Download Cardiac Conduction System

Cardiovascular: Heart
Pericardium & Heart Wall
p 718
p 722
Heart Valves
Mass & Heat Flow Model
Flow from high pressure to
low pressure
Driving Force?
Resistance?
p 737
Heart Valves
ONE WAY flow
p 718
Cardiac Conduction System
= specialized myocytes
that do not contract,
instead generate action
potentials
Components
•Sinoatrial Node
•Atrioventricular Node
•Atrioventricular Bundle
•Bundle Branches
•Purkinje Fibers
p 729
Cardiac Muscle
Myocardium has
two networks;
•Atrial network
•Ventricular network
Gap Junctions allow Na+ to pass through from cell
to cell, so action potential can pass from myocyte to
myocyte
All myocytes in a network contract as a unit
SA Node Physiology
Membrane starts at -60 mV and slowly depolarizes as
Na+ flows in thru leak channels (pacemaker potential)
At -40 mV voltage-gated FAST Ca++ channels open
and Ca++ flows into myocyte
p 732
SA Node Physiology
At about 0 mV, K+ channels open and K+ flows out
Membrane repolarizes to -60 mV, when K+
channels close and pacemaker potential resumes
p 732
SA Node Physiology
0 mV is an action potential in the SA node myocytes
This action potential spreads throughout entire atrial
network through the gap junctions = contraction
p 732
Cardiac Conduction System
Action potential traveling over atrial network
reaches AV node in about 50 msec (1/20th
of a second)
Action potential is delayed in AV node about
100 msec due to fewer gap junctions
This gives ventricles time to fill with blood
Cardiac Conduction System
Action potential travels
down AV bundle,
branches, & Purkinje
fibers to many areas of
ventricular network
starting from the apex
Action potential travels
from these areas to rest
of network thru gap
junctions = contraction
p 729
Myocardium Action Potential
Resting membrane potential = -90 mV
p 733
Systole = period of contraction
Diastole = period of relaxation
End-systolic Volume (ESV) = volume of
blood remaining in one ventricle at the end
of systole
End-diastolic Volume (EDV) = volume of
blood remaining in one ventricle at the end
of diastole
Preload = amount of tension in ventricular
myocardium right before systole
Greater EDV = greater preload
p 734
Cardiac Cycle
p 739
Cardiac Output (CO) = volume of blood
ejected from each ventricle in one minute
Stroke Volume (SV) = volume of blood
ejected from each ventricle in one systole
Heart rate = contractions (beats) in one
minute
EDV minus ESV = ?
SV times heart rate = ?