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Formation of the Cardiac Septa
Ass. prof. Dr. Malak A. Al-yawer
The major septa of the heart are formed
between the 27th and 37th days of development, when the embryo grows in length from 5 mm to approximately 16 to 17 mm.
Septum are formed by
Endocardial cushions merging of two expanding portions of the wall of the heart.
Endocardial cushions
(1) two actively growing ridges approach each other until they fuse.) AB( (2)a single actively growing cell mass (C). Such tissue masses are called Endocardial cushions
Formation of Endocardial cushions
depends on 1.synthesis and deposition of extracellular matrices and 2.cell proliferation.
Endocardial cushions
develop in the atrioventricular and conotruncal regions.
they assist in formation of the atrial and ventricular (membranous portion) septa, atrioventricular canals and valves aortic and pulmonary channels.
A narrow ridge forms between the two expanding portions of the wall of the heart.
a narrow strip of tissue in the wall of the atrium or ventricle should fail to grow while areas on each side of it expand rapidly.
Such a septum partially divides the atria and ventricles
Such a septum never completely divides the original lumen but leaves a narrow communicating canal between the two expanded sections. It is usually closed secondarily by tissue contributed by neighboring proliferating tissues.
Septum Formation in the Common Atrium
Septum primum ostium primum
Ostium secundum Septum secundum
foramen ovale its valve
After birth
Further Differentiation of the Atria
Left atrium
Right atrium
The original embryonic right atrium becomes the trabeculated right atrial appendage containing the pectinate muscles, and the smooth-walled sinus venarum originates from the right horn of the sinus venosus.
absorption of the pulmonary vein into the left atrium
Atrial septal defect (ASD)
B,C. Ostium secundum defect caused by excessive resorption of the septum primum.
Atrial septal defect (ASD)
Premature closure of the oval foramen
Occasionally, the oval foramen closes during prenatal life. This abnormality leads to massive hypertrophy of the right atrium and ventricle and underdevelopment of the left side of the heart. Death usually occurs shortly after birth.
Septum Formation in the Atrioventricular Canal
Atrioventricular canal
Septum Formation in the Atrioventricular Canal
Atrioventricular Valves
Mitral and tricuspid valves
Persistent common atrioventricular canal
This abnormality is always accompanied by a septum defect in the atrial as well as in the ventricular portion of the cardiac partitions.
Persistent common atrioventricular canal
B. Valves in the atrioventricular orifices under normal conditions.
C. Split valves in a persistent atrioventricular canal.
Septum Formation in the Truncus Arteriosus and Conus Cordis
Truncus cushions (swellings)
During the fifth week, pairs of opposing ridges appear on the right superior wall (right superior truncus swelling) and on the left inferior wall (left inferior truncus swelling)
Aorticopulmonary septum
Conus swellings-----conus septum
Neural crest cells
migrate from the edges of the neural folds in the hindbrain region contribute to endocardial cushion formation in both the conus cordis and truncus arteriosus.
Septum Formation in the Ventricles
Septum Formation in the Ventricles
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
Interventricular septum
The interventricular foramen
Membranous part of the interventricular septum
Complete closure of the interventricular foramen forms the membranous part of the interventricular septum.
semilunar valves
Semilunar valves
When partitioning of the TA is nearly completed, the semilunar valves begin to develop from three swellings of subendocardial tissue around the orifices of the aorta and pulmonary trunk.
The semilunar valves
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.
Clinical Correlates
Heart Defects
Ventricular septal defect (VSD)
Tetralogy of Fallot
Persistent truncus arteriosus
Transposition of the great vessels
valvular stenosis (atresia) of the pulmonary artery
The trunk of the pulmonary artery is narrow or even atretic The patent oval foramen then forms the only outlet for blood from the right side of the heart. The ductus arteriosus, always patent, is the only access route to the pulmonary circulation.
aortic valvular stenosis
Formation of the Conducting System of the Heart
Thank you Next lecture Vascular system
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