Physiology of the heart I. - Szegedi Tudomá · PDF file1 Physiology of the heart I....
Transcript of Physiology of the heart I. - Szegedi Tudomá · PDF file1 Physiology of the heart I....
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Physiology of the heart I.
Features of the cardiac muscle
The cardiac cycle
The heart as a pump
Cardiac sounds
(Learning objectives 35-36)
prof. Gyula Sáry
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Cardiovascular physiology
•Cardiac function, pumping activity of the heart
•Cardiac cycle
•Characteristics of the cardiac muscle
•Electrophysiology of the heart
•The normal electrocardiogram (ECG)
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Things to consider:
• blood flows „downhill”, follows a pressure gradient
• pressure gradient is generated by the heart
• the heart can not store blood –
what comes in, must get out
• the circulation is a closed loop
• valves in the heart only play a passive role
• the heart must cope with different needs
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Cardiac, skeletal and smooth muscles
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Characteristics of skeletal, cardiac and smooth muscle
cross striated muscles
Characteristics skeletal muscles cardiac muscles smooth muscles
Thickness 40-100 µm 10-20 µm 5-10 µm
Lengthup to 20 cm
(M. sartorius)100-150 µm 30-200 µm
Nucleusmany, on the
peripheryone central nucleus one central nucleus
Organization of the
contractile fibresparallel, in sarcomers parallel, in sarcomers
no sarcomers, net-like
meshwork
Neuronal supply somatic nerves autonomic nerves autonomic nerves
Communication
between cellsno
fast, through gap
junctionsthrough gap junctions
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Physiologic anatomy 1.
• sarcomers (~ 2 μm)
• 30-60 sarcomers covered with sarcolemma
= cardiac muscle fibre
• T- and axial tubular system, sarcoplasmic reticulum
• mitochondria (sarcosomes, 30% of the myocardial cells)
• capillaries (up to 4000/mm2)
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Physiologic anatomy 2.
• gap junctions
(connexon, 6 subunits, 2 nm space to pass ions)
• longitudinal conduction is very fast
gap junctions at end-to-end
no transversal gap junctions
• functional syncytium
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Action potential lengths in the excitable tissues
Refractory periods
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Tetanic contraction in skeletal muscle NO tetanic contraction in cardiac muscle
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plateau phase
repolarization fastdepolarization
time (ms)
pote
ntial (m
V)
membrane
intracell.
extrtracell.
time (ms)
perm
eabili
ty
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Electromechanical coupling in the myocardiac cell
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Ca2+
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Ca++ and cardiac muscle contraction;
extracellular Ca++ acts as a trigger
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Ca2+ channel open muscarinergic receptor
inhib. G protein stimulating G protein
beta receptor
cell membrane
cardiac muscle cell
Stimulation and inhibition of Ca++ channels
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• no external neural impulse, automatic
• gap junction---very fast conduction
• all the fibres contract - unlike in skeletal muscles
• AP and contraction lasts for hundreds of ms
• Ca++ also from extracellular space (trigger)
• removal: Ca++ pumps and Ca++ antiporter
• contraction force depends on Ca++
symp. stimulation
extracellular Ca++ increase
cardiac glycosides
Contraction of the myocardium
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The cardiac cycle
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left ventricular pressure
time [s]
bal kamrai nyomás
bal kamrai térfogat
Pressure changes during the cardiac cycle
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right
atrium
right
ventricle
left
atrium
left ventricle
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left ventricular
pressure (mmHg)
left ventricular
volume (ml)
isovolumetric
contraction
ejection
isovolumetric
relaxation
filling
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The cardiac cycle (0.8 sec)
Systole 0.27 sec
isovolumetric contraction
maximal (rapid) ejection
decreased ejection
Diastole 0.53 sec
isovolumetric relaxation
rapid filling
slow filling
atrial contraction
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Blood volumes during the cardiac cycle
• end-diastolic volume (EDV) : 110-160 ml
• stroke volume (SV) : 70 - 80 ml
• end-systolic volume (ESV) : 40 - 80 ml
• ejection fraction: SV / EDV ~ 50 - 70%
increasing stroke volume:
increasing the EDV and/or decreasing the ESV
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valve plane in systole
shifts down
the valve plane in diastole
moves back ejection of blood
ventricular filling
The valve-plane mechanism
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The atria contribute to the diastolic filling of the
ventricles
• 75-80 % of the blood volume flows directly through the atria into the
ventricles
• atrial contraction („atrial systole”) can contribute 20-25%
(increases effectiveness and speed of filling)
• under normal conditions „atrial systole” has only minimal
importance
• heart rate & exercise
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Function of the valves
• A-V valves prevent backflow during systole
• semilunar valves prevent backflow during diastole
• the valves act passively !
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The jugular pulse
• Fluctuations in the right atrial pressure cause
pressure oscillations in the jugular vein.
• Physiologically only visible during increased venous
pressure (weight lifting, Valsalva manouvre).
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carotid pulse
jugular pulse
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Normal jugular venous pulse:
A, a positive wave due to contraction of the right atrium;
C, a positive deflection due to bulging of the tricuspid valve toward the atria at the onset
of ventricular contraction;
X, a negative deflection due to atrial relaxation during the ventricular systole;
V, a positive deflection due to filling of the right atrium against the closed tricuspid valve
during ventricular contraction;
Y, a negative deflection due to emptying of the right atrium upon ventricular relaxation.
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The heart as a pump
• stroke volume x heart rate = cardiac output
• cardiac output = blood volume leaving the ventricle in 1 minute
~ 5.5 l/min
• cardiac index = cardiac output/body surface
~ 3.1 l/m2/min
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• Since the time of
Hippocrates (5th Century
BC) doctors usually placed
their ears on a patient's
chest to listen to the
heartbeat and lung sounds.
• Faced with a breasty
woman, Dr Rene Laennec
modestly insisted on using a
rolled-up sheet of paper as
shown on picture. Thus, in
1816, the first stethoscope
was conceived.
Aorta valve: 2R2
Pulmonary valve: 2L2
Tricuspidal valve: 4-5R1
Mitral valve: 5L6-8
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Cardiac sounds
auscultation on the chest
1. (systolic) sound: contraction, valves, ejection of blood
2. (diastolic) sound: valves, can be split
3. (diastolic) sound: cuspidal valves during rapid filling
4. (late diastolic) sound: atrial contraction
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