CVS lecture series
Michaelmas
Organisation of the cardiovascular system
The heart
The electrocardiogram
The cardiac cycle
Hilary
Cardiac output
Haemodynamics
Properties of blood vessels
Blood pressure
Regional circulations
Things to note
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The text book human is:
 Male
 70kg
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Learn important numbers for physiological variables
 Absolute level
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Magnitude of change
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e.g. resting pulse (HR) = 70 bpm; blood pressure (BP) = 120/80
e.g. from rest to heavy exercise – HR increase from 70 to 200 (3 fold)
Range
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Rarely do we encounter a textbook person
e.g. resting HR ranges from 60 – 85; maybe <30 with aerobic training
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Defining the CVS
CARDIOVASCULAR SYSTEM
[kardia,
kardia, heart + vasculum,
vasculum, little vessel]

In its simplest form, the CVS has 3 components:
Heart: pumps blood at high pressure
Blood vessels (vasculature): distribute blood to all parts of the
body and return it to the heart
Arteries, arterioles, capillaries, venules, veins
Blood: transport medium in which materials to be transported
are dissolved or suspended
Blood
On average, 5L of blood (approx 8% body weight)
Arterial Blood
Blood leaving the heart
Bright Red
High oxygen content
(oxyhaemoglobin)
oxyhaemoglobin)
Venous blood
Blood returning to the heart
Darker colour
Lower oxygen content
(deoxyhaemoglobin)
deoxyhaemoglobin)
Cellular portion of blood (45% blood volume)
a) Erythrocytes (red blood cells): oxygen transport
b) Leukocytes (white blood cells): immune function
c) Platelets: Blood clotting
Plasma (55% blood volume)
a) Water
b) Dissolved solutes eg.
eg. ions
c) Plasma proteins
d) Other components eg.
eg. metabolites, hormones, enzymes, antibodies.
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Defining the CVS
CVS comprises multiple serial components
Two circulations
 Systemic

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supplies most organs and tissues
Pulmonary

supplies the lungs
Two pumps (Heart)
 Systemic pump (Left side)


propels blood around the systemic circuit
Pulmonary pump (Right side)

propels blood around the pulmonary circuit
Defining the CVS: functions
Transport of substances


Respiratory: oxygen & carbon dioxide
Nutritive: absorbed products of digestion
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Removal of wastes: metabolic wastes delivered to liver and kidneys
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from digestive tract to all tissues for metabolism
from digestive tract to Liver/Adipose tissue for storage
Water
heat
Regulation & protection: Hormones, immune cells, clotting proteins
to specific target cells
Regulation

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Hormones
Thermoregulation (skin blood vessels)
Protection
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Blood clotting (protects against haemorrhage)
Pathogens (immune system)
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CVS arrangement

Serial circuit
Pump 1 → Circuit 1 → Pump 2 → Circuit 2

OR
Left H. → Systemic C. → Right H. → Pulmonary C.
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Flow is unidirectional

More complex than 2 circuits

Systemic circuit comprised of:
 A circuit for each organ system
 i.e. many parallel circuits
Sherwood,
Sherwood, fig 9-1
CVS arrangement
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Pulmonary circuit is a single circuit
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Low pressure circuit as only one circuit, therefore
Right heart is a weaker pump
Systemic circuit comprises many parallel circuits, therefore
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requires greater pressure for flow to many organs
Systemic circuit often referred to as high pressure circuit
Left heart is a stronger pump
Sherwood,
Sherwood, fig 9-2
4
Silverthorn,
Silverthorn, fig 14-1
Characteristics of the circulation
Pressure
Flow
Resistance

Driven by properties of:
Heart
Provides pulsatile driving force i.e. it is a pump (on – off – on – off)

Provides for all flow volume


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Cardiac Output = Heart Rate x Stroke Volume
NB: flow refers to volume not velocity. Heart Input = Heart Output
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Characteristics of the circulation
Blood vessel circuits
Provide flow in one direction only, via


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Directional pressure head from heart
Valves throughout veins
Provide for blood storage, via


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High elasticity of veins – Capacitance
Allows for immediate Δ’s in Flow without Δ’s in Pressure
Characteristics of the circulation
Blood vessel circuits

Provide Resistance to flow via Vessel radius



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Systemic circuit = Peripheral resistance
Total PR = sum of regional (organ circuit) Resistances
High level of control
The Cardiovascular system obeys the law
(F ∝ ΔP/R)
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Poiseuille’s Law R ∝ 1/r4
Silverthorn,
Silverthorn, fig 14-5
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