2. The intrinsic conduction system
The intrinsic conduction system consists of
noncontractile cardiac cells specialized to
initiate and distribute impulses throughout
the heart in a sequential manner.
Autorhythmic cells have an unstable resting
potential that continuously depolarizes.
3.
4. Pacemaker potentials are spontaneously
changing membrane potentials that initiate
action potentials in order to trigger rhythmic
contractions.
Fast Ca+2 channels cause autorhythmic cells
to develop an action potential using calcium
instead of sodium.
5.
6.
7. Sequence of excitation
Impulses travel across the heart in the order
of the following autorhythmic cardiac cells:
1) Sinoatrial node
2) Atrioventricular node
3) Atrioventricular bundle
4) Right and left bundle branches
5) Purkinje fibers
8. Defects in the intrinsic conduction system
can cause irregular heart rhythms known as
arrhythmias.
Fibrillation is a condition of rapid and
irregular or out-of-phase contractions.
9. The cardioacceleratory center in the
medulla oblongata increases both the rate
and force of heartbeat.
The cardioinhibitory center, also in the
medulla oblongata, slows the heart through
parasympathetic inervation.
10.
11. Electrical currents generated and
transmitted through the heart also spread
through the body and can be monitored with
an instrument called an electrocardiograph.
The graphic recording produced by an
electrocardiograph is called an ECG.
12.
13.
14. The cardiac cycle
Systole refers to the contraction period of
the heart.
Diastole refers to the relaxation period of
the heart.
The cardiac cycle includes all events
associated with the flow of blood through
the heart during one complete heartbeat.
15. Events of the cardiac cycle
1) Ventricular filling
2) Ventricular systole (isovolumetric
contraction phase)
3) Isovolumetric relaxation
The length of the cardiac cycle is about 0.8
seconds, half of which is a period of total
relaxation called the quiescent period.
16.
17.
18. Heart sounds
Two distinguishable sounds can be heard,
called heart sounds, when the thorax is
auscultated.
Abnormal or unusual heart sounds are
called murmurs.
19.
20. Cardiac output
Cardiac output is the amount of blood
pumped out by each ventricle in 1 minute.
Stroke volume is the volume of blood
pumped out by a ventricle with each beat.
The difference between resting and
maximal CO is referred to as cardiac
reserve.
21. End diastolic volume represents the amount
of blood that collects in a ventricle during
diastole.
End systolic volume represents the volume
of blood remaining in a ventricle after it has
contracted.
22. The Frank-Starling law of the heart states
that the critical factor controlling stroke
volume is the preload, or the degree of
stretch of the cardiac muscle cells just
before they contract.
23.
24.
25. Contractility is an increase in contractile
strength that is independent of muscle
stretch and the EDV.
Afterload is the pressure that must be
overcome for the ventricles to eject blood
from the heart (the back pressure exerted on
the aortic and pulmonary valves by arterial
blood).
26.
27. Regulation of heart rate
The heart exhibits vagal tone due to the
dominant influence of inhibitory autonomic
inervation.
The atrial reflex is a sympathetic reflex
initiated by an increase in venous return and
blood congestion in the atria.
