1. Heart Pt. II

2. Heart Actions The heart chambers function in coordinated fashion
Atria contract (atrial systole) while ventricles relax (ventricular diastole);
Followed by contraction of the ventricles (ventricular systole) while atria relax (atrial diastole)

3. Cardiac Cycle
During a cardiac cycle, the pressure in the heart chambers rises and falls
In atrial systole and ventricular diastole:
Blood flows passively into the ventricles
The remaining 30% of blood is pushed into the ventricles
The A-V valves open and the semilunar valves close
The ventricles relax
This causes an increase in ventricular pressure
In ventricular systole and atrial diastole:
The A-V valves close
The chordae tendinae prevent the cusps of the valves from bulging too far into the atria
The atria relax
The blood flows into atria
The ventricular pressure increases and opens the semilunar valves
The blood flows into pulmonary trunk and aorta

4. Heart Sounds
A heart beat through a stethoscope sounds like “lub-dub” or “lub-dup”
The “lub”
The first heart sound
It occurs during ventricular systole
The A-V valves are closing
The “dup”
The second heart sound
It occurs during ventricular diastole
The pulmonary and aortic (semilunar) valves are closing
Murmur – abnormal heart sound from the cusps not completely closing

5. Myocardial
muscle fibers
Cardiac Muscle Fibers
Cardiac muscle fibers form a functional syncytium
This is a mass of cells that function as a unit, connected by intercalated discs
Two such areas exist in the heart:
In the atrial walls called the atrial syncytium
In the ventricular walls called the ventricular syncytium

6. Cardiac Conduction System
Atrial syncytium
Junctional fibers
Bundle branches
Purkinje fibers
SA node
AV node
AV bundle
Ventricular syncytium
Cardiac Conduction System
Heart is autorhythmic
1% of heart tissue specialized to not contract
Transmits signals to cells that contract
Self-excitable
Generate and transmit impulses
Clumps or strands of specialized cardiac muscle tissue which initiate and distribute impulses throughout the myocardium
The cardiac conduction system coordinates the events of the cardiac cycle
A node is just a compact mass of cells.

7. Ventricular syncytium
Purkinje fibers
Interatrial septum
Left
bundle
branch
Interventricular septum
Right bundle
Junctional
fibers
AV node
SA node
AV bundle
Atrial syncytium
Junctional fibers
Bundle branches
Purkinje fibers
SA node
AV node
AV bundle
Ventricular syncytium

8. Regulation of the Cardiac Cycle
SA Node – controls heart rate
Also, sympathetic & parasympathetic fibers, and regulatory reflex centers
Additional factors that may influence heart rate:
Physical exercise
Body temperature
Concentration of various ions (including K+, Ca2+)
Parasympathetic impulses decrease heart action
Sympathetic impulses increase heart action
Cardiac center regulates autonomic impulses to the heart

9. Internal Anatomy of the Heart: Terms to Know
Aortic semilunar valve
Atrioventricular node
Atrioventricular septa
Bicuspid valve
Chordae tendinae
Coronary sinus
Coronary arteries
Foramen ovale
Fossa ovalis
Interatrial septum
Interventricular septum
Moderator band
Papillary muscles
Pectinate muscles
Pulmonary semilunar valve
Sinoatrial node
Trabeculae carnae
Tricuspid valve

10. EKG/ECG (Electrocardiogram)
Recording of the electrical charges in the myocardium
Electrodes placed on skin
Assesses heart’s ability to conduct impulses

11. EKG Deflections or Waves: P Wave – atrial depolarization
Reduction in voltage across cell membrane
Indicates stimulation/receiving impulse
SA Node impulse – spreads through atria, atria contract (atrial systole)
QRS Complex (3 waves) – ventricular depolarization
Electrical impulses spreading through ventricles
More muscle – more charges
Ventricular systole (contraction)
T wave – ventricular repolarization
Restores ventricles to resting state
Ventricles relax (ventricular diastole)

14. +1 –1
120
100 80 60 40 20
160 P Q S T R
0.3
0.6
0.9
seconds
Heart sounds
Electrocardiogram (ECG)
Pressure changes
Aortic pressure
Atrial pressure
Volume (mL)
Millivolts
Pressure (mm Hg)
One cardiac cycle
Atrial
systole
Ventricular
diastole
Aortic
semilunar
valve
opens
AV valve
closes
AV valve opens
Ventricular pressure
Aortic semilunar
valve closes
Ventricular volume
Lubb: AV
valves close
Dupp: Semilunar