Download 21-Development of cardiovascular system

Development of
Cardiovascular System
Department of Histology and Embryology
Medical college in Three Gorges University
1.Establishment of the Cardiogenic Field
• The heart (like all blood vessels ) is
mesodermal in origin. The mesoderm is
constitutes the cardiogenic field (area). It
is closely related to the pericardial cavity
and heart tube.
Heart
tube
Cardiogenic area
As a result of growth of the brain and
cephalic folding of the embryo, the
buccopharyngeal membrane is pulled forward, while the heart and pericardial cavity
move first to the cervical region and
finally to the thorax.
• Before the folding:pericardial cavity (dorsal)
Heart tube(ventral)
After the folding: heart tube (dorsal )
pericardial cavity(ventral)
Thus the heart tube consists of three layers:
(a) the endocardium, forming the internal
endothelial lining of the heart;
(b) the myocardium, forming the muscular
wall;
(c) the epicardium or visceral pericardium,
covering the outside of the tube.
• The heart is at first seen in the form of right
and left endothelial heart tubes that soon
fuse with each other. The single tube thus
formed shows a series of dilations.These
are :
(1) Bulbus cordis.
(2) Ventricle(primitive ventricle)
(3) Atrium (primitive atrium)
(4) Sinus venosus
Exterior of the Heart
U-shaped Bulbo-ventricular loop
S-shaped(atrium and sinus venosus come
to lie behind and above the ventricle)
• Atrioventricular canal: The ventricle and
atrium are connected by a narrow.
• The bulbus cordis lies at the arterial end
of the heart.
the conus: proximal part
truncus arteriosus: is continuous distally
with the aortic sac. (distal part )
• The sinus venosus lies at the venous end of
the heart.It has right and left horns.one
vitelline vein (from the yolk sac ),one
umbilical vein (from the placenta ) and one
common cardinal vein (from the body wall )
join each horn of the sinus venosus.
The fate of five dilatation:
Truncus arteriosus(T)
Aorta
Pulmonary trunk
Smooth part of right ventricle
( cornus arteriosus)
Bulbus cordis (B)
Smooth part of left ventricle
(aortic vestibule)
Primitive ventricle(PV)
Trabeculated part of right ventricle
Trabeculated part of left ventricle
• Primitive atrium(PA)
Trabeculated part of right atrium
Trabeculated part of left atrium
Smooth part of right atrium
Sinus venosus
Coronary sinus
Oblique vein of left atrium
• 2. Formation of the Cardiac Septa
• The Atrioventricular (AV) septum
• Atrial septum
• Interventricular septum
• Aorticopulmonary septum
• SEPTUM FORMATION IN THE
ATRIOVENTRICULAR CANAL:
• The Atrioventricular (AV) septum divides
the AV canal into the right AV canal and left
AV canal.
• Formation: The dorsal and ventral AV
cushion fuse to form the AV septum.
• Clinical correlations:
Unventricular heart
Tricuspid atresia
Inferior and superior
• SEPTUM FORMATION IN THE COMMON
ATRIUM
Formation:
(A)At the end of the fourth week, a sickleshaped crest grows from the roof of the
common atrium into the lumen. This crest is
the first portion of the septum primum.
The two limbs of this septum extend toward
the endocardial cushions in the
atrioventricular canal.
The opening between the lower rim of the
septum primum and the endocardial
cushions is the ostium primum. It is
obliterated (closed)when the septum primun
fused with the AV septum.
(c ) Before closure is complete, however,
cell death produces perforations in the upper
portion of the septum primum. Coalescence
of these perforations forms the ostium
secundum, ensuring free blood flow from
the right to the left primitive atrium.
(D) At the beginning of fifth week,a new
crescent-shaped fold appears in the right of the
septum primum . This new fold, the septum
secundum, never forms a complete partition in
the atrial cavity. Its anterior limb extends
downward to the septum in the atrioventricular
canal.
(E) The opening left by the septum secundum
is called the oval foramen (foramen ovale),
the remaining part of the septum primum
( the upper part of the septum primum
gradually disappears) becomes the valve of
the oval foramen.
It is a valvular aperture that allows blood to
flow from right to left, but not from left to
right.
After birth, when lung circulation begins
and pressure in the left atrium increases, the
valve of the oval foramen is pressed against
the septum secundum, obliterating the oval
foramen and separating the right and left
atria.
• Clinical correlations: Heart defects involving
the atrial septum are called atrial septum
defects(ASDs)
• (1) Foramen secundum defect is caused by
excessive resorption of the septum of the
septum primum, septum secundum,or both.
• (2)Premature closure of foramen ovale is
the closure of the foramen ovale during
prenatal life. This results is hypertrophy of
the right side of the heart and
underdevelopment of the left side.
• SEPTUM FORMATION IN THE
VENTRICLES
• Formation:
• (1) The muscular interventricular septum
develops in the floor of the ventricle it
grows toward the AV cushions but stops
short leaving the interventricle foramen.
• (2)The membranous IV septum forms by
the fusion of three components: the right
bulbar ridge,left bulbar ridge, and AV
cushions. This fusion closes the IV foramen.
• CLINICAL CORRELATES
Ventricular septal defect (VSD) involving
the membranous portion of the septum is the
most common congenital cardiac
malformation, occurring as an isolated
condition in l2/10,000 births.
SEPTUM FORMATION IN THE TRUNCUS
ARTERIOSUS AND CONUS CORDIS
Aortucopulmonary (AP) septum: The AP
septum divides the truncus arteriosus into
the aorta and pulmonary trunk.
(1)Formation: Pairs of opposing ridges, in the
the truncal and bulbar ridges which grow in
a spiral fashion and fuse to form the AP
septum. (not straight )
Left truncus ridge
Right truncus ridge
Left bulbar ridge
• Clinical corralations:
(1)Persistent truncus arteriosus
(2) D-Transposition of the great vessels
(complete):
(3)Tetralogy of Fallot,
Four cardiovascular alterations:
(a) a narrow right ventricle outflow region, a
pulmonary infundibular stenosis
(b)a large defect of the ventricular septum
(c) an overriding aorta that arises directly
above the septal defect.
(d) hypertrophy of the right ventricular wall
because of higher Pressure on the right side
Aortic arches
•
•
•
•
I
disappeared
II:
III: the carotid arteries
IV:right----subclavian artery
left -----the arch of the aorta
• V: disappeared
• VI :pulmonary artery,( the left is connected
to the aorta through the ductus arteriosus
during the fetal life)
• Circulation Before and After Birth:
• Fetal Circulation:
The circulation in the fetus is essentially the
same as in the adult except for the following:
(1) The source of oxygenated blood is not the
lung but the placenta
(2)Oxygenated blood from the placenta comes
to the fetus through the umbilical vein,
which joins the left branch of the portal vein.
• the greater part of this blood passes direct to
the inferior vena cava through the ductus
venosus.
• (3)Most of the blood in the right atrium
flow into the left atrium through the
foramen ovale
• (4) Only a small portion of the pulmonary
trunk reaches the lungs, the greater part is
short-circulation by the ductus arteriosus
into the aorta.
• Changes in the circulation at Birth:
(1)Closure of the umbilical arteries
(2) Closure of the lumen of the umbilical
veins and the ductus venosus
(3) Closure of the ductus arteriosus, so that
all blood from the right ventricle now goes to
the lungs.
(4)The valve of the foramen ovale is occluded.
• The vessels that are occluded soon after birth
are, in due course, replaced by fibrous tissue,
and form the following ligaments:
• Vessels
Remant
Umbilical arteries Medial umblical ligaments
Left umbilical vein ligamentum teres of the liver
Ductus venosus
ligamentum venosum
Ductus arteriosus
ligmentum arteriosum