Transcript Cardiovascular Anatomy

Cardiovascular
Anatomy-Histology Correlate
By: Michael Lu, Class of ‘07
NOTE:
Heart in Situ
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Visceral pleura is in direct contact with the lungs,
while parietal pleura is everything else. The same
applies to pericardium and the heart.
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4 sections of parietal pleura: cupola, costal,
diaphragmatic, and mediastinal.
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Potential spaces of the costomediastinal and
costodiaphragmatic recesses, where there is no
lung tissue.
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Mediastinum located between the lungs extending
from the sternum anteriorly to vertebrae posteriorly.
a) superior – bounded by horizontal line through
sternal angle below and rib 1 above
b) anterior – bounded by sternum in front and
pericardium in back
c) middle – includes heart and pericardium
d) posterior – bounded by pericardium in front and
vertebral bodies in back; includes esophagus and
aorta
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Phrenic nerves (right and left) – motor nerves to
diaphragm that travel along the side of the heart in
the pericardium in front of the root of the lung
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Pericacardiacophrenic arteries and veins
traveling with the phrenic nerves.
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Thymus gland – immune tissue, becomes fatty
tissue with age
Heart – Anterior Pericardial
Sac Removed
NOTE:
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The superior vena cava, aortic arch, and
pulmonary trunk exiting the base of the heart.
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The internal and external jugular veins joining
the subclavian vein to become the
brachiocephalic veins that drain into the superior
vena cava.
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Since the superior vena cava is on the right, the
left brachiocephalic vein is longer than the right
brachiocephalic vein and crosses midline.
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The aorta bending left and inferiorly, its arch giving
off 3 main branches:
a) brachiocephalic trunk, which gives off right
subclavian and right common carotid arteries
b) left common carotid artery directly off aorta
c) left subclavian artery directly off aorta
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The veins are situated anterior to the arteries.
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The pulmonary trunk giving off right and left
pulmonary arteries to the lungs.
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Ligamentum arteriosum attached between the
aortic arch and left pulmonary artery.
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Vagus n. running in the mediastinum behind the
lung root, giving off the recurrent laryngeal n. on
the left side under the aortic arch.
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Right ventricle of the heart is situated most
anterior and the apex is left of midline.
NOTE:
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With the heart removed, the openings of the great
vessels at the base of the heart: superior and
inferior vena cava, pulmonary trunk bifurcating
into left and right pulmonary arteries, left and
right pulmonary veins, and ascending aorta.
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Once again, the phrenic nerves running anterior
to the roots of the lungs and the vagus nerves (not
shown here) running posterior.
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The transverse pericardial sinus situated behind
the pulmonary trunk and ascending aorta (easily
felt by inserting a finger from behind these great
vessels from the left with heart in situ).
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The oblique pericardial sinus behind the
diaphragmatic surface up to the base of the heart
(easily felt by lifting the apex and sliding fingers
behind the heart).
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Throughout the cardiovascular system, like all
other organ systems in the body, structure
correlates with function. This is true from the heart
all the way down to the capillary. In the following
slides, we will look closely at the histological details
of arteries and veins, starting with the great
vessels.
AORTA (intima)
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All vessel walls are divided into 3 tunica (starting
from inside): intima, media, and adventitia.
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The inner intima layer consists of simple
squamous epithelium and underlying connective
tissue.
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The border between the tunica intima and tunica
media may not be easy to recognize. As a general
rule of thumb, the intima ends and the media
begins where the first distinct elastic sheet or
lamella is located.
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In the figure below, the elastic sheet is indicated by
arrowheads, and the intima is indicated by the
bracket.
Thickening of Tunica Intima
Thickening of the tunica intima may occur in 2 ways – arteriosclerosis and atherosclerosis.
Arteriosclerosis is a part of normal aging. There is an increase in connective tissue,
fibrosis, and fragmentation of elastic lamellae. Atherosclerosis, on the other hand, is a
pathological process involving eccentric fibrous intimal thickening, lipid deposition, and
dystrophic calcification. Intima thickening within coronary arteries, which nourish the
myocardium of the heart, is a major cause for myocardial infarcts. Shown below are
examples of tunica intima thickening. As a reminder, the presence of elastic lamellae, or in
this case a distinct internal elastic membrane, separates the tunica intima from the tunica
media.
AORTA (media)
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The tunica media consists of circularly arranged
smooth muscle and abundant elastic tissue. In
the H&E stain below, the arrows point to a smooth
muscle cell nucleus and elastic lamella (E).
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The Masson-aldehyde fuchsin stain accentuates
the abundance of elastic lamellae within the tunica
media.
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The smooth muscle cells, not fibroblasts,
synthesize the elastic fibers, in addition to
collagen and various proteoglycans.
AORTA (adventitia)
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The outermost layer of the vessel wall, the tunica
adventitia, is mainly a connective tissue sheath
surrounding the vessel.
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The media ends and adventitia begins where the
elastic lamellae are not found.
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The H&E stain below shows the border between
the media and adventitia. In larger vessels, such as
the aorta in this case, the adventitia contains small
arteries and veins, also called vasa vasorum, and
their smaller branches (arrowheads) that supply
nourishment to the outer half of the media.
Adventitia of vein
Comparison of Artery and Vein
There are several criteria that can help you distinguish
between arteries and veins.
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Arteries experience a much higher blood pressure
than veins and therefore have a much higher wallto-lumen ratio (structure correlates with function).
On the other hand, venous pressure is much lower
and thus veins have a lower wall-to-lumen ratio,
or wider lumen and thin wall.
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Veins are more variably shaped than arteries.
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Most arteries contain a distinct internal elastic
membrane (labeled as iem), while veins do not.
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In an artery, the media is thicker than the
adventitia. Once again, the media contains
abundant smooth muscle and elastic fibers. The
adventitia does not contain any muscle.
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In a vein, the adventitia is thicker than the
media. The media consists of circumferentially
oriented smooth muscle fibers, while the adventitia
contains longitudinal smooth muscle fibers. The
adventitia is the thickest layer.
NOTE:
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The heart serves as a mechanical pump to supply
the entire body with blood, both providing nutrients
and removing waste products.
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The great vessels exit the base of the heart.
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Blood flow: body→vena cava→right atrium→right
ventricle→lungs→left atrium→left ventricle→body
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The heart consists of 3 layers – the endocardium,
myocardium, and epicardium. The epicardium
(bottom left) consists of arteries, veins, nerves,
connective tissue, and variable amounts of fat.
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The myocardium contains branching, striated
muscle cells with centrally located nuclei. They
are connected by intercalated disks (arrowheads).
-Coronary arteries and cardiac veins supply the muscular tissue of the heart. The left and right coronary arteries
immediately branch off of the ascending aorta and further give off the left anterior descending (LAD),
circumflex, SA nodal, right marginal, posterior descending, and atrial branches.
-The small cardiac, middle cardiac, and great cardiac veins all drain into the coronary sinus, which wraps
around the heart and drains into the right atrium.
-The following slide details the 4 chambers of the heart – left and right atria and ventricles. Two features to notice
are the fossa ovalis and the ligamentum arteriosum, which are remnants of shunts that were open during
circulation through the fetal heart in order to bypass the lungs.
Right Atrium
Left Atrium
Right Ventricle
Left Ventricle
Endocardium of Atrium and Ventricle
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These sections of heart are both taken near the
atrio-ventricular sulcus that contains a coronary
artery and cardiac vein. They also exhibit all 3
layers of the heart wall – epicardium, myocardium,
and endocardium.
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Notice (both here and in the previous slide) that the
myocardium in the ventricle is much thicker
than that in the atrium.
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The endocardium (marked by the black bracket) is
magnified in the lower panel and compared
between the atrium and the ventricle.
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The atrial endocardium is much thicker than the
ventricular endocardium and contains a welldeveloped network of elastic fibers.
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Right beneath the ventricular endocardium are
conducting fibers that will be covered in the next 2
slides.
Conducting System of the Heart
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The heart continuously pumps
blood to the entire body without
input from elsewhere.
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Nerve impulses initiate from the
sinoatrial (SA) node and travel
down to the atrioventricular
(AV) node. They continue down
the bundle of His and spread
out among the Purkinje fibers
towards the apex of the heart.
This mechanism provides
regular, synchronous
contractions of the myocardium.
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The Purkinje fibers can be
found immediately beneath the
endocardium of the ventricular
papillary muscle or in other
regions immediately underneath
the ventricular endocardium.
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The Purkinje conducting fibers
are modified cardiac muscle
cells, specialized for the
conduction of electrochemical
impulses. They appear much
larger and paler than cardiac
muscle fibers.
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The square near the left bundle
is enlarged in the next slide.
- This section was taken near the interventricular septum. The nerve tissue of the AV bundle, or bundle of His
(lighter staining enclosed in bracket), must travel through the cardiac skeleton down a small fascicle of muscle
fibers. The nerve fibers then travel down the interventricular septum towards the apex of the heart as Purkinje
fibers.
- The cardiac skeleton consists of dense connective tissue surrounding the cardiac valves, on which all the muscle
fibers of the heart insert. When the cardiac muscles contract, they pull toward these insertion points and empty the
atria and ventricles.
Cardiac Valves
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As shown in the previous slide, the heart contains 4
valves – the tricuspid, pulmonary, mitral, and
aortic valves. The valves prevent regurgitation of
blood flow.
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The cardiac valves are essentially plates of dense
connective tissue extending from the cardiac
skeleton covered with endothelium. They are
avascular.
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The side of the valve that faces oncoming blood
flow exhibits an extensive elastic fiber network.
As the blood is squeezed out of the heart chamber,
the increased blood pressure pushes the valve
open. As the blood flows past the valve and the
pressure drops, the elastic fibers recoil and help
the valve to close. The other side of the valve
contains abundant collagen fibers.
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Both atrial valves, the tricuspid and mitral valves,
are attached to papillary muscles in the ventricles
via chordae tendineae. The papillary muscles and
chordae tendineae do NOT pull open the valves. All
valves open and close passively. Instead, these
structures hold the tricuspid and mitral valves shut
to prevent regurgitation of blood back into the atria
when the ventricles contract. The blood exits the
ventricles via the pulmonary and aortic valves.