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OBJECTIVES
• Overview
• Relationship between pressure and flow
• Understand the differences between series and
parallel circuits
• Cardiac output and its distribution
• Cardiac function
• Control of blood pressure
• Review of lab
Berne and Levy 2005
Properties of Pressure
• Hydrostatic
pressure
Pressure=0 cm water
Hydraulic
pressure
Created by pushing fluid through a tube

Pump
H=100 cm
Pressure=100 cm water
Height of water column is~pressure
Units of Pressure
• Atmospheric pressure is considered to be zero
• The common units is based upon the height of a
column of mercury
• Since mercury is 13.6 times denser than water a 100
mmHg is equivalent to 136 cm of water
• In more common units 136 cm of water is equal to
54 inches or 4’6” of water
120
80
systolic
Pressure
(mmHg)
mean
diastolic
What is a normal arterial pressure
• Diastolic<80 mmHg
• Systolic<140 mmHg
• High blood pressure places a large strain on
the arterial blood vessels
• High blood pressure increases the work of the
heart
Blood moves down a tube if the
inflowing pressure is greater than
the outflowing pressure
P=100 mmHg flow
P=10 mmHg
If resistance increases pressure has
to increase if flow is kept constant
• If you narrow a tube and try to keep flow
constant you will have to exert a larger
pressure to pump the same amount of
fluid through the tube
• If the pressures at the beginning and the
end of the tube are the same there will
be no flow no matter how great the
pressure
Is there flow in this tube?
Answer: FLOW=0
P=100 mmHg
Which flow is greater?
P=100 mmHg
Answer: A=B
P=200 mmHg Flow A
P=100 mmHg
P=100 mmHg Flow B
P=0 mmHg
∆P=FLOW X RESISTANCE
RESISTANCE= ∆P/FLOW
∆P=FLOW X RESISTANCE
RESISTANCE= ∆P/FLOW
Series Circuit
P=0 mmHg
P=100 mmHg
R1
R2
R3
R4
Series Circuit
120
Pressure
(mmHg)
100
80
60
40
20
0
R1 R2
R3
Rt=R1+R2+R3+R4
R4
Parallel Circuit
R1
P=100 mmHg
R2
R3
R4
P=0 mmHg
Pressure
R=100
Q=1
R=25
Q=4
R=5
Q=20
Comparison of series and parallel
circuits
• In a series circuit the largest resistor is the
major determinant of total resistance
• In a parallel circuit the lowest resistor is the
major determinant of total resistance
Berne and Levy 2005
Resistances
•
•
•
•
•
Large arteries=1
Arterioles=14
Capillaries=4
Veins=1
Total resistance=∑Ri=20
Control of tissue blood flow
• Intrinsic
• Extrinsic
BLOOD FLOW
Rate of metabolism
Extrinsic Control
• Autonomic Nervous system
• Circulating hormones
Autonomic Nervous System
pregang lionic
cholinergic
Sympathetic
thoracico-lumbar
postganglionic
adrenergic
Paravertebral
Exception: sweat glands
Parasympathetic
cranial & sacral
postganglionic
cholinergic
preganglionic
cholinergic
at organ
Autonomic Nervous System
Nerves
Neurotransmitter Distribution
Effect
SNS
Cervical
Thoracic
Pregang:
ACH
Postgang:
NE
Heart,
Arteries &
Most veins
β1(↑HR)
α1
β2
PNS
Vagus
and lumbar
Pregang:
ACH
Post gang
ACH
Heart
Vessels of
Genitalia &
colon
↓HR
Epinephrine
• Source: Adrenal medulla
• Increase heart rate and contractility (β1)
• low concentrations vasodilation (β2)
• high concentrations
– vasoconstriction (α1)
– decrease venous compliance (α1)
Norepinephrine
• Source: Adrenal medulla
• Increase heart rate and contractility (β1)
• Limited effect on β2
• At all concentrations
– vasoconstriction (α1)
– decrease venous compliance (α1)
Control of tissue flow
• Intrinsic Control
• Extrinsic control
• Long term control (vascular remodeling)
OBJECTIVES
• Overview
• Relationship between pressure and flow
• Understand the differences between series and
parallel circuits
• Cardiac output and its distribution
• Cardiac function
• Control of blood pressure
• Review of lab
Determinants of Cardiac Output
• Heart rate
• Stroke volume
– Ventricular end-diastolic volume
– Contractility
– Afterload (aortic pressure)
Berne and Levy 2005
Determinants of stroke volume
• Volume in heart at end of diastole
– Time to fill
– Filling pressure
– Property of ventricle
• Stiffness
• Ability to relax after contraction
• Ability to eject (systole)
– Contractility
– After load (arterial pressure)
We have two major systems to
sense and control arterial pressure
Control of pressure
• Short term
– Arterial barroreceptors
• Long term
– Renin angiotensin system ( Kidney and volume
regulation)
Arterial Baroreceptors
The heart is under net basal
parasympathetic tone
120
110
100
Heart rate
(bpm)
Propranolol
90
80
Atropine
70
60
50
40
Propranolol
Atropine
Activation of Barroreceptor reflex
In response to an increase in arterial pressure
• Withdrawal of sympathetic tone
• Activation of parasympathetic tone
• Results:
– Decrease heart rate and contractility
– Arterial vasodilation
– Decrease in venous compliance
The lab
• Chronically catheterized conscious rat
– Epinephrine (β1, β2 + α agonist)
– Norepinephrine (β1 + α agonist)
– Phentolamine (α-receptor antagonist)
– Propranolol (β-receptor antagonist)