Lecture 10 Controlling the heart and blood pressure Flashcards
The left ventricle pressurises the
systemic circulation
High pressure in the large systemic arteries
Linked to ventricular contraction and ejection of blood.
Pulsatile in major arteries (systolic / diastolic).
Arterial blood pressure curve
Rises and falls
High point pressure is systolic
Low point pressure is diastolic
Blood pressure in arteries
Always high
Rises and falls in a narrow range
Mean arterial blood pressure (MAP)
Driving force important
determinant of blood flow
High
Sacrifice anything else to maintain the MAP high
Unidirectional flow
If MAP falls
The difference between arteries and veins will become much less
Greatly reduce the flow through the system
The blood will not get to our extremities (brain)
Major problem
what do you need to get unidirectional flow of blood in our system?
high mean arterial blood pressure
What drives unidirectional flow of blood is
Difference in pressure between the arteries and veins
Vein pressure
Very Low
Doesn’t contribute to the difference very much
Q = ΔP/R
Q = flow
ΔP = Large difference in pressure between the arterial and venous sides.
R = Resistance
What creates the driving force for blood flow?
High to low pressure
What maintains arterial blood volume and blood pressure?
Ejection of blood into the arterial system
What determines arterial blood pressure
Amount of blood flow into arteries
Amount of blood flow out of arteries
Arteries
rigid thick tunica media low compliance pressure on blood is driven by amount of blood in arteries more blood in (higher pressure) more blood out (lower pressure)
Blood flow in to arteries
volume and pressure
fills arteries
increases arterial blood volume and pressure
Blood flow in
Ejected blood from heart
Ventricle contracts
Cardiac output
what effects blood pressure?
Cardiac output and arterial resistance
Cardiac output
Amount of blood sending out into the vessels
or pushed from heart every heart beat
Blood flow out of arteries
volume and pressure
Drains arteries
Decreases arterial blood volume and pressure
What is arterial blood volume and pressure determined by?
balance between blood flow in and out
Blood flow out
Drains out of arteries into capillaries (capillary flow)
Controlled by resistance of the arteries
Balance of mean arterial pressure is coming from
Blood flow into arteries
Resistance of the flow out of arteries
Increase MAP
Balance flow in / out determines pressure
Increase cardiac output (heart pushes more blood into arteries) increase inflow
Increase resistance (decrease outflow)
Increase arterial volume and pressure
Arterial pressure
Cardiac output
Total peripheral resistance
equation
MAP = CO x TPR
Pressure
Flow
Resistance
equation
P = Q x R
What is cardiac output determined by?
incl equation
Stroke Volume
Heart Rate
CO = SV x HR
Cardiac output
incl units
Amount of blood coming out of the heart and going into arteries
L/min
Stroke volume
incl units
Amount of blood pushed out of the heart for each beat
L/beat
Pulse strength
The higher the stroke volume
the stronger the heart beat
more blood gets pushed out
Heart rate
incl units
Number of times heart is beating
beats/min
Pulse speed
What do you need if you drain more blood out (exercise)?
more blood in to maintain MAP (at a constant rate)
To increase cardiac output…
Increase heart rate
Increase stroke volume
How does the system know what’s going on with MAP?
Coordinated via the brainstem
Afferent input from both CNS and periphery
Efferent output to heart and vessels
Afferent input
Signal coming into the brain about blood pressure.
from both CNS and periphery
Efferent output
Signal the brain is sending out to the body about blood pressure.
to heart and vessels
Why can The heart beat without any input from the brain?
The pacemaking function comes from SA node
What are blood pressure sensors?
Baroreceptors
Baroreceptors
what is it, location, receptors, signal type
Sensors of blood pressure
Located on aortic arch (above heart) and carotid artery (on either side of neck)
Stretch receptors (any stretch reduction of artery)
Afferent signal
What happens if blood pressure goes up?
vessels, receptors, signal type
More blood going into vessels
Vessels will stretch
Baroreceptors sense the stretch of the artery walls and sends signal to brain
Brain knows blood pressure is up (and makes a move to get back to baseline)
Afferent signal
what happens If blood pressure falls?
vessels, receptors, signal type
Vessels will contract a bit
Less stretch of vessel wall
Baroreceptors will reduce signal down
Brain knows blood pressure is down (and makes a move to get back to baseline)
Afferent signal
What does the brain do in response to cardiac output?
Send efferent output to adjust cardiac output
what are the 2 systems the brain uses to change cardiac output?
Parasympathetic system
Sympathetic system
Parasympathetic system
Rest and digest
Sleeping, relaxing, eating, digesting food
brake
Sympathetic system
Fight or flight response
Danger, exercise,
Drives system to work harder
Accelerator
What system do you stimulate if you want the cardio system to work faster?
Sympathetic system to get system working harder
What system do you stimulate if you want the cardio system to work slower?
Parasympathetic system to get system working slow
Brain coordinates the 2 systems and the amount of signal it sends down the pathways determines
What the cardiac output of the heart is
Parasympathetic pathway (use pathway why, signal type, sends signal through, vagus nerve connection between, signal tells, result)
High blood pressure
Reduce pressure
Efferent output signal from the brain
Brain sends signal directly to heart through vagus nerve
Vagus nerve connects brain directly to SA node and AV node in the heart
Tells SA node to Slow down fewer beats/min
Tells AV node to lengthen the pause
Slower heart rate
SA node
Sets a pace for heart contraction
AV node
pause before it allows the SA node to continue down into the ventricles.
blood pressure is high
Bring it down
Reduce amount of flow out of heart
Slows heart rate down
Sympathetic pathway (use pathway why, signal type, sends signal through, where the nerves go to, signal tells, result)
Low blood pressure
Increase pressure
Efferent signal from brain
Sends sympathetic signals to SA node, AV node, Purkinje fibres and into ventricular walls
signal goes into spinal column, and into the sympathetic chain/trunk ganglion (set of nerves), the nerves go directly to the SA node and AV node
Tells SA node to send more signals quicker for more contractions
Tells AV node to shorter the pause
Signal goes into the ventricular wall to stimulate the cells to release more calcium
Increases heart rate
Increase stroke volume
Increases blood flow into arteries
To get a stronger heartbeat
Release more calcium into the system
Cause more actin and myosin interactions
Increase cross bridge formations
More pulling on actin filaments
Stronger stroke volume
Tilted upright from supine (lying) position effects
stroke volume, cardiac output, heart rate, MAP, TPR
Decrease a lot stroke volume quick
Decrease cardiac output (less than SV)
Increase heart rate
MAP barely moved (constant high)
Increase TPR (vascular resistance)
Gravity
