Download The Conduction System of the Heart

The Conduction System of the
Heart
The Conduction System
• The heart is controlled by the autonomic
nervous system(ANS) – it
increases/decreases contraction, but it
does NOT initiate it.
• The heart has its own regulating system =
conduction system
• The conduction system is composed of
specialized muscle tissue that generates
action potentials within cardiac tissue.
Components of the Conduction
System
1. SA NODE
• Located in the right atrial wall below the opening
to the superior vena cava
• Initiates heartbeat  pacemaker
• Average = 75 beats/minute
2. AV NODE
• Located in the interatrial septum
• Receives the action potential from the SA node
• Action potential slows considerably  allows
time for the atria to empty into the ventricles
Components of the Conduction
System
3. AV BUNDLE
• Receives impulse from the AV node
• Located at the interventricular septum
• Passes impulse onto the bundle branches
4. BUNDLE BRANCHES
• Located below the AV bundle
• Passes impulse onto the conduction myofibers
5. Purkinje Fibers
• Located in the ventricular myocardium
• Receives impulse from bundle branches and passes it
onto ventricular myocardial cells to complete ventricle
contractions.
The Heart Beat
The Heartbeat- usually heard by a stethoscope. The sound
a ‘normal’ beating heart makes is ‘lub-dub’, this is known
as a double beat.
Problems can arise when the blood is not pumped properly.
An ECG is used record electrical impulses sent by the
heart. It measures:
-Any damage to the heart
-How fast your heart is beating and whether it is
beating normally
-The effects of drugs or devices used to control the
heart (such as a pacemaker)
-The size and position of your heart chambers
The Cardiac Cycle
Systole: the phase of contraction of a chamber
(Systolic Number – This is the TOP number in
your blood pressure…related to the pressure of
contraction in the heart that is placed on the inside
of the vessels)
Diastole: the phase of relaxation (Diastolic
Number – This is the BOTTOM number in your
blood pressure…related to the relaxed phase of
your heart that is then transferred to your vessels)
Blood Pressure
- Pressure exerted on the vessels as the blood is
pumped through the heart.
- Average blood pressure is 110-130/70-90 for
average teenager.
- Measure using BP cuff (sphygmomanometer)
- Depends on 2 factors- cardiac output and the
resistance in the arteries, which is related to their
elasticity.
- BP varies according to what factors?
Cardiac Output
• Cardiac Output: the amount of blood ejected
from the left ventricle into the aorta OR the right
ventricle into the pulmonary trunk per minute
• It is determined by:
1. The amount of blood pumped by the left
(or right) ventricle during each beat
2. The number of heart beats per minute
• The amount of blood ejected by a ventricle
during each contraction is called = ?
Cardiac Output
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For an adult at rest…
Stroke volume = ~70 mL (average)
Heart rate = 75 beats per minute (average)
Therefore, Cardiac Output (CO) = Stroke
Volume x Beats per Minute
CO = 70 mL x 75/min
CO = 52.50 mL/min or 5.25 L/min