UNSW Embryology
Cardiovascular System Development- Stage 13/14
© Dr Mark Hill (2008)
Introduction
In this class we will follow the path of oxygenated blood through the embryo then look at the passage of venous blood through the cardinal veins.
At this stage of development the embryo trunk consists mainly of heart, liver and embryonic kidney.
Use the list on the right or Next Page above to go through specific aspect of blood flow through the embryo. Each image is an
excerpt from the complete st13/14 Pig embryo and should also be looked at in the entire slice, to see the relationship of vasculature with other developing systems. Alternatively you can work
through the text list of Stage 13/14 Pig sections.
Page Links: Introduction | Stage 13/14 Pages |
Blood flow through the Embryo | Ventricles to Aortic System |
Caudal Path of Arterial Blood | Venous Inflow to Heart |
Cardinal Veins | Cardinal Veins | Timecourse | Serial Section table (Stage 13/14) |
Stage 13/14 Cardiovascular 3D Model
The individual serial slices have also been incorporated into a 3D model of this embryo Cardiovasular System.
Stage 13/14 Pages
In addition to the pathway text listings below, are individual pages with cross-section excerpts covering the following blood pathways:
Blood flow through the Embryo
G7
An overview of blood flow through the embryo of
oxygenated blood. Note the umbilical artery and
veins anastomose within the chorion of the
placenta, there is no direct connection of maternal
and foetal blood.
Maternal Blood
umbilical vein
liver
anastomosis
ductus venosus
sinus venosus
atria ventricles
truncus arteriosus
aortic sac
aortic arches
dorsal aorta
pair of umbilical arteries
Maternal Blood
Ventricles into Aortic System
Follow the high pressure pathway from the
ventricles into the aortic system. Start from the cardiac apex on D7 and check that no heart
structure is seen below this level in E1. (More? ventricles into the aortic system)
- D7:
Apex of left ventricle: spongy network of
endocardium; a small dorsal cavity (part of the
intra-embryonic (I-E) coelom which will become
the pericardial cavity - no pericardium yet);
mesenchymal jelly of body wall.
- D6,D5:
Tip of right ventricle; left ventricle; I-E
coelom; liver, with its ventral transverse
border, the septum transversum.
- D2:
Trabeculae of L and R ventricles;
interventricular septum; interembryonic coelom;
sinus venosus caudal tip of part of left atrium
= L auricular appendage.
- Dl:
R auricular appendage. Endocardial jelly at
dorsal wall of interventricular septum.
- C7:
Ventricles; incomplete interventricular septum;
dorsal endocardial jelly; communication of l
auricle and L atrium; R atrium; R auricle.
- C6:
Aperture in interatrial septum, the ostium
(foramen) primum. L and R atrioventricular
canals.
- C5:
Communication of L auricle with left
atrium.
- C4:
Transition from R ventricle to the outflow
tract, including the truncus arteriosus complete
interatrial septum (cf. C5).
- C3:
Truncus arteriosus. Atria. Right venous valve in
R atrium.
- C7-C3:
Return to C7 and proceed to C3, noting how left
ventricular blood has to pass obliquely across
right ventricle to exit from heart via the
outflow tract and truncus arteriosus.
- C2,
C1 Truncus arteriosus shifting to
midline. Jelly and mantle of the truncus.
Cranial end of R venous valve. Note also extent
of I-E coelom; thin body wall.
- B7-B5:
Attachment of truncus to ventral body wall and
to dorsal roof of intra embryonic coelom. Note
the anlage of the transverse pericardial sinus
in B6, caudal to the attachment of the
truncus.
- B5-B4:
Entry of truncus arteriosus into aortic sac,
completely embedded in pharyngeal arch
mesectoderm. Note position of aortic sac in
relation to pharynx and pharyngeal arches. 4th
pharyngeal arch artery on left. Return to B5 and
note the small "6th" pharyngeal arch artery
either side of the laterally-compressed
pharynx.
- B3:
Cranial end of aortic sac. 4th pharyngeal arch
arteries and emerging 3rd pharyngeal arch
artery. Note dark thyroid primordium ventral to
origin of 3rd arch arteries.
- B2:
(lst and 2nd pharyngeal arch arteries not seen.
3rd arch arteries. Bilaterally, communication of
4th arch artery (at sides of pharynx) with
dorsal aorta.
- B1:
3rd arch arteries. Dorsal aortae. (Superior
cardinal veins lateral to aortae).
- A7:
On left side, communication of 3rd arch artery
with aorta (i.e. occurring cranial to the 4th
arch communication). From here on the arterial
blood is distributed through fine branches to
vessels outside the brain (pial plexus).
Caudal path of the Arterial Blood
Follow the caudal path of the arterial
blood Noting the position of the dorsal aortae, go
back down the embryo from A7 to D3. (More? caudal path of the arterial blood)
- D3:
Tiny dorsal branches of paired dorsal aortae.
(Inferior cardinal veins lateral to aortae, also
with small dorsal branches). move to D6.
- D6:
Dorsal aortae close together.
- D7,E1:
Fusion of dorsal aortae into a midline
vessel.
- E2,E6:
Dorsal branches of single dorsal aorta.
- F5:
Dorsal aorta giving rise to a ventral branch
(mesenteric artery), and branch to mesonephros
(the developing kidney).
- F7:
Dorsal aorta sending branch into mesonephros (to
glomerulus).
- G2,G3:
Dorsal aorta curving around flexed trunk of
embryo. Note spinal cord cut twice.
- G4,G5:
Sections gradually passing dorsally beyond
curvature of single dorsal aorta.
- Return to G4. We now will follow the aorta
in the lumbar region of the embryo as it passes
into the sacral region.
- G2,G1:
Single dorsal aorta ventral to sacral (smaller)
spinal cord.
- F7-E7:
Bifurcation into paired dorsal aortae.
- E6,E5:
Lateral major branch of dorsal aorta becomes
umbilical artery: it reaches a crest in E5 (i.e.
not seen in E4) and then "descends" in the
ventral body wall to F2, where it enters the
body stalk. We will follow this complex twisting
again when we study the development of the
hindgut.
Venous Inflow to the Heart
Follow the umbilical and vitelline (yolk sac) venous inflow to the heart.
Start with F6. (More? venous inflow to the heart)
- F6:
Oblique section through both umbilical veins in
body wall. Follow them to E6.
- E6-E4:
Both umbilical veins with a large vitelline vein
in the central, mesenteric region.
- E1,D7:
Umbilical veins enter liver, along with
vitelline. Most venous blood drains through the
liver region into the sinus venosus, which
nestles in the cranial surface of the growing
liver. This is the site of the caudal attachment
of the free heart to the body mesenchyme.
- D3,D2:
Entry of venous blood into sinus venosus. Note
smaller left horn of sinus
- venosus, and location of sinus venosus
caudal to atria.
- D1-C7:
Drainage of right horn of sinus venosus into
right atrium.
- We now trace the low pressure pathway of the
embryo's venous blood.
- B1:
Identify the large veins lateral to dorsal
aortae - these are the superior or anterior
cardinal veins which drain the head region. Now
go directly to D6.
- D6:
Identify the large veins lateral to dorsal
aortae - these are the inferior or posterior
cardinal veins which drain the lower part of the
embryo.
Cardinal Veins
Follow alternately, the course of the
superior cardinal veins caudally, and the course of
the inferior cardinal veins cranially until they
emerge about Dl -C5 into the common cardinal
veins. (More? embryo's venous blood)
- C7:
Left common cardinal entering sinus
venosus.
- C5:
Right common cardinal entering sinus
venosus.
- Finally examine the atria in more detail.
Note there is only one interatrial septum, the
septum primum with its ostium primum. Note in
C4, the attachment of septum primum to the most
cranial of the endocardial cushions.
Timecourse
- forms in mesenchyme of precordal plate
region
- cardiogenic region
- growth and folding of the embryo moves
heart ventrallly and downward into anatomical
position
- week 3 begins as paired heart tubes
- fuse to form single heart tube
- begins to beat in Humans- day 22-23
- heart tube connects to blood vessels
forming in
- splanchnic mesoderm
- extraembryonic mesoderm
Week 2 pair of thin-walled tubes
Week 3 tubes fused, truncus arteriosus
outflow, heart contracting
Week 4 heart tube continues to elongate,
curving to form S shape
Week 5 Septation starts, atrial and
ventricular
Septation continues, atrial septa remains
Serial Section table (Stage 13/14)
UNSW Embryology ISBN: 978 0 7334 2609 4
UNSW CRICOS Provider Code No. 00098G
Comments
In human embryos the heart begins to beat at about 22-23 days, with blood flow beginning in the 4th week.
See also the 3D reconstruction of these slices 3D Cardiovasular
The heart is therefore one of the earliest differentiating and functioning organs. Most texts will separate heart development from vascular development in order to simplify
their descriptions of cardiovascular development, though the 2 are functionally and embryologically connected.
The heart develops from cardiogenic mesoderm that
originally lies above the cranial end of
the developing neural tube. Enlargement of
the cranial neural fold brings this region
ventrally to its correct anatomical
position. The original paired cardiac
tubes fuse, with the "ventricular"
primordia initially lying above the
"atria". Growth of the cardiac tube flexes
it into an "S-shape" tube, rotating the
"ventricles" downward and pushing the
"atria" upward. This is then followed by
septation, a complex process which
converts this simple tube into a four
chambered heart. A key part of this
process is the separation of cardiac
outflow (truncus arteriosus) into a
separate pulmonary and aortic arch
outflow. During embryonic development
there is extensive remodelling of the
initially r/l symetrical cardiovascular
system and a contribution from the neural
crest to some vessels.
Please email Dr Mark Hill if you wish to make a comment about this current project.
