Heart
•
General
Circulatory system
heart and blood vessels
walls have 3 layers (inside to outside)
1-Tunica interna: aka tunica intima
innermost layer--lumenal layer
lumenal epithelium--endothelium
simple squamous epithelium
squamous cells + underlying CT + SMFs
•
•
•
•
•
•
•
•
1
Heart
•
2-Tunica media:
middle layer (media ='middle')
muscle fibers (smooth or cardiac).
•
•
•
•
•
•
•
3-Tunica externa: aka tunica adventitia
outermost layer
dense irregular CT.
Smaller blood vessels
no t. externa and/or t. media
t. interna is usually present
•
2
3
•
Heart
Heart = pump
force pushes the blood
through the CV system
Mammalian heart
right and left ventricles (RV, LV)
right and left atria (RA, LA)
auricle; lower, outer part of atrium
auricle = 'ear'
looks like a dog's ear.
•
•
•
•
•
•
•
•
•
Pressure pushes blood into the atria
70% of the blood flows into the
ventricles before atrial contraction
Atrial contraction sends remaining
blood into the ventricles.
•
•
4
Heart
Ventricles contract, ejecting blood into the
elastic arteries.
•
•
Animal heart is myogenic
•
muscle tissue generates contraction
no exogenous stimulation
Heart rate (bpm) and
•
stroke volume (volume pumped per
beat)
•
regulated by nervous and endocrine
systems
•
With adequate 02 and chemical energy
heart will beat
total absence of all neural or
hormonal stimuli.
•
5
Heart
•
Wall structure
•
Tunica interna: endocardium.
Small hearts (example: mouse)
endocardium ;simple tissue:
endothelium.
•
•
Medium to large hearts
•
subendothelial layer of loose CT.
•
May contain elastic and collagen fibers
•
sometimes smooth muscle fibers.
Rat's heart ; subendothelial layer
not visible.
•
6
7
Heart
•
Tunica media: myocardium.
entirely cardiac muscle
tissue;
larger blood vessels and
some adipose tissue.
•
•
•
Tunica externa: epicardium.
simple squamous
epithelium + dense
interwoven CT.
Rat's heart ; dense C.T.
may be too thin.
Adipocytes
•
•
•
8
9
•
•
Heart
Special structures:
Cardiac Valves
Two sets of one-way valves;
prevent blood back-flow
tricuspid and bicuspid valves (R
and L AV)
between atria and ventricles
•
•
•
R and L semilunar valves
between ventricles and aortic
or pulmonary trunks
Composed of two or three
flaps of thick endocardium
(dense CT).
•
•
No myocardium or
epicardium
•
10
Heart
Chordae tendonae and papillary
muscles
Tension-cords
prevent inversion of the
tricuspid and bicuspid valves
In ventricle’s lumen
tendinous cord;
papillary muscle.
•
•
•
•
•
•
Ventricles contract, cords prevent
valve inversion
Papillary muscle contracts
because the length of cords
shortens during ventricular
contraction.
•
11
Heart
The tunica media of all four chambers
of the heart are continuous
from the RA to the LA
from the interatrial septum to the
interventricular septum.
•
•
•
Membrane impulse begins at sinoatrial (SA) node
•
•
'pacemaker'
SA node lies near the opening to
superior vena cava
•
from SA node the membrane
impulse spreads to the LA.
•
12
Heart
Medium to large hearts, Purkinje
fibers
•
cardiac muscle fibers; unusually
high diameter
•
rapidly transmits electrical signals
through the atrial cardiac muscle
tissue.
•
•
Only weakly contractile;
•
for high speed conduction
•
more abundant in the ventricles
13
Heart
Impulse reaches the inter-atrial
septum and the auricle 0.1 sec later.
•
Atrial cardiac muscle tissue contracts
instantly
Bottom of the inter-atrial septum;
impulse reaches the atrioventricular
node (AV node)
•
mass cardiac muscle fibers of
unusually low diameter.
•
•
speed of conduction slows
Takes another 0.1 sec to pass through
the AV node
Delay provides time for ventricular
filling.
•
15
Heart
Atrial tunica media thinner than
that of the ventricles
•
less force needed to pump blood
into the ventricles.
•
•
impulse leaves the AV node
enters the inter-ventricular
septum
•
then the bundle of His > Bundle
branches
•
•
speed increases
16
Heart
Purkinje fibers extends down the
interventricular septum and
•
•
extend into ventricular wall
smaller branches into the ventricular
myocardium
•
Membrane impulse reaches the upper
ventricular walls
only 0.1 after reaching the bundle of His.
•
ventricles contracts together
17
Heart
The outer wall of the RV is much
thinner than that of the LV.
•
Less force is required to pump
blood into the pulmonary trunk
than into the aortic trunk.
•
Thickness of the inter-ventricular
septum = outer wall of the LV.
•
LV lumen much more apparent in
sections of the heart than lumen
of the RV.
•
18
19
Heart
20
Heart
The heart sounds; closure of the
two sets of valves.
•
First sound ('lubb') does not
occur when the atria contract,
•
but rather when the
ventricles contract
•
closure of the tricuspid and
bicuspid valves
•
•
Second sound ('dupp')
occurs when the ventricles
relax
•
closure of the semilunar
valves
•
21
Heart
The depolarization and
repolarization of the cardiac
muscle tissue
•
can be detected with electrodes
placed on the skin
•
Electrical patterns detected
represent the EKG
electrocardiogram
•
22
Heart
•
P wave
is due to atrial depolarization
•
•
QRScomplex
ventricular depolarization
•
T wave
ventricular repolarization.
no wave due to atrial repolarization
included in the QRS
23