Download Extraembryonic blood vessels form during the early

Cardiovascular Development:
1. Development of the Heart
2. Development of the Vasculature
Pamela Knapp, Ph.D.
Professor, Dept. Anatomy & Neurobiology
MSB1 - Rm. 411
6-7570
[email protected]
Extraembryonic blood vessels form during the early 3rd week
A.
B.
C.
Yolk sac blood islands
D.
Yolk Sac
Longitudinal (head) folding moves the developing heart
region in a ventral direction
Transverse folding brings the right and left endocardial
heart tubes into apposition, allowing them to fuse
~ beginning 4th week
Schematic showing relationship of parts of
primitive heart tube, aortic arches and aortae in a
mid-4th week embryo
Note the 3 pairs of veins (vitelline, umbilical and
cardinal) which empty intothe inflow end of the
heart (sinus venosus). The aortic arches and
dorsal aortae are paired structures.
BLOOD FLOW THROUGH THE PRIMITIVE HEART
•Blood enters the caudal end of the tube, the sinus venosus.
•From the sinus venosus, blood flows cranially into the primitive atrium.
•From the atrium, blood enters the primitive ventricle.
•From the ventricle, blood is pumped to the bulbus cordis and then to the truncus arteriosus.
•The truncus is continuous cranially with the expanded aortic sac, from which arise the aortic
arches. Blood flows from the aortic arches into the dorsal aortae.
Developing heart undergoes characteristic folding, because it
is fixed in position at both ends while it elongates/grows
(Posterior /dorsal
view)
B-v
sulcus
LEFT
RIGHT
RIGHT
LEFT
LEFT
RIGHT
(dorsal view)
LEFT
RIGHT
(Posterior /dorsal
view)
(Posterior /dorsal
view)
Primitive atrium forms portions
of both adult atria
-adult rt atrium also contains
the rt horn of the sinus venosus
-adult left atrium also contains
exstrophied portions of the
primitive pulmonary veins.
Conus
Cordis
LEFT
RIGHT
LEFT
RIGHT
Exstrophy of the primitive pulmonary vein
-Left auricle is rough/trabeculated
-Rest of wall of the left atrium is smoother
What is happening to the heart cavities internally?
Heart is still a tube!
-Note opening between ventricles
(interventricular foramen)
-Note opening between ventricle and atrium
(atrio-ventricular foramen)
-Can’t see the foramen between the atria in
these views … but it is there.
Partitioning the Primitive Heart: 4 walls
(1)
(2)
(3)
(4)
separate atria from ventricles
Separate right and left atria
Separate right and left ventricles
Pulmonary trunk from ascending aorta
(1) Formation of the atrio-ventricular canals
A
A
V
V
(2) Formation of the atrial septum
-2 phases: partial septum formed before birth is completed at/after birth
B.
A.
Muscular
interventricular
septum
The septum primum and secundum
together make the inter-atrial septum.
Prior to birth the pathway/opening between
them is the foramen ovale. It allows
blood flow between the atria before birth
(mostly right-to-left)
After birth, higher left side pressure closes
the foramen by pushing the septum
primum against the septum secundum.
Atrial Septal Defects
Congenital anomalies of the heart and great vessels are overall relatively
common (6-8 per thousand live births).
-multiple causes - teratogens, environmental, genetic
-isolated vs. grouped (ex. Tetralogy of Fallot)
-may be well tolerated during fetal life
1. Patent foramen ovale - most common ASD
-probe patent (25% of population) vs. fully patent
-may be clinically insignificant
-right to left shunt possible with other complications
2. Secundum ASDs - abnormally short septum secundum, or one with
fenestrations.
-left to right shunt under normal pressure conditions
3. Cor trioculare biventriculare - failure of interatrial septum formation.
3 heart chambers - 2 ventricles, 1 big atrium.
4. Premature closure of foramen ovale - usually results in heart muscle
hypertrophy.
(3) Formation of the ventricular septum
-2 parts: muscular & membranous
Muscle cells in wall of bulbus cordis (rt v) and
primitive ventricle (left v) proliferate and
muscular septum increases in height.
Approaches, but does not fuse with, endocardial
cushions.
Ridges of tissue growing out of the wall of the
conus cordis (bulbar or conotruncal ridges) are
referred to as the “membranous” component of
the interventricular septum.
They meet and fuse with the muscular septum
AND with the endocardial cushions to complete
the IVS.
Open communication between the 2 ventricules until the end of the 7th week through the
interventricular foramen.
Formen is closed by development of the membranous portion of the septum.
Tissue of membranous septum: right and left conotruncal/bulbotruncal ridges & endocardial
cushions
Tissue of the muscular septum: floor of the ventricle/muscular interventricular septum
Ventricular Septal Defects
-25% of all heart malformations are VSDs
-can be membranous (common) or muscular (rare) in origin
-With normal vascular pressure, always involve a
left-to-right shunt of blood.
-Large left-to-right shunts cause pulmonary
hypertension.
-Uncorrected VSDs can lead to death from
congenstive heart failure.
-Small defects can close spontaneously.
(4) Formation of the aortico-pulmonary septum (partitioning bulbus cordis
and truncus arteriosus)
Without partitoning, there would be only 1 outflow path from the 2 ventricle.
Development of the aorticopulmonary septum creates 2 outflow paths, the aorta and the
pulmonary trunk, one from each ventricle.
Development is timed to coincide with the closure of the interventricular septum.
Thus, and fortunately, at the time that there are 2 completely separate ventricles, there are
also 2 completely separate outflow pathways!
The aorticopulmonary septum forms a spiral, due to the position of the initial outgrowth of the
swellings at successive levels.
Instead of simply growing towards out towards each other from the same position all the way
up to the aortic sac, the outgrowth region of the ridges spirals along opposite sides of the
truncus.
- When the free edges of each ridge unite in the center of the truncus lumen, they form a spiraling
wall, the septum.
- A split develops in the medial plane of the septum, resulting in complete separation of the ascending
aorta and pulmonary trunk with the pulmonary trunk twisting around the ascending aorta.
Anomalies of the great vessels
Persistant truncus arteriosus
-Failure of TA to divide along part/entire length.
-Due to failure of conotruncal ridges to develop properly.
-Pulmonary arteries and aorta may arise from common
artery, or from the TA. Sometimes they are absent and
bronchial arteries are only blood supply to the lungs
Transposition of the Great Arteries/Vessels (TGA)
-Most common cause of cyanotic disease in newborn.
-Aorticopulmonary septum growns straight instead of
spiraling.
-Aorta arises from right ventricle and pulmonary trunk
arises from left ventricle…thus 2 circulations.
-MAY involve VSD.
-Not immediately fatal due to mixing of blood through foramen
ovale and ductus arteriosus.
Overriding aorta or pulmonary trunk
-Unequal TA division results in one great artery being
larger than the other. Misplaced aorticopulmonary septum
misaligns with intraventricular septum, causing VSD.
Larger artery sits over (overrides) VSD.
d. Tetralogy of Fallot
-Group of 4 cardiac defect occurring together, driven by
misplaced aorticopulmonary septum (overriding aorta),
which causes VSD, stenosis in the outflow region of the
right ventricle (pulmonary stenosis), and pulmonary
hypertension.