Lecture 10- Controlling the heart and blood pressure Flashcards
What does the left ventricle generate pressure for? What does this mean?
The systemic circulation, therefore need a powerful beat as blood has to get out to the far reaches of the body.
What is MAP and what is it critically important for maintaining?
- Mean arterial blood pressure
- Important determinant of blood flow
- Is the P in the haemodynamics equation.. Q = DP/R
What is the blood pressure like in the major arteries?
- High
- Oscillatory due to pulse pressure (cycles of high and low correspond to beats of the heart)
What happens to blood pressure as we go down the supply chain?
- Blood pressure falls steeply across the arterioles, capillaries, and venules
- Oscillatory nature is reduced (pulse pressure disappears)
In general what is the blood pressure in veins like?
-Blood pressure is very low in veins.
What does the difference in blood pressure in the supply (arteries) side and drainage (veins) side cause?
-Creates a driving force for blood flow
What is arterial blood pressure and volume determined by?
-Balance between blood flows “in” and “out”
What does blood flow into the arteries cause?
- Fills arteries
- Increases arterial blood volume
- Raises arterial pressure.
What does blood flow out of the arteries cause?
- Drains arteries
- Decreases arterial blood volume
- Lowers arterial pressure.
Why does the pressure in arteries fluctuate so much depending on the volume of blood passing through?
Walls are rigid so can not expand and dilate like that of veins
What is blood flow into the arteries called?
- Cardiac output
- Measured in relation to time
What is blood flow out the arteries determined by?
- Arterial Resistance
- Can either hold up the blood or make it easier for it to leave
Arterial pressure =
Cardiac output x Total Peripheral Resistance
MAP = CO x TPR
What equation is the arterial pressure equation just a rearrangement of?
P = Q x R
rearranges to… Q=P/R
What is cardiac output determined by?
Stroke volume x Heart rate
What combinations of factors will result in increased arterial volume and Pressure?
- Increase cardiac output (increase inflow)
- Increase resistance (decrease outflow)
Basically more blood= higher pressure
What is meant by the term stroke volume? What unit is it measured in?
- Contraction strength i.e. the volume of blood pushed out with every beat
- L/beat
What is meant by the term heart rate? What unit is it measured in?
- Contraction speed
- beats/min
What is the unit for cardiac output?
L/min
In the ‘ putting it all together’ diagram what is the SV?
The difference in ventricular volume before and after ejection
What is the approach for a mouse to meet cardiac output?
- Stroke volume every small but heart rate is very fast to compensate
- Means that oxygenated blood can reach far parts of the body (just as we need)
What is the approach for a whale to meet cardiac output?
-Stroke volume very large (has huge, powerful heart)
so heart rate can be a lot slower and still meet demands
In a healthy human heart how do we meet demands for cardiac output?
- Method quite balanced
- Both stroke volume and heart rate are moderate
What do we see in failing human hearts in terms of maintaining cardiac output?
- Stroke volume is reduced as heart is not as efficient at pumping everything out
- As a result heart rate goes up to compensate
- The results in further damage as the heart is having to work so much harder to maintain mean arterial blood pressure
Is cardiac output fixed?
No, its variable due to changes in heart rate and/or stroke volume E.g. when exercising metabolic needs go up so cardiac output needs to increase and thus stroke volume and heart rate also do to meet this
What part of the brain measures +controls mean arterial blood pressure?
Coordinated within the brainstem
What are the two parts of the mechanism that coordinates mean arterial blood pressure?
- Afferent input: part of the body (includes both the CNS and ‘periphery’) sends signals to the brain to let it know what the current blood pressure is.
- Efferent output from brain to heart and vessels in order to make a change
What is the important structure of the afferent input system?
-Baroreceptors are blood pressure sensors
How do Baroreceptors function?
- They are stretch receptors. Normally will feel a little bit of stretch in the arteries due to the blood passing through this results in sending a constant beating signal that lets the brain know everything is fine
- If there is too much blood the walls of arteries stretch. This results in a faster signal to the brain (fast beat) and so it knows blood pressure is up.
- If there is too little blood the walls of arteries shrinks. This results in a slower signal to the brain (slow beat) and so it knows blood pressure is down.
- The efferent pathway then causes the response immediately to counteract the feedback the brain is receiving
What are the two places where baroreceptors are found and why are these important places for them to be?
- Aortic arch: First branch from the heart, so tells brain that something is wrong as fast as possible
- Carotid sinus: Lead up to the brain. Therefore vital that problems with the supply here are detected. Brain needs oxygen otherwise it is deadly.
What are the two efferent pathways for control of cardiac output?
-Parasympathetic pathway (rest and digest= go slower)
From the brain a signal down the vagus nerve hits the SA node and tells the signal to slow down. In addition, when reaches the AV node a greater pause is put the signal that causes contractions. Overall this lowers cardiac output and blood pressure falls.
-Sympathetic pathway (fight or flight= go faster)
From the brain a signal down the sympathetic cardiac nerve reaches the SA node. This results in the signal the SA send out being faster, the AV node also pauses the signal less. Therefore, the heart rate goes up (more beats). In addition, in cardiac muscle the signal causes greater release of calcium so there is more cross bridge formation and an increase stroke volume. As a result of both increased heart rate and increased stroke volume there is greater cardiac output.
In the neural control of cardiac output what is the brake and what is the accelerator?
- Parasympathetic/ Vagus nerve= break
- Sympathetic/ sympathetic cardiac nerve= Accelerator
What happened in the whole body tilt experiment?
- Once moved into vertical vessels are working against gravity. Stroke volume is therefore reduced. Heart rate therefore goes up in an attempt to keep cardiac output the same.
- However, if you look at the graph the cardiac output has reduced slightly so there must be more factors effecting it…
- We see that in tilted position the mean arterial blood pressure has decreased. This is equal to Cardiac Output X Total Peripheral Resistance. If cardiac output has reduced and resistance hasn’t compensated for it resistance most have increased. This occurs by tightening up the vessels and making it therefore more difficult to drain blood into rest of body.
What can we extend the MAP equation to be?
MAP= (stroke volume x heart rate) x TPR
