Reflex control of circulation Flashcards
Central pathways
Medulla relay station (nucleus tractus solitarius)
Vagal motor neurons (nucleus ambiguous)
Pre-sympathetic neurons (RVLM)
Examples of excitatory inputs
arterial chemoreceptors, muscle metaboreceptors
What reflexes are stimulated by excitatory inputs?
Stimulation of reflexes
Increase cardiac output, TPR, and blood pressure
PRESSOR RESPONSE
Examples of inhibitory inputs
arterial baroreceptors, cardiac-pulmonary receptors
What reflexes are stimulated by inhibitory inputs?
Stimulation of reflexes
Decrease cardiac output, TPR, and blood pressure
DEPRESSOR RESPONSE
Why are arterial baroreceptors vital?
Vital to maintain blood flow to brain and myocardium
Where does the body monitor blood pressure?
The body monitors blood pressure in carotid and coronary arteries
What is cardiac output equivalent to ?
CO = blood flow (both have units of vol/time)
What does a decrease in Pa reflect and what does this compromise?
A decrease in Pa reflects a decrease in CO or TRP which compromises blood flow to the brain and heart
What do BP sensors in walls of the carotid arteries inform?
Blood pressure sensors in the walls of the carotid arteries/aorta informs the brain of pressure changes in these key feeder vessels
What do the BP sensors actually detect and what are these sensors known as?
Sensors detect arterial wall stretch
BARORECEPTORS
How do baroreceptors respond to increase in pressure?
As pressure increases, there is fast firing which eventually slows down and becomes constants, but at a higher level than before
ADAPTATION to a new normal
How do baroreceptors respond to decrease in pressure?
For a decrease in pressure, the firing slows down proportionately
What happens to baroreceptors in long term hypertension?
long term hypertension – baroreceptors become normalised at the new pressure and are less activated
Effect of increased BP on baroreflex
Pulse pressure falls (decreased stroke volume)
Vasodilation decreases TPR & BP
Decreased sympathetic nerve activity
Increased vagus nerve activity
Effect of decreased BP on baroreflex
Termed unloading (e.g. haemorrhage)
Increased sympathetic activity
Decreased vagus activity
Increased HR and force of contraction so increased CO
What does arteriolar constriction increase?
Increased TPR
What does venous constriction increase and what does this maintain?
Venous constriction increases CVP as well as SV and CO due to Starling’s Law
This all maintains blood pressure and therefore blood flow to vital organs
Equation for BP
BP=COxTRP
What does vasoconstriction decrease and what does this lead to the increase of?
Vasoconstriction decreases capillary pressure which increases absorption of interstitial fluid which also increases blood volume
What are nociceptive sympathetic afferents?
- Chemo-sensitive ventricular afferent fibres
What are nociceptive sympathetic afferents stimulated by?
- Stimulated by K+, H+ (lactate), bradykinin during ischaemia