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Lecture 11

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Michelle French

Lecture 11  Distribution of Blood  “We move around 5L of blood per minute”  Cardiac Output  Variables that affect Venous Return and End Diastolic Volume  Any change at one level has direct consequences at other levels  I.e. Sympathetic Nervous System  Venoconstriction  Venous Pressure  Venous Return  EDV  Blood Flow  Blood flow through individual blood vessels is determined by vessels resistant to flow  In a closed system, the total volume of input flow equals the total volume of the output flow  In the circularity system, blood is being carried to different organs such as liver and kidneys and they are not all carried by the same size vessels; some maybe under sympathetic nervous stimulation.  When one vessel is constricted, resistance increases and blood flow decreases. Flow from the constricted vessel is redirected to other vessels with lower resistance  Flow is inversely proportional to Resistance  Flow is proportional to Pressure/Resistance - Blood flows when pressure is present  Pressure effects can occur in arterioles, capillaries and veins  Blood pressure throughout the systemic circulation  Blood pressure is the highest in the arteries and decrease continuously as it flow through the circulatory system  Left ventricle contracts, generates pulse; great fluctuation in pressure  Why is there no fluctuation (drop) in the artery? Hence why the Aorta has a thick Tunica Media (elastin and smooth muscle)  Pulse Pressure  Pulse = Systolic – Diastolic  Mean arterial pressure is a function of cardiac output and resistance in the arterioles  Mean Arterial Pressure is proportional to Cardiac Output X Resistance  Elastic Recoil in Arteries  Ventricular Contraction  1) Ventricle contracts  2) Semilunar Valve opens  Aortic valve  3) Aorta and arteries expand and store pressure in elastic walls  Ventricular Relaxation  1) Isovolumic ventricular relaxation  2) Semilunar valve shuts, preventing flow back into ventricles  3) Elastic recoil of arteries send blood forward into rest of circulatory system  Blood Pressure  Blood Pressure = Systolic P – Diastolic P  Average pressure  120/80  = 40 mmHg  Mean arteriol pressure (MAP)  In the cardiac cycle, 2/3 of time, the heart is at rest (diastolic)  MAP = 2/3 diastolic + 1/3 systolic  = 93 mmHg  Pulse  Pulse – pressure wave of circulating blood  Monitored at pressure points where pulse is easily palpated  Measuring Arteriol Blood Pressure  Measured at the Brachial Artery  Korotkoff’s Sound  The “cuff” closes the brachial artery shut. The pressure is released slowly by opening the cuffs valve.  1) The snapping sound first heard at the systolic pressure. Clear tapping, repetitive sounds for at least two consecutive beats is considered the systolic pressure.  2) Murmurs heard for most of the are
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