Short term control of BP Flashcards
What is involved in short term control of BP
- arterial baro reflex (cardiopulmonary baroreceptors) is involved
- Revolves around MAP ( mean arterial pressue) exceeding. If MAP is too low=fainting ( syncope) and if too high=hypertension.
State the baroreceptors involved in the arterial baroreflex
Aortic arch baroreceptors
Carotid sinus baroreceptors
MAP calculation
MAP = CO x TPR
Where are these baroreceptors located? Describe the mechanism of the arterial baroreceptors
-Arterial baroreceptors are stretch receptors that signal a rise/fall(mainly) in arterial pressure with a reduced action potential firing rate.
Aortic arch baroreceptors
- located in the walls of the aortic arch
- afferent fibres run in the via the vagus nerve to the medullary centres.
Carotid sinus receptors
- located in the walls of the carotid sinus ( before bifurcation)
- afferent fibres runs via the glossopharyngeal nerve to the medulllary centres
The response is dependennt on the stimuli which is either sympathetic/parasympathetic. If sympathethetic, it will stimulate adrenal medulla and cause venoconstriction/aerteriolar constriction in order to elevate the LBP. Vice versa
Other inputs to medullar CVS centres
- cardiopulmonary barorecpetors
- central chemorecptors
- chemoreceptors in muscle
- joint receptors
- higher centres
Regulation of BP in the long term
- revolves around BVol
- main sensors are the cardio-pulmonary barorecptors
- effects tend to be hormonal
- act on BVs and kidneys
Regulation of BP in the long term
Renin - angiotensin ( aldosterone system -angiotensin 2 causes arteriolar constriction aand increases TPR -aldersterone increases and Na+ reabsorption and increase in PV Vasopressin ( ADH) -causes arteriolar constriction and there increases TPR - increases water permeability of collecting duct and increases PV Atrial natriuretic peptide + brain natriuretic peptide -causes arteriolar dilation + decreases TPR -Na+ excretion ( natriuresis) and decreases BV
Describe the effect of posture on BP
Effect of standing
- increases hydrostatic pressure causing pooling of blood in veins/venules of feet/legs
- this decreases VR, EDV, preload, SV, CO, MAP
- decreased baroreceptor firing rate
The reflex response ( signalled by fall in BR firing. Less AP indicated MAP is low)
- decreased vagal tone; increased HR, CO Increased Sympathetic tone -increased HR, CO, conractility, SV, -Increased venoconstriction, VR, EDV, SV, CO -Increased arteriolar constriction, TPR
Laying down
-Increased VR. Blood redirected from legs to chest area so more blood in heart throughout cardiac cycle(starlings law). SV will be increased and will have a higher CO with a lower heart rate.
Explain what happens in the valsalva maneover
- this forced expiration against a closed glottis
- There is only a small pressure difference (15-20mmHg) pushing the veins back into the heart so raised intrathoracic pressureis transmitted through the the heart will disrupt the pressure gradient between veins-RA. The great veins will be completely compressed thus reducing the venous return.This increased TP will decreases VR, EDV, SV, CO, MAP.
- The reduced venous return results in less ventricular filling during diastole, and hece EDV. Reduced EDV will decreases strength of contraction(starling’s law), thus lower SV . Essentially CO and arteral pressure falls.
- low MAP is detected by arterial baroreceps which initiate reflex increasing CO and TPR. Once the valsalva manoeuvre stops, venous return + SV is restored. Reflex still not worn off so MAP is higher.
Describe the mechanism of the arterial baroreflex
- Monitor changes in pressure by detecting stretch
- Baroreceprotrs located in aortic arch and carotid sinus will detect stretch in walls of arteries ( indirectly measuring pressure). High pressure/Low pressure, stretch receptors(baroreceptors) will detect this and activate the receptor.
- If baroreceptor in aortic arch signal >travels via vagus nerve > medullary CV centres
- Carotid sinus baroreceptors signal >travels via glossopharyngeal nerve > medullary CV centres
- In Medullary CV centres, will innervate PS/(decrease HR) S neurones ( increase HR)
Describe the mechanism of chemoreceptors in muscle
-Detects changes in K+ concentration/anything that signifies increase in metabolic activity in muscles. Response = more BF
Describe the mechanism of cardiopulmonary centres
- In heart and lungs
- mainly affected by BV than BP
- more involved in long term control of BP
Describe the mechanism of central chemoreceptors
-Indirectly measures CO2( by measuring H+ ions) levels in the CSF
Describe the mechanism of the medullar CVS centre when BP is low
Symmpathetic system and adrenalin - B1= increase contractility and HR(SAN)
B2 receptors = arteriolar dilation in heart and skeletal muscle
A1 receptors = arteriolar constriction
-decreases vagal tone
