Short Term Control of Blood Pressure Flashcards
What does blood pressure measure?
Pressures within the cardiovascular system during the pumping cycle of the heart
How is MAP calculated?
Mean arterial pressure = cardiac output (CO) x total peripheral resistance (TPR)
What is MAP the driving force behind?
Pushing blood through the circulation
Why does MAP have to be regulated?
Too low - syncope (fainitng)
Too high - hypertension
What is used for short term control of blood pressure?
The autonomic nervous system
What detects short term change of blood pressure?
Baroreceptors located in aortic arch and carotid sinus
What physical component do the baroreceptors actually detect?
Stretch
What happens when pressure increases in the arteries?
Increased pressure leads to walls of arteries stretching, baroreceptors detect that change and there is an increased firing rate of action potentials
Vice-versa
What is the integrating centre?
Medulla oblongata
What happens when there is a rise in blood pressure?
- Aortic and carotid blood baroreceptors stimulated
- Increased input to the cardiovascular centre
3a. Parasympathetic activity increased to heart
3b. Sympathetic activity inhibited to heart
3c. Sympathetic activity inhibited to blood vessels
Decreased cardiac output
Vasodilation of blood vessels
Blood pressure falls
What happens when there is a fall in blood pressure?
- Aortic and carotid blood baroreceptors inhibited
- Decreased input to the cardiovascular centre
3a. Parasympathetic activity to heart inhibited
3b. Sympathetic activity increased to heart
3c. Sympathetic activity increased to blood vessels
Increased cardiac output
Vasoconstriction of blood vessels
Blood pressure rises
What stimulation increases blood pressure?
Sympathetic stimulation
What stimulation decreases blood pressure?
Parasympathetic stimulation
When do neurons in baroreceptors increase their firing rate?
When the carotid sinus and aortic arch are stretched
Early in systole when there is a rapid increase in pressure
When is there a high and low firing rate of neurons?
High - increased pressure
Low - decrease in pressure
What nerve do aortic arch baroreceptors send their signals up?
Vagus nerve
What nerve do carotid sinus baroreceptors send their signals up?
Glossopharyngeal nerve
Where is the cardiovascular centre (integrating centre) in the brain?
Medulla oblongata aka medullary cardiovascular centres
Does the parasympathetic nervous system innervate the muscle of the ventricle and change contractility?
No
How does the parasympathetic nervous system cause brachycardia?
Outflow via vagus nerve
Innervates SA node in heart
Acetylcholine released and binds to cholinergic muscarinic receptors on the pacemaker cells - causing them to hyperpolarise
Takes longer to get to threshold causing a decrease in heart rate
How does the sympathetic nervous system increase heart rate?
Sympathetic nerve innervates SA node in heart
Noadrenaline released and binds to beta 1receptors on the pacemaker cells - causing them to depolarise faster
Increase in heart rate
How does the sympathetic nervous system increase heart rate and contractility?
Sympathetic nerves and muscle of ventricle and increase contractility
Increase release of calcium causing more acting and myosin cross Bridges to form which increases strength of excitation contraction coupling
Increase in stroke volume and force of contraction
Release of adrenaline from adrenal medulla into the blood, blood circulates and goes to beta 1 receptors in the heart which increases heart rate and contractility
They also binds to alpha one receptors on smooth muscle of blood vessels causing smooth muscle to contract causing veno- and arterial are constriction
What does venoconstriction do?
Push more blood back to the heart, causing increased end diastolic volume and increased preload
According to Starling’s law, stronger force of contraction, causing a larger stroke volume, and that will increase cardiac output.
If you increase cardiac output, you’re therefore going to increase mean arterial pressure.
What type of vessels are arterioles?
Resistance vessels
What does arteriolar constriction cause?
Makes it more difficult to push blood from the arteries into the arterials which increases peripheral resistance which increases arterial pressure
What is the most important input that the medullary CVC recieve?
From baroreceptors
What are other inputs to the CVC?
cardiopulmonary baroreceptors
central chemoreceptors
chemoreceptors in muscles
joint receptors
higher centres
What are cardiopulmonary receptors and what is their role?
Stretch receptors so they will detect when the vessels stretch
They’ll increase their firing rate of action potentials.
Their job here is to sense central blood volume.
What do central chemoreceptors do?
Sense arterial pCO2 and pO2
What do chemoreceptors in muscles do?
Sense metabolite concentrations
What do joint receptors do?
Sense joint movement
What are the higher centres of the brain?
Hypothalamus and cerebral cortex
What is responsible for short term blood pressure control?
Arterial baroreflex
What is the valsalva manoeuvre?
Forcefully expire with mouth closed
What happens in the first phase of the valsalva manoeuvre?
I: Increased thoracic pressure transmitted through to aorta - hence immediate jump in blood pressure
What happens in the second phase of the valsalva manoeuvre?
II: increased thoracic pressure makes it more difficult for blood to get to the heart, reduces the filing pressure from the veins, therefor decreases VR (venous return), EDV, SV (decrease in CO, less blood out of heart and into arteries), CO2, preload and MAP
A decrease in preload causes less less efficient excitation coupling fewer cross bridges forming, you’ll get a reduced force of contraction
Late II: the reduced MAP is detected by baroreceptors which initiate a reflex increase in CO and TPR
What happens in the third phase of the valsalva manoeuvre?
At the end of the maneuver, the decrease in thoracic pressure is transmitted through to the aorta hence the drop in blood pressure
What happens in the fourth phase of the valsalva manoeuvre?
VR is restored so systolic volume increases but reflex effects have not worn off
Why is the Valsalva maneuver clincally significant?
Test for autonomic function
Why can the baroreceptor reflex be reduced?
Older people
People with autonomic neuropathy
What happens to older people during the valsalva manoevure?
In phase two, blood pressure continues to call rather than being restored by arterial baroreflex
What happens to elderly, overweight and sedentary people when performing the Valsalva manoeuvre?
In people who are elderly, very sedentary, maybe overweight, performing the Valsalva manoeuvre when they defecate is likely the time that their heart is going to be under the greatest strain.
Preload will be decreased, so the heart needs to compensate by increasing heart rate, increasing contractility.
The heart is therefore going to be under a lot of strain, and that can increase the risk of myocardial infarction, a heart attack.
How can the valsalva manouveure help control
