Cardiovascular Reflexes Flashcards
cardiac output equation
CO = HR x SV
MAP equations
MAP = CO x SVR
MAP = SBP + (2xDBP) / 3
what is the most important factor for proper operation of the CV system
systemic arterial pressure
needs to be high enough to supply blood to heart and brain, but low enough to not put too much demand on the heart
what are short term BP regulation pathways
cardiac reflexes
what is the general pathway for cardiac reflexes
detector
afferent
coordinating center
efferent
effector
what does the parasympathetic nervous system innervate
SA + AV nodes
atrial cardiomyocytes
PNS mediators and receptors
mediator: ACh
receptors: muscarinic (M2, M3)
M: vessels –> vasodilation
M2: heart –> dec. chrono/dromo/ino/lusitropy
what does the sympathetic nervous system innervate
SA + AV nodes
ventricles
adrenal glands
blood vessels
SNS mediators and receptors
mediators: NE and epi
receptors: a1, B1, B2
a1: vessels –> vasoconstriction
B1: heart –> inc. chrono/dromo/ino/lusitropy
B2: vessels –> vasodilation
baroreceptor reflex
responds to acute changes in BP to attempt to normalize BP
baroreceptor reflex pathway
- high MAP causes vessel walls to stretch
- detected by baroreceptors
- increase firing of BRs
- afferent signal sent to the CV center in the medulla
- increase PNS, decrease SNS efferents
- vasodilation + decreased HR and contractility
- decreased MAP
when no stretch is detected, are baroreceptors firing
yes - maintain tone even at normal BPs
when does maximum BR activity occur
within normal BP ranges
responds to acute, small changes (standing, falling, etc) to prevent a large change in systemic BP
how does chronic systemic hypertension affect BR reflex
baroreceptors will adapt –> decreased sensitivity to stretch –> firing rate returns to baseline –> set point gets “reset” to a higher BP –> MAP vs stretch curve shifts right
what are baroreceptors
mechanoreceptors (stretch detectors) located in the aortic arch and carotid sinus that detect the amount and rate of stretch
carotid sinus BR afferents
hering nerve –> CN IX (glossopharyngeal)
aortic arch BR afferents
aortic nerve –> vagus nerve
bainbridge reflex
responds to acute changes in blood volume to attempt to move volume forward
bainbridge reflex pathway
- increase in atrial volume causes stretch in atrial walls
- detected by stretch receptors in walls
- increases afferent signaling to CV center
- increase SNS, decrease PNS efferent signals
- increased HR and contractility
- increased forward flow
examples of when Bainbridge reflex is used
administration of fluid bolus
respiratory sinus arrhythmia
respiratory sinus arrhythmia + bainbridge reflex
inspiration creates negative intrathoracic pressure –> increases venous return to RA –> increased atrial volume –> increase SNS, decrease PNS –> increased HR during inspiration
when is bainbridge reflex predominant vs baroreceptor reflex
high/normal blood volume: bainbridge predominates
low blood volume: baroreceptor predominates to maintain perfusion pressure
chemoreceptor reflex
responds to severe changes in pO2 and CO2 to control BP
chemoreceptor reflex mechanism
- low O2 and high CO2 and acidemia sensed by chemoreceptors in carotid sinus/aortic arch
- increase afferent signaling to CV center
- increase SNS, decrease PNS
- increase RR and MAP
