Autonomic Control of Blood Pressure Flashcards
what is the acute regulation of arterial pressure primarily mediated by?
high-pressure baroreceptor reflex (arterial baroreceptors)
describe cardiopulmonary baroreceptors
they are low pressure baroreceptors or volume receptors
what are chemoreceptors primarily concerned with?
respiratory control
what is chronic regulation of arterial pressure linked to?
volume control by the kidneys
describe baroreceptors
stretch receptors strategically placed in the walls of large systemic arteries
branched terminals of nerve fibers
where are the two most important arterial baroreceptors?
in the carotid sinus and the aortic arch
how are the impulses transmitted from the carotid sinus?
hering’s nerves carry the signal to the glossopharyngeal nerve which brings it to the nucleus tractus solitarius in the medulla
what is the integration portion of the high pressure baroreceptor reflex?
the nucleus tractus solitarius
what are the major impacts of stretching baroreceptors systemically?
vasodilation and bradycardia
what are the two major peripheral chemoreceptors?
the carotid body and the aortic bodies
why are the chemoreceptors stimulated when the arterial pressure falls below a critical level?
because diminished flow causes decreased oxygen and buildup of carbon dioxide and H+
when is the chemoreceptor reflex a powerful arterial pressure controller? what is the purpose?
when the arterial pressure falls below 80 mmHg
purpose is to have more stimulation to prevent further decrease in arterial pressure
where are the central chemoreceptors and what do they detect?
in the medulla and they are sensitive to decrease in brain pH (reflecting CO2 concentration)
what do low pressure baroreceptors detect?
changes in venous pressure/ volume
how does an increase in blood pressure translate to stimulation of baroreceptors?
the vessel is enlarged, deforming the receptors and increasing in the depolarization of the receptor and therefore an increased firing rate of the receptor’s sensory nerve
how is the baroreceptor potential different to an action potential?
it is a graded response whose amplitude is proportional to the degree of stretch
which is the most important arterial baroreceptor and why?
the carotid sinus receptor because it is more sensitive around normal operating pressure range than the aortic receptor
what pressure do not stimulate the carotid sinus baroreceptor?
0-50 mmHg
what is the difference in response of the aortic baroreceptor compared to the carotid sinus?
they operate at different pressures (30 mmHg higher than carotid)
when are the carotid sinus baroreceptors most sensitive?
during normal operating range
how does the carotid sinus nerve firing vary without a change in mean arterial pressure?
it responds to the different pressures during systole and diastole (responds more to a rapidly changing pressure than stationary pressure)
how do baroreceptors adapt to long term changes in mean arterial pressure?
it sets a new standard for normal operating range and will not fire abnormally at that higher set point
what are the nerves from the baroreceptors referred to as and why?
buffer nerves
because they buffer blood pressure changes due to daily activities
what occurs when baroreceptor nerves from the carotid sinuses and the aorta are lost?
there is a large fluctuation of blood pressure throughout the day when it is usually stable
what vessels does the sympathetic nerve fibers innervate?
all but the capillaries
how does sympathetic innervation of small arteries and arterioles decrease rate of blood flow through tissues?
it increases resistance to blood flow
what does sympathetic innervation of large veins do?
decreases the volume of these vessels and pushes blood to the heart
how does sympathetic innervation impact arterial pressure continuously?
under normal conditions, it vasoconstricts causing a partial state of contraction
what is vasomotor tone?
the partial state of contraction maintained by the sympathetic nervous system
what happens to arterial pressure with total spinal anesthesia and why?
the pressure falls because it blocks all transmission of sympathetic nerve impulses and therefore vasomotor tone is lost
what is the result of an increase in mean arterial pressure?
baroreceptors increase their firing
parasympathetic nerves are stimulated and sympathetic nerves are suppressed
heart rate is decreased and there is vasodilation
what is the end result of decreased MAP in response to a transient increase in MAP called?
baroreceptor reflex
what effect does lying down have on mean arterial pressure? how?
it increases it by increasing venous return and therefore stroke volume
what is carotid sinus massage used for?
stimulates baroreceptors by increasing MAP- slows the heart in people with atrial tacychardia
what is carotid sinus syndrome?
when a person has hypersensitive baroreceptors so that minor pressure (even from external sources) stimulates a strong reflex. it can stop the heart
where does the parasympathetic nervous system innervate in the circulatory system?
SA and AV nodes, and vessels in the genitals and lower GI tract
where does the sympathetic nervous system innervate in the circulatory system?
SA and AV nodes, artreial and venous vessels and the myocardium
what effects does the baroreceptor reflex have with high MAP and what innervation causes them?
lowering heart rate (PNS)
decreased peripheral resistance, decreased venous tone and decreased contractility (SNS)
what does falling pressure in baroreceptors elicit?
an immediate, strong sympathetic reflex that minimizes the decrease in pressure
what does the valsalva maneuver test?
the integrity of the baroreceptor reflex
describe the valsalva maneuver
patient expires against a closed glottis which increases intrathorasic pressure and decreases mean arterial pressure (decreases venous return)
what is experienced after release from the valsalva maneuver?
a rebound decrease in heart rate
where do inhibitory interneurons project from and to?
from the neucleus tractus solitarii to the vasomotor area