Transcript The Heart’s External Anatomy & Conduction System

The Heart’s
External Anatomy &
Conduction System
♥ Heart at rest
♥ Blood flows from large veins into atria
♥ Passive flow from atria into ventricles
♥ Atria (R & L) contract simultaneously
♥ Blood forced into ventricles
♥ Ventricles (R & L) contract simultaneously
♥ Atrioventricular valves close  “lubb” sound
♥ Blood forced into large arteries
♥ Ventricles relax
♥ Semilunar valves close  “dub” sound
♥ Heart at rest
Pericardium
HEART
♥Membrane sac
♥Surrounds the heart
♥Protection
♥Anchors
♥Contains serous fluid
Pericarditis
inflammation of the
pericardium decreases
serous fluid causing painful
adhesions interfering with
heart movements
Pericardium
Heart Wall
♥ Epicardium (outside) – visceral layer
of the serous pericardium.
♥ Myocardium (muscle) – cardiac
muscle layer forming the bulk of the
heart.
♥ Endocardium (within) – endothelial
layer of the inner myocardial surface.
Cardiac Muscle
♥Specialized muscle cells
♥Involuntary
♥Striated
♥Cushioned by endomysium
♥Joined by intercalated discs
♥Cardiac cell metabolism
♥Areobic
♥Large mitochondria
♥Organic fuels: fatty acids & glucose
♥Fatigue resistance
Coronary Arteries
Branch off aorta above aortic semilunar valve
♥ Left coronary artery
♥ supplies left atrium and
left ventricle
♥ Anterior interventricular
artery
♥ supplies both ventricles
♥ Right coronary artery
♥ supplies right ventricle
♥ Posterior interventricular
artery
♥ supplies both ventricles
Coronary Veins
♥ Collects wastes from cardiac muscle
♥ Drains into a large sinus on posterior surface of
heart called the coronary sinus
♥ Coronary sinus empties into right atrium
The heart beats because of the spread
of electrical impulses to the heart
muscle, causing it to contract.
Cardiac Conduction System
♥ Cardiac muscle tissue exhibits
autorhythmicity = generates its own
stimulation.
♥ This is possible because of an internal
cardiac conduction system which can
initiate and distribute electrical impulses.
Cardiac Conduction System
♥ Comprised of interconnected structures
♥ Sinoatrial node
♥ Atrioventricular node
♥ Atrioventricular Bundle
♥ Bundle Branches
♥ Purkinje Fibres
Sinoatrial (SA) Node
Atrioventricular (AV) Node
♥ Junction of atria and ventricles
♥ Spread of depolarisation - from atrial
myocardium
♥ Delay 0.15 seconds
♥ Time atria to expel blood
♥ Time for ventricular filling
♥ Protection to ventricles
Atrioventricular
node
♥ Less autonomic nervous control than SA node
♥ Sympathetic ↑conduction time
♥ Parasympathetic ↓conduction time
Linked to the nervous system
Depolorization
The heart is autorhythmic
♥ Depolarization begins
in sinoatrial (SA) node
♥ Spread through atrial myocardium
♥ Results in myocardial contration of the atria
♥ Delay in atrioventricular (AV) node
♥ To the Bundle of His
♥ AKA atrioventricular bundle
Depolorization
The heart is autorhythmic
♥ Separates into 2 main
branches left & right
♥ Located in the interventricular septum
♥ Left bundle – antero-superior division
♥ Right bundle – postero-inferior division
♥ Bundle branches divide - small, dense network
of conduction tissue called the Purkinje Fibers
Entire musculature depolarizes quickly
Electrocardiogram
Variations in electrical potential radiate
from the heart
ECG records electrical events in the heart.
P wave
Depolarization of atria
Followed by contraction
P-P = one cardiac cycle
P-Q = time for atrial depolarization
Q-T = time for ventricular depolarization
T-P = time for relaxation
QRS complex
3 waves (Q, R, & S)
Depolarization of ventricles
Followed by contraction
T wave
Repolarization of ventricles
P-Q interval
Time atria depolarize & remain depolarized
Q-T interval
Time ventricles depolarize & remain depolarized
P
T
PR
QRS
SA node Represented on the ECG as P wave
AV node conduction is represented on the
ECG as the PR Interval
The Bundle Branch and purkinje fibre depolarisation
constitutes ventricular depolarisation Represented
on the ECG as the QRS
Atrial repolarisation occurs within the QRS &
therefore is masked
Ventricular repolarisation is represented on the
ECG as a T wave
1) atrial depolarization begins
2) atrial depolarization
complete (atria contracted)
3) ventricles begin to
depolarize at apex;
atria repolarize (atria relaxed)
4) ventricular
depolarization complete
(ventricles contracted)
5) ventricles begin to repolarize at apex
6) ventricular repolarization complete (ventricles
relaxed)