regulation of mean arteriole blood pressure Flashcards
what is blood pressure
the outward (hydrostatic) pressure exerted by the blood on blood vessel walls
what is systemic systolic arterial blood pressure
the pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart contracts
what is systemic diastolic arterial blood pressure
the pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart relaxes
what is the ideal normal systolic arterial blood pressure range for an adult under 80
90-120mmHg
what is the ideal normal diastolic arterial blood pressure range for an adult under 80
60-80mmHg
what is hypertension defined as in a clinic and a daytime average
- clinic blood pressure of 140/90mmHg
- day time average of 135/85mmHg
(hyper means high)
why are the values for clinic blood pressure and daytime average different when talking about hypertension
because in a clinic peoples blood pressures may be altered by the environment e.g. feeling stressed whereas a day time average gives a more accurate result
what does the ‘/’ mean in blood pressure
systolic/diastolic
what is pulse pressure and what is a normal value for pulse pressure
the difference between systolic and diastolic blood pressure e.g. 120/80 mmHg, pule pressure = 40mmHg
- pulse pressure is normally between 30 and 50mmHg
what is the mean arteriole blood pressure (MAP)
the average arterial blood pressure during a single cardiac cycle, which involves contraction and relaxation of the heart
what is a cardiac cycle
all of the events that occur from the beginning of one heart beat to the beginning of the next
why is the MAP not obtained by taking an average off the systolic and diastolic pressures
because the diastolic portion of the cardiac cycle is about twice as long as the systolic part
- therefor you can’t compare/average them as they weren’t over the same time frame
what is the simplest way to measure the mean arterial blood pressure
MAP= [(2 X diastolic) + systolic] / 3
- in mmHg
what is a less common way to measure the mean arterial blood pressure
MAP = diastolic + (1/3 of pulse pressure)
- pulse pressure = difference between systolic and diastolic blood pressure
what is a normal range for mean arteriole blood pressure
70 - 105mmHg
what is the minimum mean arteriole blood pressure required to survive and why
60mmHg
- this is the minimum needed to perfuse (provide blood to) vital organs like the brain, heart and kidneys
(fighting against gravity to get blood up to the brain)
why must the MAP not be too high
because it could damage blood vessels or place an extra strain on organs like the brain, kidneys or eyes
where are baroreceptors
found in the wall of blood vessels and the heart
- the main ones are the carotid baroreceptor (in the carotid artery in the neck) and the aortic baroreceptors (in the aorta)
what will happen if there is a change in the mean arteriole blood pressure
- the change will be detected by baroreceptors and a message will be sent to the cardiovascular control centre in the medulla
- the control centre then sends a signal out to the effectors to bring about a change which counteracts the initial change
e.g. heart; varying heart rate or stroke volume
blood vessels; varying systemic vascular resistance
what kind of receptors are baroreceptors
mechanoreceptors that are sensitive to stretch
(when the arterial blood pressure is adequate the walls of the artery stretch, too low and it won’t, to high and it’ll stretch too much)
describe in detail what will happen when there is a change to the MAP
- baroreceptors will send afferent impulses to the cardiovascular control centre in the medulla of the brain stem
- the cardiovascular control centre receives CVS afferent information
- nucleus tractus solitarius (NTS) is site of the 1st synapse for all CVS afferents in the medulla
- NTS integrates and relays information to other regions that controls the pathways of the two divisions (parasympathetic and sympathetic) of the autonomic (“involuntary”) nervous system to heart and blood vessels
what is the cardiac output (CO)
the total volume of blood pumped by each ventricle of the heart per minute
CO = stroke volume (SV) x heart rate (HR)
what is stroke volume
the volume of blood pumped by each ventricle of the heart per heart beat
how can the MAP be calculated without the systolic or diastolic pressures
MAP = cardiac output(CO) x systemic vascular resistance (SVR)
what is systemic vascular resistance (SVR)
a sum of the resistance (used to create blood pressure) of all vasculature (blood vessels) in the systemic circulation
how can the MAP be calculated using three different things
MAP = stroke volume x heart rate x systemic vascular resistance
what 3 things could the mean arteriole blood pressure be regulated by
by regulating the
- heart rate
- stroke volume
- systemic vascular resistance
(like the equation)
where are the electrical signals which control the heart generated and what does this mean
generated within the heart meaning the heart is capable of beating rhythmically in the absence of external stimuli
- this is called autorhythmicity
what is the heart modified by
the autonomic nervous system (ANS)
what is tachycardia
acceleration of heart rate
what is bradychardia
slowing down of heart rate
how does the sympathetic division of the autonomic nervous system affect the heart
when stimulated, it accelerates the heart rate (tachycardia)
- the neurotransmitter noradrenaline (norepinephrine in America ) acts on Beta1 receptors
how does the parasympathetic division of the autonomic nervous system affect the heart
when stimulated it stimulates the vagus nerve (10th cranial nerve) and slows down the heart rate (bradycardia)
- the neurotransmitter acetylcholine acts on muscarinic (M2) receptors
what is stroke volume modified by and how is it controlled by this
the autonomic nervous system
- sympathetic nerves innervate (supply an organ with nerves) the ventricular myocardium
- stimulation increases the force of contraction and increases stroke volume
(the vagus/parasympathetic nerve has little direct effect on ventricular contraction)
when does stroke volume increase
when the contractile strength of the heart is increased
what is intrinsic (within the heart itself) control of stroke volume controlled through
the Frank Starling mechanism
what vessel has the most systemic vascular resistance
arterioles
what is systemic vascular resistance regulated by and how
smooth muscle
- contraction of vascular smooth muscle causes vasoconstriction and increases SVR and MAP (pressure upstream)
- relaxation of vascular smooth muscle causes vasodilation and decreases SVR and MAP
what type of nerve fibres are vascular smooth muscles supplied by
sympathetic nerve fibres
- the neurotransmitter noradrenaline acts on alpha receptors
what does vasomotor tone mean and what is this caused by
it means that vascular smooth muscles are partially constricted at rest (tense = tone)
- caused by tonic discharge of sympathetic nerves resulting in continuous release of noradrenaline
what is the only reason that the baroreceptor reflex will work
when there is an acute change to arterial blood pressure
- their activity decrease if high arterial blood pressure is sustained
what is control of MAP in the longer term controlled by
controlled by control of blood volume mainly via hormones
describe the different routes that could be taken when MAP is acutely increased
diagram in ppt
describe the different routs that could be taken when the MAP is actutely decreased
diagram in ppt
what will an increase in sympathetic discharge cause
an increase in the vasomotor tone causing vasoconstriction (increase SVR and MAP - more pressure upstream)
what will a decrease in sympathetic discharge cause
a decrease in vasomotor tone causing vasodilation (decreased SVR and MAP)
is there much parasympathetic innervation of arterial smooth muscle
not significantly
- the exceptions are the penis and the clitoris
