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Transcript
Cell Biology and Physiology Quiz #2 Review Matthew L. Fowler, Ph.D. Cell Biology and Physiology Block 4 Review Topics • Circulation Biophysics • Action Potentials • Frank-Starling Relationship Cell Biology and Physiology – Quiz #2 Review Circulation Biophysics Circulation Biophysics Objectives • • • • • • Where is the blood? Blood Dynamics Blood Pressure Cardiac Output Regulation of Cardiac Output Factors Affecting Blood Flow Where is the blood? • Most of the blood is in the systemic circulation – Veins, venules, and venous sinuses • Blood reservoir Blood Dynamics • Active tissues may require 20 to 30 times more blood than when it is at rest. • The heart cannot normally increase its cardiac output to more than ~7 times resting levels. Blood Pressure • Needs to average ~100 mm Hg • Autonomic control Cardiac Output • CO = HR (beats/min) x SV (mL) • SV ≅ 70 mL/beat • Example: where HR = 80 beats/min CO = 80 beats/min x 70 mL/beat = 5600 mL/min Regulation of Cardiac Output • Cardiac output is determined by peripheral input (venous return) Large Venous Return Stretched Heart More Forceful Contraction Increased HR Venous Return = HR Blood Flow • • • • Flow = CO (mL/min) CO at rest ~5000 mL/min (~5 L/min) Aortic flow at rest ~5000 mL/min (~5 L/min) Blood flows from high pressure to low pressure – Down the pressure gradient Flow, Pressure, Resistance • Flow (F) = ΔP/ΔR • ΔP = P1 – P2 • P = Force/Area • Pressure is created by the heart at the start of circulation. Pressure • Flow (F) = ΔP/ΔR • Therefore: ΔP = ΔR x F – A moving fluid has no pressure unless it encounters some resistance Resistance • R = 8/π x nl/r4 • Factors affecting flow – Vessel geometry • Length (l) (this cannot change quickly) • Radius (r) – Fluid viscosity (n) Laminar Flow (Velocity) • Affected by radius and viscosity • Radius = Laminar flow Viscosity/Shear and Flow Viscosity • Affected by layers and contacts Vessel Wall Contact • Blood contacts wall • Velocity along vessel walls is 0 Layer Contact • Less contact with layers at center • Velocity max at center Remember: Velocity = Flow Cause of Viscosity • High viscosity of blood is almost entirely related to the hematocrit (RBCs) Resistance in Series • Resistance in series is additive • Rtotal = R1 + R2 + … Resistance in Parallel • Resistance in parallels is inversely summed • Rtotal = 1/R1 + 1/R2 + … Circuit Resistance • Resistance in parallel will always be less than resistance in a series. • Fact: Total resistance for all vessels is far less than the resistance of any single blood vessel • Implications: Varicose veins, amputation, thrombosis…all increase Resistance Directional Flow of Blood Total Flow and Velocity • Total vessel cross-sectional area changes throughout the circulation, however, overall blood flow must remain the same (~5L/min) • Mathematically, the velocity of blood flow must change in order to maintain constant flow (~5L/min) in each segment. • Velocity in the capillaries is low to maximize nutrient, waste, and gas exchange Turbulent Flow • Increases resistance – Results in increases in pressure to overcome • Modifiable via velocity – Velocity is modified via pressure low pressure = low velocity = laminar flow Turbulent Flow in the Vessels • • Turbulence causes the parabolic profile of the linear velocity across the diameter of a cylinder to become blunted (blue arrow) compared to normal laminar flow (Vmax) Sounds – – Murmurs Sounds of Korotkoff