Lecture 10 - Controlling the heart and blood pressure Flashcards
The left ventricle pressurises the ________ circulation
systemic
High pressure in the large systemic arteries …
Linked to ventricular contraction and ejection of blood
Pulsatile in major arteries (systolic/diastolic)
Mean arterial blood pressure
MAP driving force important determinant to blood flow
Atrial and ventricular pressure
Low point in atria is not actually that low whereas the ventricles get much lower I.e. it is still high at its lowest point
Ventricle pressure goes very high to very low but atrial pressure always remains pretty high
What is blood pressure?
Measure of diastolic and systolic arterial pressure
Cyclical rise and fall of blood pressure that is linked to the ejection of blood from the ventricles
Blood pressures throughout the systemic circulation
Blood pressure is high in the major arteries - oscillatory
Blood pressure falls steeply across the arterioles, capillaries, and venules - oscillatory nature is reduced
Blood pressure is very low in veins
Large difference in pressure (ΔP) between the arterial and venous sides - creates a driving force for blood flow, keeps the blood moving through the system
MAP and flow
Average at the major arteries is always very high and in the veins it is much lower. Greater the difference in this pressure, the stronger the flow of blood you are able to get through the system which is why the body wants to maintain a high MAP. If pressure difference drops you get less flow to the areas of the body that need the strongest flow are the extremities, brain wants to protect its blood flow at all time because it has huge energetic and oxygen demands, if MAP falls then it means the brain is getting less oxygen which is disastrous
Ejection of blood into the arterial system
Maintains arterial blood pressure volume and pressure
Blood flow in …
Fills arteries
Increases arterial blood volume
Raises arterial pressure
Blood flow out …
Drains arteries
Decreases arterial blood volume
Lowers arterial pressure
Arterial blood volume and pressure are determined by balance between blood flows in and out
MAP can be considered as a balance between the blood that is flowing in and the blood that is flowing out of the arteries (because it is determined by home much blood is in the arteries)
Cardiac output and arterial resistance effect on blood pressure
Blood flow in …
Ventricular contraction
Ejection of blood
CARDIAC OUTPUT
Blood flow out
Capillary flow
Controlled by resistance of the arteries
Balance flow in/out determines pressure…
Increase cardiac output (increase inflow)
Increase resistance (decrease outflow) - resistance is dependent on the seize of vessels i.e. length and width
Increase arterial volume and pressure
Cardiac output
Cardiac output is the term that describes the amount of blood your heart pumps each minute.
Cardiac output = stroke volume × heart rate.
Amount of blood that leaves the heart and goes into the arteries (flow of blood out of the heart)
Mean arterial pressure equation
Arterial pressure = cardiac output x total peripheral resistance
MAP = CO x TPR
TPR is the combined resistance of all the arteries
Flow equation
Q = P/R
MAP=P
CO=Q
TPR = R
Cardiac output is determined by ….
Cardiac output is variable due to ….
Stroke volume and heart rate
Cardiac output = stroke volume × heart rate
CO=SV x HR
L/min= L/beat x beats/min
SV = stroke volume, contraction strength
HR = heart rate, contraction speed
Variable for to changes in heart rate and/or stroke volume
Cardiac output is greatly increased during exercise
Homeostasis of arterial blood pressure
MAP is tightly regulated - there is a narrow range
MAP = CO x TPR (heart (cardiac output) and blood vessels (vascular resistance))
Coordinated within the brainstem. Afferent input from both the CNS and ‘periphery’ - signal to the brain that is telling it what is happening with blood pressure. Efferent output to heart and vessels - signal the brain sends to the rest of the system to control changes based off of the afferent information.
Brain doesn’t need to tell the heart when to beat, but still gives it instructions for other things, brain doesn’t tell the heart to beat everytime but tells it to speed up or slow down
Baroreceptors - what are they? Where are they located primarily? What afferent signal do they send to the brain?
Baroreceptors are stretch receptors and respond to the pressure induced stretching of the blood vessel in which they are found.
Located …The carotid bodies are situated at the carotid bifurcation, and the aortic bodies are located near the aortic arch.
Constantly communicates to the brain about blood pressure - faster and harder signals if blood pressure increases. Drains some of the blood volume out of the blood vessels then the signal slows down from the baroreceptors
Afferent information comes from the baroreceptors and goes to the brain about blood pressure
Vagus nerve controls…
Parasympathetic system
The vagus nerve decreases heart rate
The vagus directly connects the heart to the nerve at the SA node and the AV node. Tells the AV node to increase the pause and slower impulses come from the SA node (pacemaker) which contributes to slower heart beat. Impacts on the ‘timekeepers’ of the heart. The brain can use parasympathetic signalling through the vagus nerve to directly communicate with the SA node and the AV node to say slow down (bring down cardiac output, want SA node to fire more slowly and want the AV node to put a longer pause on that signal which gives a lower heart rate which means MAP will fall back to where we want)
Known as the ‘brake’
Sympathetic cardiac nerves control …
Sympathetic cardiac nerves increase heart rate and force of contraction
MAP falls therefore need to increase it and the brain rises the sympathetic system and it does this through the sympathetic chain ganglia/trunk ganglia and down into the sympathetic cardiac nerves (goes down into the spinal cord). Also on the AV node and the SA node and it does the opposite to the parasympathetic in order to increase heart rate - causes more depolarisations and therefore more contractions. Some of the branches reach out and directly innervate the walls of the ventricle (to the Purkinje fibres and the contractile cells themselves), can’t recruit more cells to make a stronger heart beat so you need more calcium which will cause more ceros bridges to form which will causes a greater contraction
Known as the ‘accelerator’
Difference between sympathetic and parasympathetic signaling?
Sympathetic acts to increase heart rate and force of contraction/stroke volume whereas parasympathetic acts to decrease heart rate
Parasympathetic vs sympathetic
Parasympathetic
Rest and digest
Calm, just eaten
Need for great output is not there
Sympathetic
Fight or flight
Exercise
Accelerator
Baroreflex and whole body tilt
The baroreflex is the fastest mechanism to regulate acute blood pressure changes via controlling heart rate, contractility, and peripheral resistance.
Changes occur to maintain blood pressure ….
Large drop in stroke volume - cardiovascular system is working against gravity
Smaller drop in cardiac output
Heart rate increases - compensation the body makes to make cardiac output in similar state, brain recognises from afferent input from the receptors that blood pressure is falling and uses sympathetic signalling to tell the heart it wants a faster heart rate to compensate for a loss in stroke volume and prevent the cardiac output from galling too much so you get an increase in heart rate
MAP barely changes
TPR/vascular resistance - MAP didn’t fall at all, CO fell a little so TPR had to change - goes up slightly
