Reflex control of the CVS Flashcards
What are arterial baroreceptors
Pressure receptors, in carotid/coronary arteries. Maintain control over blood flow to brain and heart (adjust TPR and CO)
How do the baroreceptor sensors work
Diffuse sprayed sensory nerve ending, detects stretching movements. The afferent signals are sent to the brain via the vagus nerve or the carotid sinus nerve. The efferent signals are sent from the brain to the heart and blood vessels via sympathetic nerves and the parasympathetic vagus nerve
What is stimulation of the baroreceptors called, and the reduction of this stimulation
Loading and unloading
What does stimulation of the carotid sinus nerve cause through baroreceptors
Raised blood pressure, systolic pressure falls, heart rate decreases. Loading of the baroreceptors causes a drop in blood pressure, slowing of heart rate (depressor effect)
Describe the effect of increased vagus activity
HR decreases, decrease in sympathetic activity also reduces heart rate and causes vasodilatation as it reduces vascular tone. Preload reduced, force of contraction reduces slightly
Describe unloading
Decrease in stretching of the baroreceptors, causing a decrease in potentials generated (due to decrease in bp)
Unloading increases sympathetic activity, because the depressor is removed.
What are the hormonal effects of low bp
Increased adrenalin secreted from the adrenal medulla, the low pressure will simulate RASS and ADH secretion
Vasoconstriction of the arterioles decreases capillary pressure, absorption of more interstitial fluid, effect of increasing blood volume
What are sympathetic nociceptors
Receptors on the heart, stimulated by painful things (e.g. decrease in pH or angina). The afferent nerve from armjaw share fibre bundles with these receptors, so people with heart problems may experience pain in these areas.
The triggered reflex increases sympathetic activity
What are ventricular mechanoreceptors
Found in the right atrium and junction with great veins, signal stretch which provide information about the filling of the atria, central venous pressure.
What are veno-atrial mechanoreceptors
Signal distension of the ventricles due to an increase in cardiac filling or central venous pressure.
One effect is to reduce sympathetic tone, especially of renal arteries relax and increase GFR. Trigger release of atrial natriuretic peptide, increasing Na+ excretion, lowering blood volume which reduces ADH and RAAS activit
Why is it important for the baroreflex to stabilise blood pressure
Drop to 50 mmHg could cause insufficient perfusion, leading to organ failure
Increase to 150 mmHg could cause acute kidney injury, stroke or aneurysm
What are arterial chemoreceptors
Receptors on the carotid/aortic bodies, stimulated by low oxygen conc, high CO2 conc, low pH and K+. Responsible for regulating ventilation and drive cardiac reflexes such as the shock reflex and haemorrhage
Compensates for very low blood pressure where baroreflex doesn’t work, chemoreceptors work
Stimulating the sympathetic system gives
Tachycardia, vasoconstriction, increase of cardiac output and blood pressure
What are metaboreceptors
Found in skeletal muscle, responsive to metabolites e.g. adenosine, k+ and H+ (low pH).
Metaboreceptors produce pressor response, increasing sympathetic activity to maintain cerebral blood flow
Used in isometric exercise, to get blood flow to a continually contracted muscle
What is the NTS and describe its function
NUcleus tractus solitarius - Junction box in the medulla oblongata
NTS sends info out to the CVLM, sending a signal to the RVLM, inhibiting sympathetic activity
Overall effect reduces TPR and BP
