PBL 6 - control of BP Flashcards
what is the equation for BP?
blood pressure = CO x total peripheral resistance
what is cardiac output?
the volume of blood expelled by the heart per minute
varied to meet the demands of the body
what is the equation for cardiac output?
CO = SV x HR
what is stroke volume?
the volume of blood ejected per beat
what is the equation for stroke volume?
SV = end diastolic volume - end systolic volume
what 3 things is stroke volume affected by?
- preload
- contractility
- afterload
what is preload?
the tension in the cardiac myocytes before they contract
what happens if you increase the stretch in cardiac myocytes?
more forceful contraction
— the more you stretch them, the greater the tension, the more forceful the contraction
what is preload dependent on?
venous return
how does venous return affect preload?
the more blood that comes back to the heart, the more the ventricles will stretch, therefore more contraction force
what is contractility?
the contraction force of the myocardium for a given preload
what increases the contraction force for a given preload?
adrenaline
what is afterload?
the BP in the aorta and pulmonary trunk
how does afterload affect SV?
the greater the afterload/pressure, the harder is it for the LV to reach that pressure — increased afterload reduces SV
what things increase HR?
- adrenaline and noradrenaline
- increase in temperature
- thyroid hormone
- caffeine
what things decrease HR?
- acetylcholine
- decrease in temp
- intense visceral pain
what is total peripheral resistance?
the total pressure in the peripheral vessels
what 3 things affect TPR and how do they alter BP?
- viscosity of the blood — relatively stable so wouldn’t really use to alter resistance or BP
- blood vessel length — remains unchanged so wouldn’t really use to alter resistance or BP
- blood vessel radius — can easily be changed so regularly used to alter BP
what is vessel radius determined by?
the SNS
bloods vessels are maintained in what state?
a state of partial vasoconstriction
what does the maintenance of partial vasoconstriction of blood vessels provide?
sympathetic tone — a sympathetic nerve fibre is continuously partially constricting the vessel
what happens if you stop sending impulses through the sympathetic nerve fibre for a blood vessel?
vessel will dilate (this is a good way of rapidly changing the radius)