Cell Biology and Physiology Quiz #2 Review Matthew L. Fowler, Ph.D. Cell Biology and Physiology Block 4 MT: Application only

Review Topics Circulation Biophysics Action Potentials Frank-Starling Relationship

Circulation Biophysics 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 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 Modifiable via velocity 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