Cardiovascular Structure
and Function
Function of CV system:
Transport of O2 to tissues and remove
waste (delivery and garbage)
 Transport nutrients to tissues
 Regulate body temperature
 Right and left sides have separate
functions:

R side
Atria receives blood from systemic
circulation (superior and inferior vena
cavas)
 Ventricle pumps blood to lungs for
oxygenation via pulmonary artery

L side
Receive blood (oxygenated) from lungs
 Pump blood into the aorta (thick-walled
and muscular in nature) to systemic
circulation

4 chambered muscular organ
2 pumps, pulmonary and systemic
circulation
 Heart muscle is called myocardium
 Striated, with actin and myosin filaments,
similar to skeletal muscle
 Difference, cells are single nucleated,
interconnected in a form similar to a
lattice

Connected by intercalated disks that
allows chemical and electrical coupling
between cells
 Thick septum (interventricular septum) that
separates R and L sides

Cardiac Chambers
Atria are thin walled, sac-like chambers, low
pressure
 function is to receive and store blood while
ventricles are contracting, act as primer
pumps
 reservoir is more important than pump for
blood propulsion
Ventricles are a continuum of muscle fibers
 contract from apex to base
 R ventricle is thicker than R atria
 L ventricle is 3X thicker than the R
ventricular walls
 L ventricle can develop 4-5X more
pressure than the R ventricle
Number of valves in heart
Thin flaps of endothelium covered fibrous
tissue
 Movement of the valve leaflets are
essentially passive
 Orientation of valves is responsible for the
unidirectional flow of blood through the
heart


Atrioventricular valves prevent backflow of blood
from the ventricles into the atria
– also called tricuspid valve (three flaps or cusps) and
mitral (bicuspid two flaps or cusps) valve

Between right ventricle and pulmonary artery is
a semilunar valve (three cusps) also called
pulmonic valve
 Between left ventricle and aorta are semilunar
valve (prevents backflow of blood from aorta into
the heart)
Blood flow through the heart
1. blood flows into right atrium from superior
and inferior vena cava
2. blood travels from R atrium into R
ventricle
3. blood flows through pulmonary artery into
the lungs (for oxygenation)
4. blood returns from the lungs through the
pulmonary veins, and is deposited into L
atrium
5. from L atrium, blood flows into L ventricle
6. blood leaves L ventricle via aorta, enters
general systemic circulation
Flow of electricity through the
heart
Heart has intrinsic rhythmicity
1. originates in SA (sino-atrial) node,
superior, lateral aspect of R atrium
2. travels through both atria to AV node
(atrioventricular), this causes
depolarization of atria

3. from AV node, pause for 0.01 sec, flows
through AV bundle (aka bundle of His),
through R and L bundle branches (RBB,
LBB)
– this pause allows time for atrial contraction,
pumping the last 20-25% of blood into
ventricles
4. from RBB and LBB, signal travels to the
purkinje fibers in ventricles, which passes
the current of depolarization to the
ventricle muscle
 ventricles have a powerful contraction, and
provide the major impetus to move blood
throughout the CV system
Action Potentials in cardiac
muscle
resting membrane potential of normal
cardiac muscle is -85 to -95 millivolts
 specialized conductive fibers, purkinje,
have a resting membrane potential of -90
to -100 mV
 action potential (AP) has a magnitude of
~105 mV

this rise is ~ +20 mV greater than needed,
called the overshoot potential
 after depolarization, remains depolarized
for 0.2 sec in atrial muscle and 0.3 sec in
ventricular muscle, which gives it the
plateau
 plateau is followed by abrupt repolarization
 this plateau causes a contraction to last 315 times longer than a skeletal muscle
twitch

Differenced in cardiac and
skeletal muscle membranes:

Action potential is caused by the opening
of two types of channels: a) fast sodium
channels allow the sodium ions to enter
the cell and b) slow calcium channel are
slower to open and remain open longer
(can be several tenths of a second;
sodium can also pass through these
channels)
The permeability of cardiac muscle
membrane to potassium decreases about
5X
 This decreases the outflux of K during
plateau, preventing early recovery
 When Na and Ca channels close, influx
stops, permeability for K increases rapidly
 Rapid influx of K, membrane potential
returns to resting
