Download 12-Development_of_Heart

Dr. Ahmed Fathalla Ibrahim
EARLY DEVELOPMENT OF
HEART
•
Splanchnic mesenchymal cells
aggregate in cardiogenic area to form
two angioblastic cords
• Cords canalize to form two
endocardial heart tubes
• After folding:
1. The 2 tubes approach each other &
fuse (cranio-caudally) to form a single
heart tube
2. The heart tube becomes caudal to
oropharyngeal membrane
EARLY DEVELOPMENT OF
HEART
EARLY DEVELOPMENT OF
HEART
The heart tube elongates & forms:
1. Truncus arteriosus
2. Bulbus cordis
3. Ventricle
4. Atrium
5. Sinus venosus
EARLY DEVELOPMENT OF
HEART
• The trucus arteriosus is continuous
cranially with aortic sac from which
aortic arches arise
• The sinus venosus lies in the septum
transversum & receives umbilical,
vitelline & common cardinal veins
So:
• The arterial & venous ends of heart are
fixed by pharyngeal arches & septum
transversum, respectively
EARLY DEVELOPMENT OF
HEART
•
The bulbus cordis & ventricle grow
faster than atrium & sinus venosus:
1. The heart bends upon itself forming a
U-shaped loop
2. The atrium and sinus venosus
become dorsal
3. A track is formed between arterial &
venous end (transverse pericardial
sinus) after degeneration of dorsal
mesocardium
PARTITIONING OF
ATRIOVENTRICULAR CANAL
PARTITIONING OF
ATRIOVENTRICULAR CANAL
•
At the end of 4th week, 2 mesenchymal
thickening (endocardial cushions)
form on the dorsal & ventral walls of
atrioventricular canal
• The 2 dorsal & ventral cushions fuse
& divide AV canal into right & left
canals
• The 2 cushions contribute to the
formation of:
1. AV valves
2. Membranous part of interventricular
septum
PARTITIONING OF PRIMORDIAL
ATRIUM
PARTITIONING OF PRIMORDIAL
ATRIUM
PARTITIONING OF PRIMORDIAL
ATRIUM
• Septum primum: a crescent-shaped
septum arises from the roof of the
atrium & grows toward the endocardial
cushions.
• Foramen primum: an opening between
edge of septum primum & cushions. It
disappears when septum primum fuses
with cushions
PARTITIONING OF PRIMORDIAL
ATRIUM
• Foramen secundum: formed by fusion
of many perforations appearing in the
central part of septum primum
• Septum secundum: a crescent-shaped
septum arises from the roof of atrium
to the right of septum primum &
overlaps foramen secundum
PARTITIONING OF PRIMORDIAL
ATRIUM
• Foramen ovale: a defect between
primary & secondary septum that
allows passage of most of oxygenated
blood from right to left atrium. Later on,
the cranial part of septum primum
degenerates & its remaining part forms
a valve for the oval foramen preventing
the passage of blood in the opposite
direction
PARTITIONING OF PRIMORDIAL
ATRIUM
AFTER BIRTH:
• Due to equalization of pressure on both
atria, the foramen ovale closes & both
septa fuse to form the interatrial
septum
• Fossa ovalis: remnant of septum
primum (valve of foramen ovale), marks
site of foramen ovale
• Annulus ovalis: remnant of septum
secundum
CHANGES IN SINUS VENOSUS
CHANGES IN SINUS VENOSUS
• Initially, sinus venosus opens into the
atrium & is formed of 2 equal horns
• Right horn: enlarges & becomes
incorporated in the wall of right atrium
• The valve between right horn & right
atrium: its cranial part forms crista
terminalis; its caudal part forms valves
of IVC and coronary sinus
CHANGES IN SINUS VENOSUS
• The valve between left horn & left
atrium: forms part of interatrial septum
• Left horn: remains small & forms the
coronary sinus
Primordial pulmonary vein
Primordial pulmonary vein
• Develops as an outgrowth of dorsal
atrial wall, to the left of septum primum
• Divides into two branches then into 4
branches
• As atrium expands, the stem of
pulmonary vein & its main branches are
gradually incorporated into the wall of
left atrium
SUMMARY OF DEVELOPMENT
OF RIGHT ATRIUM
•
•
•
•
•
Muscular part: primordium atrium
Smooth part: right horn of sinus venosus
Fossa ovalis: part of septum primum
Annulus ovalis: part of septum secundum
Crista terminalis: cranial part of right
sinuatrial valve
• Valves of IVC & coronary sinus: caudal part
of right sinuatrial valve
• Interatrial septum: fused septum primum &
secundum + left sinuatrial valve
• Coronary sinus: left horn of sinus venosus
SUMMARY OF DEVELOPMENT
OF LEFT ATRIUM
• Left auricle: primordium atrium
• Rest of left atrium (smooth part): stem
of pulmonary vein & its main branches
PARTITIONING OF PRIMORDIAL
VENTRICLE
PARTITIONING OF PRIMORDIAL
VENTRICLE
• Muscular part of interventricular
septum: a crescentic fold with a
concave cranial edge arises from
the floor of ventricle (near its apex)
& grows toward fused endocardial
cushions
PARTITIONING OF PRIMORDIAL
VENTRICLE
• Interventricular foramen: an
opening between muscular part of
septum & cushions. It is closed (7th
week) as a result of fusion of : right
& left bulbar ridges + endocardial
cushions
PARTITIONING OF PRIMORDIAL
VENTRICLE
• Membranous part of
interventricular septum:
derived from an extension from
right side of endocardial
cushion
PARTITIONING OF BULBUS CORDIS
& TRUNCUS ARTERIOSUS
PARTITIONING OF BULBUS CORDIS
& TRUNCUS ARTERIOSUS
• During 5th week, mesenchyme derived
from neural crest cells proliferate to
form bulbar & truncal ridges that are
continuous with each other
• Ridges are spirally oriented
• Bulbus cordis is divided into conus
arteriosus (infundibulum) & aortic
vestibule
• Truncus arteriosus is divided into:
pulmonary trunk & ascending aorta
SUMMARY OF DEVELOPMENT
OF RIGHT VENTRICLE
• Muscular part: primordium ventricle
• Infundibulum: bulbus cordis
SUMMARY OF DEVELOPMENT
OF LEFT VENTRICLE
• Muscular part: primordium ventricle
• Aortic vestibule: bulbus cordis
DEVELOPMENT OF VALVES
•
Develop as swellings arising from
localized proliferations of tissue:
1. Around AV canals (AV valves)
2. Around orifices of aorta & pulmonary
trunk (semilunar valves)
• Swellings are hollowed out &
reshaped to form the cusps
CONGENITAL HEART DEFECTS
• Are common (0.6 -0.8%)
• Caused by genetic abnormalities,
rubella virus or by environmental
factors
• Some are with unknown cause
DEXTROCARDIA
•
•
•
•
Most frequent positional abnormality
Cause: heart tube bends to the left
Results: heart is displaced to the right
Occurrence: isolated or with situs
inversus
ATRIAL SEPTAL DEFECT
• More frequent in females
• Most common form: patent
foramen ovale (due to incomplete
adhesion between septum
primum & secundum)
ATRIAL SEPTAL DEFECT
• Other forms:
1.Ostium secundum defect: due to defect
in one or both septa
2.Endocardial cushions defects with
ostium primum: septum primum does
not fuse with cushions resulting in a
patent forament primum
3.Sinus venosus defect: incomplete
absorption of sinus venosus
4.Common atrium: failure of both septa
to develop
VENTRICULAR SEPTAL DEFECT
•
Most common type of congenital
heart diseases
1. Membranous VSD (most common):
incomplete closure of IV foramen due
to failure of membranous part of
septum to develop
2. Muscular VSD
3. Common ventricle: absence of whole
IV septum
ECTOPIA CORDIS
• Very rare
• Heart is partly or completely exposed
on the surface of thorax
• Usually associated with separated
halves of sternum & open pericardial
sac
• Cause: faulty development of sternum
& pericardium due to failure of
complete fusion of lateral folds in
formation of thoracic wall