The document summarizes the key steps in cardiac embryology: 1. The heart develops from mesoderm and appears in the third week as a linear heart tube that loops to the right. 2. Septa form to divide the heart into four chambers, with the atria separating in the fourth week and ventricles separating by the fifth week. 3. Valves develop from endocardial cushions that form in the atrioventricular canal and outflow tract. 4. The conducting system develops from pacemaker cells in the heart tube and sinus venosus.

1. Cardiac Embryology
Dr. Rezaul Hayat
Resident (Phase A)

2. Cardiovascular System is derived from
Mesoderm

3. Vascular system appears in the middle
of third week

4. Steps in the embryology of the
vascular system
• ESTABLISHMENT OF THE HEART FIELD
• FORMATION AND POSITION OF THE HEART TUBE
• FORMATION OF THE CARDIAC LOOP
• MOLECULAR REGULATION OF CARDIAC DEVELOPMENT
• DEVELOPMENT OF THE SINUS VENOSUS
• FORMATION OF THE CARDIAC SEPTAE
• FORMATION OF THE CONDUCTING SYSTEM OF THE HEART
• VASCULAR DEVELOPMENT

5. ESTABLISHMENT OF HEART FIELD

6. PRIMARY HEART FIELD
Progenitor heart cells lie in the epiblast, immediately adjacent to the cranial end of the primitive streak.
From there, they migrate through the streak and into the splanchnic layer o f lateral plate mesoderm where
some form a horseshoe-shaped cluster of cells called the primary heart field (PHF) cranial to the neural fold

7. SECONDARY HEART FIELD

8. FORMATION AND POSITION OF THE
HEART TUBE

9. 2 processes responsible for positioning
of the heart
1. Folding of the embryo in a cephalocaudal
direction
2. Simultanous folding laterally

10. Initially, the central portion of the
cardiogenic area is anterior to the
oropharyngeal membrane and the
neural plate. With closure of the
neural tube and formation of the
brain vesicles, however, the central
nervous system grows cranially so
rapidly that it extends over the
central cardiogenic region and the
future pericardial cavity. As a result
of growth of the brain and cephalic
folding of the embryo, the
oropharyngeal membrane is pulled
forward, while the heart and
pericardial cavity move first to the
cervical region and finally to the
thorax.

11. Figures showing effects of the rapid growth of the brain on positioning
of the heart. Initially the cardiogenic area and the pericardial cavity are in
front of the oropharyngeal membrane. A. 18 days. B. 20 days. C. 21 days. D.
22 days

12. Lateral folding apposes paired heart tube primordia
and brings dorsal aorta to midline
Heart primordia fuse to form tubular heart

13. FORMATION OF THE CARDIAC LOOP

15. Bulbus cordis
The bulbus cordis moves inferiorly, anteriorly
and to the embryo’s right

16. 22 days 23 days 24 days

17. Primitive ventricle
The primitive ventricle is moving ventrally ant to the embryo’s left

18. 22 days 23 days 24 days

19. The primitive atrium and sinus
venosus
The primitive atrium and sinus venosus
move superiorly and posteriorly

20. Heart of a 5-mm embryo (28 days)
Viewed from left Frontal view
The bulbus cordis is divided into the
truncus arteriosus, conus cordis and
trabeculated part of right ventricle

21. MOLECULAR REGULATION OF
CARDIAC DEVELOPMENT

23. DEVELOPMENT OF SINUS VENOSUS

24. Middle of 4th week
Sinus venosus receives
Blood from the right and
Left sinus horns
Each horn receives blood
From thre important veins
1. Vitelline vein (VIT, V)
2. Umbilical vein (UV)
3. Common cardinal vein
(CCV)

25. 5th week
Obliteration of
1. Right umbilical vein
2. Left vitelline vein

26. 10th week
Left common cardinal vein obliterated
All that remains
Of the left sinus
Horn is

27. 10th week
Now, the right horn forms the only communication
between the
original sinus
Venosus and
The right
atrium

28. FORMATION OF CARDIAC SEPTA

29. The major septa are formed between
the 27 and 37th days of development
It is a simultaneous process if the following
areas
• Septum formation in the common atrium
• Septum formation in the atrioventricular canal
• Septum formation in the truncus arteriosus
and conus cordis
• Septum formation in the ventricles

30. SEPTUM FORMATION IN COMMON
ATRIUM

31. At the end of 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.

32. 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,
how- ever, cell death produces perforations in the upper portion
of the septum primum. Coalescence of these perforations forms
the ostium secundum, ensuring free blood flow from the right to
the left primitive atrium.

33. 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 partion in the atrial cavity. The opening left by the
septum secundum is called the oval foramen (foramen ovale).
When the upper part of the septum primum gradually
disappears, the remaining part becomes the valve of the oval
foramen.

34. After birth when lung circulation begins, the
pressure of left atrium increases and the
valve of oval foramen is pressed against
septum secundum which obliterates
foramen ovale separating right & left atrium.

35. Further differentiation of the atria
Coronal sections through the heart to show development of
the smooth walled portions of the right and left atrium. Both
the wall of the right sinus horn (blue)and the pulmonary veins
(red) are incorporated into the heart to form the smooth-
walled parts of the atria.

38. SEPTUM FORMATION IN THE
VENTRICLES

39. Muscular intraventricular septum grows from floor ( end of 4th
wk). Membranous IV septum forms from endocardial cushions
and bulbar ridges (end of 5th wk). Closure of membranous
intraventricular septum is associated with partitioning of truncus
arteriosus.

40. During the fifth week
pairs of opposing
ridges appear in the
truncus. These ridges,
the truncus swelling, or
cushions, lie on the
right superior wall and
left inferior wall.
Right superior truncus
swelling grows distally
and to the left, left
inferior truncus
swelling grows distally
and to the right.

41. Growing towards the aortic sac, the swellings twist
around each other, foreshadowing the spiral
course of the future septum, dividing the truncus
into aortic and pulmonary channels.

42. Tetralogy of Fallot, the most frequently occurring abnormality of
the conotruncal region, is due to an unequal division o f the
conus resulting from anterior displacement of the conotruncal
septum. Displacement of the septum produces four
cardiovascular alterations

43. VSDs involving the membranous or muscular portion of the septum are the
most common congenital cardiac malformation. Most (80%) occur in the
muscular region of the septum and resolve as the child grows. Membranous
VSDs usually represent a more serious defect and are often associated with
abnormalities in partitioning of the conotruncal region.

44. SEPTUM FORMATION OF THE
ATRIOVENTRICULAR CANAL

45. At the end of the fourth week, four atrioventricular
endocardial cushions appear: one on each side plus
one at the dorsal (superior) and one at the ventral
(inferior) border of the atrioventricular canal.
The dorsal and ventral cushions, in the meantime,
project further into the lumen and fuse, resulting in a
complete division of the canal into right and left
atrioventricular orifices by the end o f the fifth week

46. FORMATION OF
ATRIOVENTRICULAR VALVE

47. After the atrioventricular endocardial cushions fuse, each
atrioventricular orifice is surrounded by local proliferations of
mesenchymal tissue derived from the endocardial cushions.
When the bloodstream hollows out and thins tissue on the
ventricular surface of these proliferations, the mesenchymal
tissue becomes fibrous and forms the atrioventricular valves,
which remain attached to the ventricular wall by muscular cords.

48. Finally, muscular tissue in the cords degenerates and is replaced by
dense connective tissue. They are connected to thick muscular
trabeculae in the wall of the ventricle, the papillary muscles, by
means of chordae tendineae. In this manner, two valve leaflets,
constituting the bicuspid (or mitral) valve in the left atrioventricular
canal, and three, constituting the tricuspid valve, form on the right
side these proliferations, the mesenchymal tissue

49. FORMATION OF THE CONDUCTING
SYSTEM OF THE HEART

50. 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 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:(1)
myocardial cells in the left wall of the sinus
venosus and (2) myocardial 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.

52. Thank you

53. Thank you
…….To be continued

55. Tricuspid atresia, which involves obliteration of the right
atrioventricular orifice, is characterized by the absence or fusion of
the tricuspid valves. Tricuspid atresia is always associated with [1]
patency of the oval foramen, (2) VSD, (3) underdevelopment o f the
right ventricle, and (4) hypertrophy of the left ventricle.

56. Ebstein anomaly is a
condition where the tricuspid
valve is displaced toward the
apex o f the right ventricle,
and as a result, there is an
expanded rig h t atrium and a
small right ventricle. The
valve leaflets are abnormally
positioned, and the anterior
one is usually enlarged.

57. Persistent [common] truncus arteriosus results when the conotruncal ridges
fail to form such that no division of the outflow tract occurs. In such a case,
which occurs. in 0.8/10,000 births, the pulmonary artery arises some distant
above the origin o f the undivided truncus. Because the ridges aiso
particípate in formation o f the interventricular septum, the persistent
truncus is always accompanied by a defective interventricular septum . The
undivided truncus thus overrides both ventricles and receives blood from
both sides