Chapter 14b
description
Transcript of Chapter 14b
Chapter 14b
Cardiovascular Physiology
Figure 14-15
Action Potentials in Cardiac Autorhythmic Cells• Pacemaker potential - no resting• -60mV drifts to -40 to action potential• Spread through connections to contractile fibers• If channels are permeable to both K+ and Na+
Time Time
Ca2+ in
Ca2+ in
K+ out
Net Na+ in
Lots of Ca2+
channelsopen
Ca2+ channels close,K+ channels open
Some Ca2+
channels open,If channels close
If channelsopen K+ channels close
If channelsopen
(b) Ion movements during an actionand pacemaker potential
(c) State of various ion channelsTime
Threshold
Pacemakerpotential
Actionpotential
20
0
–20
–40
–60
(a) The pacemaker potentialgradually becomes less negativeuntil it reaches threshold,triggering an action potential.
Mem
bran
e po
tent
ial (
mV)
Action Potentials in Cardiac Autorhythmic Cells
PLAY Interactive Physiology® Animation: Cardiovascular System: Cardiac Action Potential
Modulation of Heart Rate by the Autonomic Nervous System
Figure 14-16
Normal Parasympathetic stimulationNormal Sympathetic stimulation
Hyperpolarized Slower depolarization
Time (sec)Time (sec)
20
0
–60
0.8 1.6 2.40.8 1.6 2.4
(b)(a)
Depolarized More rapid depolarization
20
–20
–40
–60
0
Mem
bran
e po
tent
ial (
mV)
Mem
bran
e po
tent
ial (
mV)
Action Potentials
Table 14-3
Electrical Conduction in Myocardial Cells
Figure 14-17
Membrane potentialof autorhythmic cell
Membrane potentialof contractile cell
Contractile cell
Cells ofSA node
Depolarizations of autorhythmic cellsrapidly spread to adjacent contractilecells through gap junctions.
Intercalated diskwith gap junctions
Electrical Conduction in the Heart
Figure 14-18
1
2
3
4
5
5
4
3
2
1
THE CONDUCTING SYSTEMOF THE HEART
SA node
AV node
Purkinjefibers
Bundlebranches
AV bundle
AV node
Internodalpathways
SA node
SA node depolarizes.
Electrical activity goesrapidly to AV node viainternodal pathways.
Depolarization spreadsmore slowly acrossatria. Conduction slowsthrough AV node.
Depolarization movesrapidly through ventricularconducting system to theapex of the heart.
Depolarization wavespreads upward fromthe apex.
Electrical Conduction
• SA node• Sets the pace of the heartbeat at 70 bpm• AV node (50 bpm) and Purkinje fibers (25-40
bpm) can act as pacemakers under some conditions
• AV node• Routes the direction of electrical signals • Delays the transmission of action potentials
Einthoven’s Triangle
Figure 14-19
Electrodes areattached to theskin surface.
A lead consists of twoelectrodes, one positiveand one negative.
Right arm Left arm
Left leg
I
II III
The Electrocardiogram
• Three major waves: P wave, QRS complex, and T wave
Figure 14-20
Electrical Activity
• Correlation between an ECG and electrical events in the heart
Figure 14-21
P
Q
R
T
S P
T wave:ventricularrepolarization
PQ or PR segment:conduction throughAV node and AVbundle
P wave: atrialdepolarization
ELECTRICALEVENTSOF THE
CARDIACCYCLE
Repolarization
START
P
Q
P
Q
R
P
Q
R
T
S
R waveP
Q
R
S
S wave
Q
R
P
Q wave
Ventricles contract
ST segment
The end
P
Atria contract
S
Electrical Activity
Figure 14-21 (9 of 9)
P
Q
R
T
S P
T wave:ventricularrepolarization
PQ or PR segment:conduction throughAV node and AVbundle
P wave: atrialdepolarization
ELECTRICALEVENTSOF THE
CARDIACCYCLE
Repolarization
START
P
Q
P
Q
R
P
Q
R
T
S
R waveP
Q
R
S
S wave
Q
R
P
Q wave
Ventricles contract
ST segment
The end
P
Atria contract
S
Electrical Activity
• Comparison of an ECG and a myocardial action potential
Figure 14-22
(a) The electrocardiogram represents the summedelectrical activity of all cells recorded from thesurface of the body.
(b) The ventricular action potential is recorded froma single cell using an intracellular electrode.Notice that the voltage change is much greaterwhen recorded intracellularly.
110mV
1 mV
1 sec
1 sec
Electrical Activity
• Normal and abnormal electrocardiograms
Figure 14-23
Mechanical Events
• Mechanical events of the cardiac cycle
Figure 14-24
5
43
2
1 Late diastole—both sets ofchambers are relaxed andventricles fill passively.
Atrial systole—atrial contractionforces a small amount ofadditional blood into ventricles.
Isovolumic ventricularcontraction—first phase ofventricular contraction pushes AVvalves closed but does not createenough pressure to open semilunarvalves.
START
Ventricular ejection—as ventricular pressurerises and exceeds pressurein the arteries, the semilunarvalves open and blood isejected.
Isovolumic ventricularrelaxation—as ventriclesrelax, pressure in ventriclesfalls, blood flows back intocusps of semilunar valvesand snaps them closed.
S1
S2
Cardiac Cycle
PLAY Interactive Physiology® Animation: Cardiovascular System: Cardiac Cycle
Cardiac Cycle
• Left ventricular pressure-volume changes during one cardiac cycle
Figure 14-25
120
80
40
0 65 100 135Left ventricular volume (mL)
AB
C
EDV
ESVD
Stroke volume
Onecardiaccycle
EDV = End-diastolicvolumeESV = End-systolicvolume
KEY
Left
vent
ricul
ar p
ress
ure
(mm
Hg)
Wiggers Diagram
Figure 14-26
P PT
0 100 200 300 400 500 600 700 800
120
A
B
60
90
Time (msec)
Electro-cardiogram
(ECG)
Pressure(mm Hg)
Dicrotic notch
QRScomplex
QRScomplex
Leftventicularpressure
135
0 C
D
E
F
S1 S2
65
Heart sounds
Leftventricular
volume (mL)
Atrialsystole
Atrialsystole
Atrialsystole
Atrialsystole
Ventricularsystole
Ventricularsystole
Ventriculardiastole
Isovolumicventricularcontraction
Earlyventricular
diastole
Lateventricular
diastole
Left atrialpressure
30
Aorta
Wiggers Diagram
Figure 14-26 (13 of 13)
P PT
0 100 200 300 400 500 600 700 800
120
A
B
60
90
Time (msec)
Electro-cardiogram
(ECG)
Pressure(mm Hg)
Dicrotic notch
QRScomplex
QRScomplex
Leftventicularpressure
135
0 C
D
E
F
S1 S2
65
Heart sounds
Leftventricular
volume (mL)
Atrialsystole
Atrialsystole
Atrialsystole
Atrialsystole
Ventricularsystole
Ventricularsystole
Ventriculardiastole
Isovolumicventricularcontraction
Earlyventricular
diastole
Lateventricular
diastole
Left atrialpressure
30
Aorta
Stroke Volume and Cardiac Output
• Stroke volume• Amount of blood pumped by one ventricle
during a contraction• EDV – ESV = stroke volume
• Cardiac output• Volume of blood pumped by one ventricle in a
given period of time• CO = HR SV• Average = 5 L/min
Na+ and Ca2+ influx
Sympathetic neurons(NE)
Rate of depolarization
Heart rate
Muscarinic receptorsof autorhythmic cells
K+ efflux; Ca2+ influx
Parasympatheticneurons (Ach)
Hyperpolarizes cell and rate of depolarization
Heart rate
1-receptors ofautorhythmic cells
Integrating center
Efferent path
Effector
Tissue response
Cardiovascularcontrol
center in medullaoblongata
KEY
Autonomic Neurotransmitters Alter Heart Rate
Figure 14-27
Stroke Volume
• Frank-Starling law states• Stroke volume increase as EDV (ending diastolic
volume) increases – stretch -> more force• EDV is affected by venous return• Venous return is affected by• Skeletal muscle pump• Respiratory pump• Sympathetic innervation of vessels
• Force of contraction is affected by• Stroke volume• Length of muscle fiber and contractility of heart
Stroke Volume
• Length-force relationships in intact heart: a Starling curve
Figure 14-28
Inotropic Effect
• The effect of norepinepherine on contractility of the heart
Figure 14-29
Cardiac Output
PLAY Interactive Physiology® Animation: Cardiovascular System: Cardiac Output
bind to
that activate
resulting in phosphorylation of
1-receptors
Epinephrineand
norepinephrine
cAMP secondmessenger system
Ca2+ removed from cytosol faster
Shortens Ca-troponinbinding time
Ca2+ stores in SR
Shorterduration
of contractionMore forcefulcontraction
Phospholamban
Ca2+-ATPase on SR
Ca2+ released
Ca2+ entry from ECF
Open time increases
SR = Sarcoplasmicreticulum
ECF = Extracelllularfluid
Voltage-gated Ca2+ channels
KEY
Catecholamines Modulate Cardiac Contraction
Figure 14-30
Stroke Volume and Heart Rate Determine Cardiac Output
Figure 14-31
determined by
is influenced by
which varies with
is a function of
increases
increases
determined by
CARDIAC OUTPUT
aided by
Heart rate
Due toparasympathetic
innervation
Sympatheticinnervation and
epinephrine
Venous returnVenous constriction
End-diastolicvolume
Rate of depolarizationin autorhythmic cells
Stroke volume
Contractility
Respiratorypump
Skeletal musclepump
Decreases Increases
Force of contraction inventricular myocardium
Summary
• Cardiovascular system—anatomy review• Pressure, volume, flow, and resistance• Pressure gradient, driving pressure, resistance,
viscosity, flow rate, and velocity of flow• Cardiac muscle and the heart• Myocardium, autorhythmic cells, intercalated
disks, pacemaker potential, and If channels
• The heart as a pump• SA node, AV node, AV bundle, bundle
branches, and Purkinje fibers
Summary
• The heart as a pump (continued)• ECG, P wave, QRS complex, and T wave
• The cardiac cycle• Systole, diastole, AV valves, first heart sound,
isovolumic ventricular contraction, semilunar valves, second heart sound, and stroke volume
• Cardiac output• Frank-Starling law, EDV, preload, contractility,
inotropic effect, afterload, and ejection fraction