Download CRRM1.26 - Regulation of Arterial Blood Pressure

CRRM1.26: REGULATION OF ARTERIAL BLOOD PRESSURE
04/02/08
LEARNING OUTCOMES
Describe the role of reflexes and of the heart in the control of blood pressure
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Short-term control of blood pressure (BP) is managed by the baroreceptor reflex
o Baroreceptors are high pressure receptors located in the aortic arch and the carotid sinuses
and continuously monitor BP
o Increased BP causes them to fire more action potentials via afferent nerves to the CVS centre
in the brainstem
o The CVS centre has three ‘regions’ contained within the nucleus tractus soliatius (NTS) of the
medulla oblongata:
 Cardio-excitatory – sympathetic output
 Cardio-inhibitory – parasympathetic output (vagus)
 Vasomotor – sympathetic output (adrenergic and cholinergic)
Other receptors involved in short-term control of BP include chemo-, proprio- (joint) and
cardiopulmonary receptors (low pressure receptors)
The Bainbridge reflex is triggered by cardiopulmonary receptors sensing an increased BP in the right
atrium due to increased venous flow / pressure and induces tachycardia
Describe the role of blood vessels in the control of arterial blood pressure
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Arterial blood pressure needs to be maintained for adequate perfusion of the brain and heart
Elastic arteries (e.g. aorta) convert intermittent output from the heart to a steady flow through
capillaries via the arterioles (high resistance vessels)
The aorta stretches during ventricular contraction storing potential energy which is used to contract
the aorta in ventricular relaxation to maintain continuous blood flow
Mean arterial pressure (MAP) reflects the overall driving pressure generated by (left) ventricular
contraction
o MAP = CO x TPR
(Mean arterial pressure = Cardiac output x Total peripheral resistance)
o MAP can be estimated as MAP ≈ Diastolic pressure + 1/3(Pulse pressure)
o The above equation can be used to calculate TPR but it is not determined by CO or MAP