Flashcards in Control of arterial blood pressure - 1 Deck (23)
What is blood pressure?
The outwards (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 (not exceed 140mmHg)
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 (not exceed 90mmHg)
What is pulse pressure?
The difference between systolic and diastolic blood pressure
What is mean arterial blood pressure and why is the value closer to the diastolic arterial pressure?
Its the average arterial blood pressure during a single cardiac cycle which involves both contraction and relaxation of the heart
-The diastolic portion of the cardiac cycle is twice as long as systolic
How is mean arterial blood pressure estimated?
MAP= [(2 x diastolic) + systolic] divided by 3
What is the normal mean arterial pressure?
Why is mean arterial blood pressure needed to be regulated within a narrow range?
-pressure is high enough to perfuse internal organs including the brain, heart and kidneys
-pressure is not too high to damage the blood vessels or place an extra strain on the heart
What is total peripheral resistance?
The sum of resistance of all peripheral vasculature in the systemic circulation
What are the major resistance vessels?
What does contraction of vascular smooth muscles cause?
-increase TPR and MAP(i.e. pressure upstream)
What does relaxation of vascular smooth muscles cause?
-decreases TPR and MAP
What is vasomotor tone?
When vascular smooth muscles are partially constricted at rest
What causes vasomotor tone?
Caused by tonic discharge of sympathetic nerves resulting in continuous release of noradrenaline
What does increased sympathetic discharge have on vasomotor and what does it result in?
Increase vasomotor tone and results in vasoconstriction (increase TPR and MAP- pressure upstream)
What does decreased sympathetic discharge have on vasomotor tone and what does it result in?
Decrease in vasomotor tone resulting in vasodilation (decrease TPR and MAP)
What is the effect of parasympathetic on arterial smooth muscles?
No significant parasympathetic innveration of arterial smooth muscles - except penis and clitoris
What are the 2 types of baroreceptors?
-Carotid ( in carotid sinus)
-Aortic (in aorta)
What does the baroreceptor reflex do?
Short term regulation of mean arterial pressure
How does the baroreceptors work?
The baroreceptors ( pressure centres) detect signal, move to the medulla (control centre) and goes to the heart and blood vessels ( effectors)
What is the only type of changes that baroreceptors respond to?
After "re-set" of baroreceptors, when will they fire again and what does this show?
Fire again only if there is an acute change in MAP above the new higher steady state level
-this shows baroreceptor cannot supply information about prevailing steady state blood pressure