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===Overview of Developmental Anatomy of the Heart===

===Overview of Developmental Anatomy of the Heart===

===Cardiac Tube Formation===

===Cardiac Tube Formation===

Within the cardiogenic plate, mesoderm derived angiogenic cells cluster, giving rise to a horseshoe-shaped structure known as  the endocardial tube. The lateral limbs of the horseshoe-shaped construction form the left and right endocardial tubes. The mesodermal cells anterior to this form the septum trnsversum. The embryonic disc undergoes a process of folding and the endocarcial tubes and septum tranversum are rotated 180 degrees. The endocardial tubes are brought together and fuse to form the cardiac tube. The wall of the tube differentiates into the endocardium and the myocardium. The myocardium secretes an extracellular matrix known as caridac jelly, this causes areas of the tube to distend forming distinct regions, the Bulbus cordis, the Primitive ventricle, the Atrioventricular sulcus, the Primitive atria and the Sinus venosus.

Within the cardiogenic plate, mesoderm derived angiogenic cells cluster, giving rise to a horseshoe-shaped structure known as  the endocardial tube. The lateral limbs of the horseshoe-shaped construction form the left and right endocardial tubes. The mesodermal cells anterior to this form the septum transversum. The embryonic disc undergoes a process of folding and the endocarcial tubes and septum tranversum are rotated 180 degrees. The endocardial tubes are brought together and fuse to form the cardiac tube. The wall of the tube differentiates into the endocardium and the myocardium. The myocardium secretes an extracellular matrix known as cardiac jelly, this causes areas of the tube to distend forming distinct regions, the Bulbus cordis, the Primitive ventricle, the Atrioventricular sulcus, the Primitive atria and the Sinus venosus.

At this point blood enters the caridac tube at the posterior end. The bulbis cordis loops to the right and forms two new bulges, the conotruncus and the right ventricle. This causes the primitive atrium to be displaced dorsally. The ventricles expand while the conotruncus divides into two further bulges, the truncus areteriosus (anterior) and the conus cordis (posterior). The atria expand dorsally and also on either side of the truncus arteriosis, this gives rise to the formation of two chambers, the left and right atria. The sinus venosus is located  on the dorsal aspect of the interconnected atria. The sinus venosus is composed of a left and right horn, the majority of the left horn is lost, meaning that the communication between the sinus venosus and the atria, the sinoatrial opening, is confined to the right atria. This means the left side is devoid of blood vessels . The developing heart combats this by sprouting blood vessles that connect the left atrium to the lungs. The sprout splits into four channels, providing two vessels per lung.

At this point blood enters the caridac tube at the posterior end. The bulbis cordis loops to the right and forms two new bulges, the conotruncus and the right ventricle. This causes the primitive atrium to be displaced dorsally. The ventricles expand while the conotruncus divides into two further bulges, the truncus areteriosus (anterior) and the conus cordis (posterior). The atria expand dorsally and also on either side of the truncus arteriosis, this gives rise to the formation of two chambers, the left and right atria. The sinus venosus is located  on the dorsal aspect of the interconnected atria. The sinus venosus is composed of a left and right horn, the majority of the left horn is lost, meaning that the communication between the sinus venosus and the atria, the sinoatrial opening, is confined to the right atria. This means the left side is devoid of blood vessels . The developing heart combats this by sprouting blood vessles that connect the left atrium to the lungs. The sprout splits into four channels, providing two vessels per lung.

===Atrial Septation===

===Atrial Septation===

Septation of the tubular heart begins in the atrioventricular canal. Four masses of cardiac mesenchymal tissue, known as endocardial cushions, extend towards each other, the dorsal (inferior) and the ventral (superior) cushions grow more then the left and right cushihons and eventually fuse. The fused endocardial cushions form the Septum Intermedium, which divides the common atrioventricular canal into left and right atrioventricular canals. The myocardium secretes factors which cause and epithelial to mesenchymal change in the endocardium. These mesenchymal cells go on to form the bicuspid and tricuspid atrioventricular valves.

Septation of the tubular heart begins in the atrioventricular canal. Four masses of cardiac mesenchymal tissue, known as endocardial cushions, extend towards each other, the dorsal (inferior) and the ventral (superior) cushions grow more than the left and right cushions and eventually fuse. The fused endocardial cushions form the Septum Intermedium, which divides the common atrioventricular canal into left and right atrioventricular canals. The myocardium secretes factors which causes an epithelial to mesenchymal change in the endocardium. These mesenchymal cells go on to form the bicuspid and tricuspid atrioventricular valves.

As the endocardial cushions proliferate the initial atrial septum forms in the common atrial chamber. The Septum Primum emerges from the roof of the common atrium and extends down through the chamber, eventaully fusing with the Septum Intermedium to create a seperate left and right atria. Programmed cell death occurs and a large hole is created in the septum primun allowing blood to flow between the left and right. A muscular sheet known as the Septum Secundum then grows on the right of the  Septum Primum. This occludes the majority of the hole in the Septum Primum, only the small Foramen Ovale is left. The window in the Septum Primum is slightly offset from the window in the septum Secundum and this creates a valve like effect so that blood can only flow in one direction between the atriae.

As the endocardial cushions proliferate the initial atrial septum forms in the common atrial chamber. The Septum Primum emerges from the roof of the common atrium and extends down through the chamber, eventaully fusing with the Septum Intermedium to create a seperate left and right atria. Programmed cell death occurs and a large hole is created in the septum primun allowing blood to flow between the left and right. A muscular sheet known as the Septum Secundum then grows on the right of the  Septum Primum. This occludes the majority of the hole in the Septum Primum, only the small Foramen Ovale is left. The window in the Septum Primum is slightly offset from the window in the septum Secundum and this creates a valve like effect so that blood can only flow in one direction between the atriae.

Further information on development of the heart can be found [http://www.meddean.luc.edu/lumen/MedEd/GrossAnatomy/thorax0/heartdev/main_fra.html here]

Further information on development of the heart can be found [http://www.meddean.luc.edu/lumen/MedEd/GrossAnatomy/thorax0/heartdev/main_fra.html here]

The fate of the aortic arches are described [[http://w01.rvcwiki.wf.ulcc.ac.uk/index.php/Vascular_Development_-_Anatomy_%26_Physiology#Fate_of_the_Aortic_Arches here]]

The fate of the aortic arches are described [[Vascular_Development_- Anatomy & Physiology#Fate_of_the_Aortic_Arches|here]]

===Ventricular Outflow Septation===

===Ventricular Outflow Septation===

===The Development of the Semilunar Valves===

===The Development of the Semilunar Valves===

The semiluanr valves prevent blood from flowing from the aortic and pulmonary trunks back into the ventricles. They form after septation of the outflow tract occurs. The endocardium swells in three places at the origins of the aortic and pulmonary trunks, these swellings grow towards each other but never fuse. The swellings form shelf like projections which are then remolled to form three thin walled cusps, which prevent back flow.

The semilunar valves prevent blood from flowing from the aortic and pulmonary trunks back into the ventricles. They form after septation of the outflow tract occurs. The endocardium swells in three places at the origins of the aortic and pulmonary trunks, these swellings grow towards each other but never fuse. The swellings form shelf like projections which are then remolled to form three thin walled cusps, which prevent back flow.

===Links===

===Links===

[http://www.meddean.luc.edu/lumen/MedEd/GrossAnatomy/thorax0/heartdev/main_fra.html www.meddean.luc.edu]

[http://www.meddean.luc.edu/lumen/MedEd/GrossAnatomy/thorax0/heartdev/main_fra.html www.meddean.luc.edu]