Short Term Control of Blood Pressure Flashcards
Why is it important we maintain MAP?
Its the main driving force behind circulation, too high or low and we get ill
What happens when MAP is too high?
Hypertension.
OVertime it damages capillary beds leading to stroke, heart attack etc.
What happens when MAP is too low?
Hypotension Syncope occurs (Fainting)
How are MAP, Cardiac output and total peripheral resistance related?
MAP = CO x TPR
What are baroreceptors and what do they respond to?
Stretch receptors in the walls of arteries that fire more when the arteries stretch under high pressure
Where are the main baroreceptors found?
Teh aortic arch & carotid sinus
Where is the carotid sinus?
Where the internal & external carotid arteries split.
How does the AP firing rate of baroreceptors change through the caridac cycle?
Its highest during systole and lowest during dystole
Whats another name fore cardiopulmonary baroreceptors?
Low pressure baroreceptors
What happens to the baroreceptors firing rate during hyper/hypotension?
Increases in hypertension
Decreases in hypotension
How are baroreceptor signals from the carotid sinus transferred tot he medullary CV centres?
Carotid Sinus -> Glossopharyngeal Nerve -> Medullary CV centres
How are baroreceptor signals from the aortic arch transferred to the medullary CV centres?
Aortic Arch -> Vagus Nerve -> Medullary CV Centres
What mechanisms reduce blood pressure in the baroreceptor reflex?
Decreased Symp. Tone reduces: Veno/arteriolar constriction Adrenaline production in adrenal medulla Contractility HR
Increased Vagal Tone lowers HR
What mechanisms increase blood pressure in the baroreceptor reflex?
Decreased Vagal Tone increases HR
Increased Symp. Tone increases:
- Adrenaline production in adrenal medulla
- Veno & arteriolar constriction (increased venomotor tone)
- Contractility
- HR
What carries signals durin the baroreceptor reflex from the medullary CV centres to the Sinoatrial Node?
(when reducing and increasing HR)
Vagus (parasympathetic fibres)
Sympathetic Nerves
What carries signals durin the baroreceptor reflex from the medullary CV centres to the cardiac muscle?
Sympathetic Neves
How do signals travel from the medullary CV centres to the veins/arteries smooth muscle?
Sympathetic Nerves
What carries signals from the medullary CV centres to the adrenal medulla?
Sympathetic Nerves
From which spinal levels do sympathetic fibres supplyin the heart arise?
T1-T4
Whats another name for cardiopulmonary baroreceptors?
Low pressure baroreceptors
To what do central chemoreceptors respond?
Changes in the pH of the CSF brought on by changes in CO2 levels.
CSF is very closely related to blood
How does activating central chemoreceptors affect MAP?
They activate at high CO2 levels causing increased HR & contractility -> increased CO -> increased MAP
When do muscle chemoreceptors activate?
During exercise
Why do muscle chemoreceptors cause a MAP increase?
They signal the heart to increase HR/contractility so CO increases and they get more blood. This increases MAP
When are joint receptors activated?
During repeated movement, same reasoning as muscle chemoreceptors
How do higher centres affect MAP when you know your about to do exercise?
Higher centres act as a feed forward mechanism.
They increase HR & contractility in anticipation of increased need for blood to certain muscles.
Whats the importance of the arterial baroreceptor reflex when standing up?
Without it youd faint standing up as all the blood rushes to your lower limbs.
How does standing effect MAP?
Blood pools in legs (venous distension)
• VR, EDV, preload, SV, CO, MAP
How does standing effect MAP?
Blood pools in legs (venous distension) leading to lower VR
- > lower EDV
- > lower preload
- > lower SV
- > lower CO
- > lower MAP
Define the valsalva manoeuvre?
Forced Expiration against a Closed Epiglottis.
Shitting, repressuriing on a plane etc.
What does the forced expiration of the valsalva manoeuvre cause first?
An increased thoracic pressure
How does increased thoracic pressure affect the aortic pressure?
Its transmitted through to the aorta where its added to the aortic pressure, hence MAP rises
How does increased thoracic pressure affect venous return?
Increased thoracic pressure reduces venous return because it squashes the veins near the heart preventing blood flow.
How does lowered venous return affect MAP?
As less blood gets back to the heart EDV lowers. Hence CO lowers and MAP falls. This happens steadily so you get a gradual reduction in MAP back towards normal.
What is the bodies response to lowered MAP?
When MAP falls below normal (due to reduced VR) it triggers the baroreceptor reflex which makes MAP rise again
When the valsalva manoeuvre ends the decreased thoracic pressure is transmitted to the aorta, what effect does this have on the MAP?
It reduces MAP, a large drop below resting level.
How does the return to normal venous return after ending the valsalva manoeuvre affect MAP?
After the valasalva manoeuvre thoracic pressure returns to normal so venous return does too.
This mean EDV returns to normal and MAP quickly rises again.
Since the baroreflex is still active MAP rises well above normal
What happens after the baroreflex wears off after the valsalva manoeuvre?
BP returns to normal
What is the risk of the valasalva manoeuvre in someone old& sedentary?
They’re CVS cant cope with the variations in MAP, particulary the sudden hypotension when thoracic pressure returns to normal and they have heart attacks.
