Reflex control of circulation Flashcards
(24 cards)
Barorecptors detect changes in ???
Pressure
or arterial wall stretch
What is “blood flow” equivalent to?
Cardiac output
A decrease in pressure means a decrease in ?
Cardiac output or TPR
Where are the cardiac baroreceptors found?
Carotid arteries + aortic arch
How is an increase of pressure sensed by the brain?
Baroreceptors send out more action potential more rapidly
What happens if there is continious high or low pressure?
Becomes the new normal
for example long term hypertension - baroreceptors become normalised at the new pressure and less activated.
How is a decrease of pressure sensed by the brain?
Action potentials are sent less often
What does “loading” mean in this context?
Increase in blood pressure
(eg. stress or exercise)
Two compenmsatory mechanism to decrease blood pressure?
Decrease heart rate - decreases cardiac output
Vasodilation - decreases TPR
What is a decrease in blood pressure known as ?
unloading
Where are the arterial chemorecptors found?
Carotid and aortic bodies
What are they stimulated by?
Low O2
high CO2
H+ / K+
When the BP is below the range of the baroreflex (maximally unloaded) what happens?
Chemorecptors compensate
What is the pressor response
Raising of blood pressure
What are muscle metaboreceptors?
work receptors
What do Muscle metaboreceptors do ?
Induce a pressor response
Increase sympathetic activity.
Tachycardia, increase arterial/venous
constriction.
Increase cardiac output/blood pressure.
What happens after increased action potential are fired from barorecptors?
(sympathetic response)
1.Reaches nucleus tractus solitarius (NTS)
via afferent fibres
- Sends information out to the Caudal Ventrolateral Medulla (CVLM).
- The CVLM sends information to the
rostral ventrolateral medulla (RVLM). - INHIBITION of sympathetic
efferent nerves to heart and vessels. - Less sympathetic efferent signals result in
reduction in HR, less vasoconstriction,
lower BP etc.
What happens after increased action potential are fired from barorecptors?
(parasympathetic response)
The signal from the NTS stimulates
the nucleus ambiguous (vagal
nuclei).
Vagal parasympathetic impulses
are sent to the heart and these
have a depressor effect.
List the parts of the brain the signal fires to
NTS
CVLM
RVLM
what is sinus tachycardia?
Fast heart rate caused by stress, exercise or other factors
What is vasovagal syncope?
Fainting caused by decreased
cerebral blood flow due to
sudden drop in arterial cardiac
output & blood pressure
How can emotions cause syncope?
Limbic system (emotional centre)
stimulates NTS which in turn stimulates
the nucleus ambiguus causing
increased activity of the vagal nerve
and depressor effect on the AV and SA
nodes.
Is heart rate faster or slower when inhaling
slightly faster during inhalation
How does vagal parasympathetic outflow contribute to sinus tachycardia? (4)
Vagal parasympathetic outflow exerts inhibitory control over heart rate by releasing acetylcholine onto muscarinic receptors in the sinoatrial node.
-Decreased vagal tone or withdrawal of vagal input allows sympathetic influence to predominate, leading to an increase in heart rate.
-Sinus tachycardia often occurs in response to stress, exercise, or other factors that increase sympathetic activity or reduce parasympathetic tone.
-Respiratory sinus arrhythmia may modulate heart rate during the respiratory cycle, with slight increases in heart rate during inspiration due to reduced vagal activity.
