Cardiovascular Physiology
Heart Physiology
for the heart to work properly contraction and relaxation of chambers must be
coordinated
cardiac muscle tissue differs from smooth and skeletal muscle tissues in
several ways that suit its function in the heart
Histology of Heart
cardiac muscle fibers (=cardiocytes)
relatively short, thick branched cells, 50-100 µm long
striated myofibrils are highly ordered
usually 1 nucleus per cell
rather than tapering cells are bluntly attached to each other by gap junctions
= intercalated discs
myocardium behaves as single unit
but atrial muscles separated from ventricular muscles by conducting
tissue sheath
atria contract separately from ventricles
need constant supply of oxygen & nutrients to remain aerobic
greater dependence on oxygen than skeletal muscles
Conducting System
cardiac muscle cells are not individually innervated as are skeletal muscle cells
they are self stimulating
the rhythmic beating of the heart is coordinated and maintained by the heart
conducting system
heart has some specialized fibers that fire impulses to coordinate
contraction of heart muscle
innervated by autonomic NS
Human Anatomy & Physiology: Cardiovascular Physiology Ziser 2404 Lecture Notes, 2005 1
, sympathetic stimulation can raise rate
parasympathetic stimulation can lower rate
conducting system consists of:
SA Node
intrinsic rhythm
70-75 beats/min
initiates stimulus that causes atria to contract
(but not ventricles directly due to separation)
AV Node
picks up stimulus from SA Node
AV Bundle (Bundle of His)
connected to AV Node
takes stimulus from AV Node to ventricles
Purkinje Fibers
takes impulse from AV Bundle out to cardiac mucscle fibers
of ventricles causing ventricles to contract
the heart conducting system generates a small electrical current that can be
picked up by an electrocardiograph
=electrocardiogram (ECG; EKG)
ECG is a record of the electrical activity of the conducting system
ECG is NOT a record of heart contractions
R
P T
Q S
P wave = passage of current through atria
from SA Node
conduction through atria is very rapid
QRS wave = passage of current through
ventricles from AV Node – AV Bundle – Purkinje
Fibers
impulse slows as it passes to ventricles
T wave = return to “resting” conditions
by comparing voltage amplitudes and time intervals
between these waves from several leads can get
Human Anatomy & Physiology: Cardiovascular Physiology Ziser 2404 Lecture Notes, 2005 2
Heart Physiology
for the heart to work properly contraction and relaxation of chambers must be
coordinated
cardiac muscle tissue differs from smooth and skeletal muscle tissues in
several ways that suit its function in the heart
Histology of Heart
cardiac muscle fibers (=cardiocytes)
relatively short, thick branched cells, 50-100 µm long
striated myofibrils are highly ordered
usually 1 nucleus per cell
rather than tapering cells are bluntly attached to each other by gap junctions
= intercalated discs
myocardium behaves as single unit
but atrial muscles separated from ventricular muscles by conducting
tissue sheath
atria contract separately from ventricles
need constant supply of oxygen & nutrients to remain aerobic
greater dependence on oxygen than skeletal muscles
Conducting System
cardiac muscle cells are not individually innervated as are skeletal muscle cells
they are self stimulating
the rhythmic beating of the heart is coordinated and maintained by the heart
conducting system
heart has some specialized fibers that fire impulses to coordinate
contraction of heart muscle
innervated by autonomic NS
Human Anatomy & Physiology: Cardiovascular Physiology Ziser 2404 Lecture Notes, 2005 1
, sympathetic stimulation can raise rate
parasympathetic stimulation can lower rate
conducting system consists of:
SA Node
intrinsic rhythm
70-75 beats/min
initiates stimulus that causes atria to contract
(but not ventricles directly due to separation)
AV Node
picks up stimulus from SA Node
AV Bundle (Bundle of His)
connected to AV Node
takes stimulus from AV Node to ventricles
Purkinje Fibers
takes impulse from AV Bundle out to cardiac mucscle fibers
of ventricles causing ventricles to contract
the heart conducting system generates a small electrical current that can be
picked up by an electrocardiograph
=electrocardiogram (ECG; EKG)
ECG is a record of the electrical activity of the conducting system
ECG is NOT a record of heart contractions
R
P T
Q S
P wave = passage of current through atria
from SA Node
conduction through atria is very rapid
QRS wave = passage of current through
ventricles from AV Node – AV Bundle – Purkinje
Fibers
impulse slows as it passes to ventricles
T wave = return to “resting” conditions
by comparing voltage amplitudes and time intervals
between these waves from several leads can get
Human Anatomy & Physiology: Cardiovascular Physiology Ziser 2404 Lecture Notes, 2005 2
