Flashcards in Autonomic Control of Blood Pressure Deck (38)
What is the equation for MAP?
CO X TPR
What are the three ways that MAP is monitored?
1- High pressure baroreceptors
2- Renal juxtaglomerular apparatus
3- Low-pressure baroreceptors
Where are High pressure baroreceptors typically found?
the arterial side of circulation
Where are low pressure baroreceptors typically found?
the venous side of circulation
What is the single most import mechanism providing short term regulation of arterial pressure?
High pressure baroreceptor reflex
What are two major locations of arterial (high pressure) baroreceptors?
1- carotid sinus
2- aortic arch
An increase in the arterial pressure stretches the baroreceptors and causes the baroreceptors to do what?
It causes them to transmit more AP to the CNS medullary control center. "Feedback" signals are then sent back through the ANS to the circulation to reduce arterial pressure
How are signals from the "carotid baroreceptors" in the carotid sinus transmitted?
Submitted through small Hering's nerves to glossopharyngeal nerves (IX) in the high neck, and then to the nucleus tractus solitarius (NTS)
Where is the nucleus tractus solitarius (NTS) located?
In the medulla
How are signals from the "aortic baroreceptors" in the aortic arch transmitted?
Through vagus (X) to the NTS in the medulla
At what arterial pressure is the chemoreceptor reflex a powerful arterial pressure controller?
When arterial pressure falls below 80 mmHg
(at lower pressures this reflex becomes important to help prevent further decreases in arterial pressures)
Where are central chemoreceptors located?
in the medulla
What are central chemoreceptors sensitive to?
They are sensitive to decreases in brain pH (which reflects an increase in arterial PCO2)
What two factors work together to enhance vasoconstriction?
A low Po2 acting on peripheral chemoreceptors and a high PCO2 acting on the central chemoreceptor
Where are peripheral chemoreceptors located?
in the carotid and aortic bodies
they are in close contact with arterial blood
What are the baroreceptors in the carotid sinus and aortic arch?
They are branched terminals of myelinated and unmyelinated sensory nerve fibers. They are intermeshed within the elastic layers
What does an increase in transmural pressure difference cause?
1- enlarges the vessel
2- deforms the receptors
3- increases firing rate of the baroreceptor's sensory nerve
Do baroreceptors increase or decrease their rate of firing in response to stretch (increased MAP)?
They increase their rate in a frequency dependent manner
Describe the increase in frequency of APs in response to stretch?
Following a large initial depolarization (the dynamic component) is a more modest but steady depolarization (the static component)
Basically, after the initial burst, it settles into a patter that is reflective of the pressure step
Do baroreceptors respond slowly or rapidly to changes in arterial pressure?
They respond rapidly to changes
Within what range are baroreceptors most sensitive?
They are most sensitive in the normal operating range (about 100 mmHg for Carotid sinus baroreceptors and about 130 mmHg for aortic arch baroreceptors)
Are carotid sinus baroreceptrs stimilated by pressures between 1 and 60 mm Hg?
No they do not
If there are no baroreceptors, what is the effect on MAP?
It fluctuates a lot
What types of blood vessels does the sympathetic nervous system innervate?
All except the capillaries
Sympathetic innervation of small arteries and arterioles allows for what?
increase resistance to blood flow, and a decreased rate of blood flow through the tissues
Sympathetic innervation of large vessels allows for what?
decrease the volume of the vessels...they push blood into the heart and thereby play a major role in regulation of cardiac output
What is vasomotor tone?
The partial state of contraction in blood vessels
When you inhibit SNS, what is the effect on the vasomotor tone?
It is lost, which corresponds with a marked decrease in MAP
Explain what happens when there is an increase in MAP
1- baroreceptros are stretched and activated
2- increased firing of baroreceptors that sends signal through the afferent pathway
3- the coordinating center in the medulla receives the message and sends signal back to restore MAP to set point
4- response signal is sent via efferent pathway to effectors in tissue
5- Bradycardia and vasodilation counteract increased MAP
Can baroreceptor reflex adapt to long-term changes in MAP?
yes-- for example in hypertension, the set point is raised
What type of change in made by the baroreceptor reflex when changing posture from a standing to a lying posion?
This position change leads to a reflex to decrease MAP
Does the vagus have any effect on blood vessels or the heart?
The heart, but not vessels
A change in posture from standing to lying down increases venous return and has what effect on stroke volume and MAP?
It inceases SV and increases MAP
What does carotid sinus massage achieve?
Stimulates baroreceptros and reflexly slows the heart in people with atrial tachycardia
When going from supine to standing position, the MAP.....
What can be used to test the integrity of the baroreceptor reflex?
The valsalva maneuver
What is the valsalva maneuver?
Subject is asked to expire against a closed glottis which increases the intrathoracic pressure and a decrease in venous return to the heart which causes decrease in CO and MAP
Intact baroreceptors will sense the decrease in MAP and direct an increase in SNS and decrease in PNS outflow to the heart and vessels, the increase in HR is measured
A rebound decrease in HR is noted after release from the maneuver