Download Development of the heart 1

Development of the heart 1
Objectives:
Understand early development of blood vessels.
Basic understanding of the early stages of heart
development.
Describe the formation and position of the heart
tube.
Discus the development of sinus venosus.
Describe partioning by septa and chambers
formation.
Discus congenital malformations.
Gain knowledge of fetal circulation.
THE CARDIOVASCULAR SYSTEM
The cardiovascular system is the first
functional system; blood begins to
circulate by the end of the third
week of development.
Blood vessels:
Mesenchymal cells of the splanchnic
mesoderm group together to form
blood islands (angiogenic clusters).The
clusters develop a lumen.The cells on
the periphery become endothelium; the
cells in the middle become blood
cellsThe clusters spread toward one
another and fuse to form the vessels.
Heart Formation:
The cardiogenic area develops
cranial to the oropharyngeal
membrane during the third week of
development; the cranial folding of
the embryo pushes the
cardiogenic area caudally. This
area (one on each side) develops
into the endocardial heart tubes.
As the embryo folds, the
endocardial heart tubes
approach each other and fuse
to form a single endocardial
tube.Differential growth in the
heart tube causes the heart to
bend.
Blood flow thourgh the primitive
heart:
Common cardinal viens, umbilical
veins and vitelline veins drain into
the sinus venosus--> atrium ->atrioventricular canal--> venricle-> bulbus cordis--> truncus
arteriosus--> aortic sac--> aortic
arches--> dorsal aortae.
Looping of heart tube (Days 2328): The primitive atrium loops
up behind and above the
primitive ventricle and behind
and to the left of the bulbus
cordis.
As the heart is bending and
enlarging, the internal partitioning
of the original single chamber is
occurring; this partitioning is
occuring simultaneously in the
atrium and the ventricle during
days 27-37.The atrioventricular
partition produces one atrium and
one ventricle.
The endocardial cushions (which
contain neural crest cells)
approach each other and fuse,
leaving an opening on each side
which
is the site where the
atrioventricular valves develop
(tricuspid and bicuspid).The atrial
septum divides the primitive
atrium into two atria.
The septum primum:
Grows toward the developing
endocardial cushions from the
superior part of the atrium.The
space between the inferior flap
of the septum primum and the
endocardial cushions is the
foramen primum.
The foramen primum is a space
that is gradually getting smaller
as the septum primum extends
downward.Eventually the
foramen primum is obliterated
BUT by the time it is
obliterated, a second foramen
has appeared in the upper part
of the septum primum .
This second foramen is the
foramen secundum; thus, the
flow of blood from the right
atrium into the left atrium is
maintained. This is one of the
mechanisms to bypass the
non-functional fetal lungs.Both
the foramen primum and the
foramen secundum are in the
septum primum.
The septum secundum:
This is a second flap that develops
and grows downward from the
atrium toward the ventricle and
upward from the ventricle to the
atrium (there are two segments to
this septum); it is located just to
the right of the septum
primum.The two segments of the
septum secundum do NOT fuse
together.
The septum secundum overlaps the
foramen secundum in the septum
primum, forming an incomplete
partition, the foramen ovale. Most of
the atrial septum is formed by the
septum primum.The interventricular
septum grows from the bottom of the
ventricle and fuses with the
downgrowing part of the endocardial
cushion.The bottom part = the
muscular part of the septum. The top
part = membraneous part of septum.
Right atrium:
As the heart continues to grow, the right
side of the sinus venosus is
incorporated into the right side of the
primitive atrium. The primitive atrial wall
is pushed ventrally, eventually becoming
the right auricle. In the adult heart, the
right auricle contains pectinate muscle
derived from the primitive atrium,
whereas the sinus venarum is derived
from the sinus venosus and therefore
smooth-walled.
Left atrium:
The left side of the primitive atrium
sprouts a pulmonary vein which
branches and sends two veins toward
each of the developing lungs. The trunk
of this pulmonary vein is incorporated
into the left side of the primitive atrium,
forming the smooth wall of the adult left
atrium. The left side of the primitive
atrium is pushed forward and eventually
becomes the trabeculated left auricle.
What embryonic structures are incorporated into the
adult right atrium?
Thank You