Download Circulatory System

The Circulatory System
Lesson #2
Heart Beat and the Cardiac Cycle
- the events of each heartbeat are called the cardiac
cycle
- the heart is highly coordinated so that both atria contract
together and then both ventricles contract together
- then all of the chambers relax
- the term systole refers to the contraction of heart muscle
- the term diastole refers to the relaxation of heart muscle
- normal heart rate at rest is about 60-80 beats per minute
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- the familiar “lub-dup” heart sounds are produced by
turbulence and tissue vibration as valves close
heartbeat sounds:
"lub”:
- atrioventricular valves close after atria contract, then
ventricles relax & fill with blood
"dub":
- semi-lunar valves close after ventricles contract,
meanwhile atria relax & fill with blood
Heart Murmurs: - problems with valves closing
1 - Atrial Systole
5 - Late
Ventricular
Diastole
4 - Early
Ventricular
Diastole
2 - Early
Ventricular
Systole
3 - Late
Ventricular
Systole
•
Atrial Systole •
•
Early
•
Ventricular •
Systole
•
atria contract
AV valves open
semi-lunar valves closed
atria relax; ventricles contract
AV valves forced closed
semi-lunar valves still closed
Late
Ventricular
Systole
• atria relax; ventricles contract
• AV valves remain closed
• semi-lunar valves forced open
Early
Ventricular
Diastole
• atria relax; ventricles relax
• AV valves and semi-lunar valves close
• atria fill with blood
Late
Ventricular
Diastole
•
•
•
•
atria relax; ventricles relax
atria continue to fill with blood
AV valves open
semi-lunar valves closed
Intrinsic Control of Heartbeat
*not under conscious control – it is involuntary and automatic
Nodal Tissue: nerve/muscle characteristics
SA (sinoatrial) node (pacemaker):
sends out signal from upper back wall
of right atrium to make atria contract
automatically every 0.85 s
AV (atrioventricular) node:
- SA signal received at base of
right atrium near septum
- another signal sent to ventricles via
Purkinje fibres (conducting fibers)
causing ventricular contractions that
move up like a wave
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The Normal Conduction Pathway
1. The SA node in the right atrium initiates an electrical
signal (called an action potential).
2. The action potential spreads throughout atrial muscles.
3. The action potential is conducted to the AV node which
slows the impulse slightly before sending it to the AV
bundle.
4. The AV bundle conducts the impulse down through the
septum and branches into many small Purkinje fibers
that distributes the impulse throughout both ventricles
ventricle
Extrinsic Control of Heartbeat
Medulla Oblongata:
- contains cardiac control center that can alter heart rate (HR)
via autonomic nervous system
Adrenal medulla (on top of kidneys):
- releases protein hormones epinephrine/norepinephrine to
↑HR in response to stress (fight or flight!!)
Stimuli:
- cause HR to change (pH/CO2 /O2 /blood pressure levels)
R
Electrocardiogram (ECG):
- record of electrical activity of heart
P wave: - atria contract
QRS wave: - ventricles contract
T wave: - ventricles relax
T
P
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Q
S
Circulatory System Review - Matching
1. signals atria to contract
2. signals ventricles to contract
3. strengthens ventricular contraction signal
4. contraction of heart muscle
“lub“
“dub“
diastole
systole
AV node
5. relaxation of heart muscle
SA node
6. atrioventricular valves closing
Purkinje fibres
7. semilunar valves closing
heart murmur
8. problem with valves closing
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Circulatory System Review – Labelling
ventricular systole + atrial diastole
ventricular diastole
atrial systole
R
T
P
Q
S
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