Transcript Where is the blood?

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
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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
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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
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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
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Total vessel cross-sectional area changes
throughout the circulation, however, overall
blood flow must remain the same (~5L/min)
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Mathematically, the velocity of blood flow must
change in order to maintain constant flow
(~5L/min) in each segment.
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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
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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
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Murmurs
Sounds of Korotkoff