Controlling the CVS Flashcards
What must arterial pressure be maintained at? (the accepted values for heart pressure for a healthy adult)
120/80mmHg
When must wide variations in blood flow to different organs occur (general)?
When the demand arises
What are the 4 main control systems involved in maintaining blood pressure?
- Arterial BP
- CO
- The local circulation
- Blood and ECF volume
What does MABP equal?
CO x TPR
What does CO equal?
HR x SV
What is the NTS in the feedback loop?
Nucleus Tractus Solitarius
What do arterial baroreceptors detect?
Pressure at different points in the arterial tree
Where are baroreceptors present?
In the carotid sinus and aortic arch
- Blood is going to the brain from the carotid artery - carotid arch detects pressure of blood as it leaves the heart - allows information to be relayed to the brain quickly
What do baroreceptors respond to?
Stretching (pressure changes)
Which baroreceptor is more important?
The carotid receptor as it is more sensitive (60-180mmHg)
- It is the most sensitive around MAP
- Input to NTS in brain
A decrease in the arterial pressure decreases the baroreceptors firing. What does this cause the SNS and PNS to do?
- There is a reflex via the medullary cardiovascular centre which decreases the parasympathetic outflow to the heart
- There is an increase in the sympathetic outflow to the heart, arterioles and veins
Where are alpha-2 adrenoreceptors found?
On the nerve terminals
What do bulbar circulatory centres do?
Inhibit the action of the vagal nucleus
What do alpha 2 adrenoreceptors activate and inhibit?
Activate: Vagal nucleus
Inhibit: Bulbar circulatory centres
What do beta 1 adrenoreceptors activate and inhibit?
Activate: Bulbar circulator centres
Inhibit: The vagal nucleus
What is the effect of the activation of the vagal nucleus by alpha-2 adrenoreceptors on the heart and blood vessels ?
- Vagal nucleus releases ACh which attaches to M2 receptors which decreases cardiac output and decreases peripheral resistance
- Also inhibits the action of the bulbar circulator centres so prevents them from secreting NA
What is the effect of the activation of bulbar circulatory centres by beta-1 adrenoreceptors on the heart and blood vessels?
- Bulbar circulatory centres release NA which attaches to alpha-1 adrenoreceptors on the blood vessels and beta-1 adrenoreceptors on the heart to increase the peripheral resistance and cardiac output
- Also inhibits the action of the vagal nerve so prevents the release of ACh
If blood pressure drops, what area if the brain does it affect and what is the response to this?
- Positive output of sympathetic nerves
- Affects the adrenal medulla which causes BP to increase
What does Clonidine- alpha-2 agonists activate?
- Activates presynaptic receptors in brain vasomotor centre to lower sympathetic output
- In the NTS, fools the brain into thinking catecholamine levels are higher so responds by lowering tone to adrenal medulla
What can be a problem of prescribing Clonidine-alpha2 agonist as a drug to decrease blood pressure?
- Problem = rebound hypertension
- It keeps the blood pressure low but when the patient stops using the drug or forgets to take the drug then there is a huge rush in blood pressure which increases the chance of stroke etc
When is alpha-methyldopa prescribed as a medicine and what does it do?
- Sometimes used in hypertension of pregnancy
- It is used in pregnancy as it does not harm the baby
- It is a prodrug
- It is converted to alpha-methylnoradrenaline and acts as a central alpha-2 agonist
- It inhibits DOPA-decarboxylase so reduces production of peripheral neurotransmitters
- It decreases the amount of dopamine in the body
What is meant by a prodrug?
It has to be metabolised to have its affect
What can constrict the arteriolar radius?
- Sympathetic nerves
- Noradrenaline
- Alpha-1 adrenoreceptors
What can dilate the arteriolar radius?
- Sympathetic cholinergic nerves
- Acetylcholine
- Muscarinic
- Plasma adrenaline
- Beta-2 adrenoreceptors
- Local controls
- decrease in PO2
Increase in K+ - Increase adenosine
