Short Term Control of Blood Pressure Flashcards
What happens when MAP is too low?
- Less venous return to the brain (syncope)
- Less venous return to the heart = lower preload = lower EDV = lower SV/CO
What happens when MAP is too high?
Hypertension, peripheral oedema
Where are the arterial baroflexreceptors located? (3)
- carotid sinus baroreceptors = bifurcation of the internal common carotid arteries (x2)
- aortic arch baroreceptor
What type of receptors are the arterial baroreceptors?
What type of pressure do they respond to?
Stretch receptors
indirect pressure
What happens when the wall of the artery is stretched?
The baroreceptors detect this and AP will begin to fire according to the stretch.
The stretch in the arteries will be due to an increase in ________.
MAP
As MAP increases, the ___________ of AP increases.
firing rate
Below what MAP do baroreceptors not fire?
40mmHg
Above what MAP does a baroreceptors firing rate stop increasing?
120mmHg
What is the centre in the brain that integrates information about BP from baroreceptors?
Medullary Cardiovascular centre (brain stem)
Which nerve transmits AP from the aortic arch baroreceptors to the medullary cardiovascular centre?
vagus nerve
Which nerve transmits AP from the carotid sinus baroreceptors to the medullary cardiovascular centre?
Glossopharyngeal nerve
Which nerve carries signals from the medullary cardiovascular centre to the heart to bring about a parasympathetic response?
Vagus nerve
What is the parasympathetic response from the medullary cardiovascular centre on the heart in response to increase MAP?
Causes a decrease in heart rate.
What is the sympathetic response from the medullary cardiovascular centre on the heart in response to decreased MAP? (2)
Increased heart rate and increased contractility
What do the sympathetic fibres from the medullary cardiovascular centre do apart from increasing heart rate and contractility to increase MAP? (2)
- Cause venoconstriction and arteriolar constriction
- cause release of adrenaline from the adrenal medulla
- i.e. fight or flight
Other than the arterial baroreceptors, what are the other inputs to the medullary cardiovascular centres. (5)
- Cardiopulmonary baroreceptors
- Central chemoreceptors
- Chemoreceptors in muscle
- Joint receptors
- Higher centres
Describe how cardiopulmonary baroreceptors monitor blood pressure? (3)
- located in the walls of heart and lung vessels.
- low pressure parts of the circulation.
- stretch receptors also, which respond to an increase in MAP.
Describe how central chemoreceptors monitor and alter blood pressure? (3)
- located in the medulla oblongata
- detect changes in CO2 in the blood
- mainly affect respiratory drive, but can also increase HR and SV to alter BP.
Describe how chemoreceptors in muscles work? (2)
Give an example.
- respond to any increase in metabolic activity in the muscle.
- e.g. during exercise, they fire more AP which ensures adequate blood flow to muscles to wash away waste molecules and supply adequate O2 and nutrients.
How do joint receptors work to alter MAP?
- Detect increase movement of joint.
- increase blood flow to these regions to supply hard working muscles with adequate blood..
How do higher centres control blood pressure?
The hypothalamus increases blood pressure in response to a stimulus that requires an increased BP, e.g. seeing danger, fight or flight
What are the main receptors for the long-term control of blood pressure?
cardio-pulmonary baroreceptors
The regulation of blood pressure in the long term revolves around what?
blood volume (CO)
Regulation mechanisms of long term blood pressure act on both the what?
blood vessels and kidneys
How does standing up affect blood pressure?
- increased hydrostatic pressure
- pooling of blood in veins in legs/feet
- reduced VR
- reduced EDV/preload
- reduced CO/SV
- reduced MAP (BP)
- less AP being sent to medullary centres
What might happen to a person who stands up as a result of the drop in blood pressure?
syncope
What would the parasympathetic reflex response to a drop in blood pressure e.g. in standing up?
- reduced vagal tone
- increased HR
- increased CO/SV
- increased MAP
- arterial baroreceptors detect the MAP returning to normal.
What would the sympathetic reflex response to a drop in blood pressure be i.e. would it up/down-regulate?
- upregulate sympathetic tone
- increased HR
- increased SV/CO
- increased MAP
How would the sympathetic reflex response to drop in BP affect systemic veins?
- venoconstriction
- increased VR
- increased EDV/preload
- increased SV/CO
- increased MAP
How would the sympathetic reflex response to drop in BP affect systemic arterioles?
- arteriolar constriction
- increased TPR
- increased MAP
What is the Valsava manoeuvre?
What can this be thought of as?
Forced expiration against a closed glottis
e.g. think of a cat doing a poo.
Explain how the valsalva manoeuvre can transmit thoracic pressure through to the aorta.
- Phase 1: increased thoracic pressure = increased MAP (aorta)
Phase 2:
- increased thoracic pressure
- decreased VR
- decreased EDV/preload
- decreased SV/CO
- decreases MAP (BP)
Phase 3:
- MAP is detected by baroreceptors which initiate reflex
- increased in CO (venoconstriction)
- increased TPR (arteriolar consriction)
Phase 4:
- decrease in thoracic pressure transmitted to aorta
Phase 5:
- VR restored
- SV/CO increases
- reflexes still in action
Phase 6:
- MAP restored
