Control of Blood Pressure Flashcards
Why must arterial blood pressure be kept relatively constant?
- too low: insufficient blood flow to organs, organ failure
- too high: some organs and tissues are sensitive to pressure changes and are damaged
Why must the distribution of total cardiac output be regulated?
- 5L/min is not sufficient for perfusion of whole body
- needs to be adapted to tissue demands
What are the components of the reflex control system?
- internal variable to be maintained
- receptors sensitive to change in the variable
- afferent pathways from the receptors
- an integrating centre for the afferent inputs
- efferent pathways from integrating centre
- target effectors to alter activities
How to calculate MABP?
MABP = cardiac output x total peripheral resisitance
What are baroreceptors?
pressure sensing organs in cardiovascular control centres
Where are the main baroreceptors locations for the feedback control of MABP?
- walls of aorta: afferent fibres follow vagus nerve
- carotid artery: afferent fibres follow glossopharyngeal nerve
Describe baroreceptor activity in the feedback control of MABP
- stretch receptors
- firing rate of APs increases when BP increases
- firing rate of APs decreases when BP decreases
- sensitive around a set-point
What is the main purpose of the baroreceptor reflex?
to reduce minute to minute variations of arterial pulse maintaining the pressures within tight windows
What are cardiopulmonary baroreceptors sensitive to?
- central blood volume
- low pressure receptors
Where are cardiopulmonary baroreceptors found?
- atria
- ventricles
- veins
- pulmonary vessels
Describe the activity of cardiopulmonary baroreceptors
- decreased blood volume, MABP decreases and cardiac output decreases
- rate of cardiopulmonary baroreceptors firing decreases
- sympathetic nerve activity to heart and blood vessels increases
- parasympathetic nerve activity to the heart decreases
What is the atrial reflex control of BP referred to as?
Bainbridge reflex
Describe the atrial reflex control of BP
- sympathetic mediated reflex in response to increased blood in atria
- increased heart rate
- increased contractility
- prevents build up of bloods in vein
What effect can high pressures have on the Bainbridge reflex?
it can cause it to override which is why it needs regulation
What is responsible for regulation of BP?
- medullary cardiovascular vasomotor centre
- sensory area: input from baroreceptors
- lateral portion: efferent sympathetic nerves
medial portion: efferent parasympathetic nerves
What is the predominate tone of the heart at rest?
parasympathetic NS
What control does the sympathetic NS have on the heart?
- stroke volume
- heart rate
What control does the sympathetic NS have on blood vessels?
- total peripheral resistance:
- exerts vasomotor tone on vessels
- keeps vessels partially constricted
- cardiac output:
- decreases capacitance in veins
- increases venous return
- increases stroke volume
- increases cardiac output
Describe the CNS ischaemic response
- decreased blood flow to brain
- decreased blood to medullary cardiovascular vasomotor centre
- increases peripheral vasoconstriction almost occluding some vessels
- increases sympathetic stimulation of heart
- greatly increases systemic arterial pressure
How do organs auto-regulate blood flow?
- reactive/active hyperaemia
- independent innervation/hormonal control
What intrinsic processes are in place for maintenance of blood pressure when it increases?
- myogenic theory (acute auto-regulation): stretch induced depolarisation of smooth muscle
- metabolic theory (acute auto-regulation): increase of O2 and washes out local factors
