1) The cardiovascular system begins developing in the third week as heart progenitor cells migrate to form the cardiac tube. 2) By the fourth week the heart tube develops blood islands, bends to form cardiac loops, and differentiates into three layers. 3) Septa form between the fourth and fifth weeks, dividing the heart into four chambers and separating the outflow tract into the aorta and pulmonary trunk. Valves form at the atrioventricular junctions and semilunar arteries.

1. Cardiovascular System
School of heath and science A.U

2. Establishment of the cardiogenic field
CVS is the first system to function in the embryo.
As the embryo grows the development of the
cardiovascular system become essential to the
developing embryo so cardiovascular system develops
during the third week. The cardiac progenitor cells lie in
the epiblast. From there they migrate through the streak.
Cells destined to form the cranial segments of the heart
migrate first, and cells forming more caudal portions
( right ventricle, left ventricle sinus venosus respectively
migrate in a sequential order.

3. Cont……..
Here they reside in the splanchnic layer of the
lateral plate mesoderm ultimately they form a
cardiac myoblasts. Blood islands also appear in
the mesoderm where they will form a blood
vessels by the process of vasculogenesis. With
time the islands unite and form a horse shoe-
shaped endothelial lined tube surrounded by a
myoblast this region is known as cardiogenic
field.

4. Formation and position of the heart tube
Initially the central portion of the cardiogenic
area is anterior the buccopharyngeal
membrane and the neural plate with closure of
the neural tube and the formation of the brain
vesicles. As a result of the growth of the brain
and cephalic folding of the embryo the
buccopharyngeal membrane is pulled forward,
while the heart and the pericardial cavity move
first to the cervical region and finally to the
thorax.

8. CONT..
The crescent part of the horse shoe shaped area expands
to form the out flow track of ventricular regions, thus the
heart becomes continuous expanding tube consisting of an
inner endothelial lining and outer myocardial layer.
A mesothelial cells from the regions of the sinus vensus
migrate over the heart to form epicardium thus the heart
tube consist of three layers.
Endocardium: forming internal endothelial lining of the
heart.
Myocardium: forming the muscular walls.
Epicardium: covering the outside of the tube. This outer
layer is responsible for formation of the coronary arteries
including their endothelial lining and smooth muscles.

9. Formation of the
cardiac loops
• The heart tube continue to enlongate and bend on
day 23. The cephalic portion of the tube bends
ventrally, caudally and to right and to left. This
bending creates the cardiac loop. It is a complete by
a day 28. while the cardiac loop is forming, local
expansions become a visible throughout the length
of the tube. The atrial portion forms a common
atrium. At the end of loop formation, the smooth
walled heart tube begins to form a primitive
trabeculea ( a cord of tissue that serves as a
supporting structure).

11. Cont….
• The bulbus cordis has three parts:
I. Proximal part which forms the trabeculated part of
the right ventricle.
II. Middle part known as cornus cordis forms out flow
track of both ventricles.
III.Distal part known as truncus arterioses forms the
roots and proximal portions of the aorta and the
pulmonary artery

14.  Is the most caudal portion of the
primitive heart tube.
 In the middle of the 4th week it consists
of
 small transverse portion
 Right and left sinus horns

16. • It receives all veins of the body
• Each horn receives blood from 3 important veins
 vitteline vein from the yolk sac .
 umbilical vein from the placenta .
 common cardinal vein from the body of the
embryo.

18. The left sinus horn
• The left sinus horn losses its importance
rapidly because of the left to right
shunts.
• Blood which is from the embryo itself
and the one from the placenta change
their direction to the right side of the
sinus venosus.

19. • The left umbilical vein is obliterated at 5mm.
• The left vitteline vein is obliterated at 7mm.
• The left common cardinal vein is obliterated
at 60mm.
The remaining parts of the left sinus horn
forms.
• coronary sinus and.
• Oblique vein of the left atrium.

21. Right sinus horn
• The right sinus horn becomes incorporate into the
right atrium and forms the smooth walled part of the
right atrium.
• RIGHT AND LEFT VENOUS VALVES.
• Entrance of sinus venosus into the atrium is called
sino-atrial orifice.
• On each side of it is guided by a valve called venous
valves

22. • The two valves meet and fuse above to form aridge known
as septum spurium.
The fate of these valves are as follows :
.The left venous valve degenerate rapidly and fuse into the
interatrial septum.
The upper part of right venous valve will later form the crista
terminals which is a ridge in the wall of the right atrium
extending from the front of the opening of the s.v.c. to the
front front opening of the i.v.c.
The lower part of the right venous valve is divided into two
part .

23. • The valve of the inferior vena cava and .
• The valve of the coronary sinus.

25. Formation of the cardiac septa
• It is formed between 27th and 37th days of the
development .
• When the embryo grows in length from 5mm to
17mm.
1). Two actively growing masses of tissue approach
each other until they fuse . There by
dividing the lumen into two separate channels.
2).
Growth of the single mass of tissue which continue
expanding till it reaches the opposite sides of the
lumen .

26. • Masses known as endocardial
cushion develop in the
atrioventricular . In these locations
they assist the formation of the
atrial and ventricular septum, atrio-
ventricular canals and the aortic and
pulmonary canals.

27. Septum formation of
common atrium
• Two septa ( the septum primum and septum
secondum)are essentials to divide the cavity of primitive
single atrium into two channels.
The septum primum
• Grows at the 4th week as asickle shaped crest from the
roof of the comman atrium into the lumen .
• The two limbs of this septum extend into the direction
of the endocardial cushions in the AV canal .
• The opening bt septum primum and the endocardial
cushions is the ostium primum.

28. • During further development the endocardial
cushions grows towards the septum primum
thereby closing the ostium primum.
• Before the closure is completed perforations
appear in the septum primum which fuse to
form
ostium secundum

29. The septum secundum
• When the lumen of the right atrium expands as a
result of incorporation of the sinus horn , anew
crescent –shaped fold appear .this new fold is
called septum secundum. The septum secundum
never forms a complete partition in the cavity of
the atrium.
• The lower free border of septum secundum and
osteum secundum form Oval foramen.
• Which allows free passege of blood bt the two
atria .

31. Further differentiation
of the atria
• Primitive atrium enlarges by incorporation of the
right sinus horn.
• Right atrium has two parts :
 Smooth posterior part { sinus venarum } and
 Rough anterior part { pactinate part } containing
the pactinate muscles..

33. Septum formation in the
atrioventricular canal
•The major septa of the heart are formed between the
27th and 37th days of development.
•Two actively growing masses of tissue or endocardial
cushions located on opposite sides of the
atrioventricular canal begin to grow toward each other
to form the septum intermedium.
•They continue to grow toward each other until they fuse,
thereby dividing the lumen into two separate canals.
•This septum now divides the common atrioventricular
canal into left and right atrioventricular canals.

35. Atrioventricular Valve Formation:
•After the atrioventricular endocardial cushions fuse, each AV
orifice is surrounded by localized proliferations of mesodermal
tissue.
•When tissue located on the ventricular surface of these
proliferations becomes hollowed out and thinned by the
bloodstream, valves are formed that remain attached to the
papillary muscles of the ventricular wall by muscular cords
(chordae tendineae).
•Finally, muscular tissue in the cords degenerates and is replaced
by dense connective tissue.
two valve leaflets are formed in the left AV canal -- mitral
(bicuspid) valve.
three valve leaflets are formed in the right AV canal –
tricuspid valve.

38. SEPTUM FORMATION IN THE TRUNCUS
ARTERIOSUSAND CONUS CORDIS
•During the fifth week, pairs of opposing ridges appear in the
truncus.
•These ridges, the truncus swellings, or cushions, lie on the
right superior wall (rightsuperior truncus swelling) and on the
left inferior wall (left inferior truncus swelling) .
•The right superior truncus swelling grows distally and to the
left
•and the left inferior truncus swelling grows distally
and to the right.

39. • •Hence, while growing toward the aortic sac, the
swellings twist around each other, foreshadowing the
spiral course of the future septum .
• •After complete fusion, the ridges form the
aorticopulmonary septum, dividing the truncus into an
aortic and a pulmonary channel.

40. Septum formation in the ventricles

41. It is the end of the fourth week when the primitive
ventricles begin to expand. The medial walls of the
expanding ventricles become apposed and gradually
merge, forming the muscular interventricular septum.
The interventricular foramen which is above the muscular
portion of the interventricular septum, shrinks on
completion of the conus septum. The IV foramen is
closed by the conal ridges, outgrowth of the inferior
endocardial cushion, and connective tissue from the
muscular interventricular septum. This portion of the I.V.
septum is called the membranous part of the
interventricular septum

42. Semilunar Valves
• When partitioning of the truncus is almost complete,
primordia of the semilunar valves become visible as
small tubercles found on the main truncus swellings.
•One of each pair is assigned to the pulmonary and
aortic channels, respectively.
•Gradually the tubercles hollow out at their upper
surface, forming the semilunar valves.
•Recent evidence shows that neural crest cells
contribute to formation of these valves.

43. Longitudinal sections through the semilunar valves
• 6th week 7th week 9th week

44. The membranous portion
Isolated defect in the membranous portion of
Of the septum is the most the interventricular septum. Blood from the
common congenital cardiac left ventricle flows to the right through the
malformation interventricular foramen (arrows).

46. Formation of the Conducting
System of the Heart
• •Initially the pacemaker for the heart lies in the caudal part of the left
cardiac tube.
• •Later the sinus venosus assumes this function, and as the sinus is
incorporated into the right atrium,
• •pacemaker tissue lies near the opening of the superior vena cava. Thus,
the sinuatrial node is formed.
• •The atrioventricular node and bundle (bundle of His) are derived from
two sources:
• –(a) cells in the left wall of the sinus venosus,
• –(b) cells from the atrioventricular canal.
• Once the sinus venosus is incorporated into the right atrium, these
cells lie in their final position at the base of the interatrial septum.

48.  There are two main parts of vascular system:
 Arterial system:
Aortic arches
Vitelline arteries
Umbilical Arteries
 Venous System:
Vitelline veins
Umbilical veins
Cardinal veins

50. Aortic Arches
 Aortic arches arises from the aortic sac.
 These arches are embedded in mesenchyme of the
pharyngeal arches and terminal part in the right &
left dorsal aorta.
 The sac contributes a branch to each new arch as it
form, giving rise to a total of five pairs of arteries.
 During further development, this arterial pattern
becomes modified, and some vessels regress
comletely.

52.  Aortic pulmonary septumdivides the truncus
arteriosus ,causing the division of the outflow
channel of the heart into ventral Aorta &
pulmonary arteries.
 As a result, the aortic sac forms the right horn,
which gives rise to brachiocephalic arteries,
and the left horn, which also gives rise to
aortic arch.

53. Developmen
t of aortic
arch
• 1st aortic arch: disappears although small portion persist
to form Maxillary arteries.
• 2nd aortic arch: disappears , but the remaining parts are:
Hyoid & Stapedial arteries.
 With further development the aortic arch system loses its
original symmetrical and the following changes occur:
• 3rd aortic arch: forms common carotid artery and
the first part of the internal carotid artery.
• 4th aortic arch: on the left it forms part of the arch of the
aorta. On the right it forms the most proximal segment of the
right subclavian artery.rtical

55. • 5th aortic arch: either never forms or forms incompletely and then
regress.
• 6th aortic arch: known as pulmonary artery. The distal portion of its
right side loses the connection with the dorsal aorta and
disappears. But the distal part of its left persists during intrauterine
life as ductus arteriosus
 There are other changes occur include:
 The dorsal aorta btw 3th and4th arches ,carotid duct,
obliterate.
 The right dorsal aorta disappears btw origin of the 7th
intersegmental artery & the junction with the left dorsal aorta.
 The heart will pushed into thoracic cavity which resulted

58. From the cephalic folding and elongation of the neck.
 As a result, the caudal shift of the heart and
disappearance of the various portions of the aortic
arches, the course of the recurrent laryngeal
nerves differentiate on both side.

60. Vitelline artery
• A number of paired vessels.
• They fuse and form arteries in dorsal
mesentry of the gut.
• In the adult they represented by:
 celiac: which supply foregut.
Superior mesenteric artery: supply the midgut.
Inferior mesenteric artery: supply the hindgut.

61. Umbilical arteries
> Umbilical arteries – paired branches of
dorsal aorta – to placenta (allantois) in
embryonic stalk or later in umbilical cord
> It persist as internal iliac and superior
vesical arteries .

63. There are three major pairs of veins:
A.Vitelline vein.
B. Umbilical vein.
C. Cardinal vein.

64. Vitelline veins
 Vitelline veins form apluxes around the duodenum and pass
through the septum tranversum.
 The growing liver interrupt the course of the vein and form
hepatic sinusoids.
 Right hepatocardiac channel is formed ,and as result,
blood from left side of the liver is rechanneled to ward the
right.
 Network around the duodenum develops into single vessel
Portal vein.
 Distal portion of L.vetlline disappears.
 The superior mesentric vein derived from R. vetilline.

66. Umbilical vein
 They pass through each side of the liver but some
connect to the hepatic sinusoid.
 disappearance of the Proximal of both umbilical
veins and right umbilical vein .
 Duct veinouses will form B/w left umbilical vein nad
right hepatocardinal channel.
 After birth left umbilical vein obliterate and form
legementum teres hepates.
 Ductuses veinouse will form lemgentum venesoum.

67. Cardinal vein
 Cardinal vein is the main venouses drainage system
of the embryo.
 this system consist of :
I. Anterior cardinal vein.
II. Posterior cardinal vein.

68.  During the fifth to the seventh week ,number of
veins will form:
A.subcardinal vein: which mainly drains the
kidneys.
B.sacrocardinal vein: drain the lower
extremities.
C.supracardinal veins: drain the body wall.

69. Vena cava system:
I. Posterior vena cava.
II. anterior vena cave.

70.  Formation of the vena cava system is characterized
by anastomoses .
 Anastomoses B/w anterior cardinal will develpe
into left brachiocephalic veins.
 Anstomoses B/W subcardinal veins will form left
renal vein
 The anstomoses B/W sacrocardinal veins formthe
left common iliac vein.

72. The fetal circulation
Circulatory changes at birth
Lymphatic system

73. Fetal circulation
• The circulation of blood in the embryo
is a good example of (economy) in
which well oxygenated blood from the
placenta is (shunted) to important
structures such as the (brain) and the
(heart) while relatively desaturated
blood is left for less important
structures.

75. • PLACENTA umbilical vein
ductus venosus I.V.C
• Rt. ATRIUM Lt. atrium
Lt. ventricle AORTA.

76. The umbilical veins transport blood rich in
oxygen and nutrients from the placenta to
the fetal body.
Most of the blood enters a shunting vessels
called the ductus venosus, that bypasses
(short-circuiting) the liver.
A smaller amount enters liver sinusoids and
mixes with blood from the portal circulation.

77. Then the blood flows directly into the
vena cava by way of ductus venosus.
There, the oxygenated blood from the
placenta is mixed with deoxygenated
blood from the lower parts of the fetal
body. This blood continuous through
the vena cava to the right atrium.

78. As the blood relative high in oxygen
enters the right atrium of the fetal
heart, a large proportion of it is
shunted directly into the left
through an opening in the atrial
septum called oval foramen.

79. The more highly oxygenated blood that
the left atrium through the foramen
ovale is mixed with a small amount of
the deoxygenated blood returning from
the pulmonary veins. This mixture
moves into the left ventricles and
pumped into the aorta.

81. Circulatory changes at birth
At birth the lung expands.
Expansion of the lungs creates negative
pressure inside the thoracic cavity which
sucks blood and, therefore, the blood flow in
the pulmonary arteries increases.
Blood now reaches the Lt. atrium from the
lungs in the large quantities and as a result
the pressure in the Lt. atrium “rises”

82. Ligature of the umbilical cord at
birth, will stop the flow of blood
through the umbilical vein and
the ductus venosus to the I.V.C,
as a result the pressure inside
the Rt.atrium drops.

84. There will be a number of closures within the vascular
system at the time of birth:
 Closure of the umbilical arteries, accomplished by
contraction of smooth musculature in their walls.
Distal parts of the umbilical cord forms the medial
umbilical ligaments, and the proximal part remain
open as the superior vesicle arteries.
 Closure of umbilical vein and ductus venosus, the
U.V forms the ligamentum teres hepatis. The ductus
venosus forms the ligamentum venosum.

85. Closure of ductus arteriosus, it forms
the ligamentum arteriosum.
Closure of oval foramen is caused by an
increased pressure in the left atrium,
combined with a decrease in pressure
on the right side.

86. The lymphatic system
The lymphatic system develops later than
the cardiovascular system appearing at the
fifth wk of gestation originating as five
sacs:two jucular, two iliac,one
retroperitonealand one cisterna chyli.
Numerous channels form to connect the sacs
and provide drainage from other structures.

88. Cont’
• Ultimately the thoracic duct forms from
anastomosis of the right and left
thoracic duct, the distal part of the right
duct , and the cranial part of the left
thoracic duct. The right lymphatic duct
develops from the cranial part of the
right thoracic duct.