Blood Pressure Regulation

General Definitions: Blood Flow: the volume of blood flowing through a vessel, organ or the entire circulation in a given period (ml/min) Blood Pressure: the force exerted on a blood vessel by blood (mmHg) Resistance: opposition to blood flow. A measure of friction within blood vessels Blood Viscosity: thickness/ “stickiness” of blood itself, which will provide internal resistance to flow

Important Points Blood flow is controlled by changes in pressure Blood will always flow from areas of high pressure to low pressure Average blood pressure: Right: 24/8 mmHg Left: 120/80 mmHg *Both sides eject the same volume of blood simultaneously

Cardiac Output CO= SV x HR Cardiac Output (CO): the amount of blood pumped out by each ventricle in one minute CO= SV x HR Stroke volume (SV): the volume of blood pumped out by each ventricle in each beat Heart rate (HR): the number of heart beats per minute (CO also = EDV- ESV)

Regulations of Stroke Volume 1. Preload: amount that the ventricle is stretched when it is full of blood 2. Contractility: the contractile force of cardiac cells 3. Afterload: the pressure exerted by blood in the large arteries back on the heart

Mean Arterial Pressure (MAP) The pressure that propels blood to the tissues throughout the cardiac cycle Two ways to determine MAP: 1. MAP= diastolic pressure + 1/3 pulse pressure 2. MAP= CO x TPR

Total Peripheral Resistance The total resistance to blood flow in the body Affected mainly by: Arteriolar radius Blood viscosity

Blood Pressure Regulation Short-term mechanisms: Neural controls Vasomotor center in brain Baroreceptor reflexes Chemoreceptor reflexes Chemical controls Sympathetic response (epinephrine) ANP- decreases blood volume ADH- conserves water Angiotensin II- vasoconstriction Inflammatory chemicals- vasodilation Alcohol- inhibits ADH

Blood Pressure Regulation Long-term mechanisms Renal Regulation (kidney) Renin-Angiotensin mechanism Renin angiotensin ADH aldosterone