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Lecture 1

# BIOLOGY 3U03 Lecture 1: Introduction to Circulation

Department
Biology
Course Code
BIOLOGY 3U03
Professor
Michael O' Donnell
Lecture
1

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Circulation & Pressure-Flow Relationships (Ch. 14, 15, 16, 17)
Circulatory Systems
- Fish
o Single circulation (one pump drives blood through gills body heart)
o Single ventricle perfuses two resistances in series
o De-oxygenated blood returns to a single atrium
- Amphibians, Reptiles
o Partially divided circulation
o Single ventricle perfuses two resistances in parallel
o Oxygenated blood returns to left atrium
o Deoxygenated blood returns to right atrium
o Mixing seems inefficient but because fogs hieate at the otto of a pod ad ae’t
using their lungs for most of the year it allows them to oxygenate blood through the skin
or through the lungs
- Birds, Mammals
o Double circulation 2 separate circuits in series
Flow rate going in and coming out of the heart are equal
o Two separate ventricles, two separate atria
o Blood is pumped twice as it passes through the body
o Left heart pumps oxygenated blood while right pumps de-oxygenated blood
Overview of the Double Circulation = 2 Circuits in Series
- 3 components
1. Heart = pump (2 chambered) 2. Blood = carrier fluid 3.Vessels = plumbing
- Systemic circuit (body): driven by left ventricle
o High pressure, resistance, volume
- Pulmonary circuit (lungs): driven by right ventricle
o Low pressure resistance, volume
o Low pressure prevents bleeding from the lungs during exercise do’t lo apillaies
o For efficient gas exchange, you need to max out surface area (diffusion limited by
distance), use many very thin walled vessels
o Low volume but same total flow rate
Overview of Pressures in the Two Circuits (Human)
- Systolic = peak (higher pressure)
- Diastolic = trough (lower pressure)
- Dashed line = MAP
- Plethysmography: measures changes in volume
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2
The Fundamental Law of the Circulation
- F = ΔP / R
- F = blood flow rate between 2 points in circ. System
- ΔP = pressure difference between same 2 points
- P = force/area exerted by blood against blood vessel wall =
energy content/volume of blood
o generated by heart contractions
- R = resistance = hindrance to blood flow caused by friction
o 2 sources of resistance in blood flow
Internal (viscosity) and External (Interaction with vessel wall)
- Other useful forms: ΔP = FR Oh’s Law ad R = ΔP/F
- At moderate velocities, flow is close to laminar with a parabolic profile
- Figure: A. dyed fluid and colourless fluid in tube
o B. apply pressure to the coloured fluid see a parabolic shape =
laminar flow
o Think of it in a series of layers 2D or as centric circles in the
second diagram
Fluid at the edges have resistance from the side of the
tube
Centre has least interaction with the walls gets ahead
o C. Tubulent flow fluid moves across the long axis of the tube
(rough flow in contrast with laminar); tends to occur at higher
velocities
Hagen-Poiseuille Law
-    
 since 
,   

- Assumes: perfectly round, perfectly straight tube with non-turbulent flow
- Length (L) of blood vessels fairly constant
- Viscosity (η) does’t hage uh ude oal oditios
o Polycythemia, decreased temperature, burns, blood doping, hypoxia
Burns damage capillaries loss of plasma blood flowing through burned
region loses plasma but maintains blood cells increasing viscosity (localized form
of polycythemia (too many blood cells)
Regulate our body temperatures fairly well, not as important as
polycythemia/anemia
o ↓ Aeia, ieased tepeatue
- Radius (r) is very important in this eq. raised to the power of 4, so a small change in radius will
have a big impact on pressure/flow
o Also tends to be very variable biggest way to control flow
- High viscosity accompanying polycythemia is a serious problem in chronic mountain sickness &
progressive cardiac failure
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- Graph is relative to water
o As you remove blood cells, plasma viscosity is only
slightly higher (blood plasma proteins have charged
interactions)
o Normal blood is a lot higher due to hematocrit
- People/animals living in higher altitudes tend to produce
more blood cells
o Make more erythropoietin which produces blood
cells
o Leads to some tissues being hypoxic stimulates
more blood production
Pressure-Flow Relationships in a Typical Vascular Bed
- Steeper slope = lower resistance
- Flatter slope = higher resistance
- At some point there is no flow critical closing pressure
o Occurs when pressure drops too low to push blood
vessels open
o Ex. Arterial pressure drops below 20
- True driving force for blood flow = difference in total fluid
energy (E) between two points
o E1 E2 = F x R
o Blood pressure is only part of total fluid energy
Measurement of Blood Pressure
- Use of Korotkoff Sounds
- Blood jetting through the partly occluded brachial artery
o Turbulence
o Vibrations of the vessel wall (heard through stethoscope on
antecubital artery)
- Ex. Garden hose ping it slightly feel vibrations from turbulence
(changes in flow and direction)
- Graph: straight line = cuff pressure
o Pump cuff up then release When you begin to hear sounds, the brachial artery is no
longer being completely occluded
o Pressure continues to fall a bit more sounds get clearer as more blood flows through
o When the sound begins to get muffled disappears, somewhere inbetween = diastolic
pressure
o Pressure too low no more turbulence = no occlusion at all
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