure, increase the heart rate so the total peripheral resistance increases.
The heart rate increases more and the venous pressure drops lower. The problem is worse and heart rate can become very high.
How can you increase arterial pressure in haemorrhages?
Increase the total peripheral resistance. However, this decreases venous pressure so the original problem is not solved.
How do you treat haemorrhages? (in pressure terms)
You have to replace the blood lost which is achieved by increasing venous pressure (veno constriction)
*This is called an auto transfusion)
What change in venous and arterial pressures does the control system struggle to cope with?
Arterial and venous pressure changing in the same direction.
What organ controls blood volume?
What happens to venous pressure when blood volume is increased for days?
What does a long term increase in blood volume result in?
An increase in cardiac output.
An increase in arterial pressure.
An increase in venous pressure.
*these all force more blood through the tissue so auto regulation and increased total peripheral resistance increases, making the arterial pressure increase and stay up.*