Download 8. Cardiac Muscle Physiology

The Heart
• Circuits
• Chambers
• Valves
(one-way-flow)
• Myocardiocytes
Volumes?
Pressures?
heart –> lungs –> heart
heart –> body –> heart
Artery =
Vein =
Trace a RBC!
The Heart has 4 Valves
To prevent retrograde flow of blood.
2 atrioventricular valves (AV)
between the atria and ventricles.
1) Right AV (tricuspid) valve
2) Left AV (bicuspid/mitral) valve
2 semilunar valves
between a ventricle and artery.
1) Aortic semilunar valve
2) Pulmonary semilunar valve
Two heart sounds: “Lub” and “Dup”
1. Closure of AV valves = “Lub”
2. Closure of Semilunar valves = “Dup”
http://www.openheartsurgery.com/heart_murmur.html
Disorders of Heart Valves
Normal
Heart Valves
Problem
Heart Valves
Problems Opening:
Stenosis – narrowing of valve,
when a valve doesn't open
completely.
Turbulence = noise = murmur.
Problems Closing:
Prolapse –overlapping or when
valve doesn't close tightly. Also
termed valvular insufficiency
(regurgitation)
Retrograde flow = noise = murmur.
Myocardiocytes:
1) Autorhythmic
2) Contractile
Action Potentials for Autorhythmic Myocardiocytes
Action Potentials for Contractile Myocardiocytes
stimulus
Myocardiocytes: Calcium induced Calcium release
Graded Contraction of Heart
Force generated by myocardiocyte contraction is:
1. Proportional to amount of Calcium ions (Ca2+)
 [Ca2+] => more crossbridges, more force & speed.
Graded Contraction of Heart
Force generated by myocardiocyte contraction is:
1. Proportional to amount of Calcium ions (Ca2+)
 [Ca2+] => more crossbridges, more force & speed.
2. Modulated by Autonomic N.S.
=> Sym  HR and Force
=> Para  HR
Sympathetic – speeds heart rate by  Ca2+ influx.
Parasympathetic – slows rate by  K+ efflux,
 Ca2+ influx.
Graded Contraction of Heart
Force generated by myocardiocyte contraction is:
1. Proportional to amount of Calcium ions (Ca2+)
 [Ca2+] => more crossbridges, more force & speed.
2. Modulated by Autonomic N.S.
=> Sym  HR and Force
=> Para  HR
3. Stretch-Length-Tension Relationship
 stretch, =>  Ca2+ entering =>  contraction force
Factors Influencing Stroke Volume
The Cardiac Cycle
http://www.youtube.com/watch?v=rguztY8aqpk
The Cardiac Cycle:
Mechanical Events of the Heart
1. Late Diastole: “Heart at rest” all chambers relaxed
filling with blood (passive filling ~ 80% full).
2. Atrial Systole: atria contract, adds the last 20% of
blood to ventricles (top off ventricles)
Occurs after P-wave on EKG
End Diastolic Volume (EDV) = Maximum ventricular volume*
3. Ventricular Systole (part 1):
Ventricular contraction begins - Pressure (P).
Closure of AV valves = 1st heart sound ("lub")
Sealed Compartment – all valves are closed.
Isovolumetric ventricular contraction:
=> pressure builds as volume stays the same.
4. Ventricular Systole (part 2):
Ejection phase: P pushes open semilunar valves,
blood forced out into artery leaving ventricle.
Pulmonary Semilunar => 25 mmHg (minimum pressure)
Aortic Semilunar => 80 mmHg (minimum pressure)
End Systolic Volume (ESV) = volume remaining in
heart after ejection (~½)*.
Stroke Volume = EDV - ESV (ml/beat)
5. Ventricular Diastole:
Relaxation of ventricles, artery back flow slams
semilunar valves shut = 2nd heart sound ("dup").
Sealed Compartment again – all valves are closed.
Isovolumetric ventricular relaxation:
=>  pressure as volume stays the same.
The AV valves then open, refilling starts –
back to start of cycle.
Cardiac Output (C.O.)
= Heart Rate x Stroke Volume
*Heart Rate = beats/min
*Stroke Volume = EDV-ESV (vol/beat)
e.g. calculation:
Electrical Conduction System
Sino Atrial (SA) Node
Atrial Ventricular (AV) Node
AV Bundle (of His)
L and R Bundle Branches
Purkinje Fibers
Trace of an ElectroCardioGram (ECG)
The ECG
P wave:
PR interval:
QRS complex:
T wave:
Ventricular Assist Devices
http://www.youtube.com/watch?v=D3ZDJgFDdk0