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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 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 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