Control of Blood pressure Flashcards
Why is there the need to maintain tissue perfusion across the whole body?
Maintain a relatively constant BP, as if its too low then organs would fail and if too high would damage vessels and organs. And to control distribution of the total cardiac output so that it can response to tissue demands.
Describe how quickly the nervous system can change blood pressure
It can increase arterial pressure to twice the normal within 5-10s and it can decrease arterial pressure to 50% of the normal within 10-40s
What are the main baroreceptor locations?
Walls of aorta - Afferent fibres follow vagus nerve.
Carotid artery - Afferent fibres follow glossopharngeal nerve
Describe the baroreceptor activity?
They are stretch receptors. The firing rate increases when the BP increases and if firing rate decreases when the BP decreases
What is the primary purpose of the baroreceptors reflex?
It is to reduce the minute-to-minute variation or arterial pulse.
What type of changes in pressure do the aortic and carotid sinus baroreceptors tolerate?
Carotid sinus detects small changes in BP so firing will saturate at a lower BP where as aortic baroreceptors detects large changes in BP so the firing will saturate at a higher BP
Describe what the cardiopulmonary baroreceptos sense
Changes in central blood volume in the atria, ventricles, veins and pulmonary vessels.
What occurs if the rate of cardiopulmonary firing decreases?
This means there is decreased blood volume so the sympathetic nerve activity to the heart and blood vessels increases and the parasympathetic nerve activity to the heart decreases.
What is the bainbridge reflex?
It is the atrial reflex control of BP. If there is increased blood in the atria then the sympathetic nervous system increases HR and contractility to prevent damning of blood in the veins. It can over-ride aortic and carotid baroreceptors which would sense the increase in BP and would try to control it.
Where is the integrated control centre for blood pressure?
Medullary cardiovascular control “vasomotor” centre (MCVC)
Name and describe the defined regions within the medullary cardiovascular control centre
Sensory area - receives input from baroreceptors.
Lateral portion - Contains efferent sympathetic nerves.
Medial portion - Contains efferent parasympathetic nerves
Describe how the sympathetic and parasympathetic nerves effect the heart
SNS - significantly effects stoke volume and rate.
PSNS - predominates tone by suppressing the natural heart rate so it is slower.
Describe how the sympathetic nervous system effects vessels (PSNS has no effect)
Continuous low-level tone affects total peripheral resistance which keeps vessels partially constricted. It also effects veins by decreasing capacitance which increases venous return, and increases stroke volume and therefore increases cardiac output.
Describe the CNS ischemic response
It is an emergency pressure control system. It occurs when blood flow to the medullary CVCC is very low then it causes extensive peripheral vasoconstriction that almost even occludes some vessels, it increases sympathetic stimulation of the heart and therefore increases systemic arterial pressure (as high as 250mmHg for 10mins)
What are some of the fine controls of blood pressure
Organs auto-regulate blood flow which is independent of innervation and hormonal control. It occurs via active or reactive hyperemia.
Myogenic theory - Stretch induced constriction of smooth muscle in pre-capillary sphincters due to high arterial pressure. Metabolic theory - If there is too much oxygen then this is interpreted as too much blood flow which also causes reflex constriction of pre-capillary sphincters and arterioles.
