CHAPTER 20
THE HEART
I. HEART ANATOMY
A.Location
1.
mediastinum of thoracic cavity
2.
base
a.
superior and center-right
b.
apex
1.
between 5th and 6th left ribs
B.
Layers of the heart
1.
Outer covering
a.
pericardium
1.
fibroserous sac
2.
fibrous pericardium
3.
dense CT attaches to nearby structures
4.
parietal pericardium
5.
visceral pericardium or EPICARDIUM on surface
6.
pericardial fluid
2.
Myocardium
a.
cardiac muscle
b.
also contains connective tissue for strength
1.
collagen
2.
elastin
3.
reinforces valves
3.
Endocardium
a.
lines inside chambers
b.
endothelium
1.
same as lining of blood vessels
2.
endothelial cells on a basement membrane of connective
tissue
C.
Chambers
1.
2 atria (atrium - singular)
a.
auricle - external part of atrium
2.
2 ventricles
3.
right and left hearts
4.
internal separations
a.
interventricular septum
b.
interatrial septum
5.
external separations
a.
coronary sulcus
1.
atria/ventricle
b.
anterior interventricular sulcus
2.
left/right ventricles
6.
pectinate muscles
a.
muscle bundles inside atria
7.
papillary muscles
a.
muscles within ventricles
D. Great Vessels
1.
Enter Right Atrium
a.
Vena Cava
1.
Superior
2.
Inferior
b.
Coronary Sinus
1.
blood from heart or coronary circulation
2.
Exit Right Ventricle
a.
Pulmonary Trunk (Artery)
3.
Blood enters pulmonary circulation to exchange gases
4.
Enters Left Atrium
a.
Pulmonary Vein
5.
Exits Left Ventricle
a.
Aorta
1.
branches to deliver blood to all tissues
E.
Draw the chambers and vessels of the heart
II. BLOOD FLOW THROUGH THE HEART: CHAMBERS,
VALVES AND VESSELS
A.
Right Heart
1.
pulmonary circuit
a.
receives deoxygenated blood
b.
pulmonary artery
1.
delivers deoxygenated blood to lungs
c.
pulmonary vein
2.
delivers oxygenated blood to heart
2.
not a pressure pump like left ventricle
a.
wall is thinner
b.
resistance is less in pulmonary circuit
B.
Left Heart
1.
systemic circuit
a.
functions to deliver blood to systemic
circulation
2.
wall thickens with work or load
a. identify by a thicker myocardium
b. pumps against great resistance throughout
body
C.
Work together
1.
Must pump same amount of blood at same time
D.
Valves
1.
Atrioventricular
a.
cusps - valve flaps
b.
Chordae Tendineae
1.attach
cusps to papillary muscle of ventricular wall
2. collagen fibers
c.
ventricle begins to contract
blood
in ventricle pushes valves closed
chordae
tendineae hold valves to prevent
pushing
them into atrium
d.
AV valves prevent blood from being pushed into
atria
instead of out artery
d.
between atria and ventricles
1.
Tricuspid - righT
2.
MitraL -Left (also bicuspid)
2.
Semilunar
a.
need valves to prevent blood from flowing
back into ventricles when relaxing
b.
want to build up pressure within closed
ventricles before releasing blood -
when pressure
is greater in ventricles that
arteries it will push valves open into
artery
blood will enter arteries. As ventricles
relax pressure drops and valves close
c.
each has three pocketlike cusps
d.
between VENTRICLES and ARTERIES
1.
aortic semilunar valve
a.
left ventricle and aorta
2.
pulmonic semilunar valve
a.
right ventricle and pulmonary artery
3.
Normal function with some improper valve closures
E.
Coronary Circulation
1.
Diffusion of
nutrients from blood in heart chambers is not effective in
supplying the
working cardiac muscle.
2.
Capillaries need to delivery nutrients/oxygen to muscle fibers.
3.
Heart requires a constant supply via the coronary arteries.
a.
branch from aorta
b.
separates to Right and Left Coronary Artery at aortic trunk and
divides into branches over external
heart surface anterior and posterior
4.
Left Coronary Artery branches
a.
anterior interventricular artery
1.
runs along interventricular sulcus
2. supplies
interventricular septum and anterior walls of right
and left
ventricles
b.
Circumflex Artery
1. supplies left
atrium and post. left ventricle
5.
Right Coronary Artery branches
a.
marginal artery
1.
supplies lateral right side of heart
b.
posterior interventricular artery
1.
to apex
2.
supplies posterior ventricle
6.
Anastomosis
a.
junctions of vessels
b.
provide collaterals
1.
alternative routes to supply same areas
7.
From arteries, enters capillaries, return via veins
a.
Cardiac Veins
1.follow
coronary arteries
b.
Coronary Sinus
1.
veins join and drain here
8.
Blockage of coronary arterial circulation
a.
angina pectoris
1.
chest pain
2.
deficiency of blood to myocardium
b.
Myocardial infarction (heart attack)
1.
lack of blood flow - ischemia
2.
damages tissue with prolonged absence
of
oxygen
3.
myocardium cannot return to functional
tissue
(amitotic) replaced with scar tissue 4. survival
depends of location of infarct
F.
Virtual Reality. You have chosen a trip through the circulatory system. At this
time you will be entering the Inferior Vena Cava. Write down the vessels, chambers, and valves in the order each is
encountered.
III. HEART PHYSIOLOGY
A.
Cardiac Muscle
1.
striated involuntary muscle
2.
1 or 2 centrally located nuclei
3.
branched fibers
a.
fibers are cells
b.
muscle cells = myocytes
c.
cardiac cells = cardiocytes or myocytes
4.
fibers connected by intercalated discs
a.
dark staining in slides
5.
More mitochondria
a.
relies on aerobic metabolism
b.
metabolizes glucose, fatty acids,- whatever is available
6.
myofibrils
a.
typical sarcomere
b.
thin filaments - Actin
c.
thick filaments -Myosin
7.
T-tubules enter at Z-lines or intercalated disc
a.
not as developed as in skeletal muscle
B.
Contraction
1.
Depolarization of muscle cells membrane= sarcolemma
2.
Cell depolarizes to contract, relaxation after repolarization
3.
Most of heart is contractile muscle fibers
a.
Action potential must be generated
1.
Sodium rushes into cell - membrane is
more
permeable to sodium (Na enters)
2. Membrane
potential becomes positive or upward movement on
graph
a.
from resting membrane potential of
-90mV
to +30mV
b.
voltage gated channels open to
allow
more sodium to enter cell
These
open and close at a given voltage
b. Depolarization of membrane causes
calcium to enter at the T-tubules through slow calcium channels. Calcium
entrance prolongs action potential
c. As calcium enters it signals
release of more calcium from the sarcoplasmic reticulum
d.
Free intracellular calcium is signal
for contraction
1. cross bridge formation by binding
myosin heads with troponin when calcium is present
e.
repolarization of membrane occurs when membrane becomes more
permeable to
potassium (K exits)
1. calcium moves back into SR and
extracellular
f.
Absolute Refractory Period
1.
second membrane potential cannot depolarize membrane
2.
250 ms in cardiac muscle
3.
300 ms duration of contraction
4.
no summation or tetany
Graph the Membrane potential(mV) vs. Time showing
the action potential. Include the time interval for contraction.
C.
Electrophysiology of the heart
1.
Automaticity
a.
intrinsic ability of the heart to depolarize and contract
b.
separate from neural excitation
1.
sympathetic innervation to speed up
a.
from medulla - cardioacceleratory
center
via spinal nerves T1-T5
2.
parasympathetic innervation to slow
a.
from medulla - cardioinhibitory center via the
Vagus nerve (X)
c.
cardiocytes in tissue culture will beat independently until contact causes
them to beat
together
d.
mediated by the Cardiac Conduction System
or
Nodal System
e.
action potential must follow a designated
pathway so that the atria contract
while ventricles are relaxed and before ventricles contract
f.
Action potential initiates at the pacemaker of the heart
1.
the pacemaker for most people is at the
sinoatrial
node - SA node
a.
discharge rate of 60-100 per minute
b.
This is the fastest rate and sets the pace for the heart beat - sinus rhythm
c.
normal sinus rhythm of 60-100 beats
per
minute
2.
can initiate at the atrioventricular node-
AV
node - rate of 40- 55 per minute
g.
Normal activation sequence
1.
SA node
2.
atrial myocardium
3.
AV node
4.
bundle of His
5.
left and right bundle branches
6.
Purkinje network
7.
Ventricular myocardium
h.
correlate to the ECG - Draw in the ECG
R
P T
Q S
a bcd e f g
0 100 200 300 400
500
200msec=0.2sec
Time (msec)
Conduction Pathway of the Heart
a.
SA node at time: 0 msec
b.
AV node 66
c.
remote atrial surface 100
d.
bundle of His 130
e.
ant right ventricle 190
f.
apex
220
g.
post left ventricle 260
2.
Electrocardiogram
a.
measure electrical activity from contracting of muscle
1.
largest signal from heart
2.
filter out noise
3.
gives a 1mv signal that must be amplified to
record on a chart
b.
isoelectric line
1.
get upward and downward deflections
called waves
c.
P wave
1.
atria depolarization
d.
QRS complex
1. produced by the upstroke of all
the action potentials throughout the ventricles
e.
S-T segment produced by plateau phase of act. pot.
f.
T wave with repolarization of ventricles- slower
g.
isoelectric segment after T wave = ventricular relaxation
h.
normal time intervals for waves and segments
P-R SEGMENT end of P to beginning of Q
P-R INTERVAL beginning of P to beginning of Q
S-T SEGMENT end of S to beginning of T
S-T INTERVAL end of S to end of T
Q-T INTERVAL beginning of Q to end of T
QRS COMPLEX beginning of Q to end of S
P-WAVE beginning of P to end of P
T-WAVE beginning of T to end of T
Knowing
the duration of each segment or interval
can
be used to identify abnormalities in the
conduction
pathway.
D.
Cardiac Cycle
Refer
to handout for all events in the cardiac cycle
as
measured in the left heart.
1.
All events in one heartbeat
a.
if heart rate is 75 then cardiac cycle is 0.8sec
(800
msec)
2.
Blood flows due to pressure changes ALWAYS goes
from
high to low pressure
3.
Systole
a.
contraction
b.
atrial systole to force blood to ventricles
1. from P-wave to S-wave
c.
ventricular systole to force blood to arteries
1. from S-wave to end of T-wave
4.
Diastole
a.
relaxation
b.
atria and ventricles in diastole from end of
T-wave to P-wave - the long isoelectric line
b.
atrial diastole while atria are filling
1. with ventricular systole
c.
ventricular diastole while ventricles are filling
1. with atrial systole
5.
Phases of the cardiac cycle
a.
atrial systole
1.
atria contracts and ejects blood into ventricles
2.
volume is small compared to amount entering
when
valves open
3.
significant with high output of heart or
failing
heart ("atrial kick")
b.
Isovolumetric contraction
1.
closing of AV
2.
volume must stay the same
3.
pressure inside ventricles rises
c.
Rapid ejection
1.
2/3rds of blood ejected
into
aorta or pulmonary artery
d.
Reduced ejection
1.
less volume,slower ejection but
more
shortening of fibers needed to
squeeze blood out
e.
Isovolumetric relaxation
1.
pressure drops rapidly in ventricles
2.
all valves closed no change in volume
3.
ventricles elongate
4.
pressure must drop lower than atrial
pressure
so that AV valves open
f.
Rapid ventricular filling
1.
immediately after opening of AV valve
2.
blood from atria rushes in 2/3rds of
filling occurs here
g.
Reduced ventricular filling (diastasis)
1.
greatest quiescence - relaxation
2.
some flow from atria but slowly
h.
back to atrial systole after the P wave
VALVES:
WHEN ARE EACH OPENED AND CLOSED
TIME (SEC)0 .1
.2 .3 .4
.5 .6 .7
.8
ATRIUM
[SYSTOLE][ DIASTOLE ]
VENTRICLE [DIASTOLE][ SYSTOLE
][DIASTOLE ]
AV VALVE
[ OPEN ][ CLOSED ][OPEN
]
SEMILUNAR [CLOSED ][ OPEN ][
CLOSED ]
HEART
SOUNDS
[IV] [I ] [II] [III]
note: atrial systole - 0.1 sec
ventricular systole - 0.3 sec
quiescent period - 0.4 sec
E.
Heart Sounds
1.
lub-dup, pause, lub-dup
2.
most audible sounds from valves closing
sounds
I and II
3.
pause - quiescent period
4.
First heart sound (I)
a.
AV valves close
b.
loudest, longer
5.
Second heart sound (II)
a.
semilunar valves close
b.
short snap
6.
Location on chest correspond to valve
a.
Locate in lab exercise
III. CARDIAC FUNCTION
A.
Cardiac Output (CO)
1.
amount of blood pumped out by each ventricle in
one minute
a.
right and left sides are in series and
must
pump same volumes
2.
Stroke volume (SV) is the amount pumped out of each
ventricle in one beat (70ml/beat)
3.
Heart rate = number of beats in 1 min
4.
CO= HR x Stroke volume
=75
beats/min x 70 ml/beat
=
5250 ml/min (approx. 5 liters/min)
5.
Total blood volume is approx. 5 liters
6.
All of the body's blood passes through each side of
the heart each minute!
7.
Cardiac reserve
a.
can increase output on demand by
1.
increasing HR
2.
increasing SV
3.
or both
4.
athlete can increase CO to 35L/min
B.
Stroke Volume
1.
Ventricles are not drained with SV of 70 ml
a. usually this is 60% of volume
2.
End diastolic volume (EDV)
a.
amount of blood during ventricle at end of
its diastole
3.
End systolic volume (ESV)
a.
amount remaining in ventricle at end of
its
systole
4.
SV= EDV (120ml)-ESV(50ml)
=
70ml/beat
5.
Frank-Starling Law of the Heart
a.
Preload of the cardiac muscle cells just before they contract determines the
stroke volume
b.preload - stretch of fibers
(related to actual volume present (EDV) established by venous return)
c.
slow heart rate or exercise
increases EDV
d.
if not explained by Starling's Law of the Heart then the heart sucks
1.
ventricle waalls
rebound suddenly and creat
negative pressures inside like
squeezing an empty container under water
6.
Epi or Norepi
a.
enhance contractility via calcium mobilization
b.
contractility refers to force of contraction
an increase
in contractility results in a more
forceful contraction of the heart
giving a
greater SV
C.
Heart Rate
1.
Pacemaker control - intrinsic
2.
autonomic control
a.
sympathetic
1.
Beta-1 adrenergic receptors-
Norepi
increases heart rate and
contractility
via these receptors
2.
Beta-blockers decrease HR by
blocking
B-1 receptors and lower BP
b.
parasympathetic
1.
returns HR to low levels after stress
2.
inhibitory effect
3.
cut vagus nerve get increase in
heart
rate of 30 beats/min
or
at about 100 beats/min as
established
by the SA node
3.
Baroreceptors
a.
sense changes in BP
b.
negative feedback mechanism to regulate BP
c.
reflex control of HR
d.
location
1.
carotid sinus
a.bifurcation
of common carotid artery
(divides
into internal/external carotids)
b. stretches as BP rises
c.
stimulates cardioinhibitory center
d.
impulses via parasym. (vagus)
e.
lowers HR
2.
aortic arch
a.
in aorta
b.
response same as carotid sinus
4.
Bainbridge Reflex
a.
atrial stretch receptors (baroreceptors)
b.
at vena cava and right atrium
c.
at pulmonary vein and left atrium
d.
as pressure in atria rises effect is to
stimulate
cardioaccelarotory center to
increase
HR and BP to prevent blood volume
increase
(congestion) in heart
5. Chemicals that influence
HR
a.
Epi and Norepi
b.
thyroxine
c.
calcium
1.
low calcium depress heart
a.
calcium channel blockers
act
to decrease contractility and
oxygen
requirement of the heart
and
used with hypertension, angina
2.
hypercalcemia
a.
greater contractions
d.
sodium
1.
hypernatremia
a.
inhibits calcium transport
and
blocks contraction
e.
potassium
1.
hyperkalemia
a.
lowers resting membrane potential
b.
may lead to heart block
2.
hypokalemia
a.
abnormal sinus rhythms