Short term control of BP Flashcards
What determines Mean arterial pressure (MAP)?
Cardiac output & Total peripheral resistance
MAP = CO x TPR
Why must blood pressure be regulated?
If MAP is too high = hypertension = everything goes wrong
If MAP is too low = syncope (fainting)
What sensory cells measure changes in pressure?
Baroreceptors
Stretch sensitive receptors that are located in the walls of the aorta and carotid arteries
What is the role of baroreceptors?
Continuously monitor pressure of blood going to the brain (carotid sinus baroreceptors) and the body (aortic arch baroreceptor)
What information is sent to the brain by baroreceptors, and how are changes in blood pressure communicated?
Baroreceptors continuously fire APs at normal BP
Increase in BP = increase in the rate of firing
Decrease in BP = decrease in firing rate
What area of the brain do baroreceptors communicate with?
Through what nerves does each BaroR do this?
Medullary cardiovascular control centre
CSBs - Glossopharyngeal nerve
AAB - Vagus nerve
What is the action of the baroreceptor reflex?
Decreased BP stimulates the Sympathetic nervous system
Increased pressure stimulates Parasympathetic nervous system
Describe the response of the baroreceptor reflex, to an increase in blood pressure
Increased BP = Increased firing rate
Medullary CVCC increases Parasympathetic stimulation
CO:
Vagus nerve releases ACh - Muscarinic receptors at SA node
Decreases slope of Pacemaker potential ∴ bradycardia
TPR:
Parasympathetic stimulation has almost no effect on arteriolar diameter ∴ does fuck all
Describe the response of the baroreceptor reflex, to a decrease in BP
Decreased BP = decreased firing rate
Medullary CVCC increases Sympathetic stimulation
CO:
Sympathetic nerves release NA & medulla releases Adr. into bloodstream
NA & A act on B1 receptors on SA node ∴ shortens conduction time & enhances force of myocardial contraction ∴ increased CO
TPR:
Peripheral resistance is under tonic sympathetic control
NA from sympathetic nerves binds to alpha receptors ∴ vasoconstriction
Vasoconstriction = higher TPR
Why is the baroreceptor the most important and effective mechanism for controlling blood pressure?
- Very sensitive
- Functions all the time, to even small changes in ABP
- Quite rapid - changes in CO & TPR occur in 2 heartbeats
- Most important short term control for ABP
Are baroreceptors ONLY involved in regulating short term blood pressure?
No - but the arterial baroreceptors are only involved in short term BP control
Long term control is mediated largely via Cardio-pulmonary baroreceptors and is more to do with hormones and all that shite
Arterial baroreceptors send sensory information to the medullary CVCC
What are the different receptors that communicate with this control centre?
Arterial baroreceptors
Cardiopulmonary baroreceptors
Central chemoreceptors
Muscular chemoreceptors
Joint receptors
Higher centres in the brain
When taking a patients blood pressure, often they are asked to stand and then lie/sit down for separate readings
Posture is a factor that influences blood pressure
Describe how Standing upright affects your blood pressure
Standing up causes increased hydrostatic pressure which causes pooling of blood in the veins/venules in the lower limbs
Pooling of blood in lower limbs = decreased Venous return (VR)
Lower VR ∴ Lower End diastolic volume
Lower EDV ∴ lower preload
Lower preload ∴ lower stroke volume ∴ lower CO
Lower CO = Lower MAP
Overall:
Standing upright = lower mean arterial pressure
Why is it that when you stand up to fast, you feel faint?
Standing up quickly = rapid decrease in MAP
Low MAP ∴ less blood reaches your head ∴ pre-syncope
Once the baroreceptor reflex kicks in, all sorted out
Describe the reflex response (in terms on nerves n stuff) to standing up…
Decreased Vagal tone:
∴ Increased HR
∴ Increased CO
Increased sympathetic tone:
∴ HR up ∴ CO up
∴ Increased contractility ∴ Increased SV ∴ increased CO
∴ Venoconstriction ∴ Venous return up ∴ EDV, SV, CO up
∴ Arteriolar constriction ∴ TPR up
