Download LATE DEVELOPMENT AND PARTITIONING OF THE HEART

LATE DEVELOPMENT AND PARTITIONING OF
THE HEART
LEARNING OBJECTIVES
• By the end of this lecture the students should be able to
understand:
• The development of heart tube its division and its rotation
• Development of Four Chambered Heart
• Interatrial and Interventricular septum formation
• Formation of Heart Valves
• Formation of Conduction System
THE HEART TUBE
• The heart tube is formed by the fusion of two endocardial tubes in the
cardiogenic area
Site of Development of Heart
* Development of heart begins in cardiogenic area, located at the cranial
edge of the trilaminar germ disc
Pos
itio
n of
Hea
rt
Tube
* Folding of head region of embryo brings the heart and pericardial cavity ventral to the
foregut and caudal to the oropharyngeal membrane
The Divisions Heart Tube
• The tubular heart develops 5 demarcations:
• Trunsus Arteriosus
•
•
•
•
Bulbus Cordis
Ventricle
Atrium
Sinus Venosus
Folding of Heart Tube
• The heart tube folds back on itself forming an “S” shaped curve.
• The bulbus cordis and ventricle grow more rapidly forming a “U” shaped
Bulboventricular loop
• Bulboventricular loop shifts the region of heart to the right and ventrally
Division of Bulbus Cordis
• Proximal dilated portion is incorporated into ventricle
• Mid-part called conus cordis, will form the outflow tracts of both ventricles.
• Distal part of the bulbus cordis along with truncus arteriosus, will form the roots and
proximal portion of the aorta and pulmonary artery
Atrioventricular Canal
• Both atrium and ventricle are connected by means of single tube, the common
atrioventricular canal
Development of Right atrium
• The sinus venosus incorporates into the dorsal heart wall.
• The right sinus horn and veins enlarge greatly and become the only communication
between the original sinus venosus and the atrium.
Development of Right atrium
• The right auricle and the rough portion of the right atrium that contain pectinate
muscles represent remnants of the original embryonic right atrium.
• The left horn of the sinus venosus become the coronary sinus
• The proximal part of the left common cardinal vein become oblique vein of the left
atrium
Development of Left atrium
• The original embryonic left atrium becomes the trabeculated left auricle.
• The smooth left atrium develops from the primitive pulmonary vein as its main
branches incorporate into the wall.
Dorsal Mesocardium
• The heart tube sinks into the pericardial cavity and
becomes dorsomedially suspended by the dorsal
mesocardium which is formed from the right and left
epimyocardial layers and later disappears, except at its
cephalic and caudal ends
Septum formation of the Heart
• Development of the primitive heart with a single atrium and ventricle, into the typical
four-chambered structure occurs between the fourth and seventh weeks by formation
of interatrial and interventricular septa
• Many congenital heart problems can develop during this crucial time
Atrioventricular septum
• Toward the end of the fourth week, dorsal and ventral endocardial
cushions are developed in the walls of the common atrioventricular
canal at junction of atrium and ventricle
Endocardial cushions
• Endocardial cushions grow toward each other and, during the sixth week, meet and
fuse, dividing the common atrioventricular canal into right (tricuspid) and left
(mitral, or bicuspid) atrioventricular canals
The Atrial Septum
• The atrial septum is responsible for the division of primitive atrium into Right and Left
Atria
• The process involves the formation of:
– Septum primum
– Septum secondum
Septum Primum
• Septum primum first forms during the fourth week as a partition in the dorsocephalic
wall of the primitive atrium
• It grows towards the Atrioventricular septum
Foramen primum
Foramen Primum
• The space between the free edge of septum primum and the developing endocardial
cushions
• It gets obliterated when the septum primum fuses completely with AV septum
Foramen Secondum
• It is formed due to obliteration of tissue in the center of septum primum
Septum secondum
• Grows alongside the Right edge of Septum primum
• It fuses with the remaining portion of Septum primum to cover the
foramen secondum, forming the Interatrial Septum
Foramen Ovale
• Defect remaining in the septum secondum even after its fusion with
septum primum
• Foramen ovale allows Right to Left shunt
Ventricular Septum
• Ventricular septum is formed as:
– Interventricular septum
– AV cushions
– Spiral (Aorticopulmonary) septum
• Interventricular septum is formed as
– Muscular septum
– Membranous septum
The Interventricular Septum
Muscular septum
• Grows upwards from the base of the primitive ventricle towards the AV
septum
• The resulting gap is called the Interventricular foramen
The Interventricular Septum
Membranous septum
• Grows downwards from the AV cushions and fuses with the muscular
septum
• The interventricular foramen is thus obliterated
Spiral (Aorticopulmonary) Septum
• Neural crest cells migrate in the conotruncal ridges forming Aorticopulmonary septum
• As the septum descends, it undergoes spiral twisting
• Truncus arteriosus is thus separated into Aorta on the left and Pulmonary trunk on
the right
Development of Aorticopulmonary Septum
The Semilunar Valves
• The semilunar valves begin to develop from three swellings of
subendocardial tissue around the orifices of the aorta and pulmonary trunk
• These swellings are hollowed out and reshaped to form three thin-walled
cusps
The AV valves
The AV valves (tricuspid and mitral valves) develop similarly from
localized proliferations of tissue around the AV canals.
Conduction System
• The SA node develops during the fifth week. It is originally in
the right wall of the sinus venosus, but it is incorporated into the
wall of the right atrium with the sinus venosus
Conduction System
After incorporation of the sinus venosus, cells from its left wall are found in
the base of the interatrial septum just anterior to the opening of the
coronary sinus. Together with cells from the AV region, they form the AV
node and bundle
• The fibers arising from the AV bundle pass from the atrium into the
ventricle and split into right and left bundle branches
REFERENCES
 Langman’s embryology
 KLM introduction to embryology
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