Physiology 7 - Control of Blood Pressure Flashcards
What is the consequence of a blood pressure that is too low?
Organ failure
What is the consequence of a blood pressure that is too high?
Damage to vessels and organs
How long might it take to double arterial pressure?
5-10 seconds
How long might it take to halve arterial pressure?
10-40 seconds
Where are the main baroreceptor locations?
Walls of aorta
Carotid artery
Which nerve do afferent fibres from the walls of the aorta follow?
Vagus nerve (Xth cranial)
Which nerve do afferent fibres from the carotid artery follow?
Glossopharyngeal nerve (IXth cranial)
What is the result on autonomic nervous system activity if cardiopulmonary baroreceptor firing decreases?
Sympathetic activity increases
Parasympathetic activity decreases
Blood volume decreases
Which nervous system are veins innervated by?
Sympathetic
What is the maximum blood pressure you can maintain temporarily?
2.5x normal
What is the predominant tone in nervous innervation of the heart?
Parasympathetic
What type of baroreceptors are regarded as ‘low pressure’ receptors?
Cardiopulmonary baroreceptors
How fast is nervous control of arterial pressure?
Can increase arterial pressure to 2x normal within 5-10s; can decrease arterial pressure to 50% of normal within 10-40s
Where are the two main high pressure locations that can sense MABP in the blood vessels?
Aortic arch
Carotid sinus
MABP = …
CO x TPR
Which baroreceptors saturate first: carotid or aortic?
Carotid
Which cranial nerve do the aortic afferent fibres follow ?
Xth cranial nerve –> vagus
Upon raised BP, what type of receptors ensure increased activity to counter this change?
Stretch receptors
What is the function of cardio-pulmonary baroreceptors?
Low pressure receptors which sense central blood volume rather than BP, lying out-with the systemic vascular system
What is the vascular effect of decreased cardio-pulmonary baroreceptor firing?
Decreased venous return
–> increased sympathetic n.s. and decreased parasympathetic n.s. firing to heart and vessels
–> increased HR & SV and constriction of veins leading to increased venous return
& on arterial side, induced vessel constriction –> increased TPR
What is the Bainbridge Reflex?
Detects an overload in the venous system and increases sympathetic mediated drive of the heart:
• ↑ HR and ↑ contractility
• Prevents damming of blood in veins etc.
MABP=
CO x TPR
How are vessels kept partially constricted?
‘Sympathetic vasoconstrictor tone’ exerts ‘vasomotor tone’ on vessels
What is the effect of sympathetic venous innervation?
↓ capacitance, therefore ↑ venous return, therefore ↑ stroke volume, thus ↑ cardiac output.
When blood flow to the medullary CVCC (cardiovascular control centre) ↓↓↓ there is:
↑ peripheral vasoconstriction. This almost completely occludes some peripheral vessels
↑ sympathetic stimulation of heart
↑↑ systemic arterial pressure, as high as 250 mmHg for 10 mins
What is the concept behind myogenic theory?
Stretch-induced vascular depolarisation of smooth muscle (causing constriction) due to ↑ arterial pressure, thereby protecting downstream tissues and capillary beds from this increased pressure.
What is the concept behind metabolic theory?
↑arterial pressure increases O2 and ‘washes out’ local factors by increasing perfusion. Washing out these factors allows the sympathetic tone to resume and smooth muscle can contract within the vessel wall, again protecting downstream tissues.
