Transcript The Heart, Day 4 (Professor Powerpoint)

The Heart
Chapter 18 – Day 4
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Wrap up Physiology
Muscle contraction in cardiac tissue
Pacemaker cells (aka cells of the SA node)
♦ Rhythmic depolarization and repolarization
♦ Triggers depolarization through internodal cells (aka – start
of action potential)
Cardiac tissue
♦ Ca2+ enters muscle cells via “slow calcium channels”
♦ This results in plateau (Fig. 18-15)
♦ Arrival of extracellular Ca2+ triggers the release of additional
Ca2+ from reserves in SR
♦ Sarcomeres shorten = muscle contraction
♦ Period of active muscle contraction continues until the
plateau ends
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Heart – Anatomy: Cardiac muscle
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Fig. 18.5
Order of Rhythm in Heart
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Fig. 18.13
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Fig. 18.15
Journal of Action Potential in Heart
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Fig. 18.12
Wrap up Physiology
Stimulates intercalated discs
♦ Moves action potential nearly instantaneously cell-to-cell
♦ Action potential simultaneously affects all tissue in the area
All muscle cells in ATRIA contract together
Action potential is transferred to AV node (100msec
delay from SA node = Ventricles contract after atria)
All muscle cells in VENTRICLES contract together
We’ve covered EKG/ECG, make sure you are
comfortable with it for lecture AND lab exam
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Heart
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Fig. 18.11
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Fig. 18.14
Cardiac Cycle
Cardiac cycle = 1 heart beat
Figure 18-16
2 important events
♦ Systole = contraction
♦ Diastole = relaxation
Each chamber has it’s own systole and diastole
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Cardiac Cycle
ATRIAL SYSTOLE
♦ Pushes blood into relaxed ventricles
Ventricles build up pressure
VENTRICULAR SYSTOLE
♦ Early – there is enough pressure to close AV valves, but not
enough to exceed pressure in blood vessels
♦ Pressure exceeds that in blood vessels = 2nd phase of v.
systole…
♦ Ejects blood out of heart into circulation
♦ Meanwhile….ATRIAL DIASTOLE is in progress
At the beginning of VENTRICULAR DIASTOLE
♦ Atria fill up with blood (returning = venous return)
In late ventricular diastole all chambers are relaxed
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Fig. 18.16
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Fig. 18.17
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Fig. 18.18
Heart Health
Resting heart rate is efficient
Cardiac cycle can give information about heart
efficiency
As the heart rate increases, less time is spent in each
phase, thus…
…blood is ejected at a different volume
Heart efficiency can be measured as CARDIAC
OUTPUT
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Cardiac Output
 = volume of blood ejected every minute
P. 523 and on board
Example
Cardiac Output = a major factor in determining blood
pressure
How hard does the heart have to work for proper
circulation
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Cardiac Output
 Depends on
♦
♦
♦
♦
Venous return
Stretching of heart muscles
Heart rate
End diastolic volume (EDV)
• Volume remaining in ventricle after contraction b/c not all blood is
ejected out
 Figure 18-23
 Amount of muscle stretching affects the force of contractions
(e.g. pulling a rubber band)
 Starlings Law of the Heart
 “Stretch” builds up resistance against the blood
♦ More blood is pushed out
 Why is C.O. important?
♦ Maintains proper BP levels to provide efficient blood supply
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Factors Affecting Stroke Volume
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Fig. 18.23
Cardiac Output
Blood Pressure
♦ Pressure of blood within blood vessels
♦ Pressure exerted on ARTERY walls
♦ How would C.O. relate??
• Higher cardiac output
◦ More blood = ↑ BP
◦ Less blood = ↓ BP
♦ Resistance of blood vessel walls
• Small diameter = ↑ BP
• Blood flow is proportional to the radius of the “pipe”
♦ Polycythemia (↑ in RBCs)
• Thicker blood viscocity = ↑ BP (↑ RBCs or loss of water)
♦ Length of blood vessel – longer length = ↑ BP
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Cardiac Output
Cardiac output can be influenced by many factors
One of these is HEART RATE
♦ Heart conduction system
♦ Autonomic nervous system
Exercise can increase C.O.
♦ Heart muscles are working out
♦ Skeletal muscle cells need a fast blood supply
♦ The heart has to meet that demand – when exercising, it
meets increased demands
♦ The force of contraction increases
♦ Blood moves faster, so venous return is faster
♦ More blood volume is pushed out
♦ Does not increase indefinitely, the Heart Rate can outcompete C.O.
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Factors Affecting Heart Rate
 Hormones, ions, nervous system…
 ANS
♦ Fibers connect to the SA node and the AV node
 Sympathetic Control
♦ Medulla – remember the cardiovascular center
♦ Norepinephrine, epinephrine
• Affects the SA node, AV node & myocardium
 Cardiac Nerve
♦ Dilates coronary vessels
 Parasympathetic control
♦ Medulla – cardio-inhibitory center
 Vagus Nerve (at S.A. node & A.V. node)
♦ Secretes ACh
♦ ACh changes ion distribution = decrease in heart rate
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Factors Affecting Heart Rate
Ions affect heart rate
♦ Ca2+ , Na+ - needed for depolarization
♦ K+ - needed for repolarization
Ion concentration in blood affects the action potential
in the heart
Increase K+ outside
♦ Less K+ will leave the cell
♦ Partial repolarization – slower action potential  HR
Increase Ca2+ outside cell
♦  force of contraction – can lead to spasms
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Factors Affecting Cardiac Output

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Fig. 18.24
Heart Problems
The normal rhythm of the heart can be disrupted in
many ways – be ready to discuss on Friday those in
book & those in handouts – you’ll also form your
groups for the case study…
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