Short term control of blood pressure Flashcards
what is the equation for mean arterial pressure
MAP = CO x TPR Mean arterial pressure = cardiac output x total peripheral resistance
what is the driving force pushing blood through the circulation
Mean arterial pressure
If your mean arterial pressure is too low what can this cause?
fainting - syncope
If your mean arterial pressure is too high what can this cause?
hypertension
what are the 2 sets of baroreceptors called
aortic arch baroreceptors and carotid sinus baroreceptors - both stretch receptors
which nerve do the carotid sinus baroreceptor signals travel up? and where do they synapse
Glossopharyngeal nerve. They synapse in group of cells within the medullary cardiovacular centres
which nerve do the aortic arch baroreceptor signals travel up? and where do they synapse
vagus nerve
medulla
what other things input into the medullary cardiovascular centres? (4)
- Cardiopulmonary baroreceptors
- Central chemoreceptors
- Chemoreceptors in muscle Joint receptors
- Higher centres
In what 2 different ways can the sympathetic system work to increase blood pressure
venoconstriction- constrict veins to squeeze blood back to the heart. This increases the end diastolic volume and the preload. Also then increases the systolic volume and blood pressure arteriolar constriction- because arterioles are resistance vessels, if you make them constrict you will increase resistance to blood flow and increase blood pressure
Describe the parasympathetic response to baroreceptor signal returning to the heart
parasympathetic travels back down the vagus nerve. It releases acetylcholine which acts on muscarinic receptors on pacemaker cells in the sinoatrial node. This causes them to depolarise to threshold later - bradychardia
Describe the sympathetic response to baroreceptor signal returning to the heart
sympathetic nerves release noradrenaline that acts on beta 1 receptors in the heart. Pacemaker cells depolarise to threshold sooner so you get tachycardia.
what happens every time you stimulate sympathetic nerves other than the release of noradrenaline?
adrenaline is released from the adrenal medulla - binds to beta 1 receptors too and increases heart rate.
Describe how noradrenaline acts on myocardial cells in the ventricles.
noradrenaline acts on beta 1 receptors on myocardial cells in the ventricles which increases the amount of Ca2+ coming in for the AP and increases the amount of Ca2+ being released from stores. More cross bridges are formed and this leads to increased contractivity
Apart from the heart, what else does the sympathetic response act on that will cause an increase in blood pressure?
veins and arterioles
What is the negative feedback system called that maintains blood pressure homeostasis?
‘arterial’ baroreflex
what can happen if the mean arterial pressure is too high
long term problems because the thin/fine vessels in the capillaries can get damaged by high blood pressure and over time as this damage progresses it can lead to heart disease etc
what is a sinus
a cavity
what are the two arteries that travel up through the neck from the heart called
L+R common carotid arteries
what happens when blood flows through vessels/aorta?
the vessel wall is stretched and as it stretches baroreceptors detect this. The receptors then send signals to the brain to let it know what is happening in the vessel.
Name 2 situations where the arterial baroreflex would come into effect
posture- standing up from sitting or lying down valsalva manoeuvre
Define the Valsalva manoeuvre?
it is a breathing technique forced expiration against a closed glottis
Describe 2 real life situations using the Valsalva manoeuvre
- when unblocking your ears- closing your mouth and holding your nose and trying to force air out of your ears
- whilst constipated - must be in sitting position on toilet - strain to help evacuate the bowel by inhaling, closing the glottis and increasing thoracic pressure to force stuff out
How does the Valsalva manoeuvre affect the heart?
it stops blood flow returning to the heart due to increased thoracic pressure (no longer the pressure gradient that is required to push venous blood back to the heart)
in summary:- decreased venous return increased thoracic pressure decreased EDV, SV, CO, MAP
why does increased thoracic pressure prevent venous return to the heart?
both the pulmonary vessels and aorta are constricted. When this pressure is released venous blood can once more return to the chest and the heart and cardiac output begins to increase.
describe the reflex response against the Valsalva manoeuvre
once the mean arterial pressure decreses the arterial baroreceptors detect this drop in BP and start the process of increasing sympathetic tone/activity so increased cardiac output and increased TPR (constrict peripheral arterioles so BP increases) Decrease in thoracic pressure causes the aorta to expand again and venous return is restored so SV increases.
what happens if you reduce filling and preload?
there is a fall in cardiac output by the Frank-Starling mechanism
what happens when you stand up after sitting or lying down?
increase in hydrostatic pressure causes pooling of blood in the veins/venules of the feet or legs this is turn causes a decrease in:- vocal resonance, EDV, preload, stroke volume, cardiac output, MAP because of this there is a decreased baroreceptor firing rate as the aorta is less stretched due to decreased CO and SV but the decrease in BP then stimulates sympathetic activity
what are the 2 reflex responses to the drop in blood pressure that occurs whilst standing?
decreased vagal tone - ie prevent activation of parasympathetic and in turn this causes increased HR and CO
increase sympathetic tone
- act on pacemaker cells and increase HR and CO
- act on myocardium which increases contractility, SV and CO.
- Stimulate sympathetic nerves in smooth muscle around veins so increase venoconstriction, venous return, EDV, SV, CO
- arteriolar constriction occurs which increases TPR, this causes increase in blood pressure
