Control Of Arterial Blood Pressure 1 Flashcards
In clinical practise what is often measured in term of blood pressure
Systemic arterial blood pressure
And express it as systolic and diastolic
What su systolic arterial blood pressure
Pressure exerted by the blood on walls of aorta and systemic arteries when heart contracts
Should not exceed 140mmHg under resting conditions
What is diastolic arterial bp
Is the pressure exerted by blood on walls of aorta and systemic arteries when heart relaxes
Should not normally exceed 90mmHg under resting conditions
What is pulse pressure
Is the difference between systolic and diastolic blood pressure
40mmHg (difference between 120mmHg and 80mmHg)
What is mean arterial blood pressure
The average arterial blood pressure during a single cardiac cycle which invokes contraction and relaxation of the heart
Why is the MAP not obtained by averaging the systolic and diastolic pressures
During a normal cardiac cycle:
The relaxation (diastolic) portion of the cardiac cycle is about twice as long as the contraction (systolic) portion of the cardiac cycle
What is the simplest formula to estimate the map
MAP = (2x diastolic) + systolic divided by 3
93.3mmHg
What is another way to estimate MAP
Map= DBP + 1/3 difference between SBP and DBP
What is normal arterial blood pressure
What is the norm,a range of the map
70-105 mmHg
What so the minimum map and what is it needed for
60mmHg
Needed to perfuse the Coronary arteries, Braun and kidney
Map must be naimteined in a narrow range to ensure
So pressure high enough to perfuse internal organs (brain, heart and kidney)
Pressure not too high to damage the blood vessels or place an extra strain on the heart
What is the map in relation to co and tpr
MAP (mean arterial pressure) = CO (cardiac output) x TPR (total peripheral resistance)
What is cardiac output
Volume of blood pumped by each ventricle of heart per minute
Co = SV x HR
What so the stroke volume
Volume of blood pumped by each ventricle of the heart per heart beat
What is the total peripheral resistance
Sum of resistance of all peripheral vasculature in systemic circulation
What is tpr regulated by
Vascular smooth muscle
What are the main sites of tpr
Arterioles
What increases and decreases tpr?
Vasoconstriction increases tpr and map
Vasodilation decreases tor and Map
What supplies the vasc smooth muscles with a nervous supply
Sympathetic nerve fibres
Neurotransmitter noradrenaline acting on alpha receps
What is vasomotor tone
Vasc smooth muscle partially constricted at rest
What causes the vasomotor tone
Tonic discharge of symp nerves resulting in continuous release of noradrenaline
What happens if the sympathetic discharge increases or decreases in relation to the vasomotor tone
If the symp inv increases - increase vasomotor tone lead to vasoconstriction increasing tpr and map
If symp is decreases - decrease vasomotor tone lead to vasodilation decreasing tpr and map
Is there parasymp inv to vasc smooth muscle
No Exocet the clitoris and penis
What is the baroreceptors reflex imp in
Moment to moment regulation of arterial bp including prevention of postural changes
Where are baroreceptors
Aortic arch
Carotid sinus
What do bothe th baroreceptors signal to
Both signal to medulla
Carotid - via 9th CN
Aortic - via 10th CN
What does the baroreceptors reflex do in relation to map
Short term regulation of map
Negative feedback acts to minimise any disturbances to controlled variables
What are some baroreceptors responses
Arterial bp increases
Carotid sinus afferent nerve fibres firing increases
Cardiac vagal efferent nerve fibres firing increases
Cardiac symp efferent nerve fibres firing decreases
Symp vasoconstrictor nerve fibres firing decrease
What does the baroreceptors do if there is a decreases in ABP.
Decreases discharge
Decrease vagal activity/ increase cardiac symp/increase symp constrictor tone
Etc
What to baroreceptors only respond to
Acute changes in blood pressure
Baroreceptors firing decreases if high blood pressure is sustained
What is blood pressure
Outward (hydrostatic) pressure exerted by the blood on blood vessels walls
