Reflex Control Of The Circulation Flashcards
Give examples of excitatory inputs
Arterial chemoreceptors, muscle metaboreceptors
Give examples of inhibitory inputs
Arterial baroreceptors, cardiac-pulmonary receptors
What are arterial baroreceptors important for?
Vital to maintain blood flow to brain and myocardium
Where does the body monitor blood pressure?
Carotid and coronary arteries
How does blood pressure monitoring tell us about blood flow?
Pa = CO x TPR
What does a decrease in Pa reflect?
Either a decrease in CO or TPR which compromises blood flow to the brain or heart
Where are the blood pressure sensors found?
In the walls of the carotid arteries/ aorta
What happens with the baroreceptors when there’s an increase in pressure?
As pressure increases, fast firing which eventually slows down and becomes constant, but at a higher level than before
What happens to the baroreceptors when there’s a decrease in pressure?
The firing slows down proportionately
What happens when there’s continued low or high pressure in the baroreceptors?
The threshold changes
What is the effect of an increased blood pressure on the heart (5)?
Increase in BP = loading
- pulse pressure falls
- vasodilation decreases TPR and BP
- decreased sympathetic nerve activity
- increased vagal nerve activity
What is the effect of decreased blood pressure on baroreflex?
Decrease in BP = unloading
- increased sympathetic activity and decreased vagal activity
- increased heart rate and force of contraction so cardiac output is increased
- arterioles constriction gives increased TPR
- venous constriction increases central venous pressure and increases stroke volume and cardiac output
What are veno-atrial mechanoreceptors stimulated by?
Increase in cardiac filling/ cardiac venous pressure
How do veno-atrial mechanoreceptors work?
Increased diuresis switches off ADH and RAAS-> less sympathetic activity to kidneys, so more glomerular filtration. This then secretes atrial natriuretic peptide
What nerve is connected to the veno-atrial mechanoreceptors?
Vagus afferents
What are ventricular mechanoreceptors stimulated by?
Over distension of vesicles
What happens when the ventricular mechanoreceptors are stimulated?
Weak reflex- mild vasodilation, lower blood pressure and preload
What are the nociceptive sympathetic afferents stimulated by?
K+, H+ and bradykinin during ischaemia
What do the nociceptive sympathetic afferents do?
Mediate pain of angina and myocardial infarction. Reflex increased sympathetic activity
What happens when afferent fibres from the baroreceptors are removed?
Arterial pressure varies enormously, but the mean isn’t that different
What happens when afferent fibres from cardiac receptors and baroreceptors are removed?
Arterial pressure varies and the mean is very different
What happens if the arterial pressure drops to 50mmHg?
Cause insufficient perfusion to end organs
What happens if the arterial pressure rises to 150mmHg?
Damage the cardiovascular system
Where are arterial chemoreceptors located?
Carotid and aortic bodies
What are arterial chemoreceptors stimulated by?
Low O2, high CO2, H+ and K+
What do arterial chemoreceptors regulate?
Ventilation and also drive cardiac reflexes during asphyxia, shock and haemorrhage
What are the arterial chemoreceptors responses?
Increased sympathetic activity, tachycardia and increased cardiac output and blood pressure
What are muscle metaboreceptors and where are they found?
Sensory fibres in group IV motor fibres located in skeletal muscle
How are muscle metaboreceptors activated?
Via metabolites like K+, lactate and adenosine
What do the muscle metaboreceptors cause?
Increase in sympathetic activity
Tachycardia -> more arterial/venous constriction
Increase cardiac output blood pressure
When are muscle metaboreceptors really important?
During isometric exercise
What happens during isometric (static) exercise?
Bigger blood pressure drives blood into the contracted muscle to maintain perfusion. These then undergo metabolic hyperaemia, which allows blood to flow to the contracted muscle
What is the central role of the nucleus tractus solitarius?
Signal from stretched baroreceptor is sent via afferent fibres and enters the NTS
NTS signals to CVLM
CVLM signals to RVLM
Sympathetic efferent nerves to heart and vessels are inhibited so lower heart rate vasoconstriction and stuff
What does CVLM stand for?
Caudal ventrolateral medulla
What does RVLM stand for?
Rostral ventrolateral medulla
How is the nucleus ambiguous stimulated and what is its effect?
Stimulated by the NTS
Causes vagal parasympathetic impulses to be sent to the heart where they have a depressor effect
What is sinus tachycardia?
An inhibitory input from the inspiration centre. Each inhalation switches off nucleus ambiguous. This increases the inhibitory parasympathetic signal to the vagus
What is the vaso vagal syncope?
Vagal parasympathetic outflow
How does the vasovagal syncope work?
The lymbic system stimulates NTS which stimulates the nucleus ambiguous which causes an increase in the activity of the vagal nerve and depressor effect on the AV and SA nodes
How do you have a vasovagal attack?
Fainting is caused by decreased cerebral blood flow due to a sudden drop in the arterial cardiac output and blood pressure
