This comprehensive document examines the intricacies of the cardiovascular system, detailing the structure, function, and electrical activity of the heart, as well as the dynamics of blood flow through the cardiovascular circuit. It explains the functional division of the heart into right and left ...
Module
5:
The
Cardiovascular
System
The
Heart
Heart
Electrical
Activity:
Structure
of
the
Heart:
→
The
heart
consists
of
four
chambers
divided
into
two
main
pumps:
1.
Right
Side
of
the
Heart
:
-
Right
atrium,
right
ventricle
-
Receives
deoxygenated
blood
from
the
body
and
pumps
it
to
the
lungs
for
oxygenation
via
the
pulmonary
circulation
2.
Left
Side
of
the
Heart
-
Left
atrium,
left
ventricle
-
Receives
oxygenated
blood
from
the
lungs
and
pumps
it
throughout
the
body
via
the
systemic
circulation
Between
these
chambers,
there
are
important
structures:
-
Septum
:
a
dividing
wall
that
separates
the
right
and
left
sides
of
the
heart
to
provent
the
mixing
of
oxygenated
and
deoxygenated
blood.
Includes
an
atrial
septum
and
a
ventricular
septum
-
Atria
and
Ventricles
:
separated
by
connective
tissue
at
the
base
of
the
heart
(not
cardiac
muscle)
which
helps
in
isolating
electrical
activity
between
teh
upper
chambers
(atria)
and
lower
chambers
(ventricles)
Electrical
Conduction
System:
→
The
heart’s
beating
is
regulated
by
its
electrical
conduction
system,
which
ensures
that
heartbeats
are
organized
and
efficient.
1.
Sinoatrial
(SA)
Node
:
-
Located
in
the
right
atrium,
it
acts
as
the
primary
pacemaker
of
the
heart
,
initiating
the
heartbeat
and
setting
the
pace
for
blood
pumping
by
generating
electrical
impulses.
-
Fires
at
100
beats/min
2.
Atrioventricular
(AV)
Node
:
-
Situated
at
the
junction
of
the
atria
and
ventricles,
this
node
acts
as
a
gatekeeper
,
slowing
down
the
electrical
signal
before
passing
it
from
the
atria
to
the
ventricles.
This
delay
allows
the
atria
to
contract
a
fraction
of
a
second
before
the
ventricles,
ensuring
efficient
blood
flow.
-
Pauses
electrical
signal;
fires
at
40-60
beats/min
3.
Bundle
and
His
and
Purkinje
Fibers: -
After
passing
through
the
AV
node,
the
electrical
signal
travels
along
the
Bundle
of
His,
which
splits
into
right
and
left
branches
in
the
ventricular
septum,
and
further
extends
into
Purkinje
fibers
that
spread
throughout
the
ventricular
walls.
This
network
coordinates
the
contraction
of
the
ventricles
.
-
Fires
at
25-45
beats/min
The
Heartbeat
Process:
1.
Depolarization
:
Initiated
by
the
SA
node,
leading
to
atrial
contraction
2.
Conduction
through
AV
Node
:
slows
the
electrical
signal,
ensuring
that
ventricles
fill
completely
before
they
contract.
3.
Ventricular
Contraction
:
triggered
by
the
signal
traveling
through
the
Bundle
of
His
and
Purkinje
fibers
4.
Repolarization
:
the
heart
muscles
relax,
and
chambers
fill
with
blood
again,
preparing
for
the
next
heartbeat
cycle.
→
This
system
ensures
that
the
heart
maintains
a
rhythm
that
meets
the
physiological
needs
of
the
body,
adjusting
the
rate
as
necessary
based
on
various
factors
such
as
physical
activity
or
rest.
Pacemaker
Potential
vs.
Action
Potential
on
Contracile
Myocytes:
-
Pacemaker
Potential
:
-
Found
in
specialized
cardiac
cells,
primarily
in
the
SA
node,
which
serve
as
the
heart’s
natural
pacemaker
-
Characterized
by
an
unstable
resting
membrane
potential,
starting
at
about
-55
millivolts
-
Leads
to
slow,
spontaneous
depolarization
during
Phase
4
-
Action
Potential
in
Contractile
Myocytes
:
-
Occurs
in
the
regular
muscle
cells
of
the
heart
that
are
responsible
for
generating
forceful
contractions
-
Typically
has
a
stable
resting
membrane
potential
and
a
rapid
depolarization
phase
-
The
duration
of
an
action
potential
is
longer
(200-220
milliseconds)
compared
to
the
150
milliseconds
of
the
pacemaker
potential
Mechanism
of
the
Pacemaker
Potential:
1.
Phase
4
:
-
Begins
at
a
resting
membrane
potential
of
about
-55
millivolts
-
Slow
depolarization
towards
teh
threshold
of
-35
millivolts
due
to
the
unique
activity
of
“funny”
sodium
channels
and
background
opening
of
voltage-gated
calcium
channels
-
Funny
channels
(l_f
channels)
are
unique
because
they
open
at
hyperpolarized
potentials
and
help
in
setting
the
pace
of
the
pacemaker
activity
2.
Threshold
and
Phase
0
: -
Once
the
membrane
potential
reaches
-35
millivolts,
there
is
a
rapid
opening
of
additional
voltage-gated
calcium
channels.
-
This
rapid
influx
of
calcium
leads
to
a
quick
depolarization
of
the
cell
(Phase
0).
3.
Phase
3
(Repolarization)
:
-
Follows
depolarization,
where
voltage-gated
calcium
channels
close,
and
voltage-gated
potassium
channels
open.
-
The
opening
of
potassium
channels
allows
potassium
to
exit
the
cell,
leading
to
repolarization
back
to
the
resting
potential
of
about
-55
millivolts.
→
The
pacemaker
cells
are
crucial
as
they
set
the
rhythm
of
the
heartbeat
by
continuously
creating
spontaneous
electrical
impulses
that
dictate
the
timing
of
heart
contractions
.
This
rhythmic
depolarization
ensures
that
the
heart
beats
at
a
rate
necessary
to
meet
the
physiological
demands
of
the
body.
Heart
Rate
(HR)
Control:
-
Basal
Heart
Rate
:
At
rest,
the
heart
typically
beats
at
a
basal
rate
of
about
70
to
80
beats
per
minute.
→
When
you
engage
in
physical
activities
such
as
running,
your
body
requires
more
oxygen,
particularly
in
the
skeletal
muscles
of
the
legs.
To
meet
this
increased
demand,
the
heart
must
pump
more
blood,
which
it
does
by
increasing
the
heart
rate.
-
Mechanism
of
Increased
Heart
Rate
:
-
The
sympathetic
nervous
system
is
activated
and
increases
the
heart
rate
by
affecting
the
electrical
properties
of
the
pacemaker
cells
-
It
shortens
the
duration
of
Phase
4
of
the
pacemaker
potential.
This
is
achieved
by
modulating
the
activity
of
the
funny
sodium
channels
and
the
voltage-gated
calcium
channels,
allowing
the
membrane
potential
to
reach
the
threshold
more
quickly.
-
During
Phase
3,
the
sympathetic
nervous
system
speeds
up
the
closure
of
the
voltage-gated
potassium
channels,
which
hastens
repolarization
and
readies
the
pacemaker
cells
for
the
next
cycle
sooner.
-
Tachycardia
:
-
Definition
:
heart
rate
that
exceeds
100
beats
per
minute
-
Is
normal
and
necessary
during
exercise
as
the
body
responds
to
increased
metabolic
demands
-
Post-
exercise,
the
sympathetic
stimulation
decreases,
and
the
parasympathetic
nervous
system
helps
slow
the
heart
rate
back
to
normal.
This
transition
ensures
that
the
heart
rate
does
not
stay
elevated
unnecessarily,
conserving
energy
and
maintaining
physiological
balance.
-
Mechanisms
of
Decreased
Heart
Rate
:
-
The
parasympathetic
nervous
system
primarily
acts
to
conserve
energy
and
slow
the
heart
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