regulation of blood pressure Flashcards
what is said to be normal blood pressure
systolic pressure - less than 140mmHg
diastolic pressure - less than 90 mmHg
= mean arterial pressure - 79-105mmHg
what is the mean arteriol pressure (MAP) needed to perfuse coronary arteries, brain and kidneys
at least 60mmHg
why must the MAP be regulated within a narrow range
to ensure;
Pressure is high enough to perfuse internal organs AND
Pressure is not too high to damage the blood vessels or place an
extra strain on the heart (afterload
how do we calculate mean arterial pressure
MAP = CO X TPR (total peripheral resistance)
OR
MAP = (SV x HR) x TPR
what is total peripheral resistance
TPR is the sum of
resistance of all
peripheral vasculature
in the systemic
circulation
What is the major resistance vessel
arterioles - account for 50% of TPR
arteries - 20%
veins 10%
capillaries 20%
how is the TPR regulated and controlled
vascular smooth muscles contracting and relaxing
- Contraction of vascular smooth muscles causes
vasoconstriction and increases TPR and MAP (i.e. pressure upstream) - Relaxation of vascular smooth muscles causes
vasodilatation and decreases TPR and MAP
how is the TPR controlled by vascular smooth muscle
neurotransmitters noradrenaline act on alpha adrenergic receptors on smooth muscle
what is meant by the term “vasomotor tone”
Vascular smooth muscles are partially constricted at
rest.
how is vasomotor tone caused
tonic discharge of sympathetic nerves resulting in continuous release of noradrenaline
describe how the TPR is modified by the autonomic nervous system
Increased sympathetic discharge will increase the
vasomotor tone resulting in vasoconstriction
(increase TPR and MAP)
- Decreased sympathetic discharge will decrease the
vasomotor tone resulting in vasodilatation (decrease
TPR and MAP) - There is no significant parasympathetic innervation
of arterial smooth muscles - exceptions are penis
and clitoris
what is the baroreceptor reflux important in
moment-to-moment regulation of arterial blood pressure including prevention of postural changes
what are baroreceptors
pressure sensitive receptors found in walls of major arteries
where are baroreceptors found
wall of carotid artery
arch of aorta
what is the role of the carotid baroreceptor and the aortic baroreceptor
monitor pressure of blood flowing towards central nervous system
monitor the pressure of blood flowing in the systemic circulation
what is the function of baroreceptors
both are mechano receptors that respond to stretch e.g. a momentary increase in pressure within an arteries = increase in pressure being applied to vessel wall = increase in stretch being applied to vessel wall = increased activation of barrel receptors, which in turn will signal the change in stimulus via CNX, CNIX. towards medulla
how do the baroreceptors regulate the mean arterial blood pressure
negative feedback loop that underlies the baroreceptor reflex.
this is used to minimise any disturbance to controlled variable(MAP)
describe the effect of baroreceptors initiated by a decrease in blood pressure
baroreceptors sense decrease and decrease signalling activity being sent to cardiovascular integrating centre in medulla, = integrating centre initiated increase in sympathetic activity and decrease in parasympathetic activity = the increase leads to increase in heart rate and contractility of cardiac muscle = increase in stroke volume = increases heart rate and stroke volume results in increase in cardiac output
what does an increase in sympathetic activity also result in
increase in vasomotor tune leading to vino and vasoconstriction
what is the result of vinoconstriction
increase in venous return to heart therefor (frank starling mechanism) increase in stroke volume
what is the result in vasoconstriction of arterioles
increase in total peripheral resistance
what is the result then of both vaso and vineconstriction
increase in both CO and TPR leads to increase in arteriole blood pressure
describe the effect of baroreceptors initiated by a increase in blood pressure
increase is sensed by baroreceptors = increase in signalling activity sent to cardiovascular integrating centre in medulla = integrating centre initiates a decrease in sympathetic activity and increase in parasympathetic activity. increase in para leads to decrease in heart rate.
increase in sympathetic activity leads to reduction in HR and reproduction of contractility of cardiac muscle = decrease in SV. therefor reduction in both HR and SV - reduced cardiac output
