Development of the heart tube and fetal circulation

Dr. Mohamed El fiky

1. Development of heart tube and fetal
circulation
Dr. Mohamed El fiky
Professor of anatomy and embryology

3. Embryonic disc

4. qAppears in the middle of third week.
qMesenchymal cells in the splanchnic mesoderm proliferate and form
isolated cell clusters known as angiogenicclusters.
qAngiogenicclusters at first located in the lateral end but rapidly spread
to cephalic end.
Angiogenic clusters.

6. qThe angiogenicclusters acquire lumen.
qThey unite to form a horseshoe-shaped plexus of small blood vessels.
qThe anterior portion of the plexus is called cardiogenic area.
qThe intraembryonic coleomiccavity located over the plexus later form
pericardial cavity.
Formation of endocardial heart tubes

7. qAfter formation of neural tube and brain vesicles CNS grows rapidly in
cephalic direction.
qIt finally extends over the cardiogenic area and future pericardial cavity.
qFinally,theprocordalplate and the cardiogenic plate are pulled forward.
qThe cardiogenic plate and pericardial cavity become located ventrally and
caudally.

8. 1. Epimyocardial cells
2. Heart tube
3. Endoderm
4. Endocardial cells
5. Notochord
6. Dorsal aorta
7. Neural crest
8. Neural fold
1. Foregut
2. Intraembryonic
coelom
3. Heart tubes
4. Dorsal mesocardium
5. Epimyocardium
6. Neural groove
7. Neural crest
8. Notochord
9. Dorsal aorta
Heart tubes
Fusion of the heart tubes

9. Embryo after folding
Head swelling
Cardiac swelling
Umbilical cord
Y.S
G
U
T

10. qThe embryo folds in cephalocaudalandtransversely bringing the two
heart tubes closer.
qThe two endocardial heart tube fuse in cephalo-caudal direction.
qThe tube is attached to the dorsal side of the pericardial cavity by dorsal
mesocardium.

11. qThe mesoderm adjacent to the endocardial tube form epimyocardialmantle.
qThe epimyocardialmantle seperatedfrom endocardial tube by cardiac jelly.
qTube consists of endocardium,myocardiumand epicardium.

12. Development of primitive heart tube
ØIt develops early in the middle of 3
rd
week , from aggregation of
splanchnic mesodermal cells, in cardiogenic area.
ØThey form 2 angioblasticcordsthat canalizeto form
2 endocardial heart tubes.
ØThe embryo folds in cephalocaudaland
transversely bringing the two heart tubes closer.
ØThe two endocardial heart tube fuse in cephalo-
caudal direction.
ØThe tube is attached to the dorsal side of the
pericardial cavity by dorsal mesocardium.

13. ØAfter lateral folding ofembryo,2 endocard.tubes fuse to form….
Single hearttube
ØThis heart tube lies inside the pericardial cavity , its dorsal wall is
connected to foregut by dorsal mesocardium
ØThe central part of dorsal mesocardium degenerates ,forming
transverse passage dorsal to heart ,called transverse sinus of
pericardium,

14. ØThe primitive heart tubeelongates and develops alternate
dilatations and constrictions :
Ø1-truncus arteriosus.
Ø2-bulbus cordis.
Ø3-primitive ventricle.
Ø4-primitive atrium.
Ø5-sinus venosus.
ØTruncus arteriosusis continouscranially with aortic sac,from which
aortic arches develop.
ØSinus venosushas right & left hornes.
ØEach horn receives umbilical, vitelline,& common
cardinal veins .

15. Main subdivisions of heart tube
ØBulbus cordis&ventriclegrow fasterthan other regions, so the heart
bends upon itself,forming U-shaped bulboventricular loop.
ØThe atrium & sinusvenosus also come to lie dorsal totruncus arteriosus,
bulbus cordis & ventricle .(S-shaped heart tube).

16. Formation of cardiac loop
qHeart tube elongates and bends.
qThe cehpalicportion: bends in ventral and caudal direction to the right.
qThe caudal portion: shifts in a dorsocranialdirection and to the left.The
bendingscreates a cardiac loop.

17. Primitive heart tube Twists

18. qLocal expansion become visible after cardiac
loop is formed.
qThe atrial portion lie outside the pericardial
cavity,
qlater incorporated inside the cavity.
qThe atrioventricular junction remains narrow
and form atrioventricular canal.
qThe bulbuscordisis narrow except its proximal
third which later forms trabeculatedpart of right
ventricle.
qThe distal part of bulbuscalled the truncus
arteriosus.
qThe conus cordisforms the outflow tract of
both ventricles.

19. qThe atrial portion of bulbusremain temporarily smooth walled.
qThe proximal portion of the bulbusform the primitive right ventricle.
qThe primitive ventricle becomes trabeculatedand form the primitive left
ventricle.

20. Development of sinus venosus
qIn 4
th
week,it consists of a
transverse portion and right and left
sinus horn.
qEach horn receives blood from three
important veins: -.
a.Vitelline or omphalomesenteric
veins.
b.The umbilical vein.
c.Common cardinal vein.
qAt 5
th
and 7
th
week the left umbilical vein and Left vitelline vein disappear.
qThe left common cardinal vein disappear at 10
th
week.
qThe remaining part in the left horn of sinus venosusis
a.The oblique vein of left atrium.
b.The coronary sinus.
qDue to left to right shunt the right sinus horn and veins enlarge.
qThe right horn is the only communication between sinus venosusand the
atrium.
qThe right horn is incorporated into right atrium to form the smooth part of right
atrium

21. qThe entrance the sinoatrial orifice is flanked n each side by right and
left venous valves.
qDorsocranially , the valves fuse , forming a ridge known as septum
spurium
qThe superior portion of right venous valve disappear.
qThe inferior part form two parts:
a.The valve of inferior vena cava.
b. The valve of coronary sinus.
qThe crista terminalis originates from right sinus horn.

22. Dividing of A-V canal , primitive atrium & primitive ventricle….. Beginsat the middle
or end of 4
th
week. It is completedby the end of 5
th
week.
Endocardial cushions: these are masses of cells and extracellular matrices
develop in the atrioventricular and conotruncal regions .
• in the atrioventricularregion they are :
–Dorsal & ventral swellings
–Fuse, dividing the single AV canal into paired canals
–Involved in formation of interatrial & interventricular septa
–Derived from neural crest
Partitioning

23. •At the end of the fourth week, a sickle-
shaped 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
Septum formation in the common atrium

24. With further development,
extensions of the superior and
inferior endocardial cushions
grow along the edge of the
septum primum, closing the
ostium primum Before closure
is complete, however, cell
death produces perforations in
the upper portion of the
septum primum. Coalescence
of these per-forations forms
the ostium secundum,
ensuring free blood flow from
the right to the left primitive
atrium,D).

25. When the lumen of the right atrium expands as a result of incorporation of the sinus horn, a
new crescent-shaped fold appears. 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 atrioventricu-lar canal. When the left venous valve and the septum spurium fuse with the
right side of the septum secundum, the free concave edge of the septum secundum begins to
overlap the ostium secundum.The opening left by the septum secundum is called the oval
foramen (foramen ovale).

26. When the upper part of the septum primum gradually disappears, the remaining
part becomes the valve of the oval foramen. The passage between the two atrial
cavities consists of an obliquely elongated cleft through which blood from the
right atrium flows to the left side.
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. In about
20% of cases, fusion of the septum primum and septum secundum is incomplete,
and a narrow oblique cleft remains between the two atria.This condition is called
probe patency of the oval foramen; it does not allow intracardiac shunting of
blood.

27. Fetus
• right side high pressure (high
pulmonary resistance, etc.)
• well oxygenated blood streams
through foramen ovale.
• valve of foramen ovale closes with left
atrial contraction.
After birth
• right side low pressure (low
pulmonary resistance).
• valve remains closed (physiological
closure).
• valve eventually fuses (anatomical
closure): fossa ovalis.

28. •By the end of the fourth week, the two primitive ventricles begin to expand. This is
accomplished by continuous growth of the myocardium on the outside and continuous
diverticulation and trabecula formation on the inside .
•The medial walls of the expanding ventricles become apposed and gradually merge,
forming the muscular interventricular septum .Sometimes, the two walls do not merge
completely, and a more or less deep apical cleft between the two ventricles appears.
The space between the free rim of the muscular ventricular septum and the fused
endocardial cushions permits communication between the two ventricles.
•The interventricular foramen, above the muscular portion of the interventricular
septum, shrinks on completion of the conus septum .During further development, out-
growth of tissue from the anterior (inferior) endocardial cushion along the top of the
muscular interventricular septum closes the foramen .This tissue fuses with the abut-
ting parts of the conus septum. Complete closure of the interventricular foramen
forms the membranous part of the interventricular septum
Septum Formation in the Ventricles

30. • Continuous set of ridges in bulbus cordis(bulbar ridges) and
truncus arteriosus (truncal ridges).
• Grow toward each other, spiraling 180º.
Partitioning of Truncus Arteriosus

31. • Fuse to form spiraling aorticopulmonaryseptum, dividing aorta
& pulmonary trunk
• Bulbar ridges involved in formation of IV septum
• Bulbar & truncal ridges derived from neural crest cells—
clinical implications
Partitioning of Truncus Arteriosus

32. 1. Placenta plays the role of lungs; lungs are not functional:
•Like pulmonary veins, left umbilical vein carries highly oxygenated
blood from placenta to heart.
•Like pulmonary artery, right and left umbilical arteries braing
deoxygenated blood to placenta.
2. Mixing potentially occurs at 4 sites:
•Left umbilical vein (Oxygen saturation ~80%) –Portal vein
(Much bypassed by ductus venosusto Inferior Venacava)
•Left umbilical vein –Inferior venacava–Portal vein (Oxygen
saturation of IVC blood is ~65%)
•Superior venacava–Right atrium (Much bypassed by Foramen
ovale)
•Pulmonary veins –Left atrium (Much bypassed by Foramen ovale
and ductus arteriosus)
Following are the important features of fetal circulation

33. Placenta
Umbilical vein
Portal vein
Inferior vena cava
Right atrium
Left Atrium
Left ventricle
Aorta
Whole body tissue
Fetal circulation
(oxygenated)

34. Superior & inferior vena cava
Right atrium
Right ventricle
Pulmonary trunk
Arch of Aorta
Descending aorta
Common and internal iliac
2 Umbilical arteries
Placenta
Fetal circulation
(Deoxygenated)

35. PATHWAY
Placenta
Umbilical Vein
Umbilical Arteries
Liver
Ductus Venosus
Inferior Venacava
Right Atrium
Foramen Ovale
Right Lung
Arch of Aoarta
Ductus Arteriosus
Left Atrium
Left Ventricle
Right Ventricle
Portal Vein

36. Overview of Fetal Circulation
1.Blood is oxygenated in the placenta.
2.Highly oxygenated and nutrient-enriched blood returns to the fetus from the
placentavia the left umbilical vein.
3.Some blood enters liver sinusoids; most of the blood bypasses the sinusoids by
passing through the ductusvenosusand enters the inferior vena cava (IVC)
4.From the IVC, blood enters the rightatrium, where most of the blood bypasses the
right ventricle through the foramenovaleto enter the left atrium.
5.From the left atrium, blood enters the left ventricle andis delivered to fetal tissues
via the aorta.
6.Poorly oxygenated and nutrient-poor fetal blood is sent back to the placenta via
rightand left umbilical arteries.
7.Some blood in the right atrium enters the right ventricle; blood in the right
ventricleenters the pulmonary trunk, but most of the blood bypasses the lungs
through theductus arteriosus.

37. Fetal circulation

38. Circulatory Changes at Birth
Changes in the vascular system at birth are
caused by cessation of placental blood flow
and the beginning of respiration. :
1-Closure of the umbilical arteries Distal
parts of the umbilical arteries form the medial
umbilical ligaments, and the proximal portions
remain open as the superior vesical arteries
2-Closure of the umbilical vein and ductus
venosus , the umbilical vein forms the
ligamentum teres hepatis and The ductus
venosus forms the ligamentum venosum.
3-Closure of the ductus arteriosus : forms
the ligamentum arteriosum.
4-Closure of the oval foramen : forms fossa
ovale

39. Congenital anomalies of the heart
1-Defects of the atrial septum:
a)Patent foramen ovale (ASD):
b)Is caused by incomplete anatomic fusion of septum primum and septum secudum.
Present in approximately 25% of people.
c)Foramen secundum defect : is caused by excessive resorption of septum primum
or septum secundum. This results in a large opening between the right and left atria.
d)Common atrium : caused by complete failure of septum primum and septum
secundum to develop.
e)Premature closure of foramen oval:closure of foramen ovale during pre-natal life.
This results in hypertrophy of the right side of the heart and under-development of the
left side of the heart.

40. Congenital anomalies of the heart
•2-Defects of atrio-ventricular canal :
a)Persistent AV canal:caused by failure of AV cushions to fuse, accompanied
by abnormal tricuspid and bicuspid valves.
b)Tricuspid atresia:Obliteration of the right AV canal, characterized by absence
of the tricuspid valve and accompanied by the following :
–1) Patent foramen ovale.
–2) I.V. septal defect.
–3) Over-developed left ventricle.
–4) Under-developed right ventricle.

41. Congenital anomalies of the heart
3. Defects of I.V. septum (VSD):
a)Membranous VSD:caused by failure of the membranous I.V. septum to
develope.
b)Muscular VSD:caused by single or multiple perforations in the muscular I.V.
septum.
c)Common ventricle:caused by failure of the membranous and muscular I.V.
septa to develope.

42. Congenital anomalies of the heart
4, Defects of the aortico-pulmonary septum:
a)Persistent truncus arteriosus:This is due to failure of development of the spiral
aortico-pulmonary septum. The truncus overrides the inter-ventricular septum and
receives blood from both ventricles.
b)Tetralogy of Fallot :characterized by four classic malformations :
c)Pulmonary stenosis, overriding aorta, inter-ventricular septal defect and right
ventricular hypertrophy.
d)Congenital aortic valve stenosis :this is due to fusion of the cusps of the aortic
valve leading to a very narrow aortic orifice. The left ventricle is markedly
hypertrophied.
e)Aortic valve atresia :The aortic orifice is completely closed. The left ventricle is
under-developed and the ascending aorta is narrow. The ductus arteriosus is
patent to carry blood into the aorta.
f)Pulmonary valve stenosis and atresia:The pulmonary trunk is narrow and the
right ventricle is under-developed. The ductus arteriosus remains patent and carries
blood in an opposite direction from the arch of aorta to the pulmonary arteries. The
foramen ovale remains patent.
g)Transposition of ascending aorta and pulmonary trunk:This is due to a
reversal development of the spiral aortico-pulmonary septum.

43. Congenital anomalies of the heart
5. Abnormal positions of the heart:
a)Isolated dextro-cardia :the heart is abnormally positioned on the right side of
the thorax. It is usually associated with other severe cardiac anomalies.
b)Dextro-cardia with situs inversus:is dextro-cardia with inversion of the
viscera.

44. Thank You
Dr. Fiky Thorax