Download AHS CVS Lecture 2

THE CARDIOVASCULAR SYSTEM
LECTURE 2:
THE HEART AND BLOOD VESSELS
Eamonn O’Connor
Applied Health Sciences
Lecture Outline
1
Electrical activity of the heart
  Anatomy and function of blood vessels (arteries,
arterioles, capillaries, venules and veins)
 
AHS Physiology - Cardiovascular System 11-12
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Electrical Activity of the Heart
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 
The Conduction System of the Heart
 
Spread of Excitation Through the Heart Muscle
 
Recording the Electrical Activity of the Heart with an
Electrocardiogram
AHS Physiology - Cardiovascular System 11-12
Conduction System
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 
Cardiac muscle doesn’t require commands from the
CNS to contract
  Contractile
 
activity of cardiac muscle: myogenic
Autorhythmicity is the ability to generate its own
rhythm
  Autorhythmic
  2
cells provide rhythm to the heartbeat
types:
  Pacemaker
cell: initiate AP’s
  Conduction fibers: transmit AP’s
AHS Physiology - Cardiovascular System 11-12
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Conduction System
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 
Pacemaker cells
  Spontaneously
depolarizing membrane potentials to
generate action potentials
  Coordinate and provide rhythm to heartbeat
 
Conduction fibers
  Rapidly
conduct action potentials initiated by
pacemaker cells to myocardium
  Conduction velocity = 4 meters/second
  Ordinary muscle fibers, CV = 0.4 meter/second
AHS Physiology - Cardiovascular System 11-12
Pacemaker Cells of the Myocardium
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 
Sinoatrial node (SA node): 70-80 APs.min-1
  Pacemaker
of the heart
Atrioventricular node (AV node): 40-60 APs.min-1
  Conduction fibres of the pericardium
 
  Internodal
pathways
  Bundle of His: 20-40 APs.min-1
  Purkinje fibres: 20-40 APs.min-1
AHS Physiology - Cardiovascular System 11-12
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Spread of Excitation Between Cells
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Atria contract first followed by ventricles (fibrous
skeleton)
  Coordination due to presence of gap junctions and
conduction pathways
 
AHS Physiology - Cardiovascular System 11-12
Figure 13.9
Anatomy of the Conduction System
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Figure 13.10
AHS Physiology - Cardiovascular System 11-12
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Spread of Excitation
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 
Interatrial Pathway
Node  right atrium  left atrium
  Simultaneous contraction right and left atria
  SA
 
Internodal Pathway: SA Node  AV Node
  Slow
conduction - AV Nodal Delay = 0.1 sec
  Atria contract before ventricles
 
Ventricular Excitation (fast conduction)
  Down
Bundle of His
  Up Purkinje Fibers
  Purkinje
Fibers contact ventricle contractile cells
contracts from apex up
  Ventricle
AHS Physiology - Cardiovascular System 11-12
Spread of Excitation
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Figure 13.11
AHS Physiology - Cardiovascular System 11-12
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Electrocardiogram
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 
ECG is used to look at some aspects of cardiac
electrical activity
  Non-invasive
 
technique
Used to test for clinical abnormalities in conduction
of electrical activity in the heart
  Body
fluids are conductors
  Currents in the body can spread to surface
AHS Physiology - Cardiovascular System 11-12
Standard ECG Trace
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 
 
 
 
 
 
 
P wave: atrial depolarization
QRS complex: vent. depolarization
T wave: vent. repolarization
P-R: AV node conduction time
R-T: vent. contraction (systole)
T-Q: vent. relaxation (diastole)
R-R: time between heart beats
Figure 13.16b
AHS Physiology - Cardiovascular System 11-12
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ECG Arrhythmias
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AHS Physiology - Cardiovascular System 11-12
Overview of the Vasculature
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 
 
Arteries – carry blood away
from heart
Microcirculation (microscopic)
  Arterioles
  Capillaries
  Venules
 
 
Veins – return blood to heart
Differences between blood
vessels:
  Structure:
  diameter
  composition
of walls
  Function
AHS Physiology - Cardiovascular System 11-12
Figure 14.6
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Arteries
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 
Carry blood away from heart
 
Thick, elastic walls
 
Large diameter, therefore low resistance to blood flow
 
Pressure remains relatively constant through arteries.
 
Pressure reservoirs because of stretch during systole elastic recoil helps maintain blood pressure during
diastole
AHS Physiology - Cardiovascular System 11-12
Arteries: a Pressure Reservoir
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 
Storage site for pressure
  Thick
elastic arterial walls
  Expand as blood enters
arteries during systole
  Recoil during diastole
  Low compliance
AHS Physiology - Cardiovascular System 11-12
Figure 14.7
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Arteries & Disease
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 
Atherosclerosis - ‘hardening of the arteries’
  A
plaque composed of cholesterol, calcium and
other substances builds up in an artery
  Plaques reduce blood flow
  They can rupture and cause clots
  Heart
  Often
 
attacks or strokes can result
occurs with age
Smoking, diabetes and obesity are other risk
factors
  Angioplasty
or stent implantation can be used
as treatments
AHS Physiology - Cardiovascular System 11-12
Arterioles
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 
 
 
 
Arterioles are resistance vessels
Walls contain smooth muscle: regulation
of radius, and thus, resistance (>60%
TPR)
Functions: Regulate blood pressure
Effect of diameter.
  Wider
diameter – vasodilation
(vasodilatation)
  Narrower diameter - vasoconstriction
  Greater diameter, greater blood flow
 
Influenced by nerves, hormones and
local effects in tissues eg. during
exercise (later lecture)
AHS Physiology - Cardiovascular System 11-12
Figure 14.17
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Capillaries
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Site of exchange between blood and tissue
  5-10 micrometer diameter - small diffusion distance
  Walls - 1 endothelial cell layer plus basement
membrane (small diffusion barrier)
  10-40 billion per body
 
  Total
SA = 600 m2
  1 mm long
AHS Physiology - Cardiovascular System 11-12
Types of Capillaries
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 
Continuous capillaries
  Most
common
  Small gaps (water filled) between endothelial cells
  Allows
small water soluble molecules
to move through (Na, K, glucose…)
Figure 14.16a
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Types of Capillaries
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 
Fenestrated capillaries (located in kidneys, liver,
intestines, bone marrow)
  Large
gaps between endothelial cells forming pores or
fenestrations
  Allows
proteins and in some cases blood cells to move
through
Figure 14.16b
AHS Physiology - Cardiovascular System 11-12
Exchange Across Capillary Walls
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 
Mechanisms:
  Diffusion
– most common mechanism
  Lipophilic
– across membrane
– through pores
  Lipophobic
  Transcytosis
– exchangeable proteins
  Mediated transport – in brain
 
Materials exchanged:
  Gases
- O2, CO2
  Glucose & Fatty acids
  Hormones etc.
AHS Physiology - Cardiovascular System 11-12
Figure 14.18
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Venules
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Smaller than arterioles
  Connect capillaries to veins
  Thin walls
  Little smooth muscle in walls
  Some exchange of material between blood
and interstitial fluid
 
AHS Physiology - Cardiovascular System 11-12
Veins
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 
 
 
Large diameter, but thin walls,
which contain blood and elastic
tissue
Valves allow unidirectional blood
flow (peripheral veins)
Volume reservoirs
  at
rest, systemic veins contain 60% of
total blood volume
 
 
High compliance
Return of blood to heart from veins
is called venous return
AHS Physiology - Cardiovascular System 11-12
Figure 14.20
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